Comparative Sedimentology Laboratory University of...

An Integrated Approach

Comparative Sedimentology Laboratory

University of Miami

Research Program Prospectus

Table of Contents

Mission of the Comparative Sedimentology Laboratory.........................................................2

A. Carbonate Systems and Reservoir Characterization..........................................................5 Patterns and Processes in Modern Carbonate Grainstone Systems...........................................6 Sedimentologic, Hydrodynamic and Facies Relationships of a Complex, Evolving Coastal System: Cape Sable, South Florida ...........................................................................................8 3D/4D GPR Imaging of Sedimentary Structures and Fractures at Submeter Resolution.......10 Three-Dimensional Sedimentologic Architecture of the Miami Oolite..................................12 Facies and Geometry of Mixed Sedimentation on an Isolated Carbonate Platform: Bocas del Toro Basin, Panama (year 2)...................................................................................................14 Relations Among High-Resolution Sequence Architecture, Diagenesis, and Mechanical Characteristics of Outcropping Lower Carboniferous Grainstones, Missouri (year 2) ..........16 Quantitative Analysis of Flexural and Tectonic Subsidence and Eustasy on the Stratigraphic Architecture of a Carbonate Ramp: the Madison Group, Idaho, Wyoming, and Montana ....18 Relationship Between Fractures and High-Resolution Sequence Stratigraphy (year 3 of 3) .21 The Demise of Shallow-Water Platforms in the Bahamas......................................................23

B. Petrophysics of Carbonates .................................................................................................26 Parameters Controlling Petrophysical Heterogeneity of Bank-Margin Grainstones, Ocean Cay, Bahamas..........................................................................................................................27 Permeability in the Miocene Marion Plateau Platforms (year 3 of 3) ....................................29 Quantifying 3-D Pore Geometry and its Effects on Ultra Sonic Velocity and Permeability in Carbonates (year 1 of 1) ..........................................................................................................32 Saturation Effects on Velocity in Carbonates (year 2 of 2) ....................................................35 Sonic Velocity and Permeability of Dolomites.......................................................................37 Origin of Uranium Anomalies in Carbonate Rocks (year 3 of 3) ...........................................39

C. Geochemistry and Diagenesis of Carbonates.....................................................................40 Surface Sediment Mapping of the Bahamas ...........................................................................41 Lower Mississippian Carbonate Geochemistry: Montana and Wyoming ..............................43 Geochemistry of Dolomitization and its Relationship with Sequence Stratigraphy (year 2 of 3)..............................................................................................................................................45

Contact Information .................................................................................................................46

Mission of the Comparative Sedimentology Laboratory

The mission of the Comparative Sedimentology Laboratory is to conduct research in facies, sequence stratigraphy, petrophysics, and geochemistry in modern and ancient carbonate systems to enhance prediction of carbonate reservoir attributes on exploration and production scale.

2004 Planned Projects A. Carbonate Systems and Reservoir Characterization

• Patterns and Processes in Modern Carbonate Grainstone Systems • Sedimentologic, Hydrodynamic and Facies Relationships of a Complex, Evolving

Coastal System: Cape Sable, South Florida • 3D/4D GPR Imaging of Sedimentary Structures and Fractures at Submeter Resolution • Three-Dimensional Sedimentologic Architecture of the Miami Oolite • Facies and Geometry of Mixed Sedimentation on an Isolated Carbonate Platform: Bocas

del Toro Basin, Panama • Relations Among High-Resolution Sequence Architecture, Diagenesis, and Mechanical

Characteristics of Outcropping Lower Carboniferous Grainstones, Missouri • Quantitative Analysis of Flexural and Tectonic Subsidence and Eustasy on the

Stratigraphic Architecture of a Carbonate Ramp: the Madison Group, Idaho, Wyoming, and Montana

• Relationship Between Fractures and High-Resolution Sequence Stratigraphy • The Demise of Shallow-Water Platforms in the Bahamas

B. Petrophysics of Carbonates

• Parameters Controlling Petrophysical Heterogeneity of Bank-Margin Grainstones, Ocean Cay, Bahamas

• Permeability in the Miocene Marion Plateau Platforms • Quantifying 3-D Pore Geometry and its Effects on Ultra Sonic Velocity and

Permeability in Carbonates • Saturation Effects on Velocity in Carbonates • Sonic Velocity and Permeability of Dolomites • Origin of Uranium Anomalies in Carbonate Rocks

C. Geochemistry and Diagenesis of Carbonates

• Surface Sediment Mapping of the Bahamas • Lower Mississippian Carbonate Geochemistry: Montana and Wyoming • Geochemistry of Dolomitization and its Relationship with Sequence Stratigraphy

Approach The general approach within the Comparative Sedimentology Laboratory to solve scientific

questions is to compare: • modern and ancient depositional systems, • outcrop and subsurface data (seismic, core and logs), and • theory and experiments. This approach guarantees to relate process and product, for example in the development of

facies, facies belts and their distribution in the ancient strata. Likewise the physical processes that form the geophysical properties of subsurface data can be assessed with the comparison to outcrop data, the modeling of outcrop data, and the assessment of the physical parameters in the laboratory. We make an effort to integrate lithologic, seismic, log and geochemical data to understand all the sedimentologic, stratigraphic and diagenetic parameters as well as the geophysical response of the strata. Overview of Data Sets and Objectives

The selected studies address either fundamental processes, provide detailed information of a certain facies belt, have relevance for exploration and production needs of the participating companies. For basic research of petrophysical and geochemical processes data sets are selected primarily based on their suitability for the experimental and theoretical work plan.

In 2004, we have chosen for an arid ramp in the Mississippian Madison Formation, which is a known reservoir in the US but can also serve as an analog for similar settings worldwide. In addition, Miocene carbonates are hydrocarbon reservoirs in many parts of the world. Our projects of drowned buildups on the Marion Plateau and in a prograding setting in Turkey will focus on the relationship between facies/diagenesis and rock properties to better understand the porosity-permeability distribution and the seismic signature of these systems.

More basic research topics include the assessment of a relationship between the high-resolution sequence stratigraphy and the fracture patterns in carbonates, continued examination of modern depositional systems, geochemical modeling, and a suite of petrophysical experiments. Our geochemical projects are driven with samples from the modern (Great Bahama Bank) and ancient (Mississippian Madison Formation). In the modern we plan to relate the geochemical facies to the depositional facies and model burial diagenesis. In the ancient example, the basin scale dolomitization pattern is investigated in order to decipher the dolomitization processes in this arid ramp.

The petrophysical studies include the quantitative assessment of pore shapes in carbonates and their relation to velocity and permeability, an experimental assessment of the dispersion in carbonates and search for the places of uranium enrichment in carbonates. Funding

The contribution of each industrial associate towards the research is $35,000. The deliverables are outlined below in the document. As in other years, most of these studies are "leveraged" by contributions from other funding agencies such as the National Science Foundation, the Petroleum Research Fund, and JOI/USSAC.

PERSONNEL Gregor P. Eberli, Ph.D. 1985, Geological Institute ETH Zürich, Switzerland

Research Interests: Seismic facies analysis and sequence stratigraphy, petrophysics of carbonates and mixed carbonate/siliciclastic systems, seismic modeling.

Mark P. Grasmueck, Ph.D. 1995, Geophysical Institute ETH Zürich, Switzerland Research Interests: Applied geophysics, reflection seismic, ground penetrating radar, 3-D depth imaging, marine geology and reservoir characterization, data integration and visualization.

Donald F. McNeill, Ph.D. 1989, University of Miami/RSMAS Research Interests: Sedimentology and stratigraphic correlation of carbonate and mixed system sediments, integrated stratigraphy (bio-stratigraphy, Sr-isotope stratigraphy, magnetostratigraphy), petrophysics of carbonates.

Eugene Rankey, Ph.D. 1996, University of Kansas Research Interests: Geomorphology and sedimentology of modern carbonate systems and ancient analogs, remote sensing, GIS, sequence stratigraphy.

Peter K. Swart, Ph.D. 1980, King's College, University of London, England Research Interests: Sedimentary geochemistry, stable isotope geochemistry of biological and geological systems, organic geochemistry, global climate change, coral reef sedimentation.

SCIENTIFIC COLLABORATORS Langhorne “Taury” B. Smith, Ph.D. New York State Museum, Albany Yue-Fen Sun, Ph.D. Columbia University, LDEO Heike Delius, Ph.D. University of Leicester, UK

POST-DOCTORAL ASSOCIATES Guillermina Sagasti Ph.D. Sandra Vega Ph.D. Steven Truss Ph.D.

RESEARCH ASSOCIATES Greta MacKenzie, Ph.D. Amel Saied

STUDENTS Kelly Bergman David Katz Gregor Bäechle Layaan Al Kharusi Matthew Buoniconti Ralf Weger Kelley Steffen Brigitte Vlaswinkel Robert Otto Kathleen Willis Eduardo Gomez da Cruz

ADMINISTRATIVE ASSISTANT Karen Neher

TECHNICIANS Alan Buck Cory Schroeder

A. Carbonate Systems and Reservoir Characterization Introduction

Carbonate depositional environments are inherently heterogeneous because of the superposition of sedimentary and diagenetic processes. One possibility to capture the heterogeneity is to quantitatively measure the sizes, shapes, and spatial trend metrics of the sedimentary bodies and relate them to the forming processes. Two projects in the modern environment, in Bear Cut and in Florida Bay, will use a combination of various types of remote sensing data and surface samples to capture the spatial trend metrics of sedimentary bodies that can be used as input parameters in geological models. Surface samples from northwestern Great Bahama Bank are intended to refine the facies maps of this classic modern platform system. In addition, a project in Panama focuses on the mixing of carbonates and clastics on an isolated platform.

Understanding flow, compartmentalization and mineralization in reservoirs depends on knowledge of the 3-D architecture of sedimentary structure and fracture network in the rock volume around the borehole. Several of our projects aim to increase our understanding of the lateral and vertical heterogeneity of facies and fractures. To achieve this goal, Mark Grasmueck developed a new generation of 3-D Ground Penetrating Radar to retrieve the sub-meter scale variability of facies and flow units from Pleistocene grainstone shoals in the Miami Oolite and for fractures in Tribes Hill Formation in Mohawk Valley in New York. In addition, we continue our research in relating mechanical stratigraphy to sequence stratigraphy; this year the focus is on mixed systems from the Paradox basin and the Mississippian around St. Louis. These projects will provide us with a methodology to predict to certain degree the fractures from facies and stratigraphic information.

Reservoir heterogeneities and the large-scale distribution of reservoir quality dolomite have been the focus of completed projects in the Mississippian Madison Formation. This year we focus on the dynamics of the evolving foreland basin and on the dolomitization processes in the Madison Formation (see Diagenesis Chapter). In addition, seismic data from the Bahamas-Cuba foreland basin is used to document platform drowning as a result of increased subsidence during the formation of this foreland basin.

Patterns and Processes in Modern Carbonate Grainstone Systems Gene Rankey and Kelley Steffen Project Purpose

For some grainstone shoals in Florida and the Bahamas, this project will: 1. Quantitatively measure and describe their morphology; 2. Evaluate and describe the distribution of sediments within that framework; and 3. Measure important controlling processes.

Scope of Work

Starting by focusing on Bear Cut near RSMAS, this project eventually will expand to other grainstone shoals. Key Deliverables

Quantitative measures of the sizes, shapes, and spatial trend metrics in grainstone shoal bodies, and description of the attributes of sediments within those bodies. Collectively, these information can be used as ‘hard’ or ‘soft’ data for input to geologic or simulation models. Project Description

Construction of meaningful geologic models requires information on these size, shape, and orientation of geologic bodies and the population of these bodies with porosity and permeability. Quantitative information of this sort is extremely rare from carbonate systems. To address this need, this project includes four general steps: 1) generating and analyzing facies maps; 2) exploring grains within the morphologic maps; 3) assessing controlling parameters; and 4) integration.

4. Remote sensing data (Landsat, SPOT, IKONOS) provide fundamental information that can be used to map facies and sedimentary bodies (e.g., Figure 1a). These maps will be calibrated by site visits, generating validated maps (schematically illustrated in Figure 1b).

5. Sediment samples provide information on the dynamics of sediment production and transport in these systems. For this project, we will collect samples from across the spectrum of environments, then analyze the samples in terms of constituents and grain size and sorting.

6. We will directly capture information on the bathymetry and flow velocity. For this project, will explore high-resolution information on bathymetry and current flow velocities in and around the Virginia Key area collected and processed using an acoustic Doppler profiler (e.g., Figure 1c).

7. Steps 1-3 provide an understanding the distribution of different bottom and sediment types and the nature of currents around Virginia Key. The final aspect of the project will include integration of these data. By placing observations within the context

provided by remote sensing imagery, we will develop an understanding of the character and controls on currents, how the sediment attributes reflect current activity, and how all of these data can be used to better understand and predict ancient grainstone analogs.

Expected Results

Quantitative metrics of the attributes of sedimentary environments and explicit linkage to the processes of sedimentation.

Figure 1. A. SPOT image of Virginia Key area; b) General geomorphic features of the area shown in Figure 1a. Note the location of the profile below (in blue) and the qualitative flow lines (illustrated in red) C) Representative cross-section of part of the inlet, illustrating a high-velocity core (red colors) in the deepest part of the channel.

Sedimentologic, Hydrodynamic and Facies Relationships of a Complex, Evolving Coastal System: Cape Sable, South Florida Brigitte Vlaswinkel and Gene Rankey Project Objectives

The overall objectives of the project are: • Document historical patterns and rates of change of various subenvironments • Identify causes for the dramatic morphological ecosystem changes observed in the

Cape Sable system (define the relative roles of prevailing processes, major hurricanes, historical sea level rise, human modifications and other);

• Forecast pattern and rate of expected changes in the coming 50-100-200 years; • Establish principles for system dynamics to be used as a protocol for the evolution

of other coastal systems Collectively, these parameters will provide information on rates of facies change, and

the processes controlling these changes, that could be used to develop forward 3D models of sedimentary systems.

Scope of Work

A combination of various types of remote sensing data will be used to map subfacies and to understand observed spatial and temporal patterns. Active morphologic and hydrodynamic changes will be studied using a sedimentologic, geochemical and oceanographic dataset obtained in 2003-2004.

Key Deliverables

This project will generate quantitative data of the historical change in sizes and shapes of a coastal beach/marl ridge/wetland ecosystem. Recently collected field data will provide quantitative information on sedimentation and erosion rates of tidal creeks and their attributes.

Project Description

Study area - Located at the crossroads of the relatively shallow, quiet waters of Florida Bay and the Gulf of Mexico, Cape Sable is subject to a variety of physical process conditions. Geomorphologically, the Cape Sable complex reflects a history of dramatic changes in coastline configuration and conditions from an area of essentially carbonate mud deposition - a typical Florida Bay environment - to the relatively high energy shell beaches of the present sandy headlands (Capes). In the lee of these features occurs a mosaic of Holocene sedimentary environments dominated by tidal and supratidal processes. The Cape Sable area offers a unique opportunity to study the sedimentologic, hydrodynamic and facies relationships of sediments deposited in transitional marine conditions and under a variety of physical-process regimes.

Problem definition - In the 1920s narrow canals were dredged across Cape Sable in an effort to drain the wetland. The cutting of these canals abruptly changed the regime within

the Cape complex from one of fresh to brackish water conditions to one of open marine, tidal conditions. Almost at the same time, sea level started to rise rapidly. The current rising sea level trend equals 30 cm/century, which is 6 times faster than before 1930. Finally, over the past 80 years, Cape Sable and close surroundings has been impacted by three major hurricanes. A combination of these three natural and artificial induced factors has severely destabilized this coastal system. Cape Sable has become a system out of equilibrium and this is being translated into rapid widening of canals, extensive shoreline erosion and complete inversions of freshwater ecosystems to marine habitats.

Approach – Three ‘program themes’ have been identified: 1) Historical and present changes, 2) Sediment Inventory, 3) Sediment transport. These themes will be investigated with respectively 1) remote sensing (aerial and satellite), 2) Sedimentological and geochemical methods and 3) hydrodynamic observations and measurements.

Figure 1. Ikonos satellite image of Cape Sable study area.

3D/4D GPR Imaging of Sedimentary Structures and Fractures at Submeter Resolution Mark Grasmueck, Steve Truss, Ralf Weger, and Sandra Vega Key Points

• 3D GPR imaging of rock volume in combination with outcrop mapping for more accurate reservoir characterization.

• Survey gridspacing of 0.1x0.2m or less reveal submeter facies architecture and fracture networks in 3D.

• Next generation 3D GPR system for efficient data acquisition available in 2004. Rationale

Understanding flow, compartmentalization and mineralization in reservoirs depends on knowledge of the 3D architecture of sedimentary structure and fracture network in the rock volume around the borehole. Cores, logs and reflection seismic data render only isolated point or low resolution information. Exposed reservoir analogues serve as an additional source of spatial information. But outcrop observations, digital photography, laser scanning and remote sensing reveal only the characteristics of exposed geology. This superficial information is also biased by the extent, geometry and quality of the accessible rock faces. We use full-resolution 3D Ground-Penetrating Radar (GPR) imaging to non-destructively extract the missing information at submeter resolution from inside the rock volume.

Figure 1. Miami Oolite pilot survey 3D GPR amplitude cube (left) and the new 3D GPR system (right).

Development and Fieldtesting of a new 3D GPR System

The main bottleneck to more widespread application of such full-resolution volume imaging is the lack of efficient and lightweight 3D GPR survey equipment. The challenge is

to acquire high density survey grids with trace spacings of 0.05 to 0.2m on natural surfaces of outcropping rock formations. In 2003 we have begun the development of a unique acquisition system which surpasses existing equipment in productivity and precision.

In 2004 we will start using the system as an integral part of our high-resolution carbonate reservoir characterization projects. Two examples are briefly described below. Full-resolution 3D and 4D GPR imaging in Oolithic Limestone

To explore facies architecture, we acquired 24x46 meter, dense (0.1x0.2m) 3D GPR pilot survey on the Pleistocene Miami Oolithic Limestone. The 3D migrated cube shows prograding foresets with bifurcations, mottled chaotic facies, migrating sand waves with rapidly changing direction and possible dissolution features. Computerized connectivity analysis of the GPR cube reveals three-dimensional continuous geobodies within the main units that may represent individual flow units.

The new highly efficient GPR equipment will enable us to acquire multiple 3D datasets over a short period of time. In 2004 we plan to acquire data at several type locations of the Miami Oolithic system which will include geological information, 2D, 3D and 4D GPR surveys, drilling plus measurements of hydrogeologic properties. Goal is to build a regional litho- and hydrostratigraphic model to derive geometric and flow properties for oolithic hydrocarbon reservoirs systems. Fracture network imaging

We have shown the capability of 3D GPR to image the geometry of steep permeable fracture zones, in a fractured limestone quarry in southeastern Spain. In a full-resolution 100 MHz 3D GPR pilot dataset covering 1200 m2 three-dimensional migration focuses diffractions at the locations of fracture discontinuities. The focused diffractions line up as elements of four discrete sets of fracture orientations. With the help of rapid animations of consecutive time slices or cross-sections, spatial continuity and dip can be visually assessed. Open fractures filled with moisture and/or air cause strong GPR reflections and more diffractions. Cemented fractures cause a weaker response. This makes the combination of full-resolution 3D GPR and migration processing a powerful geophysical tool for delineating permeable fracture zones.

For 2004 we will use 3D GPR in a collaborative study with Taury Smith from Reservoir Characterization Group at the New York State Museum. He has identified a wrench fault controlled reservoir analogue in an upstate New York quarry. 3D GPR will provide the spatial subsurface information of a reidel shear zone and help develop and test an integrated model which relates stratigraphy, dolomitization, isotopic signatures and fractures. Movies of 3D GPR cubes imaging sedimentary structures and fractures can be viewed at http://mgg.rsmas.miami.edu/groups/csl/gpr/index.htm

Three-Dimensional Sedimentologic Architecture of the Miami Oolite Kelley Steffen, Gene Rankey, and Mark Grasmueck Project Purpose

Quantitative physical property variability information is usually derived from one-dimensional sources such as boreholes and outcrops. Commonly, it is difficult for these limited 1D and 2D data sets to reflect the true, 3D internal lithologic volumetric heterogeneity of the geobody. The goal of this project is to provide a 3-dimensional characterization of physical properties from a heterogeneous carbonate ooid shoal system with complex internal architecture. Scope of work

A 3-D ground penetrating radar (GPR) data cube will be integrated with cores from the survey area to explore facies architecture in a complex carbonate system. The data cube will provide means to map details of sedimentary structures, grain and porosity/permeability attributes, and, eventually, flow through the system. Key Deliverables

This project will provide a model of sedimentologic features and lithologic units seen in cores and expand them into the third dimension with the GPR cube. Such a model allows for submeter scale analysis of connectivity and distribution of individual units which can lead to more accurate fluid flow models for similar heterogeneous systems. Further test sites on the Miami Oolite are under investigation to establish regional variations in spatial architecture that could be applied to oolithic reservoirs. Project Description Study area

The Pleistocene Miami Oolite is a tidally influenced barrier sand bar; it is 10 km wide and extends 50 km through the Miami area. Outcrops are limited, but much of the original topographic morphology has been preserved. Expected Results

This study will show heterogeneity in an ooid shoal system influenced by bedform stratigraphy and cross-cutting dissolution features. Interpreted 3-D migrated data show complex internal bedform structures, including migrating sand waves, foreset truncations and bifurcations, mottled facies, and possible karst features. Scanning the animated time slices shows variations in amplitude, continuity, and orientation of reflectors, interpreted in the context of abrupt changes in bedding geometry within the unit. Sedimentologic features identified in cores will provide calibration points for high resolution, three-dimensional interpretation of the geobody, and heterogeneity within the body.

Figure 1. Time slice, line and cross line from GPR cube of the Miami Oolite. Note the changes in GPR character from high amplitude and continuity (green box) to lower amplitude and more discontinuous (yellow box). The sedimentologic character of these features will be explored through this project. Complex internal architecture is demonstrated by the mound-like feature filled in with orange. The blue box shows the internal foresets of the mounded feature on both the cross line and time slice.

Facies and Geometry of Mixed Sedimentation on an Isolated Carbonate Platform: Bocas del Toro Basin, Panama (year 2)

Donald F. McNeill and Anthony G. Coates

Project Purpose

The goal of this project is to provide a case study of an isolated carbonate platform in a mixed carbonate-siliciclastic setting subjected to uplift. A secondary goal is to evaluate the influence of early diagenesis on the carbonate facies in a humid, tropical setting.

Scope of Work

Field mapping has produced a baseline geologic map and initial cross-sections across the platform and platform margin. Additional field mapping will concentrate on establishing the geometrical relations, specific facies attributes, and chronostratigraphy of the platform.

Key Deliverables

When complete, this field characterization will provide a case study of an isolated platform subject to varying amount siliciclastic input. Facies attributes and key geometrical and stratigraphic relations will be established.

Project Description

The project consists of three main areas: 1. Field mapping data provide a three-dimensional record of tropical reef deposits in a

mixed setting at a reservoir scale (small platform ~10 km wide by ~25 m thick). 2. Reef geometries are expressed as a combination of Pliocene clustered pinnacles

(~200 m in diameter), a broad veneer of Pliocene carbonate shelf deposits (~15 m thick by 5+ km wide), and an onlapping wedge of Pleistocene reefs in a siliciclastic matrix.

3. Porosity development is associated with the amount of siliciclastic incorporated in the reef deposits, the degree of cementation, and the influence of meteoric diagenesis. The porosity style ranges from recrystallization derived vuggy porosity to karst sinkhole and incised-valley formation in the carbonate shelf facies.

Summary of Year 1 Results

Mapping in January and February 2003 has suggested that the platform contains two generations of mixed carbonate and siliciclastic deposition. Likewise, two stages of reef deposition are proposed:

1. The carbonate platform formed as a shallow shelf adjacent to a topographic (subaerially exposed) high in the underlying (basal) siliciclastics. The outer edge of the carbonate shelf consisted of a barrier reef (east coast) series of pinnacle reefs (north coast). The platform and reefs, although predominantly carbonate, were subjected to an occasional influx of siliciclastic mud. This mud likely originated

from the erosion of either the local subaerially-exposed basal siliciclastics, or the more distal volcanic arc of the proto-Central American Isthmus mainland. The barrier reef system was dominated by the branching coral Stylophora sp. in a well-cemented carbonate sand matrix. The pinnacles show thicknesses of about 20-25 m. Seaward of the reef margin carbonate of the north coast, sands and debris were shed to the upper slope and are now exposed along the coast and on offshore islands. Today, the reef and shelf facies are heavily karstified and show extensive sinkhole development. At one location these sinkholes and caves have extensively collapsed to form an incised channel through the limestone shelf facies.

2. The second reefal facies consists of a Pleistocene unit of mixed reefs and siliciclastic sands and mud. This unit onlaps the shelf facies of the oldest limestone and pinches out at higher elevations. This unit is preserved best on the leeward (south) side of the island. The reefs in this unit often occurred as small patches (<10 m) that were subjected to the constant influx of siliciclastic sediment. These muddy conditions resulted in a coral rudstone/floatstone in matrix of siliciclastic fine sand and mud.

Year 2 Research Plan for Platform Characterization

A preliminary geologic map and section description was completed in January and February 2003 and two analysis tasks are planned during 2004:

First, the basic geological map and cross-sections will be constructed to characterize the stratigraphic and facies relationships in this mixed-system example. As part of this, petrographic and porosity evaluation will be conducted on samples collected during the 2003 mapping effort. Lithofacies analysis will form the basis for the main carbonate facies characterization, especially between the reef deposits and the calcarenite facies of the prograding upper-slope facies. Porosity type and diagenetic style will be developed for each of the main carbonate facies.

Second, a follow-up phase of fieldwork is tentatively planned for Winter-Spring 2004 to increase the spatial density of field transects and to confirm the stratigraphic relations of the key lithofacies and their geometries.

Figure 1. Left: Location of the Bocas del Toro basin with general land elevation and shelf bathymetry. Uplift of the basin is a result of the subduction of the Cocos Ridge on the Pacific side of the isthmus. Right: General topographic model for the Bocas platform with main reefal facies.

Relations Among High-Resolution Sequence Architecture, Diagenesis, and Mechanical Characteristics of Outcropping Lower Carboniferous Grainstones, Missouri (year 2) Gene Rankey, Layaan Al Kharusi, and Guillermina Sagasti

Project Purpose

Three fundamental influences control fluid flow: depositional character and sequence stratigraphy, diagenesis, and fracturing. In this study, we will explore each of these, and their relations, in well-exposed outcrops of Mississippian (Visean) grainstones near St. Louis, Missouri.

Scope of Work

Depositionally, these strata include grainstones with considerable lateral and vertical heterogeneity. We have characterized the sequence stratigraphy and the geometry and continuity of grainstones. We have begun characterizing fracture patterns and the mechanical stratigraphy of the succession. The next step involves evaluating the diagenetic framework for the succession. Diagenetically, these strata include calcite cementation and dolomitization, and we suspect that these play a role in fracture patterns. We will evaluate timing and mechanisms of diagenesis by integrating petrographic, stable isotope, and fluid inclusion analyses to understand porosity evolution. The final step will involve developing testable, predictive models of relations among depositional character, diagenesis, and fracturing, and then explicitly testing these relations.

Key Deliverables

These efforts will yield: sequence stratigraphic characterization, quantitative information on continuity of grainstone bodies, models for fracture characteristics related to depositional and diagenetic character, and quantification of the accuracy of those models.

Study Site and Methods

Our project focuses on outcrops of Lower Carboniferous (Visean) strata in the St. Louis, Missouri, region. In this area, there are numerous outcrops several 100s of meters long that provide exceptional perspectives on facies heterogeneity and fracture patterns.

Stratigraphically, our focus includes the Visean Warsaw, Salem, and St. Louis formations. Facies record a spectrum of environments from subwavebase, deeper marine to tidally influenced shoal to tidal flat. Facies group to form parasequences, generally manifest as cleaning-upward packstone-grainstone cycles, although considerable variation is present as a function of the sequence stratigraphic and paleogeographic setting. High-frequency sequences are composed of parasequences bounded by flooding surfaces. Subaerial exposure features are rare. These units form the highstand sequence set of a composite sequence and include highly progradational facies belts. Salem and Warsaw grainstones have diverse geometries, which will be explored in terms of their paleogeographic and sequence stratigraphic setting by measuring sections and interpreting photo pans.

Diagenetically, these units have not been extensively studied, but preliminary data indicates a complex diagenetic history that includes calcite cementation, dolomitization, compaction, silicification and dissolution. Our approach to analysis will include mineralogic and petrographic study within the facies and sequence stratigraphic framework, followed by analysis of selected cement phases using stable isotopes and fluid inclusions. By integrating these techniques, we will evaluate how the sequence stratigraphy influences diagenetic patterns.

Mechanically, we have focused on measuring and describing fracture length, and spacing, and using these characteristics to define the mechanical stratigraphy. The continuous exposures allowed description and collection of a statistically significant data set of attributes of mechanical properties.

To integrate these different components, we will utilize two fundamental approaches: 1) first, we will utilize data mining and visualization tools to explore relations among depositional, diagenetic, and mechanical properties; and 2) second, guided by the results of approach 1, we will use more classic statistical approaches (multiple regression, as well as nonparametric methods) to produce quantitative or semi-quantitative models of relations among these variables – given a grainstone of a certain thickness, what can we predict about fracture attributes?

Finally, we will explicitly test these models on ‘new’ outcrops in the area. For example, we can measure a section and characterize the diagenesis and ‘predict’ the characteristics of the fractures based on the empirical model (derived above). We will then measure the fractures, and compare the predicted versus the observed to test the accuracy of the model.

Expected Results

• A quantitative understanding of the relationships among stratigraphy, diagenetic history and fractures, and their possible effect in reservoir development and/or enhancement in grainstone-dominated successions.

• Explicit tests of the model in highly continuous outcrops.

Quantitative Analysis of Flexural and Tectonic Subsidence and Eustasy on the Stratigraphic Architecture of a Carbonate Ramp: the Madison Group, Idaho, Wyoming, and Montana Matthew Buoniconti, Gregor Eberli, and Taury Smith Project Purpose

To apply two- and three-dimensional flexural subsidence analyses to ramp-to-basin sequence stratigraphic cross-sections of the Madison ramp in the northern US Rockies in order to quantify the contributions and timing of thrust load emplacement, sediment loading, brittle tectonic subsidence, and eustasy to system-wide accommodation development and sedimentary architecture development in an evolving foreland basin setting. Scope of Work

High-resolution sequence stratigraphic cross-sections constructed from approximately 18 detailed measured sections in Wyoming, Montana, and Idaho will be used in two- and three-dimensional flexural backstripping analyses (e.g., Watts, 1988) of two adjacent, orthogonal Mississippian margins and the adjoining ramp top. The analyses will be used to study the flexural subsidence history of the Antler foreland basin and establish a tectonostratigraphic framework for the Madison Group. Key Deliverables

Tectonostratigraphic models for the development of a prograding carbonate ramp in a foreland basin setting. Time slice maps of the study area showing spatial and temporal changes in subsidence. High resolution sequence stratigraphic cross-sections relating tectonic subsidence patterns to facies architecture development. Project Description Rationale and Objectives

Carbonate development in foreland basins is usually limited to the early phase of foreland development, as flexure-driven accommodation development usually outpaces the keep-up capacity of the carbonate system (Dorobek, 1995). The Madison carbonate ramp is anomalous in that the system keeps up and actually progrades and fills the Antler foreland basin during the Lower and Middle Mississippian (Kinderhookian - Meramecian). Based on one-dimensional subsidence analysis of six outcrop sections in Idaho and Montana, Reid and Dorobek (1995) concluded that most of the tectonic subsidence associated with the emplacement of the Roberts Mountain allochthon bracketed Madison deposition and that only minor tectonic subsidence occurred during Madison time. Sequence stratigraphic cross-sections, which we have constructed from 18 detailed outcrop measured sections in Wyoming, Montana, and Idaho, however, suggest that syn-Madison tectonic subsidence may have been responsible for significant accommodation creation and strongly influenced the distribution of reservoir facies. The goals of this study are:

1. to establish the paleotopography of the pre-Madison depositional surface through two- and three-dimensional flexural backstripping analyses, as initial basin configuration is a first-order control on facies distributions, margin location, and energy settings on the ramp.

2. to backstrip each third-order, and possibly higher order, sequence of the Madison and calculate the geometries of the Mississippian sedimentary surfaces, and the sedimentary packages they bound. This should allow assessment of spatial and temporal variation in flexural subsidence as related to variations in thrust-belt behavior and/or basement response.

3. to compare the accommodation histories and resultant sedimentary architectures of adjacent margins of the Madison ramp, one oriented parallel to the Antler foredeep and the other perpendicular, in order to quantify the dominant forcing mechanisms controlling their development.

Location and Regional Setting

The Madison shelf stretched 600 km from the Transcontinental Arch to the seaward-facing Antler foreland basin in southwestern Montana and Idaho and 450 km to the central Montana trough, a continental re-entrant linked to the Williston Basin. The margins are delineated by marked increases in stratigraphic thickness where continuous deposition is inferred as a result of high subsidence-driven accommodation development. The basin boundaries are controlled by Precambrian basement structures, although the Antler margin lies along a single lineament (Maughan and Perry, 1985) while the central Montana margin is a broad zone of deformation due to complex fault interaction (Peterson, 1985).

Broad trends in facies architecture, development, and organization can be correlated regionally across the Madison shelf (Rose, 1976). The Antler orogeny of Latest Devonian-Early Mississippian age caused broad downwarping across the study area and backstepping of the carbonate system. A series of shoalwater complexes then prograded across the shelf. By the Middle Mississippian, barrier bars and back-barrier lagoons had aggraded to sea level, filling the remaining accommodation space. Approach

In year one of our study, we examined outcrops along the Antler foredeep ramp margin-to-basin transition. In year two, a high-resolution sequence stratigraphic study of the central Montana trough margin was begun and was completed this field season. Additionally, year three research focused on a detailed reconstruction of the carbonate foreland basin fill. Sections were measured along a transect of outcrops extending across the Antler foreland basin in Idaho.

This study will focus on integration of these data sets and those collected previously in Wyoming on the Madison ramp top in order to gain a holistic view of the system’s development. In addition to the sequence stratigraphic framework, which we have previously established, this year we look to establish a quantitatively-based tectonostratigraphic framework to help advance our understanding of the evolution of the Madison sedimentary system from a geodynamic perspective.

Current and Expected Results This study provides an opportunity to reassess the paradigm that foreland basin

carbonate systems are restricted temporally to the early phases of basin formation before backstepping or drowning and being spatially restricted to the flexural bulge. Study of the Madison will lead to new models for carbonate ramp development in foreland settings. Quantifying the relationships between tectonics, eustasy, and stratigraphy in this setting will allow for better understanding of the primary mechanisms controlling development.

Additionally Middle and Upper Mississippian ramp margin-to-basin carbonates of the Pricaspian Basin in the former Soviet Union have been shown to be major hydrocarbon reservoirs; however, few outcrop examples of coeval strata exist worldwide. The well-exposed outcrops of east-central Idaho provide an excellent analog of carbonate development at this time.

Figure 1. Formation-scale cross-section (top) across the Antler foreland basin displaying the geometry of the prograding Mississippian Madison carbonate ramp (modified from Rose, 1977). The paleogeographic map (bottom; modified from Gutschick and Sandberg, 1983) displays the locations of sequence stratigraphic cross-sections which will be used in this study (A-A’ and B-B’).

Relationship Between Fractures and High-Resolution Sequence Stratigraphy (year 3 of 3) Layaan Al Kharusi, Gregor Eberli, Gene Rankey and Mike Gross Project Purpose

The main objective of this study is to identify a relationship between mechanical stratigraphy and high-resolution sequence stratigraphy in order to predict, to a certain degree, fracture patterns from stratigraphic information. Scope of Work

Combine high-resolution sequence stratigraphy and mechanical stratigraphy in three selected strata of various ages to assess the influence the stratigraphic control on the structural style and the fracture distribution. We measure the fracture density, frequency and lengths to define mechanical units of strata in which the genetic units are known and assess the controlling parameters in these fractured carbonates. Key Deliverables

• A case-study report on the relation of mechanical to sequence stratigraphic units. • Assessment of importance of facies, diagenesis and bed composition and thickness

on the fracture behavior in carbonates. Project Description Rationale and Objectives

Results from the first two years of this study have shown that the rock properties generated by the combined effect of facies and diagenesis within in each small-scale stratigraphic unit are related to the mechanical properties of the strata. In particular, the transgressive and regressive hemicycles of each genetic unit that formed during one high-frequency sea level rise and fall coincide with mechanical unit boundaries (Figure 1). These findings give strong evidence that understanding of the stratigraphic architecture and the vertical facies variations can be used for a prediction of the fracture pattern and frequency. The completed and planned work

Our initial results of the Madison Formation at the Sheep Mountain Anticline locale in the Bighorn Basin, Wyoming, indicate that each genetic unit comprises at least two mechanical units (Figure 1).

The results from the second area in Lower Carboniferous (Visean) strata in the St. Louis confirmed these results. In addition we found that in composite beds, such cross-bedded grainstone units, the fracture length is not determined by the overall bed thickness but by the bedsets with the composite bed. This leads to a complex compartmentalization of the fractures (Figure 2).

Figure 1. Example of relationship between stratigraphic and mechanical units boundaries from the Sheep Mountain Anticline in Wyoming. Fracture terminations determine mechanical unit boundaries that coincide with genetic unit boundaries and with the turnaround from transgressive to regressive facies within a genetic unit.

Figure 2. Schematic illustration of a cross-bedded composite bed and the complex fracture pattern that is controlled by the bedset boundaries as well as the bed boundary. Consequently, bed thickness and fracture length and spacing yield a low correlation.

In the coming year, we plan to study the Pennsylvanian mixed system in Raplee Anticline of the Paradox Basin where shelfal carbonates are alternating with shales and sandstone layers (e.g. Grammer et al. 1996). This site will complement the limestone-dolostone cycles in Wyoming and the limestone cycles of St. Louis. In addition, we plan to compare the fracture and stratigraphic hierarchies from outcrop photographs.

References Grammer, G.M. et al., (1996). Rocky Mountain Section, SEPM Special Publication,

p. 235-266.

The Demise of Shallow-Water Platforms in the Bahamas Kelly Bergman and Gregor Eberli

Project Purpose

Platform drowning in foreland basin settings is a common phenomenon; yet, the relationship between tectonic movements and drowning is not well understood. Seismic and core data from the Cuban-Bahamas foreland are used to investigate this relationship. In particular, we will perform a seismic facies analysis of deep-water deposits surrounding the margins of Cay Sal Bank in conjunction with a newly developed Paleogene-Neogene age model, to:

1. assess the depositional history of drowned and backstepped shallow carbonate margins,

2. establish the age of the drowning and backstepping events, and 3. relate the depositional history to structural events of the Bahaman-Cuban collision.

Scope of Work The seismic facies analysis of newly digitized seismic data will be incorporated with the

age model from ODP Leg 166 sites and the Great Isaac Well to examine the depositional and drowning history of the shallow-water carbonate platforms (Figure 1). This chronology will be correlated to the tectonostratigraphic history of the Cuban-Bahamas foreland basin.

Key Deliverables

We will establish the shallow-water platform history within the Bahaman-Cuban seaways and identify the driver behind their segmentation and drowning.

The drowning of the platforms in the Bahamas foreland

The segmentation and drowning throughout the Paleogene and Neogene of shallow-water carbonate banks surrounding the Straits of Florida was driven by compressional movement and increased subsidence associated with the Bahamas-Cuban collision. The breakup of an Early Cretaceous platform that extended from Cuba to Florida was associated with faulting related to the onset of collision (Eberli and Ginsburg, 1989; Masaferro, 1997). Compression within the Cuban fold and thrust belt continued throughout the Paleogene, continued into the Middle Miocene and at a reduced rate into the Late Pliocene-Pleistocene and may be active into the present day (Masaferro et al., 1999). It is our working hypothesis that this late stage compression resulted in the stepwise backstep of the Cay Sal margins throughout the Paleogene and into the Miocene.

Approach

Dates from ODP Leg 166 sites will be correlated into thousands of km’s of multi-channel seismic lines in order to precisely date the deep-water carbonate facies surrounding and overlaying the edges of the Cay Sal Bank (Figure1). In the coming year, we will extend the age model to include six pre-Neogene ages from the Great Isaac well on the northwest

corner of Great Bahama Bank and correlate the additional ages throughout the seismic data set (Figure 2).

Seismic facies of drowned platforms and basin deposits

Platform edges are recognized by seismic facies transitions. Shallow-water carbonates are composed of high-amplitude, chaotic reflections or high-amplitude semicontinuous, interfingering subparallel reflections (Figure 2). The deep-water facies exhibit variable amplitude, continuous parallel to subparallel reflections that drape underlying topography. The deep-water facies can be exactly dated and thus the ages of the first sediments overlaying the drowned platforms can be established.

Preliminary Findings

The modern Cay Sal Bank is a remnant of a larger bank that backstepped and left two buried shallow water margins of distinct ages (Figure 2). The older backstepped margin is overlain by basinal seismic facies of Late Oligocene age. The age of the top of the bank is not known and consequently a hiatus could exist between the platform margin and the overlapping basinal sediments. Normal faults bounding the margin contain inversion structures draped by Late Oligocene reflections along the southeastern margin and by Late Miocene to Early Pliocene reflections along the northern margin.

The younger buried margin is found along the eastern and southeastern edges of Cay Sal bank and is characterized by a steep seaward escarpment. The platform edge is draped by Late Miocene to Early Pliocene age reflections giving a minimum age of the top of the platform but again the length of a potential hiatus is not known.

References Masaferro, J. L., 1997, Interplay of tectonism and carbonate sedimentation in the Bahamas foreland basin:

Unpubl. Dissertation, University of Miami, 147 p. Masaferro, J. L., Bulnes, M., Poblet, J., and Eberli, G. P., 2002, Episodic folding inferred from syntectonic

carbonate sedimentation: the Santaren Channel anticline, Bahamas foreland, Sed. Geology, v. 146, p. 11-24.

Masaferro, J. L., Poblet, J., Bulnes, M., Eberli, G. P., Dixon, T. H. and McClay, K., 1999, Palaeogene-Neogene/present day (?) growth folding in the Bahamian foreland of the Cuban fold and thrust belt, J. of Geol. Society, London, v. 156, p. 617-631.

B. Petrophysics of Carbonates

Introduction Assessing the controlling factors, such as porosity, pore structures, pressure, saturation

and mineralogy on sonic velocity and permeability in carbonates remains the goal of our petrophysical studies. Understanding the relative importance of all these parameters is important to assess the uncertainties that arise when using theoretical equations with certain assumptions to interpret or predict velocity, porosity and permeability trends from subsurface data sets. For example, we have shown, that one of the basic assumptions in Gassmann’s equation, which says that the dry and wet shear moduli are constant, needs to be questioned in carbonates. A project will address the causes for these shear modulus variability. Also based on initial results from last year, we expand our experiments on the effect of saturation on carbonates. The results of these experiments will provide a guidance of assessing uncertainties in AVO analysis and time-lapse seismic surveys.

In earlier studies we documented the importance of pore structures on velocity at a given porosity, and qualitatively related pore types to these velocity variations. In the coming year, we rely on an improved digital image characterization of pore structures to relate this parameter in a quantitative way to the individual samples. In addition, we increase our pore structure analysis from 2-D to 3-D by examining the pore structures from high-resolution CT –scans on plug samples. Over the last years we started to assemble a data-base on dolomites and plan to focus on the sonic velocity and permeability in dolomites to get a better understanding of the petrophysical behavior of various types of dolomite.

In addition, we embark on an integrated sedimentologic, diagenetic, petrophysical study on recently acquired cores from the grainstone belt in which we will address several of the questions regarding the pore-structures in oolithic grainstone, the influence of early cementation on sonic and hydraulic properties, and the cause for the heterogeneity in such oolithic grainstone settings.

Parameters Controlling Petrophysical Heterogeneity of Bank-Margin Grainstones, Ocean Cay, Bahamas Donald F. McNeill, Guillermina Sagasti, Ralf Weger, and Gregor Eberli Project Purpose

Margin grainstone belts are prolific yet heterogeneous reservoirs. The heterogeneity is caused by facies variations and diagenetic overprint. This project takes advantage of a series of tightly spaced core borings (22) at Ocean Cay at the western margin of Great Bahama Bank to investigate these parameters (Figure 1). The results aim to characterize the impact of facies and digenesis, in particular early cementation, on these rock properties.

Scope of Work

The shallow core borings that recover bank-margin grainstones will be described and sampled to provide data for three main characterization tasks: sedimentology, hydraulic properties, and petrophysics. In particular, we will analyze the vertical and lateral distribution of the grainstone and boundstone facies, petrographically and chemically assess the diagenetic alterations, collect whole-core hydraulic properties, and measure porosity, permeability, and sonic velocity of a large number of samples. This integrated data set will provide a comprehensive evaluation of bank-margin sands, a common reservoir type in ancient carbonate platforms.

Key Deliverables

When completed, this dataset should provide a thorough characterization of the vertical and lateral heterogeneities of these bank-margin deposits, their diagenesis, and their petrophysical character. The complete dataset will be available to the Industrial Associates for their use in forward platform models, as geological analogs, and for training purposes.

Project Description Rationale and Objectives

The availability of numerous core borings from a bank-margin setting provides the unique opportunity for an integrated analysis of the depositional system and the physical properties of these recently lithified carbonate sediments.

Approach of Each Task

1. Sedimentology-Petrography-Diagenesis (Guillermina Sagasti): Detail sedimentological descriptions and thin-section analysis will be conducted in order to develop a depositional model, assess heterogeneity, and evaluate the main diagenetic features. The multi-core set will allow a pseudo-3-D characterization of bank-margin heterogeneity with respect to facies and diagenesis. The lateral distribution can then be compared to grainstone facies heterogeneity of modern ooid sands seen on satellite images.

2. Hydraulic Properties of Bank-Margin Lithofacies (Don McNeill): The large-diameter cores provide the perfect opportunity to accumulate a lithofacies-based

dataset on hydraulic conductivity, porosity, and permeability in grainstone deposits. Whole-core falling- and static-head measurement will be used to determine hydraulic conductivity. Subsample 2.54 cm plugs will be collected to assess bed-scale heterogeneity in porosity and permeability. A gas-injection permeameter will help to characterize the vertical permeability heterogeneity in each core.

3. Petrophysical Characterization of Grainstones (Gregor Eberli and Ralf Weger): The young grainstone core samples contain a wide variety of cementation stages and are thus ideal to investigate the influence of cementation on acoustic wave propagation. Digital image analysis of thin sections will be used to derive quantitative parameters describing amount and location of contact cements. In addition, laboratory experiments under wet and dry conditions will assess the relationships between grains and pore size, and saturation on velocity. The digitally derived parameters are also used to relate permeability to pore size and shape.

Figure 1. Location map and satellite photograph of the grainstone belt along the western margin of Great Bahama Bank. The 22 core borings are from on the island of Ocean Cay and the immediate surrounding offshore areas. The site is in close proximity to the deep water of the Straits of Florida.

Permeability in the Miocene Marion Plateau Platforms (year 3 of 3)

Gregor Eberli, Heike Delius, Stephen Ehrenberg, Guido Bracco Gartner, Gregor Baechle, Ralf Weger, Kathleen Willis, and Peter Swart

Project Purpose

The study has three major objectives: 1) to assess the porosity-permeability relationship through detailed petrographic and digital image analysis. 2) to establish if permeability follows the sea-level controlled architecture or if and how much later diagenesis is responsible for the heterogeneous distribution of permeability in these platforms. 3) to search for a detection of permeability from other physical properties, in particular vp/vs.

Scope of Work

Permeability measurements on core plugs will be compared to a) the pore structure from digital image analysis to relate permeability to changes in texture and diagenesis, and b) to laboratory velocity measurements.

Key Deliverables

Permeability measurements of platform and slope carbonates of the Miocene platforms. Relationships between pore structure parameters determined with digital image analysis and permeability. Assessment of the effects of the different pore types on permeability. Description of diagenesis, in particular dolomitization on the permeability of platform carbonates.

Project Description Rationale and Objectives

Quantitative information about porosity and permeability in subsurface carbonates is important for understanding the processes of fluid flow involved in both diagenesis and petroleum exploitation. Two Miocene platforms that were drilled during Ocean Drilling Program Leg 194 on the Marion Plateau provide the unique opportunity to study fluid pathways and to assess compartmentalization of flow units as a function of the diagenesis and stratal geometries (Figure 1). To date, over 700 samples are measured in this ongoing study. The samples of mainly bioclastic limestones and dolomitized equivalents show a wide range of porosity and permeability in both dolostones and limestones, large variations between individual sites (Figure 2) and, and a better porosity-permeability correlation in the dolostones than in the limestones. Based on these results the specific questions addressed are:

• What is the relationship between rock textures, digitally-derived pore structure parameters and permeability?

• What causes dolomitization and how does the variably dolomitization influence permeability?

• What causes the differences in diagenesis, in particular leaching, that is responsible for the lateral heterogeneity between the two platforms sites?

• Can high permeability trends be detected by high Vp/Vs ratio as our initial results indicate?

Approach and Workplan

Thin sections 700 measured porosity and permeability samples are digitized and the pore structure parameters are analyzed. Digitally derived parameters (e.g. perimeter/ surface area, dominant pore size; specific parameter) will then be correlated to permeability to assess their influence on hydraulic properties. Simultaneously, a diagenetic study is performed that consists of thorough petrographic analysis and stable isotope measurements to assess the origin of the dolomite. Micro-sampling of dolomite cement will address the question of a potential evolution of the dolomitizing fluids. Sonic velocity measurements will be added to increase the data-base for a correlation between the hydraulic and elastic properties in these platform carbonates.

Expected Results

The study will help to assess the controlling factors in the porosity-permeability and permeability anisotropy and its detection in sonic data. In addition, the geochemical data will elucidate the dolomitization processes in these drowned platforms. The results will be applicable to other drowned Miocene platforms in South East Asia and other parts of the world.

Figure 1. Permeability within Miocene Southern Marion Platform within megasequence framework. Permeability is highly variable in a vertical and lateral sense, and strongly reduced in the off-platform periplatform sediments.

Figure 2. Porosity-permeability plot illustrating the various φ/K trends in each of the drilled sites. This variability is especially unexpected for the two platforms sites 1196 (light blue) and 1199 (green) that are only 6 km apart. Different leaching seems to be the major factor for this lateral variability in φ/K (Figure 3).

Figure 3. Thin section photomicrographs documenting the different leaching and permeability at Site 1196 and 1199. Both facies are dolomitized but at leaching is more pronounced at Site 1199, increasing permeability. Photos from Steve Ehrenberg.

Quantifying 3-D Pore Geometry and its Effects on Ultra Sonic Velocity and Permeability in Carbonates (year 1 of 1)

Ralf Weger, Gregor Baechle, and Gregor Eberli

Project Purpose

Establish a set of parameters that is capable of describing 3-D pore geometry quantitatively from full core plug high resolution (30µm) CT scans. Evaluate the relationship between several CT scan derived parameters (e.g. specific surface and dominant pore size) and measured velocity and permeability.

Scope of Work

Quantify digitally on full plug high resolution CT scans the porosity, homogeneity, and pore/rock system connectivity using seismic interpretation software. Measure porosity, permeability, and acoustic velocities at several pressure steps and varying saturation states on 1 inch carbonate core plugs. Relate quantitative 3-D pore structure parameters to permeability and velocity changes under variable pressure and saturation.

Key Deliverables

Data base of measured physical parameters and quantitative 3-D pore geometry parameters derived from CT scans. Quantitative description of the relationship between both physical and pore structure parameters. Assessment of the effects of pore system parameters variations have on acoustic velocities under varying pressure and saturation states.

Project Description Rationale and Approach

Our current studies have shown that 2-D digital image analysis provides parameters (e.g. Specific Perimeter and Dominant 2D Pore Size) that correlate well with physical properties, particularly acoustic velocities (Figure 1). The two-dimensional nature of thin sections, however, often can not provide information regarding connectivity that is crucial for describing the hydraulic properties of the rock. Preliminary results have shown that partial 3-D CT scan analysis can result in inconclusive results. This problem is particularly evident when relating digital image volumes to permeability. In a given rock sample, for example, the overall flow property can be determined by a small, tight spot. As a result, digital scans that are limited to only a portion of the rock sample under investigation often provide misleading results. To avoid these problems, we plan to perform CT scans on the entire core plug at 30µm voxel resolution on the same core plugs, which were used to measure physical and hydraulic properties. The digital volume will then provide an unbiased basis for comparison with the measured values of permeability and velocity.

Approach

CT scans of entire core plugs will be performed at the University of Texas. All plugs will be covered with CT-slices every 27µm with 30µm pixel resolution. The resulting 16bit

gray scale intensity images are threshold into binary images. All volumes are subsequently converted into SGY format in order to use our existing Matlab© routines for further analysis. Body Checking the volumes allows for separation of connected and unconnected porosity (Figure 2). The shape parameters calculated from connected porosity will be analyzed with respect to their influence on hydraulic properties. The seismic interpretation package SMT VolumPack will be used for volume visualization and quality control for both thresholding and bodychecking.

Expected results

• Robust correlation of 3-D pore volume derived parameters to hydraulic properties and likewise an evaluation of the relationship between 3-D rock volume connectivity and elastic properties of the sample.

• Better understanding of how to determine 3-D connectivity from either 2-D digital image parameters and/or physical parameters such as acoustic velocity

0 100 200 300-800

800Specific Perimeter vs. Velocity Deviation

Specific Perimeter

0 200 400 600 800 1000-800

800Dominant Pore Size vs. Velocity Deviation

Dominant Pore Size

Figure 1. Crossplots relating image derived parameters (Dominant pore Size and Total Specific Perimeter to the deviation of acoustic velocity from its best linear fit (VP-Best Fit). Specific Perimeter produces best results for acoustic velocities larger then the best linear fit, and Dominant Pore Size produce best results for velocities smaller then the best linear fit.

Figure 2. 3-D image of body checked CT scan, in which red areas represent connected/effective porosity and blue areas show the unconnected porosity.

Saturation Effects on Velocity in Carbonates (year 2 of 2) Gregor Bächle, Ralf Weger, and Gregor Eberli Project Purpose

Understanding the effects of saturation on the acoustic properties of porous media is paramount for using amplitude versus offset (AVO) technique and 4-D seismic analysis. We conducted saturation experiments in carbonates with the intention to fill this gap. These experimental data are used to test theoretical assumptions in AVO and seismic analysis in general. Our data document that pore fluid compressibility and variations in shear modulus due to saturation are important factors for velocities in carbonate rocks (Figure 1). In particular, we observed shear weakening and shear strengthening and observed that saturated samples show distinctive higher Vp/Vs ratios than unsaturated samples (Baechle et al. 2003). The causes for both, the shear weakening and the high Vp/Vs ratio, are not well understood. The proposed project aims to find these causes. Scope of Work

Combine extensive laboratory measurements of velocities on wet and dry samples with petrography, digital-image analysis parameters and x-ray diffraction to assess differences of samples with shear weakening from those with shear strengthening. Perform repeat velocity measurements to test if shear weakening can be reversed. Use other fluids to exclude chemical reactions as a cause for weakening Key Deliverables

• Extend data set of various experiments of velocity at different pressures and saturation.

• Visual petrographic description of pore/rock types • Precise mineralogy of samples in experiment. • Digital image analysis parameters of pore structures of measured samples. • Model for causes of shear strengthening and weakening in carbonates and its

implication for AVO and seismic time lapse analysis. Project Descriptions Rationale and Approach

Earlier studies on saturation in carbonates have shown a consistent lower shear modulus for wet samples (Japsen et al., 2002, Assefa et al., 2003). In our samples, complete saturation of the pore space separated the samples into one group that showed decreases in shear bulk modulus by up to 2 Gpa and another group that showed increase by up to 3 GPa. All these findings question Gassmann's assumption of constant shear modulus in dry and saturated rocks. Consequently, estimating saturated velocities using the Gassman equation might be inaccurate, as Wang et al. (2000) showed and our data set corroborated. We observe both overestimation and underestimation when using Gassmann to calculate P-wave velocity. Samples for which Gassmann underestimates velocity also show a shear

strengthening, while most samples for which Gassmann overestimates the velocity show a shear weakening (Figure 1).

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Figure 1. Plot of changes in shear modulus versus the difference between measured and Gassmann-predicted velocity. Gassmann underestimates the velocities in samples with shear strengthening and overestimates the velocities in samples with shear weakening.

Furthermore, preliminary results indicate that samples with shear weakening consist mostly of rocks with interparticle/intercrystalline porosity, while fluid saturation has less effect in rocks with dominant microporosity and moldic pores. To test this hypothesis we plan to use digital image analysis parameters to separate the individual pore types. Clay admixtures are often cited as cause for shear weakening. Thus, we plan to precisely assess the sample composition and evaluate the effect of such admixture in carbonates.

Expected Results

We expect to find the cause for shear weakening in carbonates. If we succeed the uncertainty in AVO and time lapse seismic can be better estimated. References Assefa, et al.., 2003, Geophys.Prospect., 51, 1-13. Baechle et al. 2003, SEG annual meeting, carbonate workshop abstract. Japsen, P., et al., 2002, SEG, international exposition and 72nd annual meeting; 72, 1881-1884. Wang, Z., 2000, , in Wang, Z. and Nur, A., Eds., Society of Exploration Geophysicists, 8-23.

Sonic Velocity and Permeability of Dolomites Ralf Weger, Gregor Bächle, Gregor Eberli, and Steve Ehrenberg Project Purpose

Earlier studies have shown that dolomites have a wide range of sonic velocities that are related to the various dolomite types that form during the transformation from limestone to dolomites. The purpose of this project is to quantitatively relate the various rock fabrics to sonic velocity and permeability using digital image analysis on the thin sections of the samples for which velocity and permeability were measured. Scope of Work

Use existing data base and measure additional dolomite samples from ODP Leg 194 and the Madison Formation to capture the wide range of sonic velocity and permeability in dolomites. Combine these laboratory measurements of velocities with the following parameters crystal size, crystal and pore structure, and mineralogy. A multivariate analysis will be used to determine the importance of each of these parameters on sonic velocity and permeability. Key Deliverables

• Characterization of sonic velocity and permeability in a wide variety of dolomites. • Digital image analysis parameters of pore structures of measured samples. • Assessment of the relationship between various types of dolomites and physical

properties. Project Descriptions Rationale and Approach

Transforming calcite to dolomite during diagenesis occurs either in a fabric-preserving or fabric-destructive manner. Fabric-preserving dolomitization maintains to a large degree the limestone rock texture and pore types. Velocities of fabric-preserving dolomites are generally fast. In fabric-destructive dolomites original rock textures are largely destroyed and replaced by an intercrystalline rock fabric (Figure 1). Depending on the crystal size micro-sucrosic or sucrosic dolomites form and limestone is dissolved. The amount of fluid flow determines the amount of dissolution, dolomitization and crystal size, producing the variety dolomite textures and resultant petrophysical properties. Understanding these variations requires an assessment of the produced rock fabrics and a correlation to the petrophysical properties. This correlation will be performed on samples from the Mississippian Madison Formation and the younger, high porosity dolomites of the Miocene Marion platforms. In regards to velocity, dolomites show a first –order correlation with porosity but as in limestones a range of velocities exist at a given porosity that is controlled by other factors, which are the focus of this project.

Figure 1 left. Illustration of fabric-destructive and fabric-preserving dolomite across the Mio-Pliocene boundary in Clino. Although both sections are 100% dolomite, their velocities differ. Figure 1 right displays the porosity-velocity plot of already measured velocities of the two main data sets used in this study. The reasons for the variations in velocity at given porosities are the main focus of this study. Expected Results

The combined analysis of velocity, porosity and permeability of samples from the Madison Formation and ODP Leg 194 from the Marion platforms with petrographic, digital image and mineralogical analyses will help to identify the controls of each parameter on the petrophysical behavior. This extensive study will improve our understanding of the sonic velocity and permeability of dolomites.

0 10 20 30 40 50

Madison

Leg194

Time-average

Origin of Uranium Anomalies in Carbonate Rocks (year 3 of 3) Heike Delius, Gregor Eberli, Guido Bracco Gartner, and Peter Swart

Project Purpose

To better understand the uranium enrichment in the various platform lithologies and calibrate the log response to times of regressive and transgressive sedimentation on drowned Miocene platforms.

Scope of Work

Use fission track methodology to locate the source of uranium in carbonate rocks.

Key Deliverables Visual images of the distribution of uranium in carbonates. Interpretation of the genesis

of uranium in carbonates and its significance in a sequence stratigraphic analysis.

Project Descriptions Rationale and Approach

ODP Leg 194 drilled two transects on the Marion Plateau carbonate platform, offshore northeast Australia. Different patterns in high natural-gamma radiation detected in core samples can be related to exposure surfaces and submarine hardgrounds. The goal is to better understand the uranium enrichment in the various lithologies and calibrate the log response to times of regressive and transgressive sedimentation.

Uranium is enriched in phosphatic crusts and glauconite, and within the platform, in dolomite. However, its position within each of these minerals is not yet clear. Two attempts to detect the source(s) and locations of the Uranium failed. Phosporus imaging and photosensitive imaging proved not to be sufficient in resolution. Detailed thin sections and fission track analyses will help to locate the uranium and allow an interpretation of its genesis.

Thin sections were radiated and the fission tracks can be examined in adjacent plastic detectors of the samples. The fission track analysis will be performed in conjunction with a thorough facies description and an integration of the gamma peaks into the sequence stratigraphic framework.

Expected Results

The integration of facies and fission track analysis will indicate the genesis of gamma radiation in individual samples, while the correlation to the logs and the sequence stratigraphy will increase the use of gamma logs in well correlations.

C. Geochemistry and Diagenesis of Carbonates Introduction

Diagenesis continuously alters carbonate rocks and consequently their petrophysical properties. Our research projects have thus a double focus; one to understand the diagenetic processes, and two, to relate the diagenetic alterations to the resulting rock properties. The project on the modern sediments on Great Bahama Bank provides a base line information about the geochemical signature of “unaltered” carbonate platform sediments. The integrated project on cores from grainstones along the western margin of Great Bahama Bank will document the effects of early diagenesis on porosity, velocity, and permeability in grainstone shoal complexes. The geochemical studies of the dolomites and limestones of Miocene Marion platform carbonates are ideal to examine the influence of shallow –burial diagenesis on the same petrophysical properties and at the same time to assess the fluid flow in isolated carbonate platforms. The Mississippian Madison Formation underwent several episodes of diagenesis from shallow to deep burial. Our current geochemical projects in this formation try to unravel these different episodes and to document the importance of each event on the reservoir quality of the formation. In addition, we test the applicability of geochemical tracers, in particular δ13C, for the stratigraphic correlation of the widely spaced section in Wyoming and Idaho and to other sections around the world.

Surface Sediment Mapping of the Bahamas Peter K. Swart, Robert Otto, John Reijmer, Gregor Eberli, and Gene Rankey Project Purpose

In order to compliment the important work of Purdy and other earlier workers, we have started a five-year project designed to collect samples from a significantly denser grid of stations than the earlier work. Over a two year period we have conducted two cruises to collect samples on a grid of approximately 10 km and have collected samples from over 200 stations in the northern portion of GBB. Rather than the Van-Veen sampler we have used the Shipek grab sampler that obtains samples by passing a scoop through the sediment and hence mud is less likely to escape from the sample. The goal of the project will be to document the distribution of sedimentary facies on the Great Bahama Bank utilizing (global positioning system) GPS and present data utilizing geographical information system (GIS) technology. These data will enable geologists to better interpret past geochemical and sedimentary facies in ancient carbonate platforms. Scope of Work 1. Collect samples from additional stations in the following critical areas.

• The sampling, which we started in 2001, concentrated to the northern portion of GBB. Although we still have areas, which need to be sampled in this area, our first priority will be to extend the sampling towards the southern region of GBB that was less intensively sampled by Purdy (1963a,b) and Ginsburg et al. (1958).

• Our current sampling was all taken from the RV Bellows, which has a draft of 2 meters. Therefore we have not sampled close to islands, which we will do from small boats.

• The original sampling carried out by Purdy (1963a,b) and Ginsburg et al. (1958) was restricted to the shallow surface waters of GBB. We intend to sample to a depth of approximately 100 meters around the margins of GBB. This will allow us to ascertain the relationship between the surface sediments and the sediment, which is being exported onto the slopes. We realize that we will not be able to investigate sediment, which may by pass the slope. However, an extensive off bank survey is outside the scope of this project.

• During the sampling we will perform salinity analyses and take samples for alkalinity and δ13C analyses of the DIC.

2. Make sedimentary descriptions and grain size analyzes on all samples • John Reijmer’s group at Kiel has already made preliminary descriptions of the

samples collected and the group is in the process of performing sample descriptions and separating different size fractions in addition to the ones that have been carried out already in Miami. Sample description will use nomenclature used by Purdy (1963a,b).

3. Measure the isotopic composition and amount of organic material in all samples and size fractions. • Geochemical analyses will be performed on all bulk samples and different size

fractions. The specific geochemical analyzes will be X-ray diffraction, trace and minor element analyzes, stable C and O isotopic analyzes of the inorganic fraction. The concentration and C and N isotopic of the organic material will also be measured.

4. Place all data within a GIS database. • Data is placed within a GIS database to enable maps to be constructed showing

spatial distribution of parameters, which we will measure during this study. 5. Relate bottom type to remote sensing data to develop more extensive maps

• More extensive, spatially continuous maps of bottom type will be done using Landsat and SPOT remote sensing images by calibrating the data collected in this study. This work will be carried out together with Gene Rankey.

6. Measure the thickness of the Holocene • During 2003 we used a shallow penetrating seismic system in order to determine the

thickness of the Holocene. Further surveys will determine the relationship of the present day sediment types to the underlying topography. We will also take selected cores in order to calibrate the facies above the Pleistocene. This work will be carried out with Gregor Eberli.

Figure 1. CHIRP profile across Great Bahama Bank, showing a depression in the Pleistocene topography that is healed by the Holocene sediment cover. The negative antecedent topography obviously did not influence the Holocene sediment distribution. References Ginsburg, RN, Lloyd, RM, McCallum, JS, Stockman, KW, and Moody, RA. (1958) Surface sediments of

Great Bahama Bank, (unpublished EPR Report 506), Shalle Development Company. Purdy, E. (1963a). Recent calcium carbonate facies of Great Bahama Bank I. Petrography and reaction

groups. Journal of Geology 71. Purdy, E. (1963b). Recent calcium carbonate facies of Great Bahama Bank II. Sedimentary facies. Journal of

Geology 71, 472-497.

Lower Mississippian Carbonate Geochemistry: Montana and Wyoming David Katz, Peter Swart, Gregor Eberli, Matthew Buoniconti, and Langhorne (Taury) Smith

Project Purpose

Previous work has shown that carbon isotope fractionation, in particular a positive carbon excursion in Sequence II, in Mississippian carbonates is a valuable tool to characterize sequences within the Madison Formation. Especially, the unique carbon record of individual third order sequences aids in our correlation of sequences from the upper ramp to the basin, especially when classical sequence boundaries are nonexistent and are replaced by subtle facies changes within cycle hierarchies, or when characteristics of individual outcrops vary drastically as is such the case in the outer Madison ramp.

Furthermore, results of this study will contribute to a better understanding of the climatologic significance of the Kinderhookian to Osagean (Sequence II) inorganic carbon excursion. Previous research related to this issue proposed that the isotope excursion is the result of a global change in the oceanic carbon pool during the onset of the Gondwana icehouse phase. Preliminary results from our study indicate the opposite, that the Sequence II carbon excursion resulted from the maturation of a stranded water mass atop the Kinderhookian-Osagean ramp (Figure 1). Scope of Work

Stable isotope, trace element and organic isotope analysis of carbon and nitrogen will be performed on an inner Madison ramp section and deep-water equivalents in the outer ramp in order to better document and understand the perturbation in the carbon record from Sequence II and the rest of the Madison Formation. We will also test the hypothesis that the carbon perturbation in Sequence II is a local effect and not a global change in seawater chemistry. In order to test this hypothesis, inorganic isotope analysis will be performed on Sequence II (Kinderhookian-Osagean) carbonates located in basin and slope settings from Idaho, Montana, Arkansas, and cores from the Tengiz platform, slope and basin. Key Points and Deliverables

• The positive δ13C values in Sequence II can be correlated to time-equivalent periplatform carbonates in Russia, Utah, Nevada, Iowa, and Western Europe, indicating its potential use as a stratigraphic tool in these regions

• Test of hypothesis that organic carbon primarily composed of δ12C in Sequence II, is sequestered by rapid burial of marine sediments during the transgressive hemicycle, while during the regressive phase, organic carbon becomes oxidized and is responsible for releasing δ12C back to the marine environment.

• Comparison of δ12C excursion in the Madison Formation with sections from other parts of the world, e.g. Tengiz platform to assess global significance of excursion.

Project Description In the ongoing sedimentologic/stratigraphic study in the Madison Formation, the

sedimentation in the evolving Antler foreland basin is investigated (see description by Buoniconti et al., this volume). Correlation of the widely spaced sections is based on bio- and sequence stratigraphy but initial results of stable isotope geochemistry has yielded a potential powerful method for correlation and, in addition, pointed to a significant climatic change during the deposition of the Mississippian Madison Formation. Carbon isotope profiles from every measured section along the upper Madison ramp, and sections from the outer ramp in Montana, except for the Bell Mackenzie section, show a strong carbon excursion within Sequence II that can be correlated over a 700-mile cross-section. The positive carbon isotope excursion reaches a maximum between +6 to +8 ‰ PDB near the 3rd and 2nd order turn-around to the next regressive event, thereby following 3rd order cyclicity of the sedimentary and stratigraphic record.

All examples from this study derive from ramp carbonates except for Bell Mackenzie and it is located at the paleogeographic toe-of-ramp where slope breccias and turbidite deposits, transported from the upper ramp, interfinger with thinly bedded open-ocean argillaceous sediments. Stable carbon isotope values of the transported slope and argillaceous deposits are ca. +6.5 ‰ PDB and +2 to +3 ‰ PDB (Mississippian seawater carbon), respectively. This would indicate that toe of slope to basin argillaceous sediments derive their δ13C/δ12C from circulating open ocean waters, or the true carbon pool. This study addresses the correlation potential of this method and the changes of the global carbon pool during this time.

Figure 1. Relative sea level and carbon flux model for SII/Kinderhookian-Osagean carbonates from Montana and Wyoming that illustrates our working hypothesis that is tested in the proposed study. During the transgressive phase (A), organic carbon mostly composed of δ12C is sequestered by rapid burial of marine carbonates. As the regressive phase (B) initiates, oxidation of organic carbon during a relative fall in sea level releases δ12C back into the marine environment.

Geochemistry of Dolomitization and its Relationship with Sequence Stratigraphy (year 2 of 3) David Katz, Peter Swart, Langhorne “Taury” Smith, and Gregor Eberli Project Purpose

The Madison offers a unique opportunity to test models of dolomitization relative to the sequence stratigraphic framework established by Sonnenfeld (1996) and Smith et al. (2003). Last year we concentrated on samples from closely spaced intervals with alternations of limestone and dolomite in Sequences 1 and 2 of the Madison Formation. The dolomites have previously been interpreted as having been formed as a result of reflux and associated with the formation of evaporates, now present as collapse breccias. Our initial results, however, indicate several episodes of dolomitization from a variety of sources. Stable isotopic and trace element geochemical analyses of these dolomite intervals will further refine the interpretation of the formation of these rocks. Scope of Work

We will investigate the dolomitization and diagenesis of the Madison with detailed geochemistry. The geochemistry of the dolomites and associated rocks provide information on the temperature of formation and the nature of the fluids involved. In addition, analysis of the organic content and its isotopic composition may provide information on the nature of migrated bitumen. This project will be carried out in conjunction with projects, which will describe the geochemistry relative to the fractures and documented the carbon isotope composition in relation to the sequence stratigraphy. Key Points and Deliverables

• Examine the patterns of stable isotope geochemistry relative to the depositional framework and ascertain the origin of the dolomitization patterns in the Madison Formation. At the present time a significant portion of the stable isotope geochemistry has been completed.

• Examine the fluid inclusions of the dolomites in order to constrain the salinity of the dolomitizing fluids.

• Examine the trace and minor element geochemistry of the dolomites to constrain the nature of the diagenetic process.

• Determine the stable isotopic composition of the organic material as an indicator of the depth of the carbonate platform and possible origin of migrated bitumen.

References Sonnenfeld, M.D.,1996. Sequence evolution and hierarchy within the Lower Mississippian Madison limestone

of Wyoming, in M.W. Longman and M.D. Sonnenfeld, eds., Paleozoic Systems of the Rocky Mountain Region, Rocky Mountain Section SEPM, 165-192.

Smith, L. B., Eberli, G. P., and Sonnenfeld, M.D., 2004, Sequence stratigraphic and paleogeographic distribution of reservoir-quality dolomite, Madison Formation, Wyoming and Montana. AAPG Memoir 80, in press.

************************************** Contact Information Gregor P. Eberli geberli@rsmas.miami.edu (305) 361 4678

Comparative Sedimentology Laboratory RSMAS / MGG University of Miami 4600 Rickenbacker Causeway Miami, Florida 33149

Donald F. McNeill dmcneill@rsmas.miami.edu (305) 361 4790

Peter K. Swart pswart@rsmas.miami.edu (305) 361 4103

Mark P. Grasmueck mgrasmueck@rsmas.miami.edu (305) 361 4858

Karen J. Neher kneher@rsmas.miami.edu (305) 361 4684

Website http://mgg.rsmas.miami.edu/groups/csl/index.htm

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