Lecture3_Facies Depositional Env From Logs

PAB 2084/PCB 2044 Well Logging & Formation Evaluation Lecture 3 Facies, Depositional Environments from LogsM D H A B I B U R R A H M A N /

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By: Md Habibur Rahman Lecturer Department of Geosciences Universiti Teknologi PETRONAS [email protected] Office 19-03-14, Extn: 7114

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OutcomeFacies, sequence and depositional environments from logs Electrosequence Analysis Fence Diagram Isometric ProjectionM D H A B I B U R R A H M A N /

Facies concept Correlation7/23/12

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in the grain sizes, it varies because of changes in clay content (the same is true for SP). However sedimentological interpretations based on gamma ray log shapes require the log to vary with grain size. This involves undiclared assumptions: Gamma ray variations are related to clay volume changes, and Clay volume changes are related to grain size differences. Care must be taken in using the gamma ray to indicate the clay volume, because clay radioactivity is not constant (it depends on the clay mineral and 7/23/12 mineral mix) and more importantly there are naturally

Gamma ray-Grain size Relationship The gamma ray doesnot vary because of the changes

Gamma ray-Grain size RelationshipThere is no doubt that a grain size-clay content relationship exists (Figure). However it is, by no means, a constant one. In some sandstones where the clay content varies with grain size , so do the gamma ray values, in others there is no relationship. Good relationship between grain size and clay content is observed in deltaic and fluvial sediments where deposition is largely controlled by flowing current energy.


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In many cases changes in grain size, which is essential to the identification of sedimentary structures or sequences do not involve changes in clay content or at least changes sufficient to affect gamma ray.M D H A B I B U R R A H M A N /

Gamma ray-Grain size Relationship

Neither the relationship between gamma ray value and clay volume nor the relationship between clay volume and grain size are constant, as they should be if the shape of the gamma ray log is to be used as universally applicable facies indicator.

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Electrosequence Analysis(a tool for sedimentological and stratigraphic interpretation)the concept: This section describes a system for the identification and analysis of log-based sequence or electrosequences.

Step 1: Interpretation of lithology

Step 2: Electrofacies annotation The annotations that should be marked on the logs are described below in a M D logical order of simple to more and more complex>

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1- Baselines 2- Trend lines 3- Shapes 4- Abrupt breaks 5- Anomalies (log values high or low peaks). Step 3: Electrosequence analysis for log-based sequences, facies and depositional environment7/23/12

Electrosequence Analysis(a tool for sedimentological and stratigraphic interpretation)

Concept


An electrosequence in an interval defined in wireline logs through which there are consistent or consistently changing log responses and characteristics, sufficiently distinctive to separate it from the other electrosequences. It will typically be tens of metre thick and correspond to the sedimentological succession of facies (i.e. a cycle). The objective of electrosequence analysis is to extract from logs as much geological information as possible by identifying vertically continuous, depositional, stratigraphic and eventually sequence stratigraphic unit. 7/23/12


Concept

Compared to the log shape study (where only one log is considered), electrosequence analysis uses all the available logs, much other data and covers all the wells, not just the sand bpdies or reservoirs. Above all, electrosequence analysis is a systematic approach to log sequence interpretation and was developed by Elf in France (Serra, 1972, 1973).M D H A B I B U R R A H M A N /

The first principle of the system is that reservoirs and non reservoirs are equally important: geology is not restricted to reservoirs.

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ConceptIn a sand-shale sequence for instance, the environmental information contained in the finegrained, non-reservoir intervals, equals or even exceed that in the reservoir zones.M D H A B I B U R R A H M A N /

The second principle is that no one log can characterize a formation: each logging tool examine the same formation but from different aspects, and all are equally characteristic.

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Steps for electrosequence analysis1.

Interpretation of lithology Electrofacies annotation Electrosequence analysis for log based sequences, facies and depositional environment

2.M D H A B I B U R R A H M A N /

3.

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Electrosequence Analysis(a tool for sedimentological and stratigraphic interpretation) Steps for electrosequence analysis 1. Interpretation of lithology


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Electrosequence Analysis(a tool for sedimentological and stratigraphic interpretation) Steps for electrosequence analysis 2. Electrofacies annotation Electrofacies: A suite of wireline log responses and characteristics sufficiently distinctive to be able to be separated from the other electrofacies.


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Electrosequence Analysis(a tool for sedimentological and stratigraphic interpretation) Steps for electrosequence analysis 3. Electrosequence analysis for log based sequences, facies and depositional environmentM D H A B I B U R R A H M A N /

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Fence DiagramsCreate 3D cross sections or fence diagrams of interpolated lithology, stratigraphy, quantitative data, colors, fractures, and aquifers. Include source log data, borders, and legends. Types of data that can be represented as fence diagrams: Lithology distribution Stratigraphic layers Quantitative data distribution (geochemistry, geophysics, geotechnical) Colors Fracture proximities Aquifer surfacesM D H A B I B U R R A H M A N /

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Fence Diagram


A fence diagram based on lithology data, with superimposed downhole data logs 7/23/12

R oc k W or ks

Lithology FencesDisplay interpolated lithology in fence panels Include a lithology color legend and view volumes of the lithology types in the 3D window .


R oc k W or ks

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Stratigraphy FencesDisplay interpolated stratigraphic surfaces in fence panels, or display "straight" linear correlations Include a stratigraphy color legend


R oc k W or ks

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Quantitative Data FencesDisplay slices of your interpolated geochemistry, geophysical, geotechnical, or other quantitative data in 3D fence panels Include color legends Display in combination with an isosurface, and/or append stratigraphic surfaces for reference


R oc k W or ks

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Fracture Fences Model fracture locations in 3D and display slices of the model as fence panels Append fracture discs on 3D logs Include a legend to colors and distances


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Aquifer FencesDisplay aquifer surface and base in 3D fence panels Combine with an isosurface representing a contaminant plume Float a reference map above the image


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Isometric projection is a method for visually Isometric projection


representing three-dimensional objects in two dimensions in technical and engineering drawings. It is an axonometric projection in which the three coordinate axes appear equally foreshortened and the angles between any two of them are 120 degrees.

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Facies and Correlation Facies

- definition - contacts and successions - Walthers LawM D H A B I B U R R A H M A N /

Correlation - basis - examples

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Facies: Definition rock that characterize it. Aspects of a

Mappable, aerially restricted part of a lithostratigraphic body that differs from it coeval equivalents.M D H A B I B U R R A H M A N /

A distinctive rock type that is characteristic of a particular environment.

A body of rock distinguished on the basis of its fossil content.

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Facies: DefinitionEnvironment: physical, chemical, biological conditions v s


Facies: sediment properties-

Lithofacie s-

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Biofacies

Facies: Definition


(AGI, 1999)

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Facies: DefinitionMeandering Stream Facies


(Boggs, p. 280)

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Facies: Contacts


(Boggs, p. 464)

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Facies: Contacts

L at er al C o nt a ct sintercalat ed gradu al

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abru pt

M D

V er ti c al C o nt a ct s

gradationa l

intertongui ng

pincho ut

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(Boggs, p. 453)

Facies: Succession s

Meanderi ng Stream

Delt a

Regressi ve Shelf

Transgressi ve Shelf

Coarsening Upward

Coarsening UpwardM D H A B I B U R R A H M A N /

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Fining Upward(Boggs, p. 260)

Fining Upward

Coarsening Upward

Fining Upward

Facies: Walthers Law Walthers Law: environmental relationshipWalthers Law states that the vertical succession of facies reflects lateral changes in environment. Conversely, it states that when a depositional environment "migrates" laterally, sediments of one depositional environment come to lie on top of another. A classic example of this law is the vertical stratigraphic succession that typifies marine trangressions and regressions. However, the law is not applicable where the contact between different lithologies is non-conformable (i.e. sedimentation was not continuous), or in instances of rapid environmental change where non-adjacent environments may replace one another. 7/23/12between lateral facies and vertically-stacked strata


Facies: Walthers Law

Transgression: landward movement of shoreline

Regression: seaward movement of shorelineM D H A B I B U R R A H M A N /

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Facies Regression (Progradation)

Time linesM D H A B I B U R R A H M A N /

(E. McBride)

Diachronous Lithostratigraphic Units

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7/23/12http://www.gpc.edu/~pgore/geology/historical_lab/stratig



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http://www.gpc.edu/~pgore/geology/historical_lab/stratig raphy.php

Correlati ondemonstrate that rocks at distant places are equivalent

- lithology / stratigraphic position - fossil content - age*


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Correlati onTypes of Data: Outcrop descriptions

9 mile s Castille Formation,NM

Cores Well Cuttings Well Logs Geophysical data


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(Anderson et al.,

Correlati on


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Correlati on

Correlation MatchingM D H A B I B U R R A H M A N /

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Correlati onBasis of Correlation:1.

trace lateral continuity lithology* rock properties stratigraphic successions fossil content chemical, magnetic, or geophysical properties

1.

1.


1.

1.

1.

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Correlati on


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http://www.gpc.edu/~pgore/geology/historical_lab/stratig

Correlati on

I rM D H A B I B U R R A H M A N /

I r

I r

I r

(Boggs, p. 7/23/12 476)

Correlati on


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Correlati on

Marker Bed Ash Fall


http://www.es.ucsc.edu/~pkoch/lectures/lectur e1.html

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Correlati on

Stratigraphic Successions


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(Boggs, p.

Correlati on


http://www.gpc.edu/~pgore/geology/historical_lab/stratig raphy.php

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Correlati on


index fossils principles of stratigraphy marker horizons geophysical properties geochemical properties

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http://www.uwsp.edu/geo/faculty/ozsvath/images/stratig raphy.jpg

Correlati on

(Boggs, p. 483)


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Correlati on

Fence Diagra msM D H A B I B U R R A H M A N /

(416M )

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Correlati on

Fence Diagra msM D H A B I B U R R A H M A N /

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(Prothero and Schwab, p. 486)

Correlation: Examples


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Name The FormationLithostratigra phy Super Group Group Formation Member / Tongue / LentilM D H A B I B U R R A H M A N /

Tongue / Bed / Flow

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Lithostratigra phy The conventional hierarchy of formal lithostratigraphic termsis as follows: Group - two or more formations Formation - primary unit of lithostratigraphy Member - named lithologic subdivision of a formationM D H A B I B U R R A H M A N /

Bed - named distinctive layer in a member or formation Flow - smallest distinctive layer in a volcanic sequence The component units of any higher rank unit in the hierarchy need not be everywhere the same.7/23/12

Formation: The primary formal unit of lithostratigraphic classification. Formations are the only formal lithostratigraphic units into which the stratigraphic column everywhere should be divided completely on the basis of lithology. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region and the detail needed for geologic mapping and to work out its geologic history.M D H A B I B U R R A H M A N /

Lithostratigra phy

No formation is considered justifiable and useful that cannot be delineated at the scale of geologic mapping practiced in the region. The thickness of formations may range from less than a meter to several thousand meters.

Formation is a mappable rock body with distinct boundaries 7/23/12

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Lecture3_Facies Depositional Env From Logs