USGS Oil and Gas

Resources

Assessments Brenda Pierce, U.S. Geological Survey

April 3, 2012

Total Petroleum System Processes

24803

Petroleum System ElementsPetroleum System Elements

120° F120° F

350° F350° FGenerationGeneration

MigrationMigration

Seal RockSeal Rock

Reservoir RockReservoir Rock

OilOil

WaterWater

Gas CapGas Cap

EntrapmentEntrapment

Source Rock

Armentrout, 2001

Conventional vs. Continuous Resources

Conceptual diagram illustrating the differences in geologic context between conventional and continuous (nonconventional) petroleum resource accumulations. Modified from Schenk and Pollastro (2002).

Conventional Reservoir

Medium-

grained, cross-

bedded

sandstone

Thin section photomicrograph

Spiro Sandstone

Core slab

Continuous Reservoir

Weakly

Laminated

Shale

Strongly

Laminated

Shale

(Slatt and others, 2011)

Thin section photomicrographs

Woodford Shale

QO QO

Photomicrograph of an

uncemented sandstone

from the Jurassic

Morrison Fm. Blue is

epoxy that fills primary

pores (between grains) and

some secondary pores that

have developed from

partial dissolution of some

detrital feldspar grains.

Photomicrograph from a tight sandstone in

the Bossier Fm. It is tight due to abundant

quartz overgrowths (QO), and porosity exists

between adjacent quartz overgrowths

Woodford Shale, OK

10 mm

SEM image of primary & secondary pores in

organic-rich Woodford mudstone. Red encircles

primary pore between clays & other framework

minerals, white arrows point to “slot” primary pores

between clay platelets, and blue arrow points to

secondary pore developed in detrital K-spar grains.

SEM image of pores in Woodford chert. Red

encircles secondary pores between authigenic

quartz crystals, arrows point to “slot” secondary

pores between authigenic quartz crystal faces.

Conventional vs Continuous Reservoir in Outcrop

Limestone

(conventional)

Shale

(continuous)

Pitkin Limestone & Fayetteville Shale

Goal of USGS Assessments

Develop geologically based and statistically

sound hypotheses concerning the quantities

of oil and gas that have the potential to be

added to proved reserves in the U.S. and the

world. USGS produces estimates of

undiscovered, technically recoverable

resources.

Assessment is an estimate of

measurement uncertainty, expressed

quantitatively.

DEVELOP

BACKGROUND

INFORMATION

GEOLOGIC ANALYSIS

AND

RISK ASSESSMENT

VOLUME & FLOW

ASSESSMENT

Economic

Evaluation

(at times)

DEFINE

ASSESSMENT

UNITS

DEVELOP

ANALOG

APPROACH

DEVELOP ANALOG

MODELS FOR

VOLUME & FLOW

Integrated Evaluation Algorithm

Assessment Unit (AU) Definition

Compile geologic information

Build geologic model

Map provinces – geologically defined

Define assessment units – all assessments

Classify assessment unit uncertainty (can do multiple levels)

13

Geologic Analysis and Risk Analysis -

Petroleum Generation Model

Oil Cracking 6-7 km

Oil Maturation 3 km

From Franke and Hinz (2005)

Continuous Methodology

Geologic definition of assessment units

Drainage areas of wells (cell sizes)

Number of potential cells (tested and

untested)

Engineering data – well production and

performance

EUR (estimated ultimate recovery)

distribution

Woodford Shale: Horizontal Well Density

AU Probability Considerations

Is there a productive well within the AU?

Is the reservoir known to contain gas?

Is charge inferred to be adequate in the AU?

Is adequate reservoir present?

Has gas been retained in the AU?

Example: Bakken

Formation (2008)

Mean total = 3.65 BBO

(F95=3.0 BBO; F5=4.3 BBO)

Changes result from improved geologic

understanding, technological developments,

other factors

USGS 1995 Bakken Assessment:

Mean total = 151 MMBO

973 MMBO

909 MMBO

868

MMBO

410 MMBO

485 MMBO

Resource Assessments

Change Over Time

Source rocks of the Alaska North Slope:

estimates (95-percent to 5-percent probability)

range from zero to 2 billion barrels of oil and

from zero to nearly 80 trillion cubic feet of gas.

http://energy.usgs.gov