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
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.
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