Overview of unconventional energy resources of Oklahoma

              Overview of Unconventional 
Energy Resources of 
Oklahoma
By Brian J. Cardott
(Oklahoma Geological Survey)
Presented at OGS Conference on  Unconventional Energy Resources 
in the Southern Midcontinent  in Oklahoma City on March 9, 2004
Unconventional Energy 
Resources of Oklahoma
!Coalbed Methane
!Gas Shales
!Oil Shales
!Tight Gas and Ultra-Deep 
Reservoirs
!Oil (Tar) Sands
Coalbed methane, gas shales, and 
tight gas reservoirs are commonly 
referred to as continuous gas 
accumulations because they are 
regionally pervasive and generally 
not buoyancy-driven 
accumulations, commonly 
independent of structural and 
stratigraphic traps 
Non-conventional (or unconventional) 
fuels that were eligible for tax credits 
under the Internal Revenue Service 
Code Section 29 from 1980 2002
o oil from shale
o oil from tar sands
o natural gas from geopressured brine, coal
seams, Devonian shale, or tight sands
o liquid, gaseous, or solid synthetic fuel, including
petrochemical feedstocks, (other than alcohol)
from coal liquefaction or gasification facilities
Non-conventional (or unconventional) 
fuels that were eligible for tax credits 
under the Internal Revenue Service 
Code Section 29 from 1980 2002
o gas from biomass (including wood)
o steam from solid agricultural by-products
o qualifying processed solid wood fuels
Coalbed Methane
See  Coalbed-Methane Activity 
in Oklahoma, 2004 Update 
Gas Shales
Gas shales and oil shales are varieties of 
hydrocarbon source rocks.
HYDROCARBON SOURCE ROCK CLASSIFICATION
Organic matter type refers to the kerogen or 
maceral type and can be lumped into gas 
generative, oil generative, or inert.  
Organic matter quantity is determined by the total 
organic carbon (TOC) content (weight percent, 
whole-rock basis).  
Vitrinite reflectance (%Ro, oil immersion) is the 
most common thermal maturity indicator.  
Vitrinite is a maceral derived from the woody 
tissues of vascular plants.  The oil window is 
considered to be from 0.5 1.3% Ro. 
Gas Shales
Definition: Gas shales are organic-rich, fine-
grained sedimentary rocks (shale to siltstone) 
containing a minimum of 0.5 wt % TOC.  
Gas shales may be thermally marginally-
mature (0.4 0.6% Ro) to mature (0.6 2.0% Ro) 
and contain biogenic to thermogenic methane.  
Gas is generated and stored in situ in gas 
shales as both sorbed (on organic matter) and 
free gas (in fractures and pores), similar to 
natural gas in coals.  As such, gas shales are 
self-sourced reservoirs.  Low-permeable 
shales require extensive natural fractures to 
produce commercial quantities of gas.
Gas Shales of the United States
Hill and Nelson, 2000
Hydrocarbon Source Rocks of Oklahoma
Johnson and Cardott, 1992
Van Krevelen Diagram
Burruss and Hatch, 1989
Woodford Shale <1-14
Caney Shale 2.02-5.4
Excello Shale 1-17
(black shale lithofacies)
FORMATION TOC (WT %)
Potential Gas Shales of 
Oklahoma
Woodford
Shale
Stratigraphy
0 50 M iles
0 50 Kilometers
2.0
2.0
1.3
1.3
Choctaw
Fault
1.3
2.0
Map of Mature Woodford Shale
Adapted from Carr (1987), 
Cardott (1989, 2001a, 2001b), and 
Comer (1992)
Woodford-Only Oil & Gas Leases
Map of oil and gas lease production 
was generated by Scott March with 
Geo Information Systems from 
Natural Resources Information 
System (NRIS) data files
24 Woodford-only gas leases
48 Woodford-only oil leases 
(oil and associated gas)
Woodford Gas Wells
27.1 Bcf gas was produced from 19 
Woodford-only wells at 1,400 12,702 ft 
from June 1961 to November 2003
Gas production data supplied by 
Petroleum Information/Dwights
LLC dba IHS Energy Group © 2004
Caney Shale members 
are differentiated based 
on paleontology rather 
than lithology
Sutherland, 1981
 False  
Caney
Andrews, 2003
 False  Caney
Andrews, 2003
 False  Caney
Andrews, 2003
Caney Shale TOC Content
• 2.02-4.04% in the Arkoma Basin (16 
samples; Hendrick, 1992)
• 4.4-5.4% in the Ouachita Mountains (3 
samples; Cardott, 1994)
Caney-Only Gas Leases
Map of gas lease production was 
generated by Geo Information 
Systems from Natural Resources 
Information System (NRIS) data files
7 gas-only leases, 1979-9/2003
Caney Gas Wells
701 MMcf gas was produced from 4 
Caney-only wells at 2,668 3,872 ft 
from February 1998 to August 2003
Gas production data supplied by 
Petroleum Information/Dwights
LLC dba IHS Energy Group © 2004
Excello
Shale
Stratigraphy
Ece, 1989
● OK Outcrop samples
■ OK Core samples from
western OK (5,560-
9,541 ft)
Ece, 1989
Black shale lithofacies have 
1.1 16.8% TOC, ave. @10%
Excello Shale Thermal Maturity
Ece, 1989
0.51-0.63% Ro 
along outcrop
0.61-1.44% Ro 
from cores 
includes 
recycled vitrinite
Excello Shale gas 
production is included with 
Mulky coalbed-methane 
production
 any shallow rock yielding oil in 
commercial amount upon 
pyrolysis is considered to be 
an oil shale  
Oil Shales
Tissot and Welte, 1984
Oil Shales
!Mudstone, siltstone, marlstone, 
or carbonate
!Cambrian to Tertiary in age
!Thermally immature to mature
!Organic rich (minimum of 5 
volume percent types I and II 
kerogen; not related to TOC)
!Near surface
Hunton Quarry
Hycrude (1986) 
hydroretorting assay test
Woodford Shale in Arbuckle 
Mountains
!Marginally 
mature
!Surface 
exposure
!Type II 
kerogen
!9.5 wt% TOC
Woodford 
Shale Pit
Hycrude (1986) hydroretorting
assay test
• Hydroretorting is the heating (>540ºC) 
of shale in a retort under a hydrogen-
rich atmosphere at elevated pressures 
(@1,000 psi).
• Evaluated 90 pounds of Woodford 
Shale
Hycrude (1986) Results
• Fischer Assay oil yield, 8.4 gal/ton
• Raw Shale hydroretorting assay oil 
yield, 22.9 gal/ton
Highgraded for 120 minutes
• Highgraded Fischer Assay oil yield, 
20.3 gal/ton
• Highgraded hydroretorting assay oil 
yield, 46.8 gal/ton
Tight Gas and Ultra-Deep 
Reservoirs
“Tight gas sands are low-permeability gas-bearing
reservoirs (in a variety of rock
types) that have an in situ permeability to
gas of less than 0.1 md, exclusive of
natural fracture permeability. The
reservoirs are areally extensive, usually
abnormally pressured, and often (but not
always) found in basin-center settings���
(Kuuskraa and Bank, 2003)
Tight Gas in the United States
Law, 2002
Tight Gas in Oklahoma
Anadarko Basin
Red Fork
Cleveland
Granite Wash
Arkoma Basin
Atoka
Prouty, 2001
Tight Gas in Oklahoma
The Red Fork play has an average EUR 
of 2,200-8,800 MMcf/well at a depth of 
9,000-13,000 ft, net pay of 7-200 ft,  
porosity of 1-18%, permeability of 0.1-
20 md, and estimated ultimate 
recoverable of 2,890.6 Bcf.
Prouty, 2001
Tight Gas in Oklahoma
The Cleveland play has an average EUR 
of 1,000 MMcf/well at a depth of 5,500-
12,000 ft, net pay of 6-55 ft,  porosity of 
3-14%, permeability of 0.001-20 md, and 
estimated ultimate recoverable of 702.9 
Bcf.
Prouty, 2001
Tight Gas in Oklahoma
The Granite Wash play has an average 
EUR of 1,500 MMcf/well at a depth of 
6,500-11,500 ft, net pay of 10-60 ft,  
porosity of 4-12%, permeability of 
0.0009-1.4 md, and estimated ultimate 
recoverable of 349 Bcf.
Prouty, 2001
Oil (Tar) Sands
 Oil sands (also called tar sands in the 
U.S.) are sandstones or carbonate 
strata containing bitumen or other 
hydrocarbons of such high viscosity as 
to be immobile under normal reservoir 
temperatures. 
Rottenfusser, 2003
Oil (Tar) Sands
 In order to be utilized, the 
hydrocarbons must be mined or 
extracted in situ from the rock by the 
use of heat or solvents. 
Rottenfusser, 2003
Petroleum-Impregnated Rocks of
Oklahoma
Adapted from 
Jordan (1964)
Dougherty Asphalt Quarry
Cardott and Chaplin (1993)
Asphalt-saturated Viola Group limestone
In-Place Bitumen Resource of 3.6 
million barrels
Production of bitumen-
impregnated limestone > 1 million 
short tons from 1890 to 1960
Sulfur Asphalt Quarry
Cardott and Chaplin (1993)
White silica veins in asphalt- saturated 
Oil Creek Formation sandstone
In-Place Bitumen Resource of 
46.4 million barrels
Production of bitumen-bearing 
sandstone > 1.5 million short tons 
from 1890 to 1962
Bitumen-impregnated rock was 
quarried from the Dougherty and 
Sulphur districts and taken by truck 
to the crushing, screening, and 
mixing plant near Dougherty.  The 
blended asphalt product was used 
as road-paving material.  Synthetic 
crude oil has never been a product 
of the Oklahoma asphalt deposits.
Geologists with Suncor Energy Inc. 
(Canada) evaluated the Sulphur oil 
sand deposit in 1998 as part of a 
worldwide exploration for oil sand 
reserves.   Brian McKinstry (formerly 
with Suncor Energy; personal 
communication June 2003) indicated 
that the Oklahoma deposits were 
structurally complex (dipping at steep 
angles) and had limited bitumen 
resources for an economic oil sand 
operation.