How Much Oil Is Really There?
Alaska Evaluation Due; Offshore California Estimate
By DAVID BROWN
AAPG EXPLORER Correspondent
Alaska - a land of great beauty, a land of great
potential. An exposure of the Kemik Sandstone - a potential reservoir
in the ANWRsubsurface - along the Canning River, with the west-plunging
Shublik Mountains in the background. Two hydrocarbon resource
assessments, one recently published and one soon to be released,
involve the most controversial and politically sensitive prospective
areas of the United States.
Those areas: Alaska and offshore California. And
to say that the findings of these reports are anxiously awaited
may be the year's biggest understatement.
First, the U.S. Geological Survey plans to reveal
results of a new oil and gas resource assessment covering part
of Alaska's Arctic National Wildlife Refuge (ANWR) at the AAPG
annual meeting in Salt Lake City in May.
ANWR tops the U.S. petroleum industry's wish list
for leasing, but Congress has prohibited to date drilling in the
The USGS is prepared for controversy over its new
"Naturally, this is a volatile topic," said David
Houseknecht, USGS energy program coordinator in Reston, Va. "The
results are likely to be met with lots of interest by both advocates
of resource development and proponents of environmental conservation."
Also, the U.S. Minerals Management Service (MMS)
recently published its "Assessment of the Pacific Outer Continental
Shelf Region," part of the 1995 National Assessment of United
States Oil and Gas Resources.
That report covers 15 assessed basins in federal
waters offshore California, Oregon and Washington. Prolific production
from the Monterey formation in the offshore California area, including
the Point Arguello oil field, once produced high industry interest.
However, the prospective areas are under a drilling
moratorium, and environmental opposition to exploration offshore
California remains strong.
Information about the MMS assessment report is
available at: http://www.mms.gov/omm/pacific
and a copy can be requested by e-mail from: firstname.lastname@example.org
'Thorough Piece of Work'
Ken Bird, research geologist for the USGS in Menlo
Park, Calif., served as project leader for the ANWR assessment.
The study covers about 1.5 million acres of the north Alaskan
Section 1002 of the federal Alaska National Interest
Lands Conservation Act of 1980 authorized evaluation of this area's
oil and gas potential by means other than drilling, and it is
often referred to as the 1002 area.
No matter how the USGS assessment is received,
Bird feels proud of the effort.
"It's by far the best and most thorough piece of
work that's been done up there," he said. "We had a very large
group of scientists working on this from many different parts
of the country."
Specialists in gravity interpretation, paleontology,
fluid-flow and many other areas contributed to the study, according
to Bird. The USGS team also used data not available in previous
assessments and made better use of existing information.
Two seasons of seismic work in 1984-85 produced
1,452 linemiles of data (607 line miles dynamite-sourced and 845
line miles vibraseis) in the 1002 area. For the new ANWR assessment,
these data were reprocessed and re-evaluated, Bird said.
In addition, data from wells drilled near the 1002
area became available for the resource study and provided valuable
well control, he added.
"I think there are 15-16 additional wells that
we had to work with this time that were not available earlier.
These are all wells that are within 15-20 miles from the 1002
boundary," Bird said.
Some well data in the area remain proprietary.
Bird said the ANWR assessment area includes a 100,000-acre expanse
of Native-owned land. An existing 15,000-foot well on that land
could have furnished additional data for the resource assessment.
"When you look at the structure maps, you see that
this well is located on one of the very biggest structures in
the entire area," Bird noted.
But that well is a tight hole. (Bird said the USGS
was able to obtain and use information from a well drilled downdip
on the flank of the same structure, in federal waters.)
"One of the biggest frustrations in terms of data
is that there are still a significant number of wells that are
as much as 18 years old that are still proprietary, that are still
tight holes, in the vicinity of ANWR," Houseknecht commented.
The new USGS assessment comes on the heels of an
ANWR resource report prepared at the request of the Interior Department.
Because the request was on a rush basis, the Survey used information
from the 1995 national resource assessment and simply did its
best to allocate resources to the ANWR area, according to Bird.
"In that 1995 (national) assessment, we did not
separate ANWR from the rest of the North Slope. We assessed it
in terms of about 11 different petroleum plays. Those plays generally
covered large areas, none of them specific to ANWR," Bird said.
Resource allocation led to estimates much lower
than expected - or wanted - by proponents of ANWR drilling. Criticism
of the study and negative comments followed, Bird recalled.
"There were all sorts of accusations that we were
politically motivated to reduce the numbers by the (Clinton) administration,"
he said, "so, that really stung.
"It caused us to decide that we really should spend
the time and the effort to do a complete assessment. We took it
upon ourselves to institute a new assessment of the project area.
This was strictly on our own."
Ahead of the Curve
Houseknecht offered another reason the USGS undertook
its voluntary study of 1002 resources. He said the Survey anticipated
future requests for assessment of the area, and wanted time to
do the job right.
"We have found that in many cases the federal decision-making
process requires technical information, but in a timeframe that
does not permit critical science to be done when a report is requested,"
Current seismic data and more well information
would have helped in the ANWR assessment, Houseknecht acknowledged.
But he feels the existing dataset proved adequate for resource
"Any time that you deal with a 2-D seismic network
that is more than a decade old, and that has a relatively low
density of coverage - naturally, any time you deal with that kind
of a dataset there is a resultant uncertainty in the assessment
of oil and gas resources," Houseknecht said.
However, he added, "for a frontier area like ANWR
this is a relatively high-quality dataset. And it's one that certainly
gives us the kind of constraints we need to evaluate the petroleum
Basic methodology for the ANWR assessment was very
similar to the approach used for the 1995 national resource assessment,
Bird said. The USGS chose a different methodology for projecting
economically and technically recoverable resources, however. It
also presented its methodology for review and comment prior to
Photos courtesy of David Houseknecht
A detailed view of the Kemik Sandstone, a potential reservoir
of Alaska's ANWR.
"We have attempted to make this assessment project
one where we have collaborated with as many people as possible,"
Houseknecht said. "We have held review meetings in Anchorage and
in Houston, where we presented the geological basis for our results
as well as our methodology."
That review process included a presentation to
the AAPG Committee on Resource Evaluation (CORE) in January. Ben
Hare is CORE chairman and chief geologist for Vastar Resources
Inc. in Houston.
Pending favorable analysis, CORE will express it's
evaluation of the USGS technical process and assessment methodology
to the AAPG Executive Committee, Hare said.
This is not the first time the committee has contributed
to an assessment review, he added.
"The CORE committee participated in the 1995 U.S.
(national oil and gas) assessment by making AAPG members available,"
Hare said. "The committee chairman at that time was Tom Barber.
Through Tom's effort we made some 75-100 AAPG members across the
country available to them, to make sure they were on the right
The MMS Pacific OCS report documents the oil and
gas commodities, resource categories, data and methodologies of
the assessment of the federal offshore area of California, Oregon
Its significant findings include:
- Nearly 11 billion barrels of undiscovered oil and 19 trillion
cubic feet of undiscovered gas in the region may be recoverable
using existing technology.
- Relatively large volumes of undiscovered oil may exist offshore
central and southern California, due largely to the presence
of Monterey-type strata, which are potential source and reservoir
- Half of the undiscovered, conventionally recoverable oil
and gas in the region may be economically recoverable under
Cathie Dunkel, MMS geologist in Camarillo, Calif., served as the
report's principal editor. She said the apparent extent of Monterey-type
plays and the possible large volume of undiscovered oil in these
plays offshore central California were the assessment's biggest
"Bottom-line, the volume of potentially fractured
siliceous rocks offshore California is much larger than we previously
thought," she said. "Only nine of the 46 plays we assessed contain
these Monterey-type reservoir rocks, but those nine plays, all
offshore central and southern California, are estimated to contain
more than half of the undiscovered oil and about a third of the
Monterey-type plays offshore central California
and in the Santa Barbara-Ventura Basin comprise the region's top
five plays, based on estimated undiscovered oil resources, she
Dunkel, a 16-year MMS veteran, found pursuing a
geologic hypothesis the most intriguing part of the assessment
process. She cited suggestions that the onset of petroleum generation
in the area's Neogene siliceous rocks (Monterey formation or correlative)
coincides with the temperature at which the diagenetic quartz
"For many years it's been recognized, or at least
speculated, that siliceous rocks of increasing diagenetic grade
are more brittle and have greater potential to be fractured, and
of course to have more fracture porosity," she added.
Using newly acquired mineralogic data from well
samples, MMS was able to identify the stratigraphic location of
the diagenetic facies in many of the wells and to correlate them
with structurally anomalous reflectors on seismic profiles, Dunkel
The resulting improved understanding of the stratigraphic
and areal extent of the siliceous rocks and their facies led to
the conclusion that larger-than-expected volumes of Monterey-type
rocks - including potentially generative source rocks and potentially
fractured reservoir rocks - exist offshore California.
In conducting its assessment, MMS was able to draw
on data and interpretations from many of the nearly 1,100 wells
and 200,000 miles of seismic-reflection profiles in the region.
"We also used available geologic and production
data from onshore and state offshore areas to assess some plays
that extend onshore. This is an improvement from past assessments,"
she noted. "Also, we received valuable information and feedback
from many members of government, geological organizations, industry
A Conceptual Approach
Resource estimates in the report are larger than
previous estimates, Dunkel said, and she offered several possible
reasons for the growth. MMS assumed a lognormal size distribution
of oil and gas accumulations, which led to the inclusion of additional
pools in many plays.
"Because we used a play-based approach for this
assessment, we included consideration of conceptual plays," she
noted. "Those are plays where no discoveries have been made -
in fact, where we don't have any hard data confirming the presence
of hydrocarbons, but for which data suggest that hydrocarbons
may have formed."
Also, "some of the rocks that are included in these
plays probably weren't given suitable consideration in prior assessments,"
she continued, "and that may be one of the reasons the numbers
Virtually all of the Pacific OCS is under oil and
gas leasing moratoria status through the year 2000, and the assessment
region is not included in the 1997-2002 OCS leasing program, Dunkel
said. In addition, some of the region's prospective areas are
in national marine sanctuaries.
Digital information from the assessment is being
compiled for release on the Internet or a CD-ROM later in 1998.
This information will include a browsable version of the report
and tabular data regarding plays and resource estimates.