Where is it? How much is there? How hard will it be to get it? Unconventional gas questions are getting answered.

A number of assessments related to the U.S. unconventional gas resource, including that portion found in tight gas sands, have recently been (or are about to be) published. The US Geological Survey (USGS), the Bureau of Land Management (BLM), the Department of Energy (DOE) and the National Petroleum Council are all playing parts in an effort to update our understanding of how much domestic unconventional gas is in place, to what degree access to the resource is restricted, and how much will be recoverable under different technology scenarios.

USGS updates 1995 assessment

Since 2000, the USGS has been in the process of updating its 1995 National Assessment of US Oil and Gas Resources. Their goal, according to USGS Project Chief Chris Schenk, is to update each of the 20 or so geologic provinces that contain 90% to 95% of the nation's hydrocarbon resources. The assessment includes both conventional and unconventional oil and gas. Unconventional resources are defined as "continuous" type accumulations lacking a water contact. According to Schenk, "The timeframe dictated by the EPCA legislation of 2000 required us to refocus our priorities a bit, so the BLM could meet their deadline." Schenk says that the updated assessments for five Rocky Mountain provinces (Uinta-Piceance, Montana Thrust Belt, San Juan-Paradox, Greater Green River and Powder River) will be made available on the USGS Web site (http://energy.cr.usgs.gov/) as they are completed. The summary results will first be posted as "Fact Sheets" on the site (the first of these, for the Uinta-Piceance, has been up since March), followed by the much more comprehensive geological reports on CD-ROM. At this writing, the Montana Thrust Belt, San Juan-Paradox and Greater Green River summaries are next in line for release. The first CDs will be available, "Hopefully before the end of 2002," says Schenk.

The fundamental methodology employed by the USGS in 1995 to assess the undiscovered, technically recoverable resource has not changed, although more of the geological framework behind the assessments will be published. The 1995 report, the first to include an assessment of unconventional gas resources, estimated a U.S. total of 308.1 Tcf (mean of probability distribution) undiscovered, technically recoverable gas in tight gas sands, gas shales and chalks, and a total of 49.9 Tcf for coalbed methane. The recent Uinta-Piceance assessment shows an increase in the mean value for the tight sand and shales category from 16.74 Tcf in 1995 to 18.89 Tcf, and a decrease for the coalbed methane category, from 10.70 Tcf to 2.32 Tcf.

The USGS Central Energy Resources Team (CERT) in Denver is the part of the survey developing these assessments. CERT has developed a Web site to deliver the assessment information in a user-friendly format. On the National Oil and Gas Assessment home page (http://energy.cr.usgs.gov/oilgas/noga/) selecting a basin from the list of assessed basins brings up a basin page that permits access directly to reports, tables, maps and data downloads. Play results and GIS data in shapefile or ArcInfo EXPORT format can be downloaded. All of the 1995 assessment data are available online, and Web site usage has been high (30,000 visits between August 2001 and May 2002). The new assessment data eventually will be available in a similar format.

BLM analysis prompted by EPCA

The BLM effort is a direct result of the Energy Policy and Conservation Act (EPCA) signed into law by President Clinton in November 2000. Section 604 of that legislation states that, "The Secretary of the Interior... shall conduct an inventory of all onshore Federal lands... identify the USGS reserve estimates of the oil and gas resources underlying these lands... and the extent and nature of any restrictions or impediments to the development of such resources... within 2 years after the date of the enactment of this section."

Of course, the largest area of overlap for Federal lands and unconventional gas resource is found in the Rocky Mountain basins. An interagency task force identified the five basins mentioned above as "priority geographic areas," based on their known resource potential and industry's interest. The BLM study employs the new USGS assessments for the five Rocky Mountain areas mentioned above and overlays a hierarchy of 10 restriction scenarios ranging from "no leasing by statute or executive order," through a number of administrative leasing restrictions and timing limitations, to conventional leasing under standard lease terms. The scenarios in play over individual geographic units will be used to determine the impact of various restrictions on the ability of the gas E&P industry to develop the resource for the nation.

The BLM assessment (which, at this writing has been completed), was scheduled for release on Nov. 5, but has been delayed pending an additional final review. The report will be available on the BLM Web site, and a limited number of printed reports will be made available to members of Congress.

DOE assessment focused on technology impacts

The DOE is concerned with the volume of the discovered resource available for the consumer and more specifically, the sort of government-sponsored research that might help to accelerate technologies that will either increase that volume or lower its cost. Matching research projects with their potential for reserves additions is an important part of the decision-making process for research funding choices. But this process requires a much more detailed description of the resource (e.g., not just how much gas is in-place in an area, but how it is distributed both vertically and horizontally, and what sort of geological characteristics might limit its economic productibility). With this information, the DOE can craft research programs with the greatest return on research investment, in terms of reasonably priced gas supply.

The DOE National Energy Technology Laboratory has already looked at the tight gas sands in the Greater Green River (GGR) and Wind River (WR) basins, following a methodology that uses hundreds of well log suites to capture the variation in key geologic parameters (depth, pay thickness, porosity, pressure and water saturation). This disaggregation of the known resource into uniquely characterized segments allows the DOE to model the response of the resource to various individual R&D scenarios (e.g., if we can reduce the cost of deep drilling by "X" or improve the accuracy of natural fracture delineation by "Y," we might add "Z" to the gas supply). The preliminary results of the GGRB and WR assessments were reported on in the Summer 2002 issue of GasTIPS, and the final results will be available soon on CD-ROM from the DOE Web site, www.netl.doe.gov. The DOE has also kicked off similar resource characterization studies for the Anadarko (Oklahoma) and Uinta (Utah) basins.

NPC to update 1992 study

In 1992, The National Petroleum Council completed a report titled "The Potential for Natural Gas in the United States." Volume II (Source and Supply) of this five-volume study examined in detail the long-term economic natural gas supply potential for the U.S. market. The update to this study, currently in progress and expected to be completed in early 2003, will address the recoverable resource base and delivery potential for conventional and non-conventional gas in the United States. Additionally, the impact of E&P technology advances and environmental compliance costs on supply availability will be modeled and analyzed.

The study group responsible for the Source and Supply portion of the NPC report will have the benefit of the earlier studies described above, plus, will be able to incorporate the resource perspectives of NPC members that include Anadarko, ChevronTexaco, ConocoPhillips, Devon Energy, ExxonMobil, Marathon, Shell, Unocal and a number of other independent producers active in domestic unconventional gas plays.
Together, these reports should provide a solid foundation for policy makers, regulators and analysts seeking to understand the importance of unconventional gas resources to our national energy supply.

AAPG summarizes unconventional gas geology

For individuals interested in the geology underlying this resource, The American Association of Petroleum Geologists (AAPG) has recently published a "theme issue" volume of its AAPG Bulletin (Vol. 86, No.11, November 2002) entirely focused on unconventional gas. The 150-page issue includes six individual articles on topics that include: coalbed gas systems (a comparison of the San Juan and Powder River Basins), basin-centered systems, fractured shales, shallow biogenic systems, natural gas hydrate and resource assessment perspectives for unconventional gas systems.

Each of these sections has not only been authored by well-known experts (e.g., Walter Ayers Jr. of Texas A&M, John Curtis of the Potential Gas Agency at CSM, James Schmoker of the USGS, among others), but has been reviewed during development by other informed experts from both public and private organizations. As such, the issue provides a good overview of the current "state-of-understanding" for unconventional gas resources. It will likely become a point of departure for E&P professionals, particularly as the development of these resources expands beyond the U.S. at a more rapid pace.

Single copies of the Bulletin are available for $24 for nonmembers and $16 for members, but a member can also access pdf and html versions of the issue online. Coincidentally, if you are an SPE member, you currently can sign up as an AAPG member for $36. Since AAPG membership gets you access to a number of online and hardcopy sources of information, that route could be a bargain for engineers with a high-speed internet connection and an interest in unconventional geology (just visit www.aapg.org).

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