Assessments of Regional Gas Accumulations at the Department of Energy

Ray Boswell
U.S. Department of Energy, National Energy Technology Laboratory, Morgantown, WV

The goal of the Department of Energy’s (DOE’s) natural gas supply program is to assure the long-term sustainability of affordable domestic natural gas supply. A key element in this effort is the development of technologies that will allow the nation to maximize the recovery of natural gas from domestic basins. One of the approaches we have taken is to conduct assessments to improve our understanding of critical underutilized gas resources. We then use that information to inform the selection of an R&D portfolio designed to expand resource recoverability. At present, the vast natural gas resources contained within regional accumulations dominated by low-permeability sandstones are expected to bear much of the burden of meeting future growth in gas demand, and are therefore a prime focus of our program. Over the past year, NETL has conducted two new assessments (selected plays of the Anadarko and Uinta basins) and has continued to test and improve our computer models using data from our previous studies in the Greater Green River and Wind River basins.

DOE resource assessments are based on the recognition that the volume of recoverable gas resource within any given play changes with time, most notably in the more technically-challenging resource segments. Therefore, in the context of supporting R&D planning, there is little value in conducting assessments that result in point-in-time estimates of technically-recoverable resources. Instead, what is needed is a way to assess all the potential resource (both the currently-recoverable as well as that which is not now considered “recoverable”) in a way that captures the capacity of technology advance to expand both technical recoverability, and most importantly, economic recoverability.

Therefore, our assessments differ from those of other organizations in several key ways; 1) characterization of resources without regard to current technical or economic recoverability; 2) the use of computer simulators to estimate the sensitivity of technical- and economic-recoverability to alternative future technology/policy scenarios, and 3) extensive disaggregration of the resource into hundreds of individually-characterized cells. This detail is needed to enable the computer models to more sensitively probe the “response” of the resource to individual R&D cases.

The external products of NETL assessments include geologic characterizations of the subject plays – including regional maps and cross-sections, log-based estimates of volumetric parameters, and estimates of regional variations in bulk permeability determined through analysis of production data and other information. These data are made available to the public on CD. NETL has also reported modeling output (technically and economically-recoverable volumes) for cases that we consider to be “most-likely” paths for future technology development (no new paradigm shifting breakthroughs) that have differed (are generally larger) from similarly-labeled estimates provided by other organizations.

Obviously, great care must be taken in comparing the results of different approaches. Taken literally, the term “technically-recoverable” would mean “all the gas that could be produced with the best, commonly-available technology without regard to economics”. The NETL approach comes very close to this ideal definition, and therefore produces estimates of technically-recoverable resources for a play or basin that are the same whether prevailing gas price is $2.00/mcf or $200.00/mcf. However, this expansive definition of technically-recoverable is not suitable for an assessment designed to estimate the size of the resource that is realistically available for production over the next 20 years or so. Therefore, many assessors work appropriate allowances for economic constraints, operator behavior, industry capacity, and other factors to produce a more “practical” assessment. Consequently, our results for recoverable resources are more a reflection of ultimate resource potential than predictions of how that potential will likely be realized. Given this methodology, it should be expected that our assessments will exceed that of other groups. We are comfortable with this result, as our primary goal is the ability to quantify the impact of technology (the ability to assess the difference between two alternative futures), and not the determination of any single absolute value for the “recoverable resource”. In short, we are most interested in knowing what could be, as opposed to predicting what will be.