Studies of Natural Gas Resources in Deep Sedimentary Basins

For strategic, economic, and environmental reasons, many U.S. drilling frontiers deserve further review. One such frontier is natural gas in deep sedimentary basins. Deep natural gas resources are distributed throughout many basins with widely different geological environments (Figure 1). According to the Potential Gas Committee (1999), the U.S. contains a total potential resource of 1,037 trillion cubic feet (Tcf) of natural gas resources including the growth of reserves in known fields and undiscovered resources. In 1995, the USGS estimated 1,074 Tcf of technically recoverable gas resources in the U.S. including gas as proved reserves, reserve growth in gas fields, undiscovered conventional and continuous gas, and gas in small fields (U.S. Geological Survey National Oil and Gas Resource Assessment Team, 1995). Dyman and others (1996) identified about 113 Tcf of deep gas (gas in undiscovered fields below 15,000 feet) from 162 deep conventional (55 Tcf) and 11 deep continuous-type plays (58 Tcf) in the U.S. based on the results of the USGS 1995 National Assessment. A more precise understanding of U.S. resources of deep gas will provide valuable economic and strategic information for future planning. In addition, an understanding of the Worldwide distribution of deep gas will provide a strategic perspective from which to view U.S. resources. The word "deep" is used in a relative sense here, and its meaning varies for different tasks in this project and for different basins or regions. For the purpose of this paper, the word deep is defined to include all resources residing below 15,000 feet (~4.5 km), but may also refer to processes occurring at great depths, relating to resources now residing in shallow basin margins. Deep is used to focus a series of tasks in this project because it is an important classification criterion for both industry and governmental planning organizations, and the term implies important economic considerations because deep drilling frontiers are very expensive, and new technology advancements may improve their economic success. This project evolved as an outgrowth of work on two previous projects, one funded by the Gas Research Institute (GRI) (Dyman and others, 1997) and the other by the U.S. Department of Energy (DOE) (Rice and others, 1992) on the geologic controls of deep gas. During both projects, important new research directions were identified. Many of these directions are addressed in this project. A precise understanding of the geologic controls governing the origin and distribution of deep natural gas resources may have a significant impact on the future energy resources of this Nation and the World. This project is a two-year project which began in April 1998 and is closely related to another DOE-sponsored project dealing with the distribution of ?new? basin-centered gas accumulations in U.S. basins regardless of depth (DOE project no. DE-AT26-98FT0031 entitled ?Basin-Centered Gas Systems of the U.S.?-- V.F. Nuccio project chief). Results described in this report represent activities of Phase 1 or the first year of the project. Results (1) describe and analyze the geologic factors that control the distribution of deep conventional and unconventional gas accumulations in sedimentary basins of the U.S., and (2) characterize the distribution of deep conventional gas Worldwide.

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