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Book Chapter

Gas Production from Non-Fractured Shale

By
David K. Davies
David K. Davies
1
GeoSystems LLP, 1410 Stonehollow Drive, Kingwood, Texas 77339
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Richard K. Vessell
Richard K. Vessell
1
GeoSystems LLP, 1410 Stonehollow Drive, Kingwood, Texas 77339
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Published:
January 01, 2003

Abstract

The long-term production history of some offshore and onshore Gulf Coast reservoirs reveals that gas production exceeds assigned reserves for no readily apparent reason. The distinct possibility exists that surrounding shales contribute significant quantities of gas during the reservoir lifecycle. Direct evidence for economic gas production from non-fractured shale intervals comes from the Devonian of the Appalachian Basin and from Tertiary-Pleistocene reservoirs in the Gulf of Mexico. Intergranular pores occur between detrital clay particles in true shales of the Devonian interval. The ability of this intergranular pore system to transmit gas (permeability) is controlled primarily by the microfabric of the shale. It is reasonable, therefore, to expect that Gulf Coast shales with similar internal characteristics will yield sufficient gas to impact reservoir economics.

The Gulf Coast area contains significant proportions of sediments deposited in distal deltaic and deep water environments. These environments produce thick, fine grained “shale” intervals that, in reality contain numerous thin (<1 inch) laminations of porous and permeable silt and/or sand separated from one another by layers rich in clay minerals (true shales). Given a large number of silt/sand interbeds, sufficient permeability thickness can be developed in the interval to yield gas at high rates. Routine methods of log analysis fail to resolve the thin-bedding in these pay intervals, many of which are therefore bypassed.

Reserve calculations can also be significantly effected by gas production from true shales in traditional reservoir settings (such as the Wilcox Formation). The amount of gas recovered in reservoirs developed in relatively thin sand bodies (generally <50ft) can be increased by gas migration from surrounding shales during production-related pressure depletion of the main reservoir body. Improved reserve calculations require that potentially productive shales are included in all aspect of reservoir evaluation, from petrophysics to simulation.

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SEPM Miscellaneous Publication

Siltstones, Mudstones and Shales: Depositional Processes and Characteristics

Erik D. Scott
Erik D. Scott
Shell International Exploration & Production, 200 North Dairy Ashford, Houston, Texas 77079
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Arnold H. Bouma
Arnold H. Bouma
Dept. of Geology & Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803
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William R. Bryant
William R. Bryant
Dept. of Oceanography, Texas A&M University, College Station, Texas 77843
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SEPM Society for Sedimentary Geology
Volume
1
ISBN electronic:
9781565760943
Publication date:
January 01, 2003

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