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Assessing Undiscovered Resources of the Barnett-Paleozoic Total Petroleum System, Bend Arch–Fort Worth Basin Province, Texas*

By

Richard M. Pollastro¹, Ronald J. Hill¹, Daniel M. Jarvie², and Mitchell E. Henry¹

Search and Discovery Article #10034 (2003)

*Online adaptation of presentation at AAPG Southwest Section Meeting, Fort Worth, TX, March, 2003 (www.southwestsection.org)

 ¹U.S. Geological Survey, Denver, CO

²Humble Geochemical Services, Humble, TX

Abstract

Organic-rich Barnett Shale (Mississippian-Pennsylvanian) is the primary source rock for oil and gas that is produced from Paleozoic reservoir rocks in the Bend Arch–Fort Worth Basin Province.  Areal distribution and geochemical typing of hydrocarbons in this mature petroleum province indicates generation and expulsion from the Barnett at a depocenter coincident with a paleoaxis of the Fort Worth Basin.  Barnett-sourced hydrocarbons migrated westward into reservoir rocks of the Bend Arch and Eastern shelf; however, some oil and gas was possibly sourced by a composite Woodford-Barnett total petroleum system of the Midland Basin from the west.

Current U.S. Geological assessments of undiscovered oil and gas are performed using the total petroleum system (TPS) concept.  The TPS is composed of mature source rock, known accumulations, and area(s) of undiscovered hydrocarbon potential.  The TPS is subdivided into assessment units based on similar geologic characteristics, accumulation type (conventional or continuous), and hydrocarbon type (oil and (or) gas).

Assessment of the Barnett-Paleozoic TPS focuses on the continuous (unconventional) Barnett accumulation where gas and some oil are produced from organic-rich siliceous shale in the northeast portion of the Fort Worth Basin.  Assessment units are also identified for mature conventional plays in Paleozoic carbonate and clastic reservoir rocks, such as the Chappel Limestone pinnacle reefs and Bend Group conglomerate, respectively.  However, Barnett continuous gas is expected to add the greatest volume of undiscovered, technically recoverable resource.  Undiscovered Barnett Shale gas will be assessed after mapping “sweet spots” and outlying areas of hydrocarbon potential, and by defining distributions of drainage (cell) size and cell estimated ultimate recovery.  An example of a Barnett “sweet spot” is the Greater Newark East area where thick, siliceous Barnett has reached the gas window, and is overlain and underlain by impermeable limestones that contain fractures that are induced during completion.