Pollastro, Richard M.¹ 
(1) U.S. Geological Survey, Denver, CO

ABSTRACT: Assessing the Giant Barnett Shale Continuous (Unconventional) Gas Accumulation, Barnett-Paleozoic Total Petroleum System, Bend Arch-Fort Worth Basin, Texas

The organic-rich Barnett Shale (Mississippian-Pennsylvanian) is the primary source rock for oil and gas that is produced from conventional Paleozoic reservoirs in the Bend Arch–Fort Worth Basin area, Texas. It is also the source and reservoir for the tight, siliceous continuous shale-gas accumulation in this area. Based on this information, a Barnett-Paleozoic Total Petroleum System is identified that includes mature Barnett source rock, all known accumulations, and an area hypothesized to contain undiscovered accumulations. 
Of particular importance is the giant gas accumulation within the continuous (unconventional) tight shale reservoir of the Barnett. Cumulative gas production from the Barnett through mid-2003, mostly from the greater Newark East field area, was about 0.7 trillion cubic feet of gas (TCFG) with proven reserves booked at more than 2.5 TCFG. Moreover, recent estimates of the technically recoverable gas in the Barnett play are between about 7 and 20 TCFG. 
Undiscovered Barnett shale gas is assessed by (1) mapping critical geologic and geochemical conditions to define assessment units or “sweet spots” with future gas potential, and (2) by defining distributions of drainage area (cell size), estimated ultimate recovery, and by estimating success ratios. Greater Newark East field is a “sweet spot” where thick, organic-rich siliceous shale is within the gas window, and is overlain and underlain by impermeable limestone barriers which confine induced fractures during well completion and maximize gas recovery. Adjacent areas where the Barnett Shale is within the gas window, but stratigraphic conditions might be less favorable for development, will also be assessed.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.