Shale Gas
Potential of the Mowry Shale in Wyoming Laramide Basins
Surdam, Ronald1, Zunsheng Jiao1,
Ramsey Bentley1, Rodney DeBruin1 (1) Wyoming State Geological Survey, Laramie, WY
The siliceous Mowry Shale in Wyoming is an outstanding
source rock and should be considered a potential shale-gas target. Total
organic carbon (TOC) from the Cretaceous Mowry Shale in Wyoming basins ranges from 0.7%
to 5.1%. The TOC content of the Mowry Shale generally increases from northwest
to southeast; and, conversely it thins from about 600 feet in the northwest to
about 250 feet in the southeast. T-max for samples ranges from 411o
C to 455o C. Vitrinite reflectance ranges to 1.7 at depths greater
than 10,000 feet. Displacement pressures range from 300 psi at 5500 feet to over
2000 psi at 13,000 feet. The 13C nuclear resonance spectra indicate
that the aliphatic carbon peak of the Mowry Shale is almost greatly diminished
at 13,000 feet. Therefore, at this depth remaining kerogen in the formation has
very little capacity to generate liquid or gaseous hydrocarbons. Thermal
maturation modeling suggests that for each gram of TOC in the Mowry Shale,
about 80 milligrams (mg) of gas was generated, 18 mg of gas was expelled, and
62 mg of gas remains (i.e., stored in shale). Sonic and seismic interval
velocities show a pronounced slowdown where significant quantities of natural
gas remain in the Mowry Shale. The Mowry attributes described above suggest
that it has significant potential as a shale-gas prospect. This suggestion is
supported by conventional Mowry production in Wyoming. With new drilling and
completion techniques, the recovery of remaining natural gas in the Mowry could
be substantial.