Print this pageGeology and Mechanics of the 
Basin
-Centered Gas Accumulation,
The Williams Fork Formation in the basin-centered gas accumulation. Most gas is produced from a
continuously gas-saturated 1,500-2,400 ft gross interval in the lower part of
the Williams Fork. During maximum burial, gas was generated and expelled from
the Cameo coal interval in the lower most part of the Williams Fork. The Cameo
is the primary source of Williams Fork gas. Both the lateral and vertical
distribution of gas and the distribution of overpressure are directly linked to
the migration of the gas as it moves upward and outward from the Cameo
deep-basin coals. The overall distribution and pressure of the gas in the
Williams Fork is probably the direct result of pore-pressure assisted
fracturing and subsequent migration through the induced fracture systems. The
first place one might expect fracture assisted migration to occur is within the
gas-generative Cameo interval. When gas generation causes critical pore
pressure to be exceeded, the rock fractures, and the rate of gas escape from
the overpressured rock rapidly increases, stabilizing
or reducing its pressure and allowing gas to flow into a lower-pressured adjacent
sand body. One might expect this process to be repeated in a daisy-chain
fashion, moving outward and upward from the gas generative parts of the Cameo.
Ultimately, the ability of a given sand to sustain overpressured conditions will depend on the balance of the
rate of gas entry with the rate of gas
escape from the sand.