Lithology of Gas-Bearing Interval

In March 2001, core was acquired at two locations along the Wilson Road seismic line to the west of Hutchinson: DDV #63 (dry hole) and DDV #67 (gas). DDV #67 was located approximately 75 ft from DDV #53, which was actively venting a high volume of gas. In the DDV #67 core, the gas-bearing 3-finger dolomite corresponds to a series of thin dolomite and gypsum layers, separated by shales. The dolomites in DDV #67 have low matrix porosity, suggesting that fractures controlled gas migration within this interval. The 3-finger interval is observed in dry hole DDV #63, but the core from this well shows that the interval is more shaly and gypsiferous than in gas well DDV #67.

Because dolomite is brittle and fracture-prone in contrast to shale and evaporites, which are in general more ductile, dolomite is likely to undergo induced fracturing and be able to maintain open fractures when subjected to high-pressure gas that exceeds the fracture pore pressure of the dolomite. An increase in the amount of gypsum and shale, both less brittle than dolomite, would tend to inhibit fracturing and prevent migration of gas.

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Last updated June 2004
http://www.kgs.ku.edu/PRS/publication/2004/AAPG/NG_Migration/P3-01.html