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ABSTRACT: McPac Field (Matagorda Island Block 487-L) New Gas Reserves in a Mature Area

Jim McCullough

The McPac field produces gas and gas condensates from lower Miocene Marginulina ascensionensis sands. These sands were deposited in a wave-dominated delta front or strandplain environment. The field was discovered in 1988 and has proven reserves of 60-70 bcf with probable reserves in the 100 bcf range. McPac field lies adjacent to Cove field, discovered in 1966, which has produced 140+ bcf. The McPac discovery resulted from the recognition of an undrilled fault block reinforced by a differential pressure seal. The majority of the reserves in the two fields occurs in the two normally pressured sands, the "ME" and "MF" Both fields overlie a complexly faulted shale diapir with hydrocarbons present only on the west half of the structure. Hydrocarbon entrapment is enhanced by he presence of differential pressure traps resulting in gas columns (1500 ft, 457 m) unusual for the Gulf Coast.

Although numerous shallower sands produce on the structure, none have the long columns associated with the "ME" and "MF" reservoirs. The same conditions responsible for these gas columns are present on other uplifts in the Marg. A trend as well as other trends of onshore and offshore Texas. A knowledge of these trapping phenomena should aid in a better understanding of geology in this area and serve as a guide to highgrade the numerous fault traps associated with similar trends such as the currently active ROB. L-ROB. M trend.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990