--> ABSTRACT: Middle-Upper Miocene Exploration Plays of Offshore Texas, by Robert A. Morton; #91030 (2010)

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Middle-Upper Miocene Exploration Plays of Offshore Texas

Robert A. Morton

Sandstone reservoirs of middle-to-late Miocene age have produced more than 150 million bbl of oil and 1.8 trillion ft3 of gas from 89 fields in coastal Texas. The largest fields are located offshore in federal waters, but fields of significant size (great than 1 million bbl of oil equivalent) are located in state waters or beneath the lower coastal plain. The fields can be grouped into nine plays on the basis of reservoir genesis, trapping mechanism, and hydrocarbon composition. Six are primary exploration plays, whereas the other three owe their accumulation to vertical migration of hydrocarbons leaking from underlying lower Miocene or Frio reservoirs. About half of the estimated recoverable reserves are associated with two faulted shelf-margin plays located a ong the delta front and subjacent slope of the South Brazos delta system and adjacent interdeltaic Galveston strand plain and slope system. These primary gas-prone plays offer the greatest potential for new field discoveries and significant reserve additions. Other less potential gas plays include the middle Miocene South Padre stable shelf system and the upper Miocene South Brazos delta system. Nearly all of the oil is produced from the salt-dome province of the Houston embayment where secondary migration is responsible for hydrocarbon accumulation. Most of these reservoirs are progradational and aggradational sandstones deposited during abrupt basinward shifts in coastal sedimentation associated with Bigenerina humblei and Bigenerina 2 regressive episodes. Both events were characterize by rapid and extensive construction of the continental platform beyond the paleoshelf margin.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.