Exploration Along Lower Cretaceous Shelf Margin--Golden Lane, Mexico, to Louisiana: ABSTRACT

Abstract

Exploration for hydrocarbons from Lower Cretaceous shelf-margin carbonates began more than 40 years ago and continues today along the Gulf Coast of Mexico, Texas, and Louisiana. The early discovery of the oil-rich Golden Lane and Poza Rica fields of Mexico provided encouragement for exploration for similar fields in Texas and Louisiana. Exploration along the shelf margin of the U.S. Gulf Coast has resulted in the discovery of smaller gas fields in south Texas. Detailed core studies along the shelf-margin indicate the existence of a nearly continuous trend of rudist banks and associated tidal bars. Seaward, argillaceous carbonate mud was deposited in deeper water; landward, shallow-water lagoon and shelf sediments were diverse and resulted in the accumulation of a wide variety of facies. In the Mexican fields, extremely high early secondary porosity in the Golden Lane is believed to have formed when the carbonates were exposed to subaerial weathering during early stages of the Laramide orogeny. In the Poza Rica field, production is from intercrystalline dolomite porosity. Along the U.S. Gulf Coast, most porosity is primary within the preserved rudist shells and permeability is very low. Originally high intergranular porosity in the grainstone facies was destroyed by several layers of calcite cement deposited during subsequent burial. The source rocks for the hydrocarbons of the entire area are probably the argillaceous, dark-colored mudstones and wackestones of the Gulf basin. The Mexican fields have been prolific and have produced a billion barrels of oil. In contrast, the south Texas fields have produced 150 bcf of dry gas and are estimated to have reserves of 1 to 1.5 tcf of gas. Major differences in postdepositional burial history account for these extreme differences in hydrocarbon production. End_of_Article - Last_Page 548------------