Statistical evaluation of oil and gas prospects in the outer continental shelf of the U.S. Gulf Coast

Areas of the U.S. Gulf Coast, both onshore and offshore, are among the petroliferous regions of the United States. In offshore Louisiana and Texas, most oil and gas is associated with structurally controlled traps on the crest or flanks of domes created by the diapiric movement of salt. These structures can be detected and mapped by seismic techniques that directly indicate favorable prospective areas. The characteristics of seismically defined structures provide information in advance of drilling about the probable size of reservoirs contained within these structures. Simple statistical relationships can be determined between the size, shape, and other attributes of structures detected by seismic mapping and the presence and size of petroleum and natural gas reservoirs. Gulf Coast OCS lease tracts presently are evaluated by the U.S. government using a Monte Carlo simulation procedure adapted from reservoir analysis. Specification of the parameters of the Monte Carlo model are obtained subjectively in advance of drilling and thus are highly uncertain. Comparisons of predrill predictions with postdiscovery reservoir evaluations show very low correlations. In contrast, predrill predictions based on regressions between seismic structural properties and reservoir volumes show highly significant correlations. In addition, statistical analysis of seismic structure is much simpler than the Monte Carlo procedure, and can be applied rapidly and inexpensively. A statistical analysis of the “Pleistocene Trend” of offshore Louisiana and Texas, an area of about 3 million acres, yielded results that are sufficiently encouraging to suggest that similar evaluations be made of the remaining Gulf Coast OCS and of OCS regions off of other coasts of the United States.