Abstract
Most of Mexico's oil has come from Cretaceous and Jurassic carbonate rocks, but, in southeastern Mexico, these formations were not productive until the significant 1972 Pemex discoveries. By the end of 1977, 15 to 20 onshore and 3 offshore Mesozoic producing sites had been drilled in the Reforma area and Campeche Bay. Eight of these pools were productive, and several have been recognized as giant fields. Conservatively, proved reserves exceed 5 billion bbl of liquid hydrocarbons and 7 Tcf of gas. Because of the extent and number of favorable structures, the additional potential is enormous. Daily production in January, 1978, was 810,000 bbl of oil and condensate, and about 900 MMcf of gas. Cumulative production at the end of 1977 was about 580 million bbl of oil, approximately 60 million bbl of condensate, and 840 Bcf of gas. Of the 249 wells drilled at that time (three of them offshore), 202 were successful. New reservoirs are mainly Cretaceous and Jurassic dolomites and microfractured limestones, at an average depth of 12,500 ft (3,810 m). Trapping is in complexly faulted rocks and overthrusted anticlines covered by a thick Tertiary shale and sandstone sequence. Salt tectonics are also involved. Miocene sandstones have produced in the area since 1960, but Mesozoic discoveries had to await development of more sophisticated geophysical and drilling techniques. In northwestern Mexico, the Baja California peninsula area has received renewed interest with the establishment of dry gas production from Upper Cretaceous marine clastic rocks in the Sebastian Vizcaino basin. Geologic studies started early in this century. Between 1944 and 1960, geologic, gravity, and seismic surveys led to the drilling of 11 unsuccessful wildcats. In 1972, more modern geophysical and geologic studies justified the drilling of six additional wells, two of which are gas producers. At present, two rigs, one onshore and one offshore, are continuing exploration.
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