Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
HGS International Meeting, Houston, Texas, March 15, 2004
Upper Miocene and Pliocene Gas and Oil Plays in the Macuspana Basin, Southeastern México
William A. Ambrose, Khaled Fouad, Rebecca Jones, Mark Holtz, Shinichi Sakurai, Edgar Guevara, Javier Meneses-Rocha, Leonardo Aguilera, Lino Miranda, Roberto Rojas, José Morales, José Berlanga, Suhas C. Talukdar, and Tim Wawrzyniec, Tim Wawrzyniec
The Bureau of Economic Geology and Pemex Exploración y Producción conducted an integrated study of the geologic, geochemical, and play framework of the upper Miocene and Pliocene in the Macuspana Basin, using a variety of well, core, and 2-D and 3-D seismic data. Structural controls for the plays consist of deep-seated faults that tap Mesozoic thermogenic gas sources, areas of intense shale diapirism and folding, and areas with structural inversion that could enhance trapping and reservoir productivity. Early Neogene thrusting south of the basin triggered evacuation of Oligocene shale along northwest-dipping listric faults in the eastern and southeastern margin of the basin. These faults are associated with large-scale rollover structures and thick (>500-m) upper Miocene shoreface and wave-dominated deltaic complexes. Traps occur as both four-way and three-way structural-stratigraphic combinations. Reservoir seal is provided by a 100- to 300-m lower Pliocene transgressive shale. Downdip pinch-out of reservoir-quality shoreface sandstones is a key risk factor in the upper Miocene in the onshore part of the basin. In contrast, the offshore upper Miocene section consists of deepwater slope systems downdip of an inferred clastic-carbonate source associated with the Yucatan Platform. Thin, calcareous, turbidite sandstones lapped onto a major turtle structure, potentially providing updip-porosity pinch-outs.
A second phase of extension in the early Pliocene formed a set of broad, southeast-dipping listric faults in the western basin, controlling thick accumulations of stacked Pliocene shoreface deposits. Sandy Pliocene shoreface depocenters formed in shale-withdrawal subbasins, primarily in the northwest part of the basin. Trap formation and enhancement in the southern basin margin are linked to late Miocene-to-Pliocene inversion. Unlike in the more productive upper Miocene, reservoir seal is a major risk factor in upper and middle Pliocene reservoirs having few thick upper bounding shales.
Three petroleum systems (Mesozoic, Paleogene/Lower Neogene, and Upper Miocene/Pliocene) contributed to the hydrocarbon accumulations, and hydrocarbon generation and migration in the basin. Principal Upper Jurassic/Lower Cretaceous source rocks generated wet thermogenic gases and oil. Secondary lower Tertiary source rocks generated dominantly dry biogenic gases. Mixtures of the two gas types are common. Numerous deep-seated growth faults and faults serve as pathways for Mesozoic-sourced hydrocarbons. Surface seeps and abundant gas shows suggest that hydrocarbons are being generated today.