Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
GCAGS Annual Meeting, Austin, Oct 31Nov 1, 2002
and Analysis of Upper Miocene and Pliocene Gas Plays
Rebecca H. Jones, William A. Ambrose, Mark H. Holtz, David C. Jennette, Bureau of Economic Geology, The University of Texas at Austin, Austin, TX, and Hector Solis, Javier Meneses-Rocha, Jorge Lugo, Leonardo Aguilera, Jose Berlanga, Lino Miranda, and Roberto Rojas, PEMEX Exploración y Producción, Macuspana, Villahermosa, and Ciudad del Carmen, Mexico
A play analysis of the Macuspana Basin by the Bureau of Economic Geology and PEMEX Exploración y Producción revealed that reservoir presence and quality and seal are the main risk elements for future gas exploration in the Upper Miocene and Pliocene. Source and migration/timing are characterized by lesser risk, and trap has some risk. In this dominantly shallow-marine basin, the best Upper Miocene and Pliocene plays comprise thick sandstones, including progradational and aggradational shoreface facies, deltaic complexes, and lowstand valley-fill deposits. Traps have four-way structures, three- and two-way structures with faults, and combinations of structure and stratigraphy. Source rock, present in both the Tertiary and Mesozoic, is supplying Tertiary biogenic gas throughout the basin and Mesozoic thermogenic gas and oil in areas having deep vertical migration pathways.
The Pliocene and Upper Miocene section was divided into mappable intervals bound by significant regional surfaces on both seismic and log sections. Facies and traps were then mapped and characterized by interval, with subinterval mapping and description showing significant differences, depending on the play. A calibration area was chosen in which the presence of 3-D seismic and the density of log data were adequate to define trap density accurately enough to extrapolate to the rest of the basin. Volumetric parameters were collected by play by analyzing production, log, and seismic data. The range of unrisked volumes was calculated using lognormal distributions of these parameters. A probability matrix that took into consideration both play and average-prospect chance was then used to determine risked volumes.