Oil and Gas Potential of Southern Arizona: ABSTRACT

Abstract

End_Page 1015------------------------------Two highly prospective areas in southern Arizona are the Pedregosa basin in Cochise County and central Yuma and Maricopa Counties. The best source rocks were deposited during the Paleozoic before the inception of thrust faulting. They include dark mudstones and dark-gray cherty limestones. In addition, the Jurassic evaporitic environment may have contained prolific growth of phytoplankton which was preserved and matured into a rich source rock. Good reservoir rocks are found in Paleozoic marine sediments (primarily Ordovician, Silurian, and Permian) and in Cretaceous marine sediments. Early Cretaceous reefs may be especially good reservoirs. Two major types of tectonism provide models for structural traps: (1) overthrust faulting, and (2) basin-and-range block faulting. Sediments resting on a glide plane of Jurassic evaporites may have been thrust over reservoir rocks. This trap would be analogous to that of the Pineview field in northern Utah with a carbonate source rock, sand reservoir, and a salt seal. The primary exploration tool is reflection seismology. Basin-and-range faulting would create the fracture systems necessary for petroleum genesis through hydrothermal convection, hydrocarbon migration, and the upward travel of Jurassic salt. Salt diapirism may have caused additional fracturing in flanking reservoir rocks, thus increasing porosity and permeability. Reconnaissance prospecting for basin-and-range traps shou d include gravity surveys to locate salt and infrared air photo surveys to detect heat flow. End_of_Article - Last_Page 1016------------