An Extraterrestrial Origin for Oil Generation and Anticlinal Growth, West Side Diatomite Trend, San Joaquin Valley, California
Jean Senteur de Boue, Cressy and Associates
Miocene diatomites produce 20-30° API gravity oil from a 20-mile wide, N-S trend of NW- to SE-plunging, en echelon anticlines on the west margin of the San Joaquin basin, California. Although 45-60% porosities result in high oil reserves, permeabilities <1 md necessitate fracture stimulation to economically produce diatomite wells. Also, compaction-driven subsidence up to 9 in/yr during production collapses anticlinal crests. Because oil migration into such impermeable reservoirs seems unlikely, in situ oil generation is more likely. However, burial depths <3,000 ft with geothermal gradients <1.5°F/100ft are inadequate to thermally mature the diatom-derived organic matter in place, unless external energy sources delivered sufficient heat for oil generation.
Meteorites glancing off the basin margin with low-angle trajectories at multiple impact points, like adolescents skipping stones across a pond, are the most likely external energy sources. Heat transferred into the subsurface at impact points matured diatom organic matter in place to generate liquid hydrocarbons, with anticlinal growth as fluid pressures associated with oil generation expanded pore spaces, like blowing up a balloon. Meteors glancing off multiple impact points along the same trajectory created anticlinal trends (e.g., Coalinga-Kettleman Hills). Release of fluid pressure during production from these structures collapses anticlinal crests, partially restoring the surface to a flat, pre-impact topography. Production-driven deflation of impact-derived anticlines on the basin margin, akin to popping zits on the valley floor, threatens to turn the west side into a pock-marked lunar landscape unless remediation is undertaken with steam and/or water injection to pump up subsidence-collapsed anticlinal crests.