Theory of 10,000-meter deep petroleum geology and the accumulation and preservation of ultra-deep oil and gas in craton basins, China

Abstract

Two drillings targeting 10,000 m strata lunched in China recently bring into focus the petroleum accumulation and enrichment theory in ultra-deep strata of craton basins.          The petroleum geology theory in ultra-deep strata is systematically summarized in this contribution, based on recent research progress discoveries. The lower limit of liquid petroleum preservation depth in basins with low-geothermal gradient can reach 9,000 m, breaking through conventional understanding of a 6,000 m depth limit. This research sheds light on the preservation mechanisms for giant paleo oil pools and gas pools, and thus redefines the ultimate lifespan of oil/gas pools and promotes significant discoveries and breakthroughs in ultra-deep petroleum exploration. The heterogeneity of ultra-deep carbonate reservoirs is extremely high. Experimental simulations have shown that caves and pores are influenced by only lithostatic pressure and can remain even at depths of 75,000 m, carbonate reservoirs therefore have no firmed depth limit. Flow and occurrence model of hydrocarbon fluids in heterogeneous reservoirs has thus been established, introducing the concept of large-area stratified cavity-fracture type bead-like pools without unified oil-water contacts, as well as the theory of accumulation in petroleum source-connecting fault zones. Ultra-deep petroleum exploration has uncovered pools with extremely high oil and gas columns of nearly one thousand meters, which breaks through conventional concept from previous petroleum geology theory and the theory of the “Golden zone in petroleum exploration”, and forms the formation theory of ultra-high oil and gas column in 10,000 meters deep and the distribution theory of oil and gas rich zone.