Heterogeneous distribution of pyrobitumen attributable to oil cracking and its effect on carbonate reservoirs: Feixianguan Formation in the Jiannan gas field, China

Few previous studies have focused on solid bitumen distribution and its effect on gas reservoir quality during oil cracking. Solid bitumen is commonly found in both gas and nongas reservoirs of the Triassic Feixianguan Formation in the Jiannan gas field. The natural gases are mainly secondary cracking gases of oil generated from source rock of the Permian Wujiaping Formation , and the reservoir experienced temperatures above 150°C (302°F) for about 35 m.y. A relatively narrow range of values and a wide range of values and widespread solid bitumen indicate that oil cracking took place in the gas field. Low concentrations of (commonly 8.0%) can be high-quality gas reservoirs after oil cracking and should be favorable targets for future gas exploration in the northeastern Sichuan Basin and adjacent areas.