Hydrocarbon Accumulation Mechanism of Total Petroleum System in Permian Fengcheng Formation，Mahu Sag

doi:10.7657/XJPG20220604

Abstract

Abstract:

The exploration practice in the Fengcheng formation in the Mahu sag，western Junggar basin，has revealed the orderly coexistence of conventional and unconventional hydrocarbons. By finely dissecting the characteristics of the total petroleum system in the Fengcheng formation in the Mahu sag，and combining with the macro-and micro-analysis and production data of the reservoirs，the hydrocarbon accumulation mechanism of the total petroleum system was analyzed. The results show that conventional oil，tight oil and shale oil accumulate in an orderly pattern in the total petroleum system，which essentially complies with the hydrocarbon accumulation pattern of “source-reservoir coupling” and “dynamic sealing” of oil and gas. In the early diagenesis stage，the present tight reservoirs and shale reservoirs were conventional reservoirs with medium-large pore throats，where hydrocarbons accumulated because of buoyancy. In the middle-later diagenesis stage，the medium-large pore throats gradually evolved to micro-to nano-pore throats，the buoyancy was weakened，and the capillary force was strengthened. The hydrocarbon in the reservoir adjacent to or integrated with the source rocks underwent primary or micro migration continuously until the source-reservoir pressure difference resulted from hydrocarbon generation and expulsion and the capillary force originated from micro-to nano-pore throats reached a dynamic equilibrium，forming a “self-sealing” continuous unconventional oil and gas accumulation. The capillary force in the present conventional reservoirs is far less than the buoyancy，so “external sealing”is needed for hydrocarbon accumulation in traps. Generally，the hydrocarbon accumulation in the Fengcheng formation is represented by the space-time evolution of the pore throat structure in the reservoir and the dynamic coupling of source rock and reservoir on hydrocarbon generation-expulsion-migration-accumulation.

Key words: Junggar basin, Fengcheng formation, conventional hydrocarbon, unconventional hydrocarbon, total petroleum system, dynamic “sealing” effect, hydrocarbon accumulation mechanism, source-reservoir coupling

CLC Number:

TE122

HE Wenjun, SONG Yong, TANG Shiqi, YOU Xincai, BAI Yu, ZHAO Yi. Hydrocarbon Accumulation Mechanism of Total Petroleum System in Permian Fengcheng Formation，Mahu Sag[J]. Xinjiang Petroleum Geology, 2022, 43(6): 663-673.

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