关键词: 断控缝洞型油气藏, 成藏过程, 异常地层压力, 成因机制, 顺北油气田, 塔里木盆地

Abstract: Marine carbonate hydrocarbon reservoirs in Tarim Basin are characterized by deep burial, considerable thickness, and substantial resource potential. The discovery of medium- to small-scale strike-slip fault-controlled fracture-vuggy hydrocarbon reservoirs has stimulated extensive exploration of deep and ultra-deep hydrocarbon resources, resulting in the identification of two billion-ton-level oilfields, namely the Shunbei oil-gas field and Fuman oilfield, in the Shuntuoguole low-uplift (Shunbei area) and its adjacent regions. Nevertheless, as exploration targets have progressively extended toward smaller-scale faults, such as secondary and lower-order faults, the increasing structural heterogeneity of fault-controlled reservoirs, the occurrence of abnormally high reservoir pressures, and elevated drilling risks have severely constrained the efficient exploration and development of fault-controlled hydrocarbon reservoirs. To elucidate the genetic mechanisms of abnormal formation pressure in fault-controlled hydrocarbon reservoirs, this study focuses on the fault zones of different orders in Shunbei area. Based on detailed characterization of these fault zones, integrated techniques including calcite U-Pb dating and microscopic analysis of hydrocarbon inclusions are employed to conduct a dynamic three- dimensional analysis of the fault-reservoir-trap-hydrocarbon accumulation system across different fault orders, thereby revealing the differential hydrocarbon accumulation processes and genetic mechanisms of abnormal formation pressure in fault-controlled fracture-vuggy reservoirs. The results indicate that reservoirs controlled by major and secondary fault zones are dominated by fracture-vuggy reservoirs. These two types of fault zones experienced sustained late-stage activity, significantly modifying the reservoir systems. In contrast, late-stage en echelon normal faults may have caused temporary trap breaching during their active periods, facilitating the upward migration of minor amounts of hydrocarbons and providing pathways for pressure dissipation. The formation pressure of these reservoirs has undergone an evolutionary process characterized by “normal pressure during early-stage hydrocarbon charging, weak pressure anomalies caused by hydrocarbon dissipation during multi-stage charging, and normal pressure maintained during late-stage charging”. By contrast, low-order fault zones are dominated by fracture-type reservoirs. These fault zones exhibit weak late-stage activity and favorable preservation conditions for fault-controlled traps. Due to the low storage space of fracture-network reservoirs, hydrocarbons tend to form relatively constant-volume reservoirs after charging. Under late-stage high-temperature conditions, in situ cracking of early-stage crude oil generates high-pressure or overpressure constant-volume hydrocarbon reservoirs. The formation pressure evolves through a process characterized by “normal pressure during early-stage charging, weak overpressure anomalies resulting from multi-stage charging, and high-pressure or strong overpressure anomalies induced by late-stage self-sealing cracking”. These findings further elucidate the distribution patterns of abnormal formation pressure in fault-controlled reservoirs and provide theoretical support for the efficient exploration and development of reservoirs controlled by faults of different orders.

Key words: fault-controlled fracture-vuggy reservoir, accumulation process, abnormal formation pressure, genetic mechanism, Shunbei oil-gas field, Tarim Basin