准噶尔盆地流体输导格架及其对油气成藏与分布的控制

Fluid-Conduit Framework and Its Control on Petroleum Accumulation in the Junggar Basin

准噶尔盆地是一个大型叠合盆地,不同构造单元具有不同的演化历史、流体动力学环境、流体输导格架和油气充注历史.盆地西北缘处于正常压力环境,发育自源岩至圈闭的断裂-不整合面贯通型流体输导格架,主要油气聚集期为三叠纪-侏罗纪.由于高效流体输导网络的发育,西北缘油气聚集期与主力源岩生排烃期一致,是该盆地油气最为富集的区域.盆地中部断裂密度低,深、浅部断层被三叠系白碱滩组区域封闭层分隔,在超压发育前和超压积蓄期为双断分隔型流体输导格架,超压的发育导致地层发生水力破裂和封闭性断层的开启,从而形成断裂-水力破裂连通型流体输导格架,构成流体和二叠系源岩生成油气的穿层运移通道.由于地层水力破裂及其控制的断裂-水力破裂连通型流体输导格架的形成晚于主力源岩的主生油期,盆地中部油气的主要聚集期晚于主力源岩的主生油期,且原油的成熟度较高.研究证明,输导格架控制区域性流体动力学环境、油气优势运移通道、油气的充注层位和充注历史.

The Junggar basin is a huge, multiple-stage basin in Northwest China. Different structural units of this basin have quite different evolution histories, fluid flow environments, fluid-conduit frameworks and petroleum accumulation histories. The northwest margin of the Junggar basin is in a normally pressured environment with a fault-unconformity conduit framework connecting source rocks and traps effectively. Due to the effectiveness of the fluid-conduit framework in this region, the major petroleum accumulation occurred almost at the same time as the main phase of oil generation. Very few faults developed in the center part of the Junggar basin, and faults in the shallow section could not connect with faults in the deeper section. As a result, petroleum generated in the Permian source rocks could not have migrated vertically into the overlying Jurassic reservoir rocks during the peak petroleum generation stage （Triassic to Jurassic） until the Cretaceous, when fracturing caused by overpressure occurred and the Jurassic reservoir rocks were connected with the Permian source rock by faults and hydraulic fractures. Because the fault-hydraulic fracturing and the resultant fault-fracture conduit framevork developed a relatively long time after peak oil generation, the major petroleum accumulation came later than peak oil generation, and the accumulated oil had a relatively high maturity. This study confirms that in an overpressured enviromnent the fluid-conduit framework is dyrarmic, and has a controlling effect on the petroleum migration pathway and accumulation intervals, as well as the injection histories.