Hydrocarbon Accumulation Mechanism And Models Of Far-source Lithologic Reservoirs In Junggar Basin

The lithologic reservoirs with which temperature-pressure characteristics of forming envoirnment are completely different from that of hydrocarbon generation envoirnment are called far-source lithologic reservoirs. The sedimentary strata has multi temperature-pressure system in Junggar Basin, providing the basic condition for the formation of far-source lithologic reservoirs. Starting from the analysis of condition and space-time structure of reservoir forming elements, this paper, taking the migration system as the masterstroke and reservoir forming mechanism and dynamic process as the key subject, studied the characteristics of temperature-pressure system, hydrocarbon migration framework and the fluid driving mechanism through using the method of basin simulation. Then, the hydrocarbon migration and accumulation process of the forming of far-source lithologic reservoirs was revealed systematically, followed the clearing of forming mechanism and model of the far-source lithologic reservoir.The hydrocarbon resources are mainly derived from Permian and Jurassic source rocks in Junggar Basin. There five reservoir-seal assemblages, such as C?T2 reservoir with T3 seal,J1b reservoir with Jis seal,J2?J3 reservoir with K1 seal, K2?E2 reservoir with E3 seal and N1reservoir with N2 seal. Controled by the space matching relation of ancient landform, provenance and sedimentary system, the lithologic traps mainly distribute in the steep slope of the eastern and western uplift and the gentle slope zone of the interior in the basin. The lithologic traps are far apart from hydrocarbon source rocks, and are vertically separated by several sets of regional seal rocks, which results in the complex reservoir forming conditions.The migration system of the far source lithologic reservoir is composed of the unconformity, vertical faults and large delta sand bodies formed by the multi cycle tectonic movement and lake level fluctuation. In each structure units of the basin, the long distance migration systems of hydrocarbon accumulation are mostly developed in the late Hercynian tectonic movement and formed in Yanshan movement. The development of the Hydrocarbon migration system in Western uplift and Mobei-Mosuowan area were reformed by the evolution of Che-Mo paleo uplift. And the morphology of the hydrocarbon migration system in other tectonic units remained unchanged after its formation. The study on the validity and mechaniem of the migration system indicates that the tectonic movement and paleo structure form of the basin have a certain effect on the hydrocarbon accumulation.In vertical, the Junggar Basin developed three sets of relatively closed strata temperature-pressure system,such as P?T3?J1?J1s and Kitg?E2-3a. The three sets of temperature-pressure system were formed in the Late Triassic, Middle Jurassic and Eocene respectively, dividing the basin into five reservoir forming internals, such as C?T3?Ji?Jis?J2?K1?K2?E3 and E3?N. The activity of fault was intense in Yanshan Stage, which caused the energy adjustment of strata temperature-pressure system and release of overpressure fluid. On the one hand, it provides the material basis for the formation of far-source lithologic reservoir, on the other hand, it provide the driving force for hydrocarbon migration and accumulation. The basin movements were mainly tilting movement with descending in the south and lifting in the north in Himalayan stage, and fault activity was weak. The temperature - pressure system was relatively stable and played mainly a role of preservation of oil and gas.The far-source lithologic reservoirs were mainly formed in Yanshan Stage in Junggar Basin. The formation and distribution of it were controlled by the morphology of paleo structure, formation and evolution of tempressure-pressure system and the validity of fault migration space. Based on the dynamic process of hydrocarbon accumulation in far-source area, it is considered that the main forming mechanism of far-source lithologic reservoir is fault-pressure controlled, hydrocarbon migration and accumulation crossed the caprock. According to the migration power of hydrocarbon accumulation and characteristics of complex migration system, the four forming model of far-source lithologic reservoir are put forward, such as high energy drive -hydrocarbon crossing the cap rock accumulation through multistage migration system,low energy drive - hydrocarbon crossing the cap rock accumulation through multistage migration system, low energy drive - hydrocarbon crossing the cap rock accumulation through singlestage migration system and high energy drive - hydrocarbon crossing the cap rock accumulation through singlestage migration system.