| The West Sichuan depression refers to the western area of Sichuan Basin since Mesozoic and Cenozoic era. The depression which has undergone nine major tectonic movements since the late Triassic is a typical superimposed foreland basin. There are many gas fields (pools) in the Xujiahe formation that super difficulty domain of petroleum exploration because of the characteristics of deep burial, tightness, super pressure and strong heterogeneity .of Xujiahe formation.The paper used dynamics theory as a guide, also surmised the specific geological features of Xujiahe formation and the pervious research findings on thermodynamics. The strata pressure formation and evolution and evolution of fluid dynamics, basic geological conditions including source rocks, reservoir, seal, preservation, migration, accumulation period, and trap types were deeply studied to present the dynamic model of gas accumulation. The models were divided into three types.A geological thermometer in western Sichuan was established using 6 methods including vitrinite reflectance, volatile matter of coal, fluid inclusions, fission track, clay minerals and pyrolysis peak temperature. The results show that the ancient geothermal field in west Sichuan depression was higher than that of present day since late Triassic, and also was greater change. in vertical and horizontal direction.The Upper Triassic source rock showed a progressive process of hydrocarbon generation and multi-period expulsion. The time threshold of hydrocarbon generation became late from west to east, but in north-south direction, the middle area is first, followed by the southern area, northern area was the latest.The strata pressure evolution of Xujiahe formation was established: The under-compaction formed in the late Indosinian, followed by hydrocarbon-generating pressurization in Yanshanian, then, pressure upgrading was mainly caused by Himalayan and Yanshanian tectonic compression. One major cause for pressurization was tectonic compression; also hydrocarbon generation had impact to extent. The acoustic reflex test results show a stronger tectonic compression strength in Himalayan than in the Yanshanian period.By analysis of hydrodynamic evolution of the western Sichuan depression, the fluid potential energy that reflects the natural gas system was obtained. Four ancient hydrodynamic fields that showed a general trend from strong to weak and strong again existed in Xujiahe formation.. In smooth tectonic period, the hydrodynamic field was nearly consistent with the gas potential energy trend.Xujiahe gas transportation system was composed by the high porosity and permeability of the sandstone beds and faults. The predominant pathways were the preferred conduit routes of oil and gas migration. The predominant pathways transported the majority of hydrocarbon but accounted for only a very small part in the transportation system.According to the dynamic and oil source characteristics, The reservoir-formed dynamic system were divided into self-source high pressure dynamic system and mix-source middle pressure dynamic system. The first is driven by the tectonic stress and hydrocarbon generation; so it was characterized by the high pressure with pressure coefficient greater than 1.5.and the "self-generation and self-storage. The late was driven by buoyancy or water power, the hydrocarbon in the system could be from long-distance migration, so is characterized by middle–low pressure with pressure coefficient from 1.0 to 1.5.The fluid power sources, including sedimentary compaction, tectonic stress, buoyancy, hydrodynamic and hydrocarbon generation were systematic studied. From late Indo-Chinese epoch to late Yanshan epoch, the Xujiahe fluid driving forces were mainly provided by the tectonic stress and sediment compaction as result of active tectonic movement. In smooth tectonic movement, fluid driving forces was buoyancy and hydrocarbon generation. In Himalayan epoch, The Xujiahe formation suffered a strong tectonic movements, the fluid driving forces which significantly affected by compaction and tectonic stress was the tectonic stress.Three gas accumulation model were constructed : high-pressure-driven ,buoyancy-driven,water power-driven accumulation models One of the three driving modes was dominant at the same time in complex geologic history , other modes was supplement. According to evaluation of Xujiahe hydrocarbon source, reservoir, seal, ancient uplift, traps reservoir and controlling dynamic factors, the six structural optimum zonesand nine key exploration areas were identified.According to comprehensive evaluation of the study area, and the principles of easy things first and the great things first, strategic deployment, strategic breakthrough, strategic preparation of three strategic levels were present to evaluate 17 targets and 25 sub-targets. The strategic deployment level 4 targets and 6 sub- targets are Xiao Quan - Xingchang area (Xu 2, Xu 4), Dayi structure (Xu3, Xu 2), Feng Gu area ( Xu 4), Gaomiaozi– Hexingchang area (Xu 2).
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