| In recent years, oil and gas basin simulation has become a hot spot in the study of geological field. The region, which is bounded by the SuiDe county, ZhiDan county, YiChuan county and LuoChuan county, has a variety of Paleozoic gas reservoirs. The gas exploration and research level is relatively low in the region, and so far there has no research in Palaeozoic thermal evolution, hydrocarbon generation history, hydrocarbon expulsion history and accumulation. Based on above reasons, the research of thermal evolution helps to evaluate objectively the exploration target and provides the optimization basis.Various erosion thickness restoration method have been used. The Cretaceous residual region used the acoustic time extrapolation method. The central areas, where has vitrinite reflectance data use the vitrinite reflectance method. The region, where is lack of geochemistry data, use the uniform thickness method. The total erosion thickness is restored. It is increased gradually from the west to the east. The ZhiDan county is less than900m. The largest amount in the eastern YiChuan county is up to2000m above. With the sedimentary stratigraphical principle and the erosion thickness relative numerical method, the majiagou erosion thickness has been restored. The erosion thickness distribution is irregular, numerical range from0m to185m.With the apatite-fission simulation, a variety of tectonic evolution model was established, and the accurate depiction of the evolution process(since early Cretaceous) has been made. The results showed that since the early Cretaceous late, the study area can be subdivided into rapid uplift stage (96Ma～40Ma), uplifting rate quickly; slow lifting stage (40Ma～23Ma) once again rapid uplift stage (23Ma～now), maximum uplifting rate.With the international most advanced basin simulation software PetroMod and practical gas exploration data, the research area burial history is established. The Paleozoic structure evolution is also been recovered. It is pointed out that the burial subsidence history can be divided into four evolutionary stages. The rapid subsidence stage is in the middle-late Triassic. After the time when the formation achieved the maximum buried depth in Cretaceous, the region experienced rapid uplift-slow rise-rapid uplift again-deposition evolution process.The paleo-surface temperature, paleo-heat flow, thermal conductivity and heat generation rate are all discussed. With the EASY%R。method, the Paleozoic thermal history has been rebuild. The thermal history has been presented in virous way, including the comparison between paleo-temperature and present temperature, horizontal and sectional temperature characters, comparison between different region. Modeling result shows that the temperature gradually increase since the sedimentation began. The Source rock enters into oil threshold in late Triassic, enters into gas threshold in early Jurassic, reaches the maximum temperature in late period of early Cretaceous, and afterwards the gradual lowering of temperature. The temperature of ZhiDan county is higher than any other places.Statistically, the source rock type, abundance and maturity have been discussed in the study area. The hydrocarbon dynamics, organic carbon recovery coefficient, hydrocarbon generation potential parameters chart are all been rebuild. In the view of2d and3d, the hydrocarbon generation capability and generation amount are all been calculated. The ShanXi formation provides the highest contributive rate, nearly about37%. The period between late Jurassic and early Cretaceous provides the highest contributive rate, nearly about72%. The hydrocarbon generation since the late Cretaceous can be divided into three sub stages:96-40Ma,40-23Ma and23Ma-now.With the material balance method and the pressure disparity method together, the proper expulsive parameters and the expulsive amount are been calculated. The maximum accumulated expulsive amount is in the center of ZhiDan-AnSai-YanAn region, reaching67%of the expulsive amount. The expulsive intensity and expulsive amount can be divided into four stages. The last stage(since late Cretaceous) can be divided into three sub stages:96-40Ma,40-23Ma and23Ma-now. The maximum expulsive intensity is to the east of ZhiDan county, reaching18.6×108m3/km2.Using hydrocarbon-generating key moment analysis method and inclusion thermometry, it is pointed out that the upper Palaeozoic hydrocarbon injection is happened in late Jurassic period (167-153Ma) and early Cretaceous(147-126Ma). Late Jurassic to early Cretaceous is the time when all the Palaeozoic plentifully expulsion happens. It is also the main gas accumulation time.The natural gas accumulation is controlled by hydrocarbon generating ability and tectonic thermal evolution history. |
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