Oil Shale Characteristics And Thermal Evolution History Of Yanchang Formation Chang 7 Member From Binxian To Tongchuan In Weibei Uplifting Of Ordos Basin

In this paper, on the basis of previous studies, we used the methods include the field geological outcrop observation, core sample test and well logging data interpretation to further study the geological features and geochemical features of oil shale. We draw some conclusions about Chang 7 Member oil shale from Binxian to Tongchuan in WeiBei Uplifting such as the abundance of organic matter is high, the kerogen type is mainly for ?1; The organic matter maturity is almost in the stage of low maturity or maturity. Meanwhile, the oil shale in the study area is mainly for medium-grade, medium ash content and low-high sulfur content. Since the oil shale is low-humidity, high-heat, it can be used as industrial fuel. According to such drilling data in the study area as logging and oil content in combination with regression analysis method, the geophysical interpretation model of oil shale in the study area is established, which can identify oil shale layer and interpret and calculate oil content much more precisely.The present geothermal gradient of Weibei Uplifting is 2.94 ?/100m according temperature-depth curve for borehole. The thermal evolution degree of Yanchang Formation oil shale in Weibei uplifting is low, the vitrinite reflectance of Chang 7 Member is between 0.51% and 0.81%, and the maturity is high in the north and midland, and low in the south, east and west. Since the vitrinite reflectance of Chang 7 Member in Weibei Uplifting increased with the increase of the depth, the thermal evolution type is buried heating type.According to sedimentary tectonic setting background, combining with vitrinite reflectance and fission track analysis, the thermal evolutional history of Yanchang Formation in Weibei Uplifting and Shanbei Slope are recovered by the tools of Basinmod and AFT solve software.The modeling results indicate that the paleo-geothermal gradient was low during the early Mesozoic; And the Chang 7 Member of Yanchang Formation reached highest paleo-geothermal gradient when the formation buried depth reached maximum during Late Mesozoic and the geothermal gradient is highest at 5.2?/100m. It has become gradually lower since late cretaceous.The temperature increased and thermal evolution when the Chang 7 Member hydrocarbon source rocks buried deep of Yanchang Formation in Weibei region from late Triassic-Early Cretaceous. In this case, thermal evolution has been constantly strengthened. In Early Cretaceous, Chang 7 Member hydrocarbon source rocks thermal evolution was strongest. The early Cretaceous is Chang 7 Member main oil-generation period and oil shale developing period. With the continue uplifting from the late early-Cretaceous, stratas were being eroded. At that time, the geothermal gradient cut down and hydrocarbon generation of Chang 7 oil shale was significantly reduced and tend to stop.