Evaluation On Gypsum Mudstone Caprock Of Eogene System In Kelasu Structural Belt Of Tarim Basin

Xujiaweizi fault depression is the key region of deep gas exploration in the north of Sonliao basin. K1yc is the main gas producing formation. As the reservoir of natural gas, the reservoir property and gas-bearing property of volcanic rocks are the important factors that restrict the prospects of natural gas resource in the fault depression, which can not be ignored. Consequently, carrying out the research on K1yc volcanic sodium salt reservoir in Xujiaweizi fault depression has important significance in guiding gas exploration in the fault depression as well as enriching and improving the theory of oil reservoir in fault depression.Based on a comprehensive summary of previous work, making use of core drilling, thin section observation and identification, analysis and test data, well logging and seismic data and so on, volcanic rock type, volcanic rock reservoir space and physical properties characteristics, volcanic reservoir digenesis and porosity evolution were researched comprehensively and systemic in K1yc in Xujiaweizi depression, and the results are that there are mainly 11 volcanic reservoir space which mostly are original porosity not filled or full, secondary dissolution porosity and fractures of a variety of causes, micro-pores of devitrified activity in spherules rhyolite, as well as pores of the volcanic ash solution in rhyolitic tuff, should be two kinds of important reservoir space. The porosity and permeability of rhyolite and self-fused tuff in lava are generally higher, while they are lower in basalt, andesite, trachyte and tuff . The upper extrusive parfacies and heat parfacies in outbreak facies have high porosity and permeability. So are the middle extrusive parfacies and hot base surge parfacies in extrusive facies. In Shengping region porosity and permeability of lava are better than them in K1yc. The thermodynamic study on carbonate and feldspar shows that their dissolution and precipitation are significantly affected by temperature. The higher the temperature is, the larger the area of stable reign is. At the same time, precipitate is dominant. It Is not conducive to the formation of secondary porosity in lava vice versa. Combined with the formation and evolution of volcanic rocks ,it can be concluded that porosity evolution of volcanic rocks of Xujiaweizi fault depression K1yc series can be divided into six stages. The first stage: the formation stage of volcanic rock - the formation stage of original pore (111Ma ~ 115Ma); the second stage: after stage of the formation of volcanic rocks and before the stage of thermal subsidence phase - devitrification and weather-worn stage (115Ma ~ K1yc); the third stage:: stage of thermal subsidence and tectonic fracture stage - the formation of structural fracture stage (begin of Yingcheng four group); the fourth stage: dissolution and the filling phase (after the stage of thermal subsidence ~ before hydrocarbon expulsion of Quantou group); the fifth stage: the formation phases of a large number of emposieu and secondary mineral (Quantou group~late period of Nenjian group); the sixth phase: the formation phases of gas migration - the form of latest secondary porosity and mineral filling (90Ma)...