Pore Structure Characteristics And Its Influence On Gas-Bearing Properties Of Continental Shale In The Shahezi Formation In The Changling Fault Depression,Songliao Basin

The organic-rich shale is well-developed in the Lower Cretaceous Shahezi Formation in the Changling Fault Depression,Southern Songliao Basin,which has a large potential for continental shale gas resources and has become an important exploration and development position.Based on the detailed literature review,this work systematically analyzed the sedimentary conditions and structural background,and clarified the pore structure characteristics,gas-bearing featuress,as well as the influence of the pore structure on the gas content of the Shahezi shale in the study area.Combined with previous research achievement,a comprehensive study on the Shahezi shale were performed with the full consideration of well drilling results,geophysical logging data,and related geochemical information.Geochemical characteristics of the Shahezi shale were clearly demonstrated by well logging interpretation so as to summarize geochemical index including the content of total organic carbon(TOC)and thermal maturity and appraise the hydrocarbon generation potential.Field emission-scanning electron microscopy(FE-SEM)observation,low-pressure gas adsorption,mercury intrusion porosimetry(MIP)and spontaneous imbibition experiments were conducted to comprehensively evaluate the pore structure characteristics.In addition,the gas bearing features were pointed through the isothermal adsorption experiment,drilling log data and model prediction.Finally,the study revealed the relationship between the shale pore structure and gas-bearing properties,and clarified its effects on the gas-bearing properties of shale.The main results are as follows:(1)The TOC of the Shahezi shale in the Changling Fault Depression is in the range of 0.5%?4.50%.The organic matter maturity is in the high-mature to over-mature stage.With small shale porosity and gas saturation,the shale is dominated by the clay minerals.(2)The well-deveoped reservoir space of the Shahezi shale is mainly dominated by micropores and mesopores,while the pore volume of macropores is relatively lower.And the Shahezi shale display the behavior of high pore fractal dimension and mixed wetting.(3)With the well gas-bearing properties,the adsorption gas volume of the Shahezi shale is between 0.05and 10.6 m~3/t,and the free gas volume is between 0.01 and 0.21 m~3/t.The total gas content is between 0.4 and 10.8 m~3/t,with an average value of 2.86 m~3/t.(4)The pore surface area of the Shahezi shale in the Changling fault depression remarkably control over the content of adsorbed gas,while the pore volume affects the content of free gas.The high fractal dimension signifies the complex pore structure.The shale wetting characteristics has significant influnce on the content of the free gas.