Study On Gas Permeability Characteristics During Triaxial Compression Fracture And Closure Of Deep Sandstone Reservoir

Deep-seated oil and gas resources are gradually becoming the main body of growth in the global proven reserves,and the permeability characteristics of deep reservoirs have a major impact on the formation of deep oil and gas reservoirs,the storage capacity of the reservoirs and the efficiency of oil and gas resource extraction.Based on this,this paper takes the deep sandstone reservoirs in the Dongying Sag area as the research background to systematically study the changes in the pore structure of rocks with different occurrence depths and bedding directions in the Dongying Sag area of Shengli Oilfield,and the law of gas permeability during triaxial compression and the law of gas permeability during confining pressure loading after rock fracture.So as to provide data reference and technical basis for deep oil and gas exploration in Dongying Sag of Shengli Oilfield.The specific research content and conclusions are as follows:(1)Through wave speed measurement,mineral composition analysis and other methods,the physical properties of sandstones with different depths and bedding directions in the deep are analyzed.In general,as the depth of the sample increases,the ultrasonic wave velocity shows an upward trend.The content of quartzite in the rock samples of different occurrence depths in the Dongying Sag area is the highest,accounting for about 50%.The content of clay minerals decreases with the increase of the occurrence depth of the rock samples.(2)Through mercury intrusion,scanning electron microscopy,and computer tomography,the pore structure of sandstones with different occurrence depths and bedding directions in the deep is analyzed.As the occurrence depth increases,the porosity of the sample decreases,the pore throat radius becomes smaller,and the rock sample becomes denser.At the same occurrence depth,the porosity of the samples in the vertical and parallel directions has no obvious regularity.(3)The gas permeability test is carried out on the samples with different occurrence depth and layering direction.When the occurrence depths are similar,the initial gas permeability changes are not obvious,and when the occurrence depths are different,the initial gas permeability changes significantly(three orders of magnitude).The initial permeability of samples with a depth of 2601 m or more in the vertical direction is greater than that in the parallel direction,and the initial permeability of samples with a depth of 2601 m or less in the parallel direction is greater than that in the vertical direction.(4)During the confining pressure loading and the confining pressure loading stage after crushing,the gas permeability shows a downward trend as the confining pressure increases.In the triaxial compression stage,in the early stage of deviator stress loading,the gas permeability decreases.As the deviator stress increases,the gas permeability of the samples at the depth of 1047 m and 1970 m increases slightly(the same magnitude),and the gas permeability of the samples at the depth of 3245 m and 3375 m has increased significantly(a difference of an order of magnitude).During the full path of stress loading,the final gas permeability of samples with depths of 1047 m and 1970 m is basically the same as the initial value.The final gas permeability of samples with depths of 3245 m and 3375 m has an order of magnitude increase from the initial value.(5)With the occurrence depth of 2601 m,the sample has low wave velocity,high porosity,large pore size and developed pore structure,showing the particularity of inconsistent changes with other occurrence depths.As a result,the gas permeability of the sample in the test process is far higher than that in other occurrence depths(more than one order of magnitude)and presents a downward trend throughout the whole process.This shows that with the change of the occurrence depth,although the gas permeability of the rock has a more consistent law.However,due to the complexity of the underground environment,in certain lithology and geological structural environments,the law of permeability changes with the depth of occurrence is not certain.The paper has 51 pictures,5 tables,and 95 references...