Research On The Geological Characteristics And Damage Mechanism Of Shihezi Formation Gas Reservoirs In Kangning District, Linxing

In recent years,in the face of national economic growth and national advocacy of clean energy,the demand of China for natural gas has been rising.However,domestic gas production is unable to meet the demand,which leading to high dependence on importing natural gas.The Linxing Kangning district is a new pilot area.The gas reservoirs in Shihezi Formation are characterized by low porosity,low permeability,high capillary pressure,high clay mineral content and complex pore throat structure.The damage caused by foreign liquids(drilling fluid,fracturing fluid,etc.),resulting in low productivity or production of gas wells.There is a loss of productivity or no productivity after fracturing in the pilot test wells in the exploratory well area.Similar conditions exist in the pilot test wells in the exploratory well area of Linxing Kangning.Therefore,deepening the understanding of reservoir characteristics,and clear the damage mechanism,and having specific aim to protect gas are of significance,which can scientifically guide the development of the gas reservoir reasonably,efficiently and continuously.Aiming at the problems existing in drilling and fracturing of exploration wells,this paper is on the basis of a large number of literature research and data analysis.The reservoir characteristics such as reservoir lithology,content and type of clay mineral,physical property and pore structure have been further studied.The damage mechanism of the reservoir is clarified.Combined with a lot of laboratory experiments,the following achievements and understandings have been achieved.(1)The main layer is in He-4 member,He-8 member,Lithology is dominated by feldspar lithic sandstone and lithic sandstone.The average content of clay minerals is 8-14.2%.The He-8 member is mainly kaolinite,illite and chlorite.With an average porosity of 7.24%and an average permeability of 0.381mD,He-8 member belongs to the ultra-low permeability-tight reservoir.The He-4 member belongs to the low permeability-ultra low permeability reservoir.The correlation between porosity and permeability is poor,and the structure of pore throat is complex.(2)The type of space is mainly composed of residual intergranular pores,intergranular dissolved pores and intragranular dissolved pores.(3)The damage degree of fluid sensitivity in He-4 member is water/salt sensitive>acid sensitive>alkali sensitive>speed sensitivity,and the degree of sensitivity damage is from weak to medium weak.The sensitivity damage degree of He-8 member is salt/water sensitivity>acid sensitivity>speed sensitivity>alkali sensitivity,and permeability damage degree is from weak to medium strong.(4)The water block damage in the He-8 member is stronger than that of He-4 member.The order of the damage degree of the water block is the filtrate of the drilling fluid>the fracturing fluid of the fracturing fluid>the formation water.The damage degree of permeability in He-4 member and He-8 member is moderately strong,and the damage degree of He-8 member is greater than that of He-4 member.Fracture fluid damage experiment combined with scanning electron microscope observation results,The damage degree of fracturing fluid system 1 is greater than that of fracturing fluid system 2.Both two kinds of gel breaking liquid of the fracturing fluid are compatible with sensitive minerals of gas reservoir.The higher the residue content is,the more serious the pore and throat was blocked,and the more serious the reservoir damage is.