Study On Seepage Characteristics And Hydrogeochemical Influence Of Fracturing Fluid In Shale Reservoir

Due to the tight shale reservoir and extremely low permeability,shale gas cannot be produced naturally.Hydraulic fracturing of large-scale horizontal well is the key technology for shale gas exploitation.The production practice shows that the flowback rate of fracturing fluid is low and the difference between different blocks is large.Moreover,the chemical composition of fracturing liquefaction is complex and contains a large number of toxic and harmful substances.Therefore,the long-term existence in the underground is not conducive to the recycling of fracturing fluid and the risk of groundwater pollution.In this paper,the sichuan basin changning shale block creek,the dragon group as the research object,through the development samples of shale porosity,permeability,mineral composition and surface characteristics of the test and analysis,temperature,pressure,different fracturing liquid property and permeability under the condition of shale porosity seepage experiments,and fracturing fluid shale mineral hydrogeochemical reactions between experiment and simulation studies,reveals the fracturing fluid seepage in the shale reservoir characteristics and its effect on the hydrogeochemical effect mechanism.The main research results are as follows:(1)Shale sample test analysis:type?rock composition is illite,quartz,calcite,pore development is good,the distribution is not uniform;Type?Rock composition is mainly quartz,feldspar,low content of clay minerals,more micropores,microfractures developed,local has good connectivity;Type?rocks with montmorillonite as the main component have few micropores with small diameter and uniform distribution;Type?rocks with chlorite as the main composition,more microcracks,local regional connectivity is better,less micropores,but the pore size is large.The porosity and permeability of Longmaxi Formation shale are 6.11%and0.0703m D.(2)The seepage experiments show that with the increase of confining pressure,the pore volume is gradually compressed,and the permeability of the solution in the shale sample decreases;With the increase of temperature,shale mineral particles expand and compress the pore and fissure space of shale,thus reducing the permeability of shale.The permeability of KCl solution in shale samples is higher than that of Ba Cl₂solution due to the different hydrophilicity and ion adsorption of shale minerals to different chemical properties of solutions.(3)In the water-rock reaction experiment,the main dissolution ions of shale minerals in distilled water are Ca²⁺,K⁺,Mg²⁺and SO₄^2-,and the higher the temperature,the higher the concentration of dissolution ions.KCl and Ba Cl₂solutions can promote the dissolution of ionic components in the solution,and the promotion effect of Ba Cl₂solution is greater than that of KCl solution.KCl solution can inhibit the dissolution of albite and dolomite and the precipitation of calcite and quartz,and promote the dissolution of montmorillonite.Bacl₂solution can promote the dissolution of albite and dolomite,precipitate calcite and quartz,and inhibit the dissolution of montmorillonite.(4)The dissolution and precipitation reaction between the solution and minerals can affect the seepage characteristics of the solution in the shale reservoir.As the temperature increases,the precipitation amount of quartz,calcite and chlorite minerals is greater than the dissolution amount of albite,dolomite and montmorillonite minerals,the pore and fracture space of the rock sample becomes smaller,and the permeability of the solution in the shale sample becomes smaller.Therefore,under the same conditions,the permeability of Bacl₂solution in shale samples is lower than that of KCl solution in shale samples.The research results of this paper have important guiding significance for guiding shale gas exploitation and analyzing the environmental behavior of fracturing fluid in underground reservoir.There are 33 figures,14 tables and 104 references in this paper.