Wettability Of Tight Sandstones In Coal Measures From Linxing-shenfu Area,Shanxi,China

Wettability is an important parameter to control the mobility of microporous fluids,determining the gas-water distribution,water flooding efficiency,and water/gas saturation of reservoir,which can effectively guide water injection development and enhance gas recovery.Therefore,the paper studies the sedimentary microfacies and the wettability of tight sandstone reservoirs from Shanxi formation to Benxi formation in the Linxing-Shenfu area.A prediction model for the wettability of tight sandstone in coal measures is established and the relationship between wettability and fluid mobility of tight sandstone is discussed.It is found that the Zeta potential of the subaqueous distributary channel sandstone of coal measures is generally higher than that of the barrier sand dam facies in the study area.The reason is that the wettability of tight sandstone in coal measures is closely related to the mineral composition.The hydrophilicity of sandstone enhances with the increase of feldspar content or the decreases of quartz content.As the clay content increases or the carbonate mineral content decreases,the hydrophilicity of the sandstone is first enhancement and then weakening.The influence of physical and chemical properties of solution on wettability of tight sandstone is revealed.With the increase of pH,hydrophilicity first increases and then decreases.With the increase of CaCl₂ concentration,hydrophilicity decreases.The porosity and permeability properties of sandstone also affect wettability.Debris particle size,pore throat radius and permeability increase,while hydrophilicity first decreases and then increases.Surface roughness increases and hydrophilicity enhances.the crystal plane structure and groups of sandstone surface particles,ion exchange,specific surface area of particles,acidity and basicity of solution and other factors are the fundamental reasons for the difference in wettability of tight sandstone.Comprehensive analysis shows that the wettability of tight sandstone in coal measures is mainly controlled by reservoir physical properties and mineral composition,and then wettability prediction model of tight sandstone in coal measures is established by fitting the weight score and the measured relative wettability index.On this basis,using the method of logging data interpretation and experimental simulation,it is found that the irreducible water saturation and water absorption of tight sandstone in coal measure increase with the enhancement of hydrophilicity in the study area.It is believed that organic matter properties,groundwater salinity and cationic valence are the key factors determining the mobility of sandstone reservoir fluids.