Sedimentary Microfacies Control Of Tight Sandstone Wettability For Coal Measure

Wettability of sandstone is controlled by sedimentation and diagenesis,which affects the productivity release and ultimate recovery of tight sandstone gas.However,little is known about the wettability of coal measure tight sandstone.Therefore,taking the Carboniferous-Permian coal measure tight sandstone in Linxing-Shenfu area as the research object,this paper focuses on the control of sedimentary microfacies on wettability by using field outcrop,core cataloguing,logging data and sample testing data,the following innovative knowledge was obtained:Through the analysis of surface force between solid and liquid,it is found that the mineral composition of sandstone determines that the wettability of all tight sandstones in coal measure is water wet,and the fluid properties and formation temperature directly affect the wettability of sandstone.The hydrophilicity of tight sandstone is positively correlated with quartz content,surface roughness,pH(>5),formation temperature,and inversely correlated with clay and carbonate content,fluid salinity and ionic valence.Sedimentary microfacies and diagenesis indirectly affect wettability by controlling sandstone composition and structure.The tight sandstones deposited in sedimentary microfacies under strong hydrodynamic conditions,such as the main part of subaqueous distributary channel,sand flat,barrier bar,are often strongly water wet or moderately water wet,while they are usually gas layers or poor gas layers with high gas recovery.The tight sandstones deposited in sedimentary microfacies under weak hydrodynamic conditions,such as the top part of subaqueous distributary channel,subaqueous natural levee,mixed flat,river mouth bar,interdistributary bay,are often weakly water wet,while they are usually dry layers or poor gas layers with low gas recovery.Based on this,the distribution of wettability of tight sandstone under sequence stratigraphic framework is summarized.Strongly and moderately water wet sandstones are mainly distributed in the sand flat and barrier bar of SQ2,the main middle parts of subaqueous distributary channels of SQ4,SQ7,SQ8 and SQ10.The middle parts of LST thick tight sandstone layers are often strongly and moderately water wet,while the top and bottom parts are mostly weak water wet.The thin tight sandstone layers of TST and HST are often weakly water wet.In tight sandstones the main pore size is nano-submicron,the irreducible water saturation is very high,while the gas-water interaction is intense and the gas-water transition zone is long.Wettability has a great influence on the occurrence and seepage of fluid in tight sandstone.In 0.05-1um pore and throat,hydrophilicity enhances the thickness of water film and capillary force while effective throat radius decreases,resulting in the increase of irreducible water saturation and the decrease of movable water saturation.Finally,the parameters closely related to wettability are selected,and the wettability evaluation and prediction model of tight sandstone is established.There are 114 figures,39 tables and 183 references in this dissertation.