The Wettability Of Tight Sandtone And Its Significance Of Hydrocarbon Accumulation Of Yanchang Formation,Ordos Basin

Tight sandstone reservoir has fine pore throat and large capillary force,so the wettability has a great influence on the migration and accumulation of tight sandstone oil.This thesis studies the tight sandstone cores in Chang6-Chang8 Member in Heshui area,Ordos basin.Based on the analysis of petroleum geology,reservoir properties,pore structures,fluid properties and distribution characteristics of Heshui area,the wettability of these tight sandstone cores is tested,and physical experiments simulating tight oil migration and accumulation in different wettability is designed and conducted.The impact factors of wettability in tight sandstone reservoirs,the characteristics of tight sandstone oil migration and accumulation,and the effect on oil migration and accumulation in different wettability of reservoir sandstone reservoirs are analyzed and summarized.Results indicate that:(1)The tight sandstone reservoir wettability in Heshui area is mainly neutral-wet and water-wet,followed by oil-wet.The lipophilicity of tight reservoirs becomes more and more stronger from Chang 7 Member,Chang 8 Member to Chang 6 Member.(2)The wettability of tight reservoir is influenced by relative content of hydrophilic wet-type(quartz,chlorite and illite),neutral wet-type(feldspar and calcite)and lipophilic wet-type(dolomite,mixed-layer illite and kaolinite)minerals.The polar components content in crude oil also has a big impact.Both the oil and hydrophilic wet-type mineral content of tight sandstone reservoir and polar components content in crude oil coupled control the reservoir wettability.(3)The migration flow characteristics of oil is influenced by permeability,viscosity and the wettability.The lower of the oil viscosity,the higher of the core permeability and the more biased of the neutral wet-type,the more easily the oil flows in the tight sandstone core.(4)When oil does not contain polar substances,the better the petrophysical condition of the core is,the more easily the oil saturation grows.When oil contains lots of polar substances,the more lipophilic of the wetting rock wet-types tends,the more easily the oil saturation grows.(5)The maximum oil saturation has no correlation with the physical properties of the core in tight sandstone petroleum accumulations.The lower the viscosity of oil is,and the more biased of oil wet-type is,the higher the maximum oil saturation in tight sandstone petroleum accumulations is.(6)After the crude oil which contains polar substances in the tight sandstone core aggregated,the wettability of core will be changed,so the wettability of the core becomes more oil-wet,and it will be beneficial to the oil filling.