Micro-scale Wetting Phenomenon In Silica Microtubes

For a long time,classic interface theory and droplet method are applied to study the wettability problem in reservoirs,which has caused confusion about the capillary pressure,imbibition and oil displacement characteristics in tight low-permeability reservoir matrix.Interface problems in reservoirs require new theoretical foundations.An optical microscope is used to observe the gas-liquid,oil-water interface morphology in silica microtubes with diameters ranging from micrometers to millimeters.The experiments observe the micro-scale wetting that the contact angle of gas-liquid and oil-water tested in microtubes is different from that tested by droplet method.For deionized water,methyl silicone oil and hexadecane,with the change of the microtube diameter,the gas-liquid contact angle tested in the microtubes is not a fixed value described by classic interface theory but a changed one in a certain law.With the decrease of the microtube diameter,the gas-water contact angle gradually decreased first and then increased rapidly,while both the gas-methyl silicone oil and gas-hexadecane contact angles increased slowly and then rapidly.The diameter range of turning point is100?500?m.With the decrease of the microtube diameter,wettability alteration occurs in methyl silicone oil-water contact angle experiment.Under the circumstance that the inner wall of the pure silica microtubes is first wetted by methyl silicone oil,when the diameter of the microtubes is greater than 40?m,the methyl silicone oil-water contact angle is less than 90°,which means that the wettability of the inner wall is water wetted;When the diameter of the microtubes is reduced to 20?40?m,the methyl silicone oil-water contact angle is close to 90°,the wettability of the inner wall is neutrally wetted;When the diameter of the microtubes continues to decrease,the methyl silicone oil-water contact angle was greater than 90°,which means that the wettability of the inner wall is reversed from hydrophilic to lipophilic.The contact angle of methyl silicone oil-water and hexadecane-water tested in pure silica microtubes is different from that tested in silica microtubes containing carbon impurities.