Research On The Mechanism Of Low-salinity Waterflooding

Low-salinity waterflooding is defined as a waterflooding method of injecting water with low concertration of soluble solids into the reservoir,which leads to the increase in recovery.So it will significantly impact the development of oil field.Based on the fundamental theory of low-salinity waterflooding,this dissertation finds out the mechanism of low-sanility-water-flooding in sandstone reservoirs after researching the data of Zeta potential experiment.The producing conditions of lowsalinity waterflooding is summarized,including reservoir rocks with clay minerals,crude oil with polar components,formation water with high cations,and the salinity of injected water in a certain range.The influence of concentration and type of injected water ions on Zeta potential are analysed after experiments of oil-rock and water-rock Zeta potential according to theory of colloid chemistry.With the decrease of salinity of injected water,the interfacial repulsion increases,following with the increase of the thickness of diffused double layer,which results in the increase of absolute value of Zeta potential.It is noticed by experiments of oil adsorption and contact angle that,on one hand the diffusion of the double layer on the surface of the sandstone occurs by abrupt decrease of salinity,on the other hand after being replaced by cations(ion exchange),the organic polar substance is desorbed from the surface of clay minerals,which demonstrates the fact that the surface of clay minerals shows more water-wet.The experimental data of low-salinity waterflooding shows that as much as 10% additional oil can be produced if low-salinity water is injected,opposed to formation brine.The recovery of NaCl injection shows more than that of CaCl2.The main mechanism of low-salinity waterflooding is researched,and other mechanism of lowsalinity waterflooding,including particle migration,surfactant and pH increase is also researched.