Surfactant Aided Imbibition In A Fractured Ultra-low Permeability Reservoir

This study describes the application of surfactant system in solving the actual problems in the Chang 9 reservoir in Honghe oilfield.The reservoir is extensively fractured,having low natural energy,low fracture reopening pressure,ultra-low permeability and slightly water-wet.Constraints are high injection pressure due to small pore throat and high water cut.Based on the screening and optimization of surfactants,the best surfactant formulations were obtained.The properties of surfactants were studied from the aspects of water stability,temperature stability,and monovalent and divalent cations salt resistance.Also,the interactions between surfactants and the ability to change the oil phase properties were also studied,including the formation of the microemulsion and the ability to reduce interfacial tension to ultra-low.The changes in wettability by Surfactants were tested by qualitative and quantitative methods.Finally,the model for fracturing a core is designed,and the modified Amott device is used to carry out the imbibition and displacement experiment on the fractured core.Using simulated reservoir water as a solvent,the mixture of anionic?AOS?and amphoteric surfactant?CHSB-35?at the ratio of 1.67:1 lowered IFT from 62.14×10^-1mN/m to 3.00×10^-3mN/m.Individual surfactants AOS and CHSB-35 lowered to 9.10×10^-3 mN/m and 0.10mN/m respectively.The surfactant system gave lower initial contact angle between 33°and 15°depicting strongly water-wet at 0.15%to 0.40%wt,with average matrix permeability 1.03×10^-4?m² the recovery factor is increased to 63.0%of the oil initial saturation.Therefore,the surfactant formulation a mixture 0.15%wt?weight ratio 1.67:1?is suitable for aiding imbibition in the Chang9 reservoir in Honghe Oilfield.