Study On The Technology Of Surfactant Reducing Injection Pressure For Tight Reservoirs

The Chang 8 reservoir in Honghe Oilfield is rich in reserves and belongs to low porosity and ultra-low permeability reservoir.Due to the development of fractures occurred in tight reservoir,there is a conflict between the pressure gradient of the displacement and the low reopening pressure of fracture.There are many channeling wells and the speed of water channeling is fast,which results in the difficulty and the poor effect of water injection.Therefore,it is necessary to investigate the surfactant system which can depressure and increase injection in Chang 8 reservoir of Honghe Oilfield,furthermore solving the problem of water injection difficulties.This paper first summarizes the reasons of difficulties in water injection in the Chang 8reservoir of Honghe Oilfield,and then analyzes the mechanism of pressure reduction and injection.The study finally decides to screen the salt-tolerant surfactant monomers based on the oil-water interfacial tension as a technical indicator.The above chosen surfactant monomer is mixed to form a surfactant system with good pressure reduction and injection enhancement properties.The compatibility,stability,temperature resistance,salt resistance,emulsifying properties,and wetting properties of the surfactant system were evaluated.Through laboratory physical simulation experiments,the effect of depressurization and injection enhancement performances of the preferred surfactant system were tested,and the surfactant concentration,injection rate,displacement amount,injection timing were optimized.Finally,through the CMG numerical simulation,the difference and relationship of parameters between the laboratory simulation and the on-site construction were analyzed.As a result,a set of process parameters suitable for on-site construction of the oilfield was obtained.Studies show that the preferred surfactant systems were 0.1%AOS,0.03%coco glucoside,and 0.025%AOS+0.015%coco glucoside by weight respectively.The interfacial tension value of oil and water is very low.The three systems have good emulsifying properties and can increase the hydrophilicity of the rock core;all three surfactant systems have good pressure-reduction and injection-strength performance,the pressure reduction rates of which are 26.40%,27.59%,and 26.79%respectively,reaching over 25%.A case in point is AOS and coco glucoside compounding system,the indoor physical simulation is carried out and the optimized construction parameters are as follows.The best injection volume is 2PV and the optimal injection concentration is 0.025%AOS+0.015%coco glucoside.The optimal injection rate is0.02 mL/min and the optimal injection timing is before the moisture content exceeds 50%.The numerical simulation of AOS and coco glucoside compounding system is performed.The optimal construction process parameters are injection volume as 0.4PV,optimal injection concentration is 0.04%,optimal injection rate is 140m~3/d.Furthermore,the proper timing is whent the moisture content is less than 60%.