Enhanced Oil Recovery By Surfactant Flooding In Low Permeability Reservoir

Low permeability reservoir is rich in resources,so it is of great significance to study and improve its production mode.Taking yang19 and Sai39 blocks of Changqing Low Permeability Reservoir as examples,surfactant flooding technology for EOR in low permeability reservoir is studied.In Changqing Low Permeability Oilfield,water injection recovery is low and injection is difficult.In order to solve these two problems,this paper focuses on the performance of surfactant in Changqing Low Permeability Reservoir,designs and optimizes surfactant flooding system in Changqing Low Permeability Reservoir,and studies surfactant flooding mechanism in low permeability reservoir1.Developed two different surfactant systems for yang19 and Sai39 blocks: for Changqing Low Permeability Reservoir,reducing interfacial tension is the most important mechanism of surfactant flooding.In order to reduce the interfacial tension as an important screening index,a series of surfactants were screened,and yang19 block system 1(has-7 / CPS)and yang19 block system 2(has-6 / chsb)were obtained;Block Sai 39 system 1(has-6 / CPS)and block Sai 39 system 2(has-6 / chsb),and comprehensive performance tests of the above four composite systems were carried out;The results show that the performance of chsb is better than that of CPS in many aspects,such as interface performance,emulsification stability,anti adsorption,temperature and salt resistance.2.The optimal sacrificial agent system corresponding to the four complex systems was developed: Yang 19 block system 1(has-7 / CPS / sodium tetraborate),Yang 19 block system 2(has-6 / chsb / sodium carboxymethyl cellulose);Block Sai 39 system1(has-6 / CPS / lignin)and block Sai 39 system 2(has-6 / chsb / sodium carboxymethyl cellulose).These sacrificial agents can reduce the static adsorption by more than 40%;The ability to resist multiple adsorption was improved.3.The mechanism of surfactant for EOR in low permeability reservoir is studied,including the interaction mechanism between surfactant system and crude oil.The distribution coefficient is used to express the distribution degree of surfactant to oilwater interface.The results show that the distribution coefficient is greatly affected by the spontaneous emulsification of the system.The distribution coefficient after emulsification is obviously higher than that of static distribution coefficient,which is greatly affected by the emulsifying performance of the system.The results show that the largest proportion of surfactant start-up remaining oil is cluster remaining oil and columnar remaining oil,both of which belong to free State remaining oil with high mobility.Whether these two types of remaining oil can be driven is the key to improve recovery after water flooding.For low permeability core,the best displacement system of the two blocks is determined: has-7 / CPS / 0.1% sodium tetraborate in yang19 block;The best displacement parameter is 0.8pv and the concentration is 0.3%.Block Sai 39 is has-6 / chsb / 0.1% CMC sodium;The best displacement parameter is 0.8pv and the concentration is 0.4%.In low permeability surfactant flooding,high emulsification performance will seriously affect the depressurization effect of surfactant;However,the low emulsification performance will limit the improvement of oil recovery and has no effect on the depressurization effect of surfactant.Therefore,the emulsification composite index of surfactant system in low permeability reservoir is better in the range of 0.3 ? 0.7.