Study On The Viscosity Reducer Assisted SAGD Technique

Steam assisted gravity drainage(SAGD)is an effective process for the thermal recovery of heavy oil and oil sand.It has been widely used around the world.However,to sustain a SAGD operation,large quantities of steam are needed and also the energy efficiency is relatively low.Moreover,the low oil price poses a great challenge to the heavy oil recovery by SAGD.Therefore,the way that utilizes viscosity reducer co-injected with steam to enhance the oil recovery of SAGD was considered.By using the super heavy oil from Fengcheng Oilfield,research on the Viscosity-Reducer SAGD was carried out.A series of viscosity reducer(VR)selection experiments were first conducted,including viscosity reduction ratio test,thermal stability test and sandpack flooding test.Then 2-D VR-SAGD experiment was carried out in order to study the production performance of VR-SAGD.Numerical simulation was also performed by using CMG.History match was conducted based on the 2-D experimental data.By using the numerical model,injection time of VR,VR / steam injection ratio and production/injection ratio were optimized.The results indicate that: WSVR8,a water soluble viscosity reducer,was suitable because its viscosity reduction ratio for the heavy oil was as high as 98.0% at 50?.It was still effective after high-temperature-high-pressure degradation and also it functioned well in the coreflood test.The 2-D physical simulation results show that VR-SAGD accelerated the oil rate from 2.22 to 4.57mL/min and improved the cumulative oil-steam-ratio from 0.106 to 0.127.Numerical simulation results indicate that the best injection time of viscosity reducer is during the middle and later period of development.The optimized VR / steam injection ratio and production/injection ratio are 1:9 and 1.2 respectively.Based on this research,the conclusion is achieved that Viscosity Reducer-SAGD combines the viscosity reduction function of both steam and viscosity reducer and accelerates the oil drainage rate on the edge of steam chamber.The use of viscosity reducer promises to improve production performance of the in-situ oilsands recovery by SAGD.