Research Of Viscosity Reducer And N₂ Assisted Thermal Oil Recovery In Chunguang Extra-heavy Oil Reservoir

Thermal chemical technology with viscosity reducer and N₂ assisted is developed in early stage in Chunguang oilfield extra-heavy oil reservoir.Due to the high oil viscosity and poor mobility in the formation,steam injection is difficult and heat loss of conventional steam stimulation tends to be large.In addition,salt-tolerance and heat-resistance of viscosity reducer are bad in case of high formation water salinity.In this study,the sensitivity factor of high viscosity for Chunguang oil is investigated,and the viscosity reducer with salt-tolerance and heat-resistance is designed.Finally,the injection parameter of viscosity reducer and N₂ is optimized based on one well group.The sensitivity factor of high oil viscosity is determined by the analysis of group composition,UV-Vis spectrophotometry and FTIR spectrum of three kinds of heavy oil.Chunguang heavy oil has high content of resin,asphalt and metallic elements such as Ni,Fe,Ca,and it contains a lot of polycyclic aromatic molecules,mainly the aromatic carboxylic acid,amine and phenolic compounds,which contributes to the high viscosity of heavy oil.The optimum viscosity reducer system is developed based on the high temperature and high salinity of Chunguang oilfield,in which the quality ratio of the HDS-63,HDS-15 and isobutanol is 70:25:5.A desirable viscosity reducing performance will be achieved when the concentration is no less than 0.3%.By physical simulation of the steam flooding with viscosity reducer-nitrogen assisted,the recovery efficiency can be improved by 18-26%.The injection parameter of viscosity reducer and N₂ is optimized by using reservoir numerical simulation technology.The best injection parameters for thermochemical oil recovery of Chunguang oilfield is as follow:the injection concentration of viscosity reducer is0.5%,the steam injection volume of single well is 10t,N₂ is injected at the second cycle injection of steam,and the cycle gas liquid ratio is 10:1,the soak time is 3-5 days.The prediction results show that the cyclic steam simulation with viscosity reducer-N₂ assisted can obtain favorable development effect in extra-heavy oil reservoirs.