基于微观剩余油启动条件变化规律的合理注采调控界限研究

Study on reasonable injection-production control limit based on the change law of microcosmic residual oil start-up conditions

明确微观剩余油动用机理及其启动条件的变化规律,对于指导油田开发过程中的注采调控有着重要意义。基于流体在孔喉中的物理特性和微观渗流机理,建立了非等径并联双孔渗流模型,得到了微观剩余油启动界限及变化规律;提出岩心中“孔喉动用率”这一评价指标,利用该指标建立了宏观注采井网尺度的储量动用评价方法,明确不同开发制度下剩余油重启界限及水驱动用规律,得到了油田分区块合理注采调控界限。研究表明,在并联双管模型中,驱动压力梯度0.03 MPa/m时,当两孔道半径比小于4.8,小孔道的剩余油能够动用;提高驱动压力梯度至0.09 MPa/m,临界启动时大、小孔道组合孔径比增大至6.1,孔喉动用率提高约25%。随注采压力梯度增加,井网孔喉动用率增加,动用率增压效益呈“先缓-再快-后缓”的降低规律;原油黏度从50 mPa·s增加至100 mPa·s,注采压力梯度提高的合理界限由0.025 MPa/m增加至0.06 MPa/m。

It is significant to determine the microcosmic residual oil production mechanism and the change law of start-up conditions for guiding the injection-production control in oilfield development.Based on the physical characteristics of fluid in the borehole throat and the microscopic seepage mechanism,a non-equal diameter parallel double-hole seepage model was established,and the start-up limit and change law of the microscopic residual oil were obtained.The evaluation index of"utilization rate of borehole throat"in the core was put forward,and the evaluation method of reserves utilization on the scale of macro well pattern was established by using this index.The restart limit of residual oil and the utilization law of water flooding under different development systems were defined,and the reasonable injection-production control limit of different oilfield blocks is obtained.The results show that:as for parallel double-channel model,when the driving pressure gradient is 0.03 MPa/m and the radius ratio of the two channels is less than 4.8,the residual oil in the small channel can be used;when the driving pressure gradient is increased to 0.09 MPa/m,the combination aperture ratio of large and small channels at critical start-up is increased to 6.1,and the utilization rate of pore throat is increased by about 25%.The utilization rate of pore throat increases with the increase of injection-production pressure gradient,and the supercharging efficiency of utilization rate shows the decreasing law of“slow first,fast then,slow later”.The viscosity of oil increases from 50 mPa·s to 100 mPa·s,and the reasonable limit for the increase of injection-production pressure gradient increases from 0.025 MPa/m to 0.06 MPa/m.