特低渗透油藏CO2非混相驱井距与产量关系研究

井距是新井井位部署及老井井位调整的关键因素,井距与产量相关;对特低渗透油藏CO_2非混相驱井距与产量关系的研究很少。在经典油气两相渗流理论的基础上,考虑CO_2溶解于原油所产生的降黏作用及油相启动压力梯度,建立了一个一维油气两相渗流数学模型。基于Buckley-Leverett非活塞驱替理论对饱和度方程进行求解,开发了井距计算软件,分析了生产压差、CO_2驱替前缘推进距离百分比、渗透率对井距与产量关系的影响。计算结果显示,产量越大,井距越小,井距变化的幅度也越小。在注气井近井带,油相黏度由1.5 m Pa·s降低到0.4 m Pa·s;在生产井近井带,油相黏度由1.5 m Pa·s降低到0.6 m Pa·s,CO_2对于原油的降黏幅度可以达到70%左右,从注气井到生产井,油相黏度逐渐升高。为特低渗透油藏CO_2非混相驱井距与产量关系研究提供了一种计算方法,绘制了井距与产量随不同参数变化的理论图版,方便油田应用。

A study on relation of well spacing and yield of CO2 immiscible flooding in extra-low permeability reservoirs

Well spacing is a critical factor to deployment of new well and well site adjustment of old well. well spacing is yield related and the study on the relation between well spacing and yield of CO₂immiscible flooding in extra-low permeability reservoirs is little. A one-dimensional two-phase mathematical model considering the threshold pressure gradient and dissolution of CO₂in the crude oil was proposed on the basis of classic two-phase porous flow. The governing equations were solved using the Bucklev-Leverett non-piston displacement theory. A software which calculated well spacing of CO₂ immiscible displacement in the extra-low permeability reservoirs was developed. The effects of production pressure difference, percentage of CO₂ flooding front advance distance and permeability on relation between well spacing and yield are analysed. The results show that the higher the yield, the smaller the well spacing, the smaller the variation of the well spacing with reservoirs parameters changed. The viscosity of crude oil is reduced from 1.5 mPa.s to 0.4 mPa.s near the gas injection well and from 1.5 mPa.s to 0.6 mPa.s near the production well. The decrease of viscosity of crude oil can reach about 70 percentage although the viscosity of crude oil gradually increases from the gas injection well to production well. A calculation approach for well spacing and yield of the CO₂immiscible flooding in extra-low permeability reservoirs is provided and theoretical plates are drawn to illustrate the relation between well spacing and yield. It is convenient for application in oil fields.