考虑流体非均质性的低渗透油藏CO2驱试井分析

CO₂ 驱是提高低渗透油藏采收率的一种重要方式，但目前对驱替过程中压力响应动态的认识不足。CO₂ 的注入使地层流体性质发生改变，形成CO₂ 区、CO₂ -原油过渡区和未波及原油区。基于复合油藏渗流理论，引入幂律型公式和牛顿插值公式来描述CO₂ -原油过渡区内流体非均质性的变化特征，建立了低渗透油藏CO₂ 驱试井模型，并采用数值方法进行求解。对CO₂ -原油过渡区内2 种流体非均质性变化形式下的试井曲线特征进行了分析。结果表明：当CO₂ -原油过渡区内流体黏度与综合压缩系数均呈幂律型变化时，其变化指数均增大，CO₂ 区与CO₂ -原油过渡区流度比和导压系数比均增加，压力导数曲线斜率增大；当CO₂ -原油过渡区综合压缩系数呈非连续性变化时，压力导数曲线因CO₂ 区与CO₂ -原油过渡区导压系数比的增加而呈现下凹趋势。最后，通过实例应用提出了CO₂ 驱试井解释方法。

Pressure transient analysis on CO2 flooding in low permeability reservoirs considering fluid heterogeneity

CO₂ flooding in low permeability reservoirs is considered as one of the most significant EOR methods.However, there is lack of clear recognition on pressure response performance during the flooding process currently.Injection of CO₂ will change the physical property of reservoir fluids, and three zones could be developed, which are CO₂ zone, CO₂ -oil transition zone and unswept oil zone, respectively. Hence, based on the seepage theory of composite reservoir model, the power?law and Newton interpolation equations were introduced to describe the variable characteri?stics of fluid heterogeneity in CO₂ -oil transition zone. The well testing model for CO₂ flooding in low permeability reservoir was presented, and it was solved by numerical differential method. The pressure transient curves at two different fluid heterogeneity variation forms were analyzed. The results demonstrate that for power-law variation of viscosity and compressibility in CO2 -oil transition zone, the mobility and diffusivity ratio between CO₂ zone and CO₂ -oil transition zone increased with variation exponents, which leads to the rise of pressure derivative curves slope. As the compressibility in CO₂ -oil transition zone varied discontinuously, since the increase ofdiffusivity ration between CO₂ region and CO₂ -oil transition region, the pressure derivative curves would drop. Finally,the well testing explanation method for CO₂ flooding was presented through the application of real case.