裂缝性油藏二氧化碳驱的多组分数值计算模型

对于预测油藏二氧化碳驱的效果，黑油模型不再适用，必须采用组分模型。研究了裂缝性油藏二氧化碳驱的
三相多组分数值计算模型，给出了相关的计算方法和公式。采用多重连续介质理论来模拟裂缝性油藏中的输运过程，
每个组分的质量传输包括传导和扩散过程。多相流体的流动采用Darcy 定律来描述；组分的扩散采用Fick 定律来描
述。二氧化碳在岩石颗粒上的吸附及油相重组分在岩石骨架上的沉淀采用非线性等温吸附来描述。用串状毛管模型
来考虑沥青质沉积对储层渗透率的影响。采用积分差分法对各组分的质量守恒方程进行空间离散，并按全隐式格式
通过Newton 迭代法进行求解。根据Soave-Redlich-Kwong 状态方程计算流体的物性。对于油–水–气（二氧化碳）三
相的相平衡计算，分别给出了平衡常数法、闪蒸计算法和最小Gibbs 自由能法的计算公式。

Model Formulation for Compositional Numerical Simulation of CO2 Flooding in Fractured Reservoirs

Compositional simulation is required in evaluating CO2 flooding in EOR operations when black-oil simulation is
no longer adequate. A three-phase compositional modeling approach for CO2 flooding in fractured reservoirs is presented. The
mathematical models and formulations are given. A generalized multi-continuum approach is adopted to handle transport in
naturally fractured reservoirs and the mass flux of each mass component is contributed by advection and diffusion processes.
The multiphase fluid flow is described by Darcy equation，and the diffusion of multi-component is described by Fick′s law.
The precipitation of heavy oil components and absorption of CO2 on the solid grains are modeled based on reversible nonlinear
isotherm. The permeability reduction effects due to asphaltene deposition are considered by a tubes-in-series model. The
governing partial differential equations for conservation of each component are discretized using an integral finite differences
method and solved fully implicitly by Newton iteration. The equation of state (EOS) by Soave-Redlich-Kwong is used to
calculate the physical properties of fluids. Three methods of three-phase equilibrium calculation for hydrocarbon-water-CO2
mixtures，K-value approach，flash calculation and Gibbs energy minimization are also presented.