Recent Progress on Phase Equilibrium Calculation in Subsurface Reservoirs Using Diffuse Interface Models
Recent Progress on Phase Equilibrium Calculation in Subsurface Reservoirs Using Diffuse Interface Models
复制标题
利用扩散界面模型计算地下储层相平衡的最新进展
DOI：
10.1007/978-3-030-27053-7_83
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发表时间：
2019
期刊：
影响因子：
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通讯作者：
Shuyu Sun
中科院分区：
文献类型：
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作者：
Tao Zhang;Yiteng Li;Jianchao Cai;Shuyu Sun
由于提高采收率、温室效应和全球变暖等问题以及非常规油气藏开发的迫切需要，地下多孔介质中的组分多相流正变得越来越有吸引力。在建立组分多相流数学模型之前，一个关键的工作是确定流体混合物的相组成，然后计算其他相关的物理性质。本文对地下油藏相平衡计算的最新进展进行了综述，并结合作者自己的分析进行了总结。相平衡计算是进行这种计算的主要方法，可以使用两种不同类型的闪蒸计算算法进行：NPT闪蒸和NVT闪蒸。NPT闪蒸计算很早就被提出，在过去几十年中得到了很好的发展，现在成为最常用的方法。然而，它在求解时往往不能保持物理意义，往往需要求解由状态方程导出的三次方程。或者，NVT flash也可以处理相平衡计算，而无需先验已知的压力。近年来，扩散界面模型（DiffuseInterface Model）被引入到相计算中，并结合了现实的状态方程（EOS），如Peng-Robinson状态方程，该模型被证明与热力学定律保持高度一致。在NVT闪光中，Helmholtz自由能被最小化，而不是NPT闪光中的Gibbs自由能，并且这个能量密度被凹凸分裂技术处理。设计了一种半隐式的数值格式来处理动力学模型，既保证了热力学稳定性，又保持了快速收敛性。为了满足热力学定律所要求的毛细压力存在时的熵增加特性，设计了一个满足Onsager互易原理的正定系数矩阵.所提出的算法的鲁棒性通过两个数值例子，其中一个有多达七个组件进行了验证。在复杂的流体混合物中，TPD函数的全局极小值以及相平衡计算得到的相包络线可以捕捉到一些特殊的现象。可以发现，在毛细管压力的存在下，单相区和汽液相区之间的边界将移动，然后每个区域的面积将相应地改变。文章最后对全文进行了总结，并对今后的研究方向提出了建议。
Compositional multiphase flow in subsurface porous media is becoming increasingly attractive due to issues related with enhanced oil recovery, greenhouse effect and global warming, and the urgent need for development in unconventional oil/gas reservoirs. One key effortpriorto construct the mathematical model governing the compositional multiphase flow is to determine the phase compositions of the fluid mixture, and then calculate other related physical properties. In this paper, recent progress on phase equilibrium calculations in subsurface reservoirs have been reviewed and concluded with authors’ own analysis. Phase equilibrium calculation is the main approach to perform such calculation, which could be conducted using two different types of flash calculation algorithms: the NPT flash and NVT flash. NPT flash calculations are proposed early, well developed within the last few decades and now become the most commonly used method. However, it fails to remain the physical meanings in the solution as a cubic equation, derived from equation of state, is often needed to solve. Alternatively, NVT flash can handle the phase equilibrium calculations as well, without the pressure known a priori. Recently, Diffuse Interface Models, which were proved to keep a high consistency with thermodynamic laws, have been introduced in the phase calculation, incorporating the realistic equation of state (EOS), e.g. Peng-Robinson EOS. In NVT flash, Helmholtz free energy is minimized instead of Gibbs free energy used in NPT flash, and this energy density is treated with convex-concave splitting technique. A semi-implicit numerical scheme is designed to process the dynamic model, which ensures the thermodynamic stability and then preserve the fast convergence property. A positive definite coefficient matrix is designed to meet the Onsager Reciprocal Principle so as to keep the entropy increasing property in the presence of capillary pressure, which is required by the thermodynamic laws. The robustness of the proposed algorithm is verified via two numerical examples, one of which has up to seven components. In the complex fluid mixture, special phenomena could be capture from the global minimum of TPD functions as well as the phase envelope resulted from the phase equilibrium calculations. It can be found that the boundary between the single-phase and vapor–liquid phase regions will move in the presence of capillary pressure, and then the area of each region will change accordingly. Some remarks have been concluded at the end, as well as suggestions on potential topics for future studies.