(497d) Multi-Scale Reservoir Simulation

A novel multi-scale reservoir simulation framework, AD-GPRS/GFLASH, that couples three length scales is described. Length scale range from 100's of meters for the reservoir, meters at the bulk fluid length scale, and nanometers at the molecular length scale. AD-GPRS, which stands for Automatic Differentiation - General Purpose Research Simulator, has been fully integrated with a multi-phase, multi-component flash program called GFLASH. AD-GPRS is a modeling and simulation tool for time-dependent multi-phase flow through porous media, is capable of handling very complex nonlinear physics, and is built on top of the Automatic Differentiation Expression Template Language (ADETL). GFLASH, on the other hand, is built around the multi-scale Gibbs-Helmholtz Constrained (GHC) equation of state, which uses a novel up-scaling equation. This up-scaling equation  relates the bulk phase length scale energy parameter in the van der Waals family of cubic equations to the internal energy of departure at the molecular length scale. Molecular information is computed a priori using NTP Monte Carlo simulations and stored in look-up tables for use in the GHC equation.

In this work we describe the algorithmic details of AD-GPRS/GFLASH, which include model formulations and associated equations and equation solving at various length scales, as well as advanced features such as the use of Schur complements and compositional space adaptive tabulation (CSAT), which are used to reduce computational overhead. Numerical results that highlight the reliability, robustness and efficiency of the proposed multi-scale reservoir simulator are presented. In particular, simulation examples will include hydrocarbon recovery processes for both conventional and unconventional resources.