An Adaptive approach for compositional reservoir simulation in conjunction with unstructured grids
Edilson Pimentel Drumond Filho1; Francisco Marcondes1; Kamy Sepehrnoori2; Ivens da Costa Meneses Lima1
1 Federal University of Ceará; 2 Center for Petroleum and Geosystems Engineering, The University of Texas at Austin
doi:10.20906/CPS/CILAMCE2017-0451
Resumo
One of the key aspects of compositional reservoir simulation is the algorithms or formulations used to solve the equations for modeling fluid flow in the permeable media. Basically, the main goal is to have algorithms that produce accurate results with efficient computational times, while maintaining computational stability for different recovery processes. A literature survey shows that several approaches have been developed in the last decades. The formulations are different partly by the choice of primary variables and implicitness level. Implicit Pressure, Explicit Composition (IMPEC) models treat a single variable implicitly, reducing the run time for each time step, while becoming more vulnerable to numerical instabilities. On the other hand, Fully Implicit (FI) schemes evaluate all primary variables implicitly, which results in a greater stability but more expensive per time level and more memory consumption. Herein, we present a dual approach that combines advantages of fully implicit and IMPEC approaches. The proposed model combines the two formulations into an adaptive method with variable level of implicitness throughout the reservoir. If the computations for an IMPEC gridblock is unstable or requires an excessively small time-step, then that gridblock is switch to FI. On the other hand, if the sources of instabilities, as in the saturation front, are not present anymore in a FI gridblock, we switch the computations in that gridblock to IMPEC. We use the CFL (Courant-Friedrichs-Lewy) number and a threshold value based on a saturation variation as switching criteria to change computations in a gridblock from IMPEC to FI and vice-versa. The main novelty of this work is the association of this Adaptive Implicit Method with the Element based Finite Volume Method scheme for unstructured meshes. The results are shown in terms of oil and gas production rate curves and CPU time.
Palavras-chave: Compositional reservoir simulation; Adaptive Implicit Method ; EbFVM; Switch criteria