Development and Testing of an Advanced Coalbed Methane Numerical Reservoir Simulator

Open Access
Author:
Aslan, Erhan
Graduate Program:
Energy and Mineral Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 07, 2013
Committee Members:
  • Turgay Ertekin, Dissertation Advisor
  • Zuleima T Karpyn, Dissertation Advisor
  • Turgay Ertekin, Committee Chair
  • Luis F Ayala H, Committee Member
  • Savas Yavuzkurt, Committee Member
Keywords:
  • Coalbed methane
  • local grid refinement
  • coalbed methane simulator
  • shrinkage and swelling
  • parallel processing
Abstract:
A three dimensional, dual-porosity, dual-permeability, two-phase and compositional reservoir simulator with local grid refinement approach is presented. A local grid refinement (LGR) protocol is used for replacing the Peaceman’s wellbore model to simulate complex wellbore geometries while Newton-Raphson procedure is used to find the improvements between each time step. The proposed LGR technique is different than the traditional reservoir simulation methodologies as it uses a high resolution grid system to identify and calculate the performances of complex wellbore structures for which traditional wellbore models are not suitable. The proposed model generates results that show that the new protocol is capable of accurately calculating the flowrate responses of simple well structures in comparison to available commercial simulators. After that the performances of complex wellbore structures, such as multi-lateral, slanted and undulating wells are compared within different reservoir configurations. Case studies show that the benefits of lateral wells diminish with increasing vertical anisotropy. Moreover, the local grid refinement technique is a significant undertaking for the computational performance. To deal with this issue, an iterative linear equation solver (GMRES) and advance matrix preconditioners (ParaSails and FASP) are incorporated to the CBM simulator. Furthermore, to increase the computational efficacy of the numerical simulator, two additional subroutines are implemented to have better initial guess at the Newton-Raphson iterations and at the same time to decrease the oscillations experienced during the Newton-Raphson iterations. These modifications yield significant decreases in the simulation time, where in some cases the simulation time was cut from a week to couple minutes1. 1 Computational platform: Intel Xeon E31125 @3.10 GHZ The proposed model generates results that show that the new protocol is capable of accurately calculating the flowrate responses of simple well structures in comparison to available commercial simulators. After that the performances of complex wellbore structures, such as multi-lateral, slanted and undulating wells are compared within different reservoir configurations. Case studies show that the benefits of lateral wells diminish with increasing vertical anisotropy. Moreover, the local grid refinement technique is a significant undertaking for the computational performance. To deal with this issue, an iterative linear equation solver (GMRES) and advance matrix preconditioners (ParaSails and FASP) are incorporated to the CBM simulator. Furthermore, to increase the computational efficacy of the numerical simulator, two additional subroutines are implemented to have better initial guess at the Newton-Raphson iterations and at the same time to decrease the oscillations experienced during the Newton-Raphson iterations. These modifications yield significant decreases in the simulation time, where in some cases the simulation time was cut from a week to couple minutes*. * Computational platform: Intel Xeon E31125 @3.10 GHZ