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A parallel adaptive-implicit black-oil reservoir simulator is described which is designed to run on shared-memory machines with the parallelism controlled by OpenMP calls. The basic design decisions leading to this choice are discussed. The changes which were required in the original non-parallel black-oil simulator to achieve parallel execution are discussed, as are the techniques for achieving good parallel speedups for simulator tasks such as building the Jacobian matrix. The simulator uses a parallel implementation of a variable degree incomplete LU (ILU) factorization followed by a parallelized GMRES iteration to solve the linear system of equations associated with the Jacobian matrix. The techniques for achieving this parallelization are discussed, as are techniques for load-balancing some solver sub-tasks. The effect upon the ILU preconditioner of the reservoir decomposition needed to achieve the solver parallelization is discussed and techniques for reducing this effect by reordering within domains are examined. The simulator has been tested on a variety of simulation problems and a number of 32-bit and 64-bit shared memory computers, with the number of processors used varying between 1 and 32. The speedups obtained are presented and analyzed, and the problems entailed in applying the simulator to very large problems (ten million to more than one hundred million active cells) are described. Results are presented for several simulation scenarios as run on several different computers. |
