Primary Depletion Reservoir Simulator for Real and Dry Gas

by
Sami Al-Naim, Ph.D.

University of Texas at Austin, 1994
Supervisors: Ben H. Caudle

A real unsteady-state gas simulator has been developed using the new gas potential formulation presented by Chien. This simulator handles the non-linearity relationship of the PVT properties and pressure within a time step. It uses an iterative method to solve for the pressure. It can handle any reservoir shape and size.

The simulator was validated for infinite and bounded reservoirs having different shape, well location, and rate schemes.

It was shown that this simulator can be used as a disk-top personal computer tool for both gas reservoir simulation studies and gas well test analysis.

This research introduces for the first time the concept of updating the bounding hydraulic diffusivity parameter. It was found that the bounding hydraulic diffusivity parameter must be updated every time the system is bounded using the average reservoir pressure.

The model was optimized to run efficiently on disk-top personal computers. The log regression approximation which replaces the extensive computer time bounding rates calculations, was found to be valid only for ideal cases with regular boundaries and constant flow rates. A new empirical equation is presented to calculate the number of bounding calculations after which the bounding rate array size can be fixed. Also the Bisection iterative method was found to be the best method for the iterative procedure that solves for the potential. It reduces the computer time by 10% compared to the standard Successive Substitution iterative method. QR factorization method for solving the overdetermined matrix generated by the bounding equation was found to be the fastest, whereas Givens Rotations method was found to have the least memory requirement.

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