Reza
Naimi-Tajdar's dissertation
by
Reza Naimi-Tajdar, PhD
University of Texas at Austin, 2005
Supervisors: Kamy
Sepehrnoori and Mark A. Miller
Naturally fractured reservoirs contain a significant amount of
the world oil reserves. A number of these fields contain several billion
barrels of oil. In naturally fractured reservoirs, fluids exist in two interconnected
systems: the rock matrix, which usually provides the bulk of the reservoir
volume, and the highly permeable rock fractures. Accurate and efficient
reservoir simulation of naturally fractured reservoirs is one of the most
important, challenging, and computationally intensive problems in reservoir
engineering. Parallel reservoir simulators developed for naturally fractured
reservoirs can effectively address the computational problem.
A new accurate parallel numerical simulator for large-scale
naturally fractured reservoirs, capable of modeling fluid flow in both rock
matrix and fractures, has been developed. The simulator is a parallel, 3D,
fully implicit, equation-of-state compositional model that uses numerical tools
for solving very large, sparse linear systems arising from discretization of
the governing partial differential equations. A generalized dual porosity
model, the multiple-interacting-continua (MINC), has been implemented in this
simulator. The matrix blocks are discretized into subgrids in both horizontal
and vertical directions to offer a more accurate transient flow description in
matrix blocks. We believe this implementation has led to a unique and powerful
reservoir simulator that can be used by small and large oil producers to help them
in design and prediction of complex gas and waterflooding processes on their
desktops or a cluster of computers. Some features of this simulator, such as
modeling both gas and water processes with the ability of two-dimensional
matrix subgridding for naturally fractured reservoirs, to the best of our
knowledge are not available in any commercial simulator. For coupling of the
fracture and matrix continua, no analytical approximations are made. Instead,
numerical methods are used to treat the transient flow of fluid between matrix
and fractures. The development was performed on a cluster of processors, which
has proven to be a very efficient and convenient resource for developing
parallel programs.
The results were successfully verified against
analytical solutions and commercial simulators (ECLIPSE and CMG). Excellent
agreement was achieved for a variety of reservoir case studies. Applications of
this model for several enhanced oil-recovery processes (including gas and water
injection) are demonstrated. The effects of matrix subgridding on the accuracy
of the results of the simulation runs are investigated. The study showed that
in some circumstances the results of simulators without matrix subgridding
generated more than 50% error in oil-recovery calculations. Simulation results
using the simulator on a cluster of processors are also presented. Excellent
speedups were obtained using the simulator in conjunction with solving a
variety of problems
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