Implementation of a Dual Porosity Model in a Chemical Flooding Simulator

by
Abdulaziz A. Aldejain, Ph.D.

University of Texas at Austin, 1999
Supervisor: Mark A. Miller
Kamy Sepehrnoori

Naturally fractured reservoirs occur worldwide and constitute an important reservoir type. The main feature that distinguishes naturally fractured reservoirs from conventional reservoirs is the presence of fractures. These fractures offer permeability enhancement. However, most of the porosity, and therefore the oil, still exists in the matrix blocks between fractures, thus requiring the oil to be transferred into the fracture network before it can be recovered. Recovery by water imbibition derived by capillary forces offers an excellent means of expelling the oil from matrix blocks and into fractures. However, this mechanism leaves behind significant amounts of oil in the matrix block in the form of residual oil. Reducing the residual oil saturation in the matrix blocks could thus lead to a higher oil recovery. One method to accomplish this is through the use of surfactants.

Numerical simulation of this process offers a means to better understand and evaluate the application of surfactants in naturally fractured reservoirs. This goal has been accomplished by taking advantage of an existing simulator, UTCHEM. UTCHEM is a 3D, multicomponent, multiphase, compositional, finite-difference simulator. Dual porosity modeling has been implemented in UTCHEM to accommodate simulation of naturally fractured reservoirs. This implementation is accomplished by adding source/sink terms to the fracture network equations to account for the matrix/fracture flow transfer for each matrix gridblock. The matrix blocks are discretized into subgrids to offer better transient- flow description. The matrix-block equations are further decoupled from the fracture equations to minimize coding.

In addition to the capability of handling surfactant applications in naturally fractured reservoirs, the simulator has many other applications. Tracer studies and the use of tracers in characterization of naturally fractured reservoirs, the use of polymers and the feasibility of such use in waterflooding of naturally fractured reservoirs, and the use of biodegradation processes in oil-spill cleanup are a few of the features available.

The simulator has been verified against an analytical solution to a single- phase, single-fracture tracer diffusion problem. The solution of a quarter-five-spot waterflood problem using ECLIPSE, a commercial reservoir simulator, has also been compared with the solution using UTCHEM to the same problem. Finally, the simulator has been used to study the effects of the use of polymers and surfactants to improve oil recovery.

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