Analysis of Matrix Acidizing by the Reaction-Transport Simulator Code CIRF.A

Yueting Chen, John Fambrough, Kirk Bartko, Ying Li, Carl Montgomery, Peter J. Ortoleva

A new two-dimensional reaction-transport code CIRF.A is used to analyze matrix acidizing procedures. Accounted for in the simulation are: (1) grain growth/dissolution kinetics; (2) pore fluid reactions; (3) changes in porosity and permeability due to mineral reactions; (4) flow via Darcy's law; (5) pore fluid transport due to diffusion, dispersion and flow; (6) energy conservation; (7) temperature, pressure and ionic strength corrected reaction equilibria and rates; and (8) nucleation.

Core acidizing experimental results are used to test the simulator. By comparing simulation results against experimental observations, reaction network, reaction rate laws and rate coefficients of mineral dissolution reactions have been determined. It is demonstrated that CIRF.A can simulate matrix acidizing processes with good accuracy.

A series of simulations have been carried out under different acidizing conditions. High injection velocity is shown to generate better stimulation results with equal or even lower injectate acid volumes. It is also shown that permeability improvement does not always increase with acidizing time. Rather, there may exist a maximum value of permeability improvement. The maximum permeability improvement is a function of injection velocity, and formation mineralogy and temperature. The time needed to reach the maximum permeability improvement (optimal acidizing time) also depends on these factors. Further acidizing beyond this optimal acidizing time will cause permeability reduction and unnecessary expenditure of acid. CIRF.A can be used to predict the maximum permeability improvement and the optimal acidizing time and thus can be invaluable in optimizing acidification treatments.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995