| Acidizing of sandstones with hydrofluoric and hydrochloric acid mixtures is most frequently applied to remove near-wellbore damage, often in reservoirs with considerable vertical heterogeneity. Taha et al. (T2) previously developed a model for such processes when acid is injected at a constant total rate while being aided by organic resin diverting agents. This work has been extended to account for any type of particulate diverting agent. In addition, the fluid placement equations were improved to account for slightly compressible fluid and rock behavior, viscosity effects for fluids injected in series, and multiple injection sequences, each at either constant rate or constant bottomhole pressure. The impact of various empirically derived porosity-permeability relationships on stimulation results were also studied.;The general model of diverting agent behavior was developed based on filtration theory. A single parameter, the specific cake resistance, is needed to model the diverting agent behavior in the acidizing simulator. Calculation procedures to determine this parameter from laboratory tests of diverting agents are presented. These tests are either constant rate, constant pressure, or variable rate and variable pressure experiments; in each case, the specific cake resistance can be extracted from the experimental data. Using these procedures, the efficiencies of various diverting agents can be compared on an equal basis.;In solving for the acid and mineral balance equations the Crank-Nicolson method was used to allow larger time-step sizes to be taken. This was necessary in lieu of the restricted time-step size offered by the explicit finite difference method originally employed by Taha et al. Furthermore, a more accurate solver for the new fluid placement equations was sought. The current solver, the Runge Kutta Fehlberg 4(5) formula, gives a higher order approximation than the formerly used Runge Kutta Fehlberg 1(2) formula. |
