SIMULATION OF SANDSTONE-MATRIX ACIDIZING IN HETEROGENEOUS RESERVOIRS.

A numerical simulator was developed to predict porosity and permeability changes and the resulting effect on well productivity in sandstones subject to matrix acidizing. While earlier acidizing models are based on homogeneous porous media, here vertical variation in permeability was accounted for by consideration of several noncommunicating zones or layers with different overall permeability-height (Kh) products. Each layer, in turn, may have radial permeability variations and different physical and chemical properties. In this manner, the presence of a damaged zone can be incorporated by a change in near-wellbore properties. During acidizing, the permeability change at a given vertical location depends on factors that affect acid penetration rate, such as initial acid concentration, mineral composition, temperature, flow rate, and cumulative acid injected at that location.