Mathematical model building for foam diversion acidizing and its application

Key words:  foam slug  diversion acidizing  heterogeneity  mathematical model

Abstract:

Foam diversion can effectively solve the problem that acid distribution among layers of different permeability is un-even during matrix acidizing. Based on gas trapping theory and mass conservation equation, mathematical models for foam diversion acidizing were established. Design methods for foam diversion acidizing were given. The mathematical model was solved by computer program. The results show that initial formation skin factor decreases during acidizing process. Wellhead and bottomhole pressure increase with foam injection, and decrease with acid injection. Flux of high-permeable layer decreases, and flux of low-permeable layer increases during foam injection, which can divert acid into low-permeable layer from high-permeable layer. Under the same formation situation, effect of foam-acid acidizing is better than that of foam slug diversion acidizing. In foam-acid acidizing, operation time is longer, and wellhead and bottomhole pressure are higher. Field application shows that foam-acid acidizing can effectively block high-permeable layer, and improve oil production. It is fit to heterogenous formation and old well with acidizing for many times.