Carl T. Montgomery

Reaction-Transport Simulation of Matrix Acidizing and Optimal Acidizing Strategies

A new type of geochemical model, CIRF.A, is used to analyze matrix acidizing procedures. The model considers the transport of pore-fluid solutes and the chemical reactions, which are either kinetic or equilibrium controlled. One of its new, distinct features is that it can predict the mineral dissolution and precipitation processes as well as their chemical natures and their consequences on porosity and permeability changes. After calibrating the model with flow-through acidizing experimental results, a series of simulations was carried out under different acidizing conditions. Those simulations show an important phenomenon: the permeability improvement does not always increase with acidizing time. Rather, there exists a maximum value of permeability improvement (MAXPI) that is a function of injection velocity and the mineralogy of formations. The time to reach the MAXPI is the optimal acidizing time (OPAT) that also depends on injection velocity and mineralogy. Further acidizing beyond OPAT lead to permeability decrease and unnecessary costs. The simulations also show that I) high injection velocity can generate better stimulation results with equal or even less amount of acid; 2) MAXPI is in inverse proportion to the amount of clay; and 3) for fixed total content of illite and kaolinite, MAXPI is in proportion to the ratio of illite/kaolinite. These results demonstrated that reaction-transport simulation can be used to predict MAXPI and OPAT and thus is a valuable tool for optimal design of matrix acidizing strategies.

Using fracturing as a technique for controlling formation failure

Conventional gravel-pack completions often reduce a well`s productivity by increasing the completion skin. This paper describes a methodology backed by a systematic technique to predict the necessary drawdown, fracture length, and conductivity to prevent formation failure and remove the completion damage. This method enables the engineer to optimize the fracture dimensions while obtaining the necessary decrease in near-wellbore drawdown that would cause the unpacked perforation to fail. This technique will greatly reduce the chance for formation failure and improve the well performance without the need to gravel pack.