TABLE OF CONTENTS There are two basic types of acid treatments applicable to carbonates. They are characterized by injection rates and pressures. Acid treatment with injection rates below formation fracturing pressure is called matrix acidizing. Matrix acidizing is applicable only to formations exhibiting formation damage. There are exceptional cases in particular, naturally fractured formations in which acidizing at matrix rates in an undamaged carbonate formation may result in an acceptable stimulation response.
Acid treatment with injection rates above fracturing pressure is called fracture acidizing or acid fracturing Fracture acidizing is applicable in both damaged and undamaged carbonate formations. Fracture acidizing is a treatment in which fracturing is initiated and propagated by a suitable fracturing fluid. The walls of the fracture are then etched with acid to create a conductive flow channel on formation closure.
Acid fracturing is a treatment in which the fracturing and etching fluids are acid. The fracture is created with a viscous acid system, for example, which also etches the walls of the fracture during the injection process. These days, either term, fracture acidizing or acid fracturing, may be used to describe the process of creating an acid-etched fracture in a carbonate formation.
The primary purpose of matrix acidizing is to improve flow...
