Abstract

While acidizing has been an accepted and successful method of well stimulation for four decades, only recently has a truly engineered approach to acidizing begun to develop. Although most of thebasic data involved in acid treatment design still hold true, time and experience have shown that it often has been misinterpreted or misapplied. Even more often it has only scratched the surface of what was actually needed or involved in engineered design for efficient acidizing treatments. A prime example has been the application of static reaction and spending time data to design treatments where the reactions occur under dynamic conditions. Field experience has also shown that many of our original conclusions concerning acid concentration were erroneous, and the advent of deep, hot wells has shown that we still had much to learn about acidizing under the severe operating conditions prevalent in many formations.

The purpose of this paper is to briefly review acidizing, eliminate some of the earlier misconceptions, and evolve the current status of the art. Presently accepted methods J materials and research are discussed and developments anticipated in the near future are outlined. Some of the long range goals of acidizing research also give a hint of things to come in the more distant future.

Introduction

Acidizing as a method of well stimulation was first attempted prior to 1900 and has been commercially available since 1932. Only during the last decade, however. has acidizing begun to evolve asan engineered science. Prior to that time acidizing recommendations were based primarily on formation solubilities and experience within a given area. While results of treatments were good, present technology indicates that the acid was inefficiently used in many treatments. New developments consisted mainly of additives to aid in cleanup and to prevent formation and precipitation of materials that might damage permeability.

The introduction of hydraulic fracturing and rapid development of fracturing technology had a drastic effect on acidizing. When acid-base materialswere considered as fracturing fluids, it was found that much of the fracturing technology applied to acidizing as well. Many of the factors not formerly considered important in acidizing were now found to be vital to the effective and economical use of acid.

This paper is intended not as a presentation of technical data, but as a general presentation ofacidizing technology to show how present technology has evolved, what factors really affect acidizing efficiency, and what developments the future might hold.

ACIDIZING TECHNIQUE

From the beginning of acidizing, acid has been used in two ways. Frequently acid was merely dumped or displaced into the wellbore. In other treatments it was injected into the formation itself. Whetheror not it was realized at the time, two techniques of application were being applied. In the dump jobs, hydrostatic pressure probably resulted in limited penetration matrix acidizing In most cases. When acid was injected into the formation, equipment limitations probably, resulted in injection at matrix rates in many cases while actual fracturing occurred in others.

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