Squeeze Cementing: State of the Art

Summary Squeeze cementing is a routine well operation that has acquired a multitude of rules of thumb or procedural gimmicks because it evolved as a nontechnical field practice. The real technology controlling squeeze cementing behavior is readily available, but current practices are often contrary to technology published and engineering logic. Maximum pressures and displaced volumes are reported meticulously, even though their effect on results is unimportant. Formation breakdown often is accomplished at a high rate, causing larger fractures and use of more cement with no better results. Assumptions are made on the basis of whole cement entering the matrix and the concept of a horizontal pancake of cement, when both ideas are invalid. Both high- and low-pressure squeeze cement in techniques have their proper application. Fluid-loss control is important in set-through applications, but fluid loss must not be too low. Reduction of slurry density is often important. Pumpability time for any cement must be determined with proper regard for the mix water anticipated and the synergistic effect of some additives. The time must be sufficient to complete the job, but not so long that a firm set is jeopardized. Strength of set cement used in squeeze operations can be quite low and still retain all the pressure differential that most pipe can withstand. Successful evaluation is not conclusive with the conventional pressure test. A reverse differential is important to obtain a definitive test and provide for optimal reperforating conditions. Introduction Squeeze cementing technology, which is straightforward and currently well documented, continues to be clouded by field practices developed over the past half century when the technique was considered an art rather than a science. Cement quality control left a great deal to be desired in the earlier usages, and little concern was given to the source of the mix water. Many currently popular practices were developed by trial and error on the part of field personnel to meet the irregularities caused by the cement, additives, and mix-water variations. The problem is compounded by the jet-hopper mixing system. The jet hopper is a simple and ingenious device that made fast mixing of large volumes of cement possible, as needed for most casing cementing operations. It was easy to adopt the same equipment for the smaller squeeze cementing operation. In practice, the hopper is not a consistent mixing apparatus, and that quality is often of critical importance in squeeze operations. Equipment and procedures or habits developed over many years are ingrained in supervisors (and many managers) who have spent much of their career closely associated with field operations. In many companies, it is difficult to encourage sincere trial of techniques well proved and documented by other operators or other divisions within the same company. The rationale of these experienced leaders is based on many years of reasonably acceptable end results and a few vivid recollections of isolated but seemingly catastrophic results, such as real or imagined flash setting of cement. Fundamental Principles The squeeze cementing process merits a very simple definition. It is an operation wherein cement slurry is forced under pressure to a specific point in a well. Uses includeexclusion of water, gas, or oil from the producing formation,recompletion from a depleted or an unwanted interval to a new interval,repair of casing or pipe failure, andrepair of a faulty primary cement job, usually called a channel. JPT P. 37^