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Abstract

Permian Basin operators who need to seal casing leaks to pass Permian Basin operators who need to seal casing leaks to pass Texas Railroad Commission mechanical integrity tests have successfully applied small particle-sized cements, which penetrate casing cracks and very small channels to effect a penetrate casing cracks and very small channels to effect a seal.

Small casing leaks plague injection operations when integrity testing results in pressure bleedoff, which indicates presence of leaks. A batch-mixed volume of 25 to 75 sacks of fine particle cement is the typical application used to seal these particle cement is the typical application used to seal these leaks. There are some critical steps that must be taken to help ensure job success; these are discussed. The paper also presents a discussion of small particle-size cements, including presents a discussion of small particle-size cements, including accounts of laboratory testing. Case histories describing techniques of casing leak repair with small particle cements are recounted.

Introduction

The Permian Basin area of West Texas is known for many waterfloods, H2S problems, and weak formations. The Permian Basin has a long drilling history, and it therefore Permian Basin has a long drilling history, and it therefore contains numerous old wells (up to 50 years old), the casings of which are subject to corrosion degradation. These characteristics make Permian Basin wells subject to casing leaks and cause wells to fail casing integrity tests established by the Texas Railroad Commission for injection wells.

Most casing leaks in the Permian Basin that have been repaired with small particle-size cement have ranged from 2000 to 12,000 ft in depth. Most of these have been shallow repairs, 5000 ft and above with some as shallow as 100 ft.

Squeeze cementing with small particle-size cement has proved to be an excellent way to seal casing leaks without requiring perforating. Small particle-size cement squeeze jobs do not perforating. Small particle-size cement squeeze jobs do not just patch the damaged area but penetrate to create a seal, Because the need to perforate is eliminated, many small particle-size cement squeeze jobs are less costly than squeeze particle-size cement squeeze jobs are less costly than squeeze jobs involving standard cement.

Many successful squeeze sealing jobs using small particle-size cement have been performed in the Permian Basin, The likelihood of a successful small particle-size cement squeeze job is enhanced by incorporating certain preparatory and procedural steps advocated within this paper. procedural steps advocated within this paper.

Small Particle-Size Cements

There are two types of small particle-size cement available; within this paper they are referred to as "fine" and "ultrafine."

Both fine and ultrafine cements are very finely ground cements with average particle sizes much smaller than standard API cement. The small particle size of these cements make them well suited for all squeeze jobs, especially casing and collar leaks in which cement must penetrate very narrow or "tight" areas. Table 1 compares physical properties of fine, ultrafine, and standard cements. properties of fine, ultrafine, and standard cements. Fine cement is a very finely ground cement with an average particle size of 8 microns and a maximum particle size of 15 particle size of 8 microns and a maximum particle size of 15 microns. Fine cement consists of 20 to 30% finely ground cement and 70 to 80% slag material.

Ultrafine cement consists of 100% very finely ground Portland cement and has an average particle size of 4 microns. Its extreme fineness makes it very reactive but provides it with excellent penetration capabilities.

The benefits of small particle-size cements have been proven in hundreds of jobs which required sealing a casing collar leak or other very narrow area. In these cases, traditional API cements bridge on the affected area, but small particle-size cements penetrate to provide a much more complete seal without requiring perforating. Other applications of small particle-size cements include penetration of gravel packs, particle-size cements include penetration of gravel packs, sealing highly permeable zones, stopping unwanted water or gas production in behind-pipe channels, and squeezing small channels.

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