Liner Rotation and Proper Planning Improve Primary Cementing Success

Abstract

Members SPE-AIME Abstract Throughout the industry's history, successfulliner cementing is one of the most difficult operations associated with drilling and completing of oil and gas wells. When utilizing liner rotation while cementing with proper displacement mechanics, it is possible to obtain an optimum liner cement job. possible to obtain an optimum liner cement job. Employing recent tool development and cementing techniques with proper displacement mechanics will result in more successful primary liner cement jobs. This paper presents an improved liner cementing technique. paper presents an improved liner cementing technique. State of the art equipment, its historic development, design, and recommended procedures are discussed. Theory, test results, and field experience of displacement mechanics are combined to illustrate the relative importance of proper planning to displace drilling mud from the annulus. Introduction The production life of a well is directly affected by the quality of the cement job. Successful primary cementing leaves no continuous channels of primary cementing leaves no continuous channels of mud capable of flowing during well treatment and production. An effective liner cement job provides a production. An effective liner cement job provides a seal between liner and borehole such that remedial cement squeeze jobs are not required—basically the same as for a production casing string. Despite improvements in cementing techniques through the years, field studies and reports indicate the percentage of good cement jobs are few. One of the most percentage of good cement jobs are few. One of the most commonly heard comments pertaining to the quality of cement jobs today is, "We cannot treat this well because of fluid channels through the cement behind the pipe." To correct fluid channels or isolate zones of production requires large expenditures. Millions of production requires large expenditures. Millions of dollars are spent each year attempting to correct behind pipe fluid channels. Developing the seal at the top and bottom of a liner as well as between the liner and open hole requires effective mud displacement by the cements lurry. The failure of conventional cementing is due to insufficient planning and the basic fact that a pumped slurry, like any fluid, will seek the path pumped slurry, like any fluid, will seek the path of least resistance. Experimental investigation has concluded that even with proper planning, sufficient muddisplacement was not achieved without pipe movement. Pipe movement, whether rotation or reciprocation, combined with the understanding of basic cement/mud displacement, will put the odds in favor of a successful cement job. First, a look at the theory, studies, and field experience for proper mud displacement and their respective conclusions. PIPE MOVEMENT PIPE MOVEMENT Many studies involved with pipe movement, either rotation, reciprocation, or both, during conditioning and cementing operations have been conducted. These studies conclude that when pipe was placed in motion, the displacement efficiency was greater in both laminar and turbulent flow regimes. Wellbore irregularities and poor centralization of the casing in the center of a borehole are two main causes for poor mud displacement. Since it is impossible to centralize casing in the exact center of a borehole it will normally be eccentric and lay close to one side. The closer the casing lays to the wall of the hole, the more difficult it is to displace the mud from the annulus. In related test of eccentric annuli, rotation of the casing removed mud channeling. Cowthran concluded that rotation was a mechanical means of breaking up the gel structure of the mud and enhancing mud displacement. Tests performed by McLean showed that rotation removed the mud even in the most eccentric setups. During rotation, mud-to-casing and cement-to-casing drag forces were effective in "pulling" the cement into the bypassed mud column. This effect is illustrated in Fig. 1. Another way to incorporate pipe movement is by reciprocation which appears to be beneficial to mud displacement. Reciprocation provides a linear drag force constantly pushing or pulling the cement. P. 13