Affiliation:
1. Halliburton Energy Services, Inc.
Abstract
Abstract
Approximately one out of six casing shoes in the Gulf of Mexico (GOM) require a cement squeeze job after primary cementing. Numerous theories exist regarding the causes of high shoe-test failure rates, but failure is often attributed to problems associated with the primary cementing job.
A GOM database containing information about more than 4,000 shoe-cementing operations was reviewed to find correlations between the success/failure rate and industry-accepted best cementing practices. The results confirm some correlations between the cementing process and shoe-test success; however, no single cementing parameter has an overwhelming effect on shoe failure. Of the industry-accepted best cementing practices, the GOM database shows the following factors to be most important for shoe-test success:pipe movement,maintenance of circulation during cementing,accurate displacement volumes,centralization, andapplication of foam cementing.
The cementing parameters that appear to have less effect on shoe-test outcomes weremud properties,displacement rates,spacer volumes, andapplication of a hesitation squeeze at the end of the primary cement job.
The review of the GOM database also showed that deeper casings are more susceptible to shoe-test failure, as are wells in deeper water. The data shows a constant rate in shoe-test failures since 1993 and a large variation in success between operators.
Introduction
After a primary cementing job and before drilling the next hole section, operators usually perform a leakoff test (LOT). Cement is drilled from the shoe track, and a small length of new formation (usually 10 ft) is opened. When pressure is applied to the new formation, the pressure-volume curve simultaneously evaluates the quality of the primary cementing job and the strength of the newly drilled formation. If the pump-in pressure is lower than the expected formation strength, or if the leakoff test exhibits unusual pressure declines, it is usually assumed that there is a cement channel.1 However, debates continue regarding the reasons for the relatively high number of shoe-squeeze failures in the GOM. Is the problem related to poor cementing practices, weak formations, or a combination of both?
A database containing information about 4,099 shoe-cementing operations was reviewed to help determine the extent to which cementing practices influence successful leakoff tests. Since 1993, data have been collected by onsite cementing operators and forwarded to a database manager. Almost every aspect of a cementing job is kept in the database, ranging from cement-slurry type to casing-thread specifications. Much of the data were collected through monitoring of industry-accepted cementing practices that achieve good production-casing cementing results, such as the use of pipe movement, large spacer volumes, and centralization. The study described in this paper used the database to help determine whether industry-accepted production-cementing practices are critical to the success of shoe-cementing operations.
Shoe Tests and Casing-String Type
Four types of casing strings (conductor, surface, intermediate, and drilling liner) were reviewed to help determine success-rate differences. The results show greater success in the shallower casings (Tables 1 through 4). Conductors and surface casings exhibited 13 and 11% failure rates, respectively. However, the database revealed 19% failure rates for both intermediate casings and drilling liners, which is an approximately 60% increase in the failure rate among deeper casings.
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