RIASSUNTO
Abstract
Over the years, cement packers have been used to provide zonal isolation above the production packer without pulling the completion. Experience has shown that the risks associated with placement of the packers is fairly high and leaks are difficult to repair. A number of ways to place cement packers have been developed over the years and a new method has been recently field trial tested in the Gulf of Mexico in the SMI 288 field. This paper introduces a novel approach developed to install a completion, in a through-tubing process, to recover otherwise uneconomical, behind pipe reserves that are above existing production packer installations. The entire process takes advantage of significantly improved mature technologies. The application of this process can increase recoverable reserves and avoid expensive workover costs when the reserve estimates are questionable. This paper will discuss the methodology used and the results of a case history included to illustrate the implementation of the process. It involved creating a window in the tubing across the new zone and placement of a cement packer above the window. The window was created so as to lower the completion drawdown and lower the risk of completing in wells requiring sand control.
Introduction
Recompletions offshore in the Gulf of Mexico are sometimes not performed due to the cost of rig mobilization, risk and reserve base remaining in the wellbore Cement packers placed above an existing production packer offer a rigless means of casing isolation and allow production from marginally economical up hole selective candidates. The concept of placing a cement packer in the tubing-casing annulus is not new. There are many variations in how this has been accomplished utilizing varying methods and different types of equipment. In the past, the success rate of placing cement packers that isolate has not been very high. Small micro channels, which develope for various reasons do not result in a complete hydraulic seal of the annular area. This restricts annular flow, but does not completely seal it off. Such leaks result in casing pressure that is difficult to remedy since injection rates/pressures are usually insufficient/too high to perform a cement squeeze repair.
An effort was made to develop a better, more reliable way to place cement packers and successfully test them. A Cement Packer Team was commissioned within Chevron in the fall of 1993. Past processes were reviewed, noting the deficiencies. The session resulted in an outline of ideas and issues that must be addressed in order to increase the reliability of the cement placement process. Additionally, at this point it was noted that a method of removing a section of tubing without having to mobilize a rig would result in better perforating performance and would also facilitate placement of a through tubing sand control means (ie, through tubing gravel pack, resin consolidation, fracture with proppant flowback additive, etc). Creation of the window in the tubing string was considered important in lowering the risk of an unsuccessful completion. It became apparent that a casing access window (CAW) completion procedure could be used with good candidate wells and that there are some wells that would require less sophisticated (and less expensive) techniques in the overall procedure.
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