Field Results of the Stressed Steel Liner Casing Patch
Authors: Kemp Gore 
Published: December 2007

The stressed steel liner was developed to reduce rig and tool costs over the more conventional methods of repairing casing leaks. A steel tube, corrugated to reduce its diameter, is run into the well opposite the leak; by means of a hydraulically operated ram, it is expanded into place forming a leak-proof sleeve. Eighty-two patches have been installed in wells with a success of 89 per cent. Rig requirements and time involved have been reduced, as well as tool costs. The method has been used successfully to seal leaks, perforations, splits and parted casing. It is particularly applicable for use in small-diameter casing.

Introduction

Casing leaks constitute one of the most critical and costly problems encountered in the maintenance of oil production. This is particularly true in the older fields, where corrosion and electrolysis are causing an ever-increasing incidence of the problem. These older fields usually cannot afford costly workovers due to low production and high lifting costs.

Development of a method of casing repair that would be quicker and less expensive than the conventional cement-squeeze or the casing-cutoff and patch-bowl methods has been a continuous process for several years. The glass fabric-plastic casing patch was developed in 1958–59 and was used for several years with reasonable success. This method had serious limitations, however, when the hole in the casing was large or when the pipe was split. It was not a satisfactory cure for parted casing.

The depth of the casing leak may be found by any ac- of the plastic patch, and it was first used in a well in July, 1961. This paper describes the tools which have been developed for field use and presents the results of 82 consecutive jobs in a five-state area.

Process And Tools

The depth of the casing leak may be found by any accurate method, but best results have been obtained by using straddle packers or bridge plug and packer. and then pressuring between them. If wireline methods of measurement are used, it is necessary to check this with pipe measurements because field experience has taught that considerable variation exists between the two methods.

An impression of the damaged area of casing may be made in order to more clearly define the size and type of the leak. Fig. 1 shows impressions taken with a sheet of vinyl on the right and uncured rubber on the left. An impression is made by attaching the material to an inflatable bladder, placing the tool opposite the damaged area, and inflating it to a pressure of 200 to 300 lb. The embossed impression material provides accurate size measurement and identifies extreme damage-such as splits and parted casing.

After the depth and the extent of damage having been determined, the casing is thoroughly cleaned with a conventional casing scraper. A gauge ring should be run to make sure that no collapse or other damage is present to obstruct the casing. To reduce rig time as much as possible, the tubing is usually pressure-tested at this point to be sure that no failure will occur while the liner is being installed. Since the average surface pressure required to place the liner is 2,400 psi, the tubing or working string is usually tested to 5,000 psi.

The patch itself consists of a mild steel tube which varies in wall thickness from 0.065 in. as used in 2 7/8-in. OD casing to 0.125 in. which is used in 5 1/2-in. OD and larger casing. This tubing is first annealed, and then its diameter is decreased by pulling it through a series of rollers to corrugate it. The tube is again annealed to relieve the stresses set up when it is corrugated.

JPT

P. 147^