An Effective Solution To Repair Severely Corroded Casing Strings: Applications in the Oriente Basin of Ecuador

Abstract

In the Oriente basin of Ecuador several operators, including the National Petroleum operator, are producing oil at approximately 455,000 B/D and having high numbers of workovers. Many wells have been closed because they were considered uneconomic, and studies have been carried out to re-open them and increase the production. Some operators have big problems because of aggressive corrosion in the old strings. In many wells the corrosion is so great that a part of the casing literally disappears. Splits and cracks are very common in old strings. Under these conditions, the life of the well is limited to the life of the casing if a good solution is not found. To solve these problems, we demonstrated a use of special fibers technology that is outside its original design purpose. From the economical side to close a well means to lose the investment made in the well and lose the oil production. For this reason, finding a good technical solution that allows the wells to be reopened adds value to an existing asset and contributes to ultimate recovery. In the past conventional cement slurries were used to address the problem with poor results; the cement could not support the pressure test. Introduction The initiative to re-open old wells has an obstacle, which is the mechanical condition of the wells after being closed for several years. Due to the design of previous cementing jobs, the cement did not cover all the strings and a corroded casingwas a certainty.. The normal casing design is a 10¾-in. string to 3,000 ft and a production string of 7 in. to 10,000 ft to 11,000 ft. In most of the cases the 10-¾ in. casing was poorly cemented. Some of the re-opened wells have cracks or splits on the surface and production casing due the severe corrosion. This problem is important because when a workover operation is conducted it is impossible to put pressure inside the casing and test it. In some extreme cases, when pumping brine in order to kill the well, the brine gets back through the 10 ¾-in. casing and 7-in. production strings and is observed around the location. To give a technical solution to this problem, the special fiber cement system was presented as an option. Its behavior in terms of resistance to tensile stresses was of interest to the operators in Ecuador. It is currently used around the worldas an effective system to control losses. The main differences between conventional slurries and those with fibers is that fiber cement can support greater resistance to tensile stressesand has a greater capacity to cure losses.. The simple addition of special fiber to conventional slurries makes an outstanding difference. The idea to add fiber to a cement matrix is not new. Before cement was discovered the first bricks were made using sludge and organic fiber to improve the resistance to tension and shear stresses. Until today the native people in Ecuador make their walls and houses using a combination of special mud and special dry grass.