Globally, many thousands of potentially productive oil and gas wells suffer internal corrosion due to H2S, CO2, and other produced gases and liquids. This limits their capability to provide a packer sealing area suitable for traditional mechanical production packers. Total E&P Qatar planned a recompletion using intelligent well technology in a well in which they expected to find some corrosion. Before initiating the recompletion, they investigated the use of alternative packer technology.
Swelling elastomer packers have been used worldwide in many applications, but verification was required in this case to assess whether such packers would hold pressure in a corroded section of casing. In addition, testing was also was needed to assess whether the completion could be pulled in the event that it became necessary to retrieve the components from the well.
A swellable packer with multiple cable feed-through was designed and manufactured to approximately two-thirds size of the originally specified packer. A sample of corroded casing, supplied by Total E&P Qatar, was used to build a test jig. The jig was equipped to simulate and record pressure, temperature, and other downhole conditions. Theoretical simulations were performed to assess the force required to overcome the anchoring forces applied by the swelled elastomer and were verified by a pull test.
It is expected that with a reliable sealing mechanism for these older wells, technically and financially viable workovers and re-completions can be performed, thereby extending field life and adding to recoverable reserves.
This paper describes the application and test procedures along with the verification and results of the testing performed.
Introduction
The Al Khalij field lays 100km offshore Qatar in 60m water depth. The first discovery dates back to 1991, when the Mishrif reservoir was confirmed as oil bearing. The field was developed in a phased manner to reduce developmental risks and to optimize development cost. First production from the field was delivered in 1997. At the end of 2005, three phases of development of the field had been completed, and currently, an infill drilling program is in progress. Presently, this vast field is produced through seven unmanned wellhead platforms and one water-separation platform. A total of 37 oil producers, six water injectors, and four water producers have been drilled and completed to date. Due to the proximity of the aquifer, significant amounts of water are produced.
Owing to the sub hydrostatic reservoir pressure, producer wells are equipped with Electrical Submersible Pumps (ESPs). The electrical generation necessary to power the ESPs is located on Halul Island, located 45 km away from the field as shown in Fig. 1. Most of the water produced is separated offshore on a process platform and is re-injected into the field with the water injector wells aiming at sustaining reservoir pressure. Additional water is produced from the Umm Er Radhuma shallow aquifer and re-injected into the Mishrif reservoir in order to achieve a full voidage replacement and further sustain reservoir pressure.1,2
The Mishrif carbonate reservoir is comprised of several thin stacked layers (three to five meters thick) with a wide range of permeabilities (five to 300mD). In order to increase the Productivity Index and the drainage area of the oil producer wells, they usually feature long to very long cased horizontal drains, which are among the most ambitious ones in the industry. Nearly all wells drilled after year 2000 feature drain lengths in excess of 2000m (see Fig. 2).
