Long-Term Zonal Isolation for Onshore Gas Wells by Use of a Monobore Cemented Completion

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 107433, "New Approach To Ensure Long-Term Zonal Isolation for Land Gas Wells Using Monobore Cemented Completion," by Salim Taoutaou, SPE, and Ron Schreuder, Schlumberger, and Martin Bosma, SPE, Jules Schoenmakers, Rob Van der Vegt, and Dave Stewart, NAM B.V., prepared for the 2007 SPE Europec/ EAGE Annual Conference and Exhibition, London, 11–14 June. A cemented completion provides an excellent opportunity for low-cost drilling techniques and simple well designs to reduce well-delivery costs without affecting safety or well integrity. In this concept, the completion is run straight into the open hole and cemented in place. There is no need to run a liner and perform a traditional clean-up. The cement effectively replaces the production packer. Achieving a good cement job is essential to a successful operation. Introduction The cemented-completion concept is a simple one whereby the reservoir openhole section is drilled to the required depth. Following electric logging (if required), the completion tubing is run into the open hole and cemented back inside the previous casing shoe or window. The Christmas tree then is installed and the well perforated in the normal manner. Cemented completions already have been used in low-cost operating areas around the world. Well CA-28S2 drilled from the Cormorant Alpha platform in June 1999 marked the first cemented completion to be performed in the North Sea by Shell. Well CA-28S2 was selected as the ideal candidate for evaluating the method because of its short 6-in. openhole length (708 ft) and near-vertical inclination. Since then, openhole lengths have been increased progressively, culminating in Well CN-28S1 that was successfully completed with 6,500 ft of 8½-in. open hole at 67°. In 2003, 79 cemented completions were installed by Shell globally, yielding considerable savings. In The Netherlands, after an initial trial with 5-in. completions in 2003, the land assets have adopted a 3½-in. cemented completion as a base case to the slimwell low-cost land drilling campaign that began in 2005 (Fig. 1). By the end of 2006, the 3½-in. cemented completion had been used successfully in eight gas wells. Benefits The advantage of a cemented over a conventional completion is that it saves 5 to 6 days of rig time during installation by eliminating such operations as running and cementing the liner, wellbore cleanup, and packer-setting procedures. In addition, the amount of liner and completion accessories required such as packers, liner hangers, polished-bore receptacles, and nipples is reduced. Savings depend on the completion and well design.