Swelling Packers Solve Zonal-Isolation Challenge in Oman High-Pressure Wells

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 100361, "PDO's Proactive Approach To Solving a Zonal- Isolation Challenge in Harweel HP Wells Using Swell Packers," by M.S. Laws, SPE, (now with Shell Abu Dhabi B.V.), J.E. Fraser, SPE, and H.F. Soek, SPE, Petroleum Development Oman, and N. Carter, SPE, Easywell UAE (now with Sensornet Ltd.), prepared for the 2006 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Bangkok, Thailand, 13–15 November. The Harweel cluster of reservoirs in southern Oman is Petroleum Development Oman's first enhanced-oil-recovery project. Zonal isolation is crucial to the success of the planned miscible-gas-injection project. Previous isolation attempts using cementing technology alone have proved to be unsuccessful. On the basis of results obtained from both laboratory and field tests, swelling packers in combination with cement have demonstrated zonal isolation in these challenging high-pressure reservoirs. This could enable a significant increase in reserves and, hence, ultimate recovery in these fields. Introduction The Harweel cluster consists of nine different deep, highly pressured reservoirs containing sour, light hydrocarbons. More than 50 wells have been drilled in and around these fields. The initial wells have a shallow 13 3/8-in. surface casing, a long 9 5/8-in. production casing, a 7-in. liner cemented over the reservoir section, and 3 1/2-in. production tubing. The cluster is being developed in a phased manner. The objective of Phase 1 was to gather data from a number of different sources to determine if a miscible-gas-injection project would be feasible in some of these fields. Phase 2 will involve primary depletion in a number of fields followed by gas injection in some, and Phase 3 will involve clusterwide depletion and gas injection in the remaining fields. To maximize ultimate recovery from these fields, gas (and water) shutoff is required during Phases 2 and 3 of the project. For this to be effective, zonal isolation over the reservoir is essential. A substantial effort has been expended during construction of the Phase 1 wells to determine if zonal isolation was being achieved with standard cementing techniques. Cement-bond logs were run over the liner section in every well to determine cement quality. These logs showed that a microannulus was being created in practically every case. During well completion, cement debonding from the production liner occurs as a result of differential-pressure effects that lead to creation of a microannulus. Once the microannulus is created, a permanent flow path between the cement and production liner can be created, preventing zonal isolation. Selective perforating during the subsequent well-testing campaign showed that this microannulus was conductive to reservoir fluids (Fig. 1). In one incident, reservoir fluids leaked all the way to surface through the microannulus.