Novel Approaches to Profile Modification in Horizontal Slotted Liners at Prudhoe Bay, Alaska

Abstract

Abstract The development of new techniques and materials for performing profile modification treatments in horizontal, uncemented slotted liner completions at Prudhoe Bay, Alaska is reported in this paper. Historically, it has been difficult, if not impossible, to perform remedial profile modification treatments in horizontal slotted liners. The lack of annular isolation and uncertainties with conventional fluid placement posed seemingly insurmountable challenges. The development and field trials of two new techniques that address these problems are presented in this paper. The first approach uses advanced gel technology for fullbore, non-selective treatments for water shut off and selective placement for gas shut off. The second uses a new thixotropic cement slurry to place a chemical packer around the slotted liner for zonal isolation - opening the door for conformance treatments. Certain preliminary successes of these techniques have prevented the need for sidetracking wells to new locations or permanently abandoning zones. This has saved the operating companies significant wellwork expenditures. Treatments have been performed on five wells to date with several more in the development stage. Treatment descriptions, operational rationale, and pre- and post-production trends are presented. The horizontal slotted liner profile modifications performed are all technical successes with 60% of the treatments also economically viable. Even though it is early in the life cycle of these technologies, the successful treatments are encouraging and have opened up a large candidate pool. These new techniques and materials are promising options allowing remedial work in horizontal wells with uncemented slotted liners. Introduction The Prudhoe Bay Field (Figure 1) contains approximately 1,200 wells that produce over 775,000 bbls of oil and NGL's per day. Along with this large oil rate, 1.3 million bbls of water and 7.5 billion scf of gas are produced each day. Water processing costs are high, and no market currently exists for gas from the North Slope. The Field is gas compression constrained, and oil production is limited to a marginal gas-oil ratio (GOR) in each well. As a result, the search for reliable water and gas shut-off techniques is an ongoing process. The Prudhoe Bay Field has an overlying gas cap and an underlying aquifer that both influx into the original oil zone (Figure 2). The Field is under waterflood and miscible gas flood in the oil rim. The remaining portions of the Field that underlie the gas cap are produced through a gravity drainage process. Four zones that characterize the reservoir rock are shown in Figure 3. Each zone has different producing characteristics. The waterflood area of the field typically produces from Zones 3 and 4 while the gravity drainage takes place in Zones 1 and 2. To obtain the greatest standoff from the encroaching gas cap, over 85% of the newly drilled wells and sidetracks of older conventional wells are horizontal through the producing interval. Typically, these wells are drilled through Zone 1 (Figure 3). The technology to drill and complete these wells has grown greatly in the past two years.1 However, remedial operations in horizontal wells have been limited, and this technology lags the drilling technology. The Prudhoe Bay Field has a rich history of coiled tubing (CT) remedial operations. P. 831^