Case Study: Successful Application of a Novel Conformance Treatment in an Extended Reach Horizontal Well in the Al Shaheen Field, Offshore Qatar

Abstract

Abstract The thin and laterally extensive Al Shaheen reservoirs are developed with extended reach horizontal wells and large-scale water injection, which over the last decade has proved to be a proficient and environmentally favorable recovery scheme. This paper describes how injection water short circuiting between two horizontal wells in excess of 20,000 ft was eliminated with a conformance treatment without the necessity of a costly and operationally risky well intervention. Traditionally, reservoir management in terms of injection or production profile modification has been achieved with rig-based work-over operations applying mechanical solutions such as cement or isolation straddles. Work-over operations utilizing drilling rigs are, however, expensive, pose inherent operational risks and delay the implementation of the ongoing development plans. When water injection was recently commenced in a well taking part of an existing line drive pattern, an immediate pressure and watercut response was observed in the adjacent producer. Attempts were made to mitigate the effect of the communication, but water injection eventually had to be ceased to allow sustainable flow from the production well. The very pronounced response in the producer suggested that short circuiting was occurring through a fracture providing conductivity several orders of magnitude higher than the prevailing matrix conductivity. A comprehensive multi-disciplinary review of static and dynamic data lead to the assessment that the fracture communication could be eliminated utilizing a conformance treatment and following laboratory testing and design, a crystalline superabsorbent copolymer was pumped from a stimulation vessel as part of an intervention- and rig-less operation. After the conformance treatment, injection was resumed with no adverse effects on the performance of the adjacent producer. The treatment is estimated to have recovered lost oil reserves of some 3 MMstb and to have reduced cost with more than USD 8 million compared to a conventional rig-based work-over operation. Introduction Maersk Oil Qatar is the operator of the Al Shaheen Field located on the central axis of the Qatar Arch some 70 kilometers north-east of the Qatar peninsula (Figure 1). The main reservoir targets include the Lower Cretaceous Kharaib B and Shuaiba carbonate formations and the Nahr Umr sandstone (Figure 2). The Kharaib reservoir is a laterally uniform carbonate platform with a full thickness of 80 ft and a reservoir target of some 10 ft. The reservoir comprises tight carbonates with inter and intra granular porosity and local natural fracture networks. The Shuaiba reservoir is a transitional marginal carbonate platform with a full thickness of approximately 200 ft thick and a reservoir target of some 20 ft. The reservoir comprises tight carbonates with inter and intra granular porosity and local natural fracture networks. The Nahr Umr reservoir comprises laterally extensive marginal marine sands with a target thickness of some 5 to 10 ft of unconsolidated, high permeable sand.