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.

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Natural dump-flood, a low-cost secondary recovery method was successfully implemented for the first time in the Malaysian offshore environment. The dump-flood was initiated by adding perforations in a high-pressure water aquifer and allowing water to cross-flow naturally into a low-pressure depleted reservoir. With investment of 0.4 million USD, the dump-flood has effectively increased the reservoir recovery factor (RF) while increasing the reservoir pressure by more than 300 psi despite being continuously produced. After 30 years of production, most solution gas drive reservoirs in Field B were idle and depleted. A low-cost natural dump-flood was implemented in reservoir S2, a depleted reservoir, by converting well D-10 into a dump-flood well. The conversion was achieved by perforating a high-pressure water aquifer underneath the S2 reservoir in the same well and allowing water to naturally cross-flow into the depleted reservoir. An existing oil producer, well D-07 was selected as the offtake well that would be produced once the pressure increased. The well operations were both simple and inexpensive as indicated above. The dump-flood initiative in the first reservoir, S2, was a complete success. A year after the dump-flood was implemented, the offtake well D-07 began to steadily produce 250 bopd compared to its earlier intermittent production. The well production increased to 600 bopd after five years. Pressure survey and production logging results confirmed the positive impact of the dump-flood. The reservoir pressure increased by 300 psi, despite continuous production throughout the dump-flood period. A reservoir simulation model indicated the dump-flood increased the recovery factor of the S2 reservoir by more than 8%. Numerous lessons learned were acquired during the implementation of this first natural dump-flood in Malaysia which serve as a reference for future application. The dump-flood in the S2 reservoir is hailed as a breakthrough, since it helps prove that secondary recovery can be implemented with minimal investment in an offshore environment. This paper provides valuable insight into the case study of maximizing oil recovery through dump-flooding in an offshore environment. The lessons learned serve as a guideline for this simple and low-cost approach, which is highly recommended for maximizing oil recovery in a mature field, especially in today's low margin business climate.