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.

The giant Al Shaheen field, offshore Qatar includes a stacked sequence of Lower Crectaceous, carbonate domimated reservoirs of a tight nature and limited thickness. A holistic development approach with real time adaption has been used to push the boundaries for the development and the field is today producing more than 300,000 barrels of oil per day in an injection supported development including the world’s longest horizontal wells of up to 12 kilometres. Innovative completion solutions, providing the means to manage reservoir heterogeneity further supports the adaptive development and have opened new possibilities for enhanced oil recovery. After discovery in the mid 1970’s the breakthrough in the development came in 1992 when Maersk Oil introduced horizontal well technology from the North Sea tight chalk fields. Effective drainage by the horizontal wells via increased reservoir contact in the thin and tight pay zones has been confirmed from pressure measurements, saturation profiles and seismic data. The horizontal wells have further allowed the 700 sq km offshore development to be developed from 9 platform locations. Development of the tight and thin reservoirs in the Al Shaheen field is challenged by lateral heterogeneities, dipping fluid contacts and varying oil viscosities. The ability to handle heterogeneity is supported through innovative horizontal completion solutions ranging. The development is based on high resoluition 3D reservoir models and development adaption to real time static and dynamic field information. Obtaining the optimal oil recovery is based on a detailed development strategy tailor made to specific reservoir characteristics and reservoir management and injection and production control.

This paper describes a case study of planning, drilling, completing and production of an extended reach horizontal infill well in the giant Al Shaheen oil field, offshore Qatar. The completion has been designed with three surface controlled zones. The completion is supplemented by a straddle on mechanical open hole packers to isolate a section which has higher risk of pre-mature water breakthrough. This completion provides flexibility for selective production, production testing and performance monitoring. Seven infill wells were planned in the Shuaiba formation for optimization of oil recovery. The first wells were brought online with higher than expected water cuts. A completion was designed for the fourth well in the area to improve reservoir management and liquid handling. The well was successfully drilled with a long step out in order to avoid installing a cemented liner for well spacing purposes in the inner section. The completion was designed based on the downhole logs and record of mud losses while drilling and was installed to 15,000ft. The completion consists of surface controlled sliding sleeves and a ball valve complemented by a pressure gauge and chemical injection. The completion was installed inside a predrilled liner which separated the liner section into zones by timer set mechanical open hole packers. In addition a straddle was installed to isolate a natural fracture zone in the outer part of the well. The completion was run and installed successfully and selective production testing has been conducted. The results show that the three zones have water cuts ranging from 5 to 50%. Selective control of the completion helps to optimise oil production and minimise water production as an integral part of an intelligent field management strategy. Net gain from this completion amounts to some 4,000 stb/day.

Production logging in ultra-long horizontal wells has long been recognized to be extremely challenging, both in terms of data acquisition and data interpretation. This paper describes the planning, execution and lessons learnt of an incident free production/injection logging (PLT) campaign completed in twelve shallow horizontal wells – water injectors and oil producers – to support the long term reservoir management strategy of the Al Shaheen field, offshore Qatar. In this giant offshore oil field, the acquisition of even partial inflow production data is considered worthwhile. A production logging programme was therefore considered as essential. A logging campaign was undertaken in twelve wells using tractor technology as means of conveyance, in a cased hole environment. The key objectives of this campaign were to:Acquire dynamic flow data to improve the understanding of the reservoir dynamics.Identify where sub-optimum patterns can be improved to maximize ultimate recovery.Assess the tractor technology as a means of conveyance in long shallow cased horizontal wells. The campaign showed that although static data are essential in understanding the flow performance of a well, they cannot solely always explain the flow profile along the wellbore. The acquisition of dynamic data is essential to understand the well behavior. Results confirmed that in some long horizontal wells the flow profile takes place uniformly along the entire logged interval, whilst in others sub-optimum conditions such as cross flow and thief zones were identified. The paper describes how the data acquired helped to identify these latter conditions along with the repair opportunities to improve oil recovery. This campaign proved that tractor is a viable means of PLT conveyance in shallow cased horizontal wells by pushing the limits of the technology to greater depths than coiled tubing – up to 14,550 ft – with less disturbance to flow. To maximize success in future well re-entries, completion design has been reviewed in new wells, in order to make them "tractor friendly". Introduction The Al Shaheen oil field in Block 5 and Block 5 Extension, offshore Qatar, consists of a stacked sequence of low permeability carbonate and high permeability clastic reservoirs at relatively shallow depths around 3,000 ft TVD. Although the field was discovered in the mid 1970's its development commenced decades later, in 1992, when Qatar Petroleum entered into an Exploration and Production Sharing Agreement with Maersk Oil Qatar (1). Today the Al Shaheen field produces ca. 300,000 barrels of oil per day and cumulative oil production exceeds 1.4 billion barrels.

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