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.

Over 15 years of production and injection history within the Al Shaheen Field has provided more details on the reservoir heterogeneities and performance of extended reach horizontal wells. This additional data, along with the lateral extent of the reservoirs, has increased the need for longer and more selective horizontal completions. Three primary reservoirs have been developed to date and have different requirements regarding liners and completions. The commonality of all reservoirs is the requirement for long liners and completions in vertically shallow horizontal wells. As the completion philosophy has changed, new approaches have been developed for both deployment and selective isolation. A number of case histories are discussed to illustrate the evolution of the completion requirements. Modifications to zonal isolation, mud over air floatation, and remote triggered packers are some of the cases discussed. Two of the three reservoirs require acid stimulation to improve the production and injection performance of producers and injectors. Effective stimulation can not be accomplished through what would be considered typical placement techniques, due to the extreme lateral departure of these wells in shallow vertical reservoirs. Two techniques used are described along with some issues regarding hole-geometry in acid stimulated wellbores. The paper concludes with some future requirements for the further development of the Al Shaheen Field. Increased selectivity and the need for active zonal control will push the completion requirements beyond where they are today. New completion concepts are being actively researched and developed so that the reservoirs can be optimally managed.

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.

Although drilling technology is now able to deliver ultra long horizontal wells (LHWs), completion technology has been slower to evolve. Running long liners, effective stimulation, and completions are some of the areas that require more attention. This paper discusses some of the challenges in the development of the Al Shaheen reservoirs offshore Qatar and how they were overcome. Some of these wells have a stepout in excess of 30,000 ft with a total vertical depth of 3,100 to 3,500 ft, and thus, they offer some unique challenges. Running and cementing liners to these depths is difficult, and some of the methods to achieve this effectively are discussed. Perforating guidelines are presented that allow sand control without having to resort to conventional sand-control practices. Stimulation of such long reservoir sections is a particular challenge, and a fine balance must be struck between acid coverage and cost, both for barefoot and perforated intervals. The so-called Q-CAJ technique of acid distribution, which has allowed acceptable stimulation despite these conditions, is presented. The technique also offers opportunities to stimulate long horizontal boreholes more effectively and at lower cost. Some of the wells are completed with multizone selective completions, which push the design limit of equipment. A number of such intelligent wells have been completed successfully, and more aggressive wells are planned. To optimize the development cost, dual-lateral wells have also been drilled with complete control over each lateral. Discussed are some of the underlying completion techniques such as running completion in stages, use of mechanical latches, hydraulic-control-line wet connects, interval control valves, and limitations imposed by control lines. The paper concludes with some of the challenges that have yet to be overcome.

The Valdemar field, located in the Danish sector of the North Sea, targets a Lower Cretaceous, "dirty chalk" reservoir characterized by low permeabilities of <0.5mD, high porosities of >20% and contains up to 25% insoluble fines. To produce economically the reservoir must be stimulated. Typically, this is by means of hydraulic fracturing. A traditional propped fracture consists of 500,000 to 1,000,000 lbs of 20/40 sand, placed using a crosslinked seawater-based borate fluid. The existing wells in the field are completed using the PSI (perforate, isolate, stimulate)1 system. This system was developed in the late 1980s as a way of improving completion times allowing each interval to be perforated, stimulated and isolated in a single trip and has been used extensively in the Danish North Sea in a variety of fields. The system consists of multiset packers with sliding sleeves and typically takes 2-3 days between the start of one fracture to the next. Future developments in this area now require a new, novel and more efficient approach owing to new target reservoir being of a thinner and poorer quality. In order for these new developments to be economical an approach was required to allow for longer wells to be drilled and completed allowing better reservoir connectivity whilst at the same time reducing the completion time, and therefore rig time and overall cost. A project team was put together to develop a system that could be used in an offshore environment that would satisfy the above criteria, allowing wells to be drilled out to 21,000ft and beyond in excess of coiled tubing reach. The technology developed consists of cemented frac sleeves, operated with jointed pipe, allowing multiple zones to be stimulated in one trip, as well as utilizing a modified BHA that allows for the treatments to take place through the tubing, bringing numerous benefits. The following paper details the reasons for developing the new technology, the development process itself, the challenges that had to be overcome and a case history on the execution of the first job of its kind in the North Sea, in which over 7MM lbs of sand was pumped successfully, as well as the post treatment operations which included a proof of concept in utilizing a tractor to manipulate the sleeves. Finally, the production performance will be discussed supported by the use of tracer subs at each of the zones.