This paper describes a case study of planning, drilling, completing and producing an extended reach (+25,000 ft) horizontal infill well in a radial water flood pattern in the giant Al Shaheen oil field, offshore Qatar. The completion was designed to accelerate oil production and maximize oil recovery from a differentially depleted, low permeability carbonate formation and to provide a high degree of flexibility for selective production, production testing and performance monitoring.
Dynamic reservoir simulation predicted both accelerated oil production and improved long term oil recovery from completing also the innermost section of the well and producing it for the first three years. This zone was originally planned to be isolated to comply with the overall injector-producer pattern. The net increase in oil recovery was estimated at some 0.5 MMstb. A surface controlled two-zone completion design was prepared, separating the ca. 17,500 ft long reservoir section into an inner zone and an outer zone. The design includes a novel combination of two different types of open hole packers: Two mechanical packers and one swell packer. The open hole packer solution was preferred to a cemented and perforated liner mainly due to cost and time saving and the potential to stimulate the inner zone more effectively. The design also includes three surface readout downhole gauges allowing for real time performance monitoring of the individual zones.
The completion was run and installed successfully and analysis of production and pressure data confirmed zonal isolation. Reservoir pressure, fluid properties and productivity were determined for each zone. The acid stimulation efficiency was determined for the inner zone by assessing pre and post stimulation well performance. With the surface controlled two zone completion in place, the zones are being selectively produced and tested when required, thereby achieving the goal of accelerating oil production and maximizing recovery.
The Al Shaheen field is located in Block 5, offshore Qatar, as seen in Figure 1. Production from the field commenced in 1992 from two thin separate Cretaceous carbonate formations and an overlying sandstone formation. The carbonate reservoirs are characterized by relatively thin oil columns with a large areal extent (25 km by 45 km) with typical permeabilities in the 1–10 mD range.
The field development philosophy centres on long horizontal wells, placed in radial and in parallel line drive patterns of alternating water injectors and oil producers. Well spacing varies from below 600 ft in the tighter carbonate reservoirs to more than 5,000 ft in the permeable sandstones.
Implementation of a large scale development plan comprising installation of new platforms, process facilities, pipelines and 163 new production and injection wells is currently ongoing. A significant part of the new wells are being drilled as infill wells in existing areas comprising both parallel and radial well patterns.