The Cretaceous (Albian) Upper Burgan Formation has been on production for circa 60 years in the Raudhatain and Sabiriyah fields in North Kuwait and significant resources remain. Key to an optimized development of this important reservoir is the introduction of Slant Well technology incorporating the use of sliding sleeve completions.
The Upper Burgan Formation in the Raudhatain Field consists of four major sand dominated layers that comprise the main producing zones. These likely represent high stand deposits that formed during a progradation of the delta system across the region. Separating the sand layers are non-reservoir mudrocks that were deposited in marginal marine settings and act as baffles or barriers to fluid flow. In order to maximize production from the Upper Burgan, KOC has instigated the use of high angle slant well technology which allows greater reservoir contact at the well bore for each sand layer. As well, all four layers are in contact with the well bore thereby maximizing the oil drainage more efficiently. Vertical wells achieve the same result, but the difference being far greater reservoir contact with the four major layers has been successfully accomplished with the Slant well, and this has afforded higher production rates. The use of the Slant well however is selective and horizontal well application is still in use in both fields where good sand continuity in a specific layer has been interpreted.
Currently the non-conventional wells make up approximately 25 percent of the producers in the Raudhatain Upper Burgan, the rest being vertical wells. Drilling the Slant well is a challenge primarily due to the long intervals of shale that are encountered between the sand layers. Shale sloughing is the major problem. The Upper Burgan is a mature reservoir with a weak edge water drive. Pressure depletion is a concern that is mitigated with the use of an active sea water and effluent water flood program that is now in place.
The first Slant well to be drilled in the Upper Burgan was RA-000A. The well, located in the southern part of the Raudhatain Field was drilled to a depth of 9858 feet with an inclination of 80 degrees through the productive intervals. The well was drilled to the top of the Upper Burgan and a 7 inch casing was landed at this depth and cemented. The productive interval was drilled with a 6 1/8 inch hole size having a length of 850 feet. The well was then completed with a sliding sleeve ICD (Inflow Control Device). The ICD completion in the Slant well allows more uniform production from different regions of the well bore with less draw down. This will minimize the water coning effect. The sliding sleeve can be used to shut off water producing intervals during the life of this producer. The successes and challenges of this well are explored in this paper.