The Bulla gas-condensate reservoir is a high pressure and deep water reservoir which is located in the north-west site of Baku Archipelago. In the past 2 years, two wells have been drilled to the VIII horizon and have been delivered successfully to the client. While drilling Well 2, a 13 3/8" intermediate casing string was run to a depth of 5093m. It was registered as the heaviest and longest 13 3/8" full-string casing in the Caspian Sea region. The objective of this paper is to share the experience of running this intermediate casing string in the Bulla reservoir and to discuss how improved well design programs can reduce the cost significantly and eliminate well-related risks associated with two-stage casing running operations.
It is very complicated and challenging to run long section casings in one run, especially when accompanied with swelling shale geological formations. Furthermore, this was accompanied by extremely heavyweight and increased equivalent circulating density (ECD) and drag. The operation was pushing the boundaries of previous drilling operations in the Caspian Sea. However, the drilling contractor company managed to overcome all these challenges by using detailed engineering calculations and selecting the most appropriate rig configuration in advance. It was achieved by using conventional casing running operations along with advanced technologies and by applying the best practices to prevent further possible problems.
A 13 3/8" full-string casing was successfully run in the first well (Well 1) to a depth of 4938m, and in the second well (Well 2) to a depth of 5093m which were registered as new weight records for the Caspian Sea Region. Totally, 66 hours were needed to complete the running operations for the second Well. Usually, that casing string would be run in two stages using liner hanger and therefore, it would create technical complexity and difficulty. This technological complexity brings its own risks, compromises, and problems. By implementing engineering approaches, the two-stage casing running operation was substituted with a simpler and more effective design. The conventional casing running technique reduces the number of casing running operations, and the target depth was reached with the optimal and the most economic well construction design.
The results and conclusions of this paper will help well design engineers to simplify well construction, to use a smaller number of casing strings, and to reduce the risks and technological complexities associated with multi-stage casing running operations.