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.
The company is executing an underground gas storage project at an unprecedented scale. The intent of this paper is to demonstrate the execution methodology and technologies that the company employed to achieve within set deadlines and deliver the work on time and under the given budget. This paper, therefore will focus on outlining all planning, design as well as drilling & completions strategies utilized by the operating company during the execution phase. During Phase 2 of the project, the Drilling Contractor was engaged to deliver a total of 40 wells within a short period of time. These wells were planned to expand the total gas storage capacity at the Tuz Golu facility to ca. 5 bcm of natural gas stored in underground salt caverns. Tuz Golu wells are vertical with three (3) casing string wells. These land wells are big bore and commence from the installation of the 30″ conductor at a depth of 120m using a small 150-ton conductor rig. Pre-installation of conductors significantly helped accelerate the project delivery schedule. Main drilling operations commenced in January 2020. Since the structure wasn't fully explored in spite of 2D seismic work and the first phase operations, a number of wells drilled encountered no salt leading to their abandonment. As a result, the total duration of the project was consequently extended. Re-Engineering and lessons learned during execution helped deliver a successful learning curve in both drilling and completion operations. The strategy of the company to drill a well in stages of top hole, main drilling and the completion using multiple rig operations was successful, bringing an overall well time from 55 at the beginning of the project to 20 days per well. Thorough planning and design of the wells allowed the company to deliver the projects with well integrity, full suitable for gas storage operations. As a result, the project was executed on time and well within the planned budget thus delivering an excellent value to the stakeholders and main client. The Drilling Contractor has been proactive to employ this staged approach from the very beginning of the project. Irrespective of the delays the Drilling Contractor continued operations with the intermittent rig count of 4 to 8 rigs. A large scale operation demanded careful planning and continuous application of lessons learnt from the first phase which were successfully embedded and implemented.
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