The objective of this paper is to share the experience of how 7-5/8" section was drilled, and cased-off to enable the zonal isolation in the depleted VII horizon and high-pressure zone with close PPFG margins by managing high risks of differential sticking and loss of circulation at Bulla gas-condensate reservoir which is one of the most complex high-pressure fields with close PPFG margins in the world. The Bulla wells are highly complex wells the Caspian region. Before drilling into the reservoir section which requires high MW, the drilling liner was run to the cased-off VII horizon and high-pressure zone, which have significant challenges such as differential sticking and loss of circulation, previously resulting in stuck pipe and losses. To overcome the challenges, under reaming/liner cementing at MW lower than PP were evaluated and applied to have good cementing across the open hole and good shoe, to drill into the reservoir section in the project. The study helped to identify the issues and actions taken that resulted in significant improvement in well delivery and reduced the risks despite having underbalanced condition during under-reaming/cementing. So is accepting the bitter truth, situation offering limited sets of options was very challenging as having: high risks of differential sticking and loss of circulation due to high MW, high- pressure interval near the setting depth, which required high MW to stabilize the well, need to isolate the high-pressure zone and depleted VII horizon for drilling into the reservoir section. However, the operation plans of managing the ECD within limits by using different MWs, higher MW for running casing and lower MW for UR and cementing have been risk-assessed with all the mitigation, and as a result, the aforementioned intervals were well isolated which was supported by CBL results. No gains or losses were observed during the operations including both casing running and cementing. Finally, having a good cement in the shoe allowed to successfully drill into the reservoir section with high MW accomplishing successful completion of the well without any major problems previously occurring. Therefore, this approach not only reduced the time, cost and also helped to deliver the quality wellbore. The case study of liner cementing at underbalanced conditions provides useful insights of how unconventional techniques can be successfully implemented to achieve the overall accomplishment in well delivery performance.
The Bulla gas-condensate reservoir is located in the north-west side of Baku Archipelago, is one of the most complex high-pressure fields in the world, with close PPFG margins and reactive clay in the overburden. The objective of this paper is to share the experience of how the challenges in the overburden section are managed to achieve improvement in the well delivery, through the application of continuous learning approach and the use of new technologies. The Bulla wells are highly complex wells in the region. The overburden shales are young sediments 250 to 1200 m to be drilled and cased off with 24" casing, this has significant challenges such as slow ROP, Bit Balling and tight hole due to the shale swelling. These challenges can lead to issues such as stuck pipe and lack of zonal isolation. To overcome the challenges and similar cases in well delivery, continuous improvement (CI) techniques and new technologies were evaluated and applied in the project. The CI approach helped identify the issues in the delivery of the overburden and actions taken resulted in significant improvement in well delivery and reduced the risks. The issues were worked on, and most feasible solution was chosen. The improvement plan has been risk assessed for the challenges of handling large volumes, possible losses, spillage etc. and risk control actions are implemented. The next well was drilled with higher operational efficiency, cost optimization and better hole quality to achieve zonal isolation by proper placement of cement. Further improvements were planned for the next wells in the field, by extending under reaming range through the application of new technologies. For 18 5/8" casing, a hole size of 24" required, this was drilled using multiple trips due to tool limitations. By using the advanced drilling dynamics software, BHA along with the required under reamer identified tools and design the section was delivered in one run. The application of this approach will not only reduce the time and cost but will also will help to deliver a quality well bore. The study provides an overview of how CI can be effectively implemented to achieve the overall improvement in the performance of the well delivery. Additionally, it gives insight on how new technologies in BHA design and reaming can improve the drilling performance.
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.
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