Old platforms are not well known for extended-reach drilling (ERD) operations mainly due to rig and hydraulics limitations. ERD wells demand robust rig capabilities, good hydraulics systems, and equipment reliability. In addition, the well profile, rotary steerable system (RSS), measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools, surveying, and new technologies are extremely important to the success in drilling an ERD well. RSS and drillpipe selection are important factors for hydraulics optimization. Surveying techniques are also important for time saving and improved efficiency. An ERD well in the North Sea Statfjord field was kicked off in the 17 ½-in. section from the openhole cement plug through a 50-m window between the 20-in. casing shoe and 13 3/8-in. casing stump, ensuring a smooth well profile and reduced doglegs compared to the whipstock window exit. The 17 ½-in. section was drilled and landed at a 79° inclination using point-the-bit RSS technology, and the 12 ¼-in. section was drilled in two runs as planned using the point-the-bit RSS withstanding more than 550 h down hole. The 9 5/8-in. liner was run and floated successfully in the ~6000-m section. Strict adherence to surveying techniques and quality control processes proved very helpful to meet Operator technical requirements. The 8 ½-in. section was drilled and landed on top of the reservoir with an inclination decrease from 88° to 35°. New MWD technology was successfully used in drilling the 6-in. section. These latest technologies as well as employing appropriate techniques help to drill ERD wells on aged platforms like those in the Statfjord field. This paper will describe the planning and execution phases of a challenging ERD well drilled in the Statfjord field.
Statfjord Field is one of the largest and oldest fields on NCS and operates with platforms Stafjord A, B and C. In recent years, slot recovery to drill more wells has posed a big challenge to deliver wells with Gas Lift design due to extensive and time & cost consuming P&A and casing cut & pull operations. As Statfjord is operating in late life phase using artificial gas lift as a secondary recovery approach, well designs to meet NORSOK well integrity casing design requirements is a key design focus. Along with the above mentioned technical challenges, improving operational excellence has driven the concept of innovative casing design with 11 ¾″ liners. This design eliminates the time spent on extensive casing retrieval operations. In addition, reduces time and risks associated with drilling 17 ½″ section that requires changing from 13 5/8″ to 21 ¼″ BOP, higher flow rates for hole cleaning and larger volume of cutting injection, and waiting 13 3/8″ casing hangers that are crucial long lead item. Installation of 11 ¾″ liner and cementing 9 5/8″ casing in tight ECD margins were identified as high priority design goals in the early planning phase. To address aforementioned challenges and meet design goal in time and cost efficient way, innovative ideas were a fundamental necessity. This paper discusses the background behind need for a new gas lift well design for well 33/12-B-42 B, casing design approach, challenges faced during planning and learnings from operations. Key operational highlights leading to successful well delivery were: optimization of 11 ¾″ liner depth to meet gas lift formation strength requirements; successful 11 ¾″ liner cement job with rotation to secure the secondary barrier envelop; and opening the narrow ECD window between 9 5/8″ casing and 11 ¾″ liner with to Low Rheology Oil Based Mud (LROBM) after drilling 10 5/8″ × 12 ¼″ section with Conventional Oil Based Mud (COBM). Successful cement job on 9 5/8″ casing facilitated the improved production profile by placement of production packer in 9 5/8″ casing instead of 7″ liner. The new gas lift well design has opened ~ 40 slots for 13 3/8″ exit on Statfjord and it is expected to reduce the time consuming casing retrieval and slot recovery operations
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