The paper will review the most recent experience with completion techniques and production performance in horizontal wells in the Statfjord field. A total of 25 horizontal/extended reach wells have been drilled and completed to date. Wells with horizontal section up to 2250 m have been drilled and the longest horizontal displacement is 7290 m. Several well interventions have been performed in these wells, primarily for re-completion purposes. The paper will describe development of completion and intervention techniques with focus on perforating, well killing, well productivity and sand free production rates. Operational consequences in well interventions due to well design will be shown. The first horizontal wells were perforated in overbalance on drillpipe, while today most intervals are perforated in underbalance with coiled tubing. Production and reservoir management for these wells will be discussed with focus on requirements for data acquisition and well intervention. Future possibilities for horizontal wells on Statfjord and technology requirements will finally be discussed in the paper. Introduction The Statfjord field is located in the North sea on the Norwegian-UK boundary line. Three filly integrated production platforms with a total oil processing capacity of 132 000 Sm3/d have been installed for the field development. Each platform has two drilling shafts and a total of 42 well slots. A total of 124wells have been drilled to date, including 10 redrills. The field is one of the largest offshore fields in the world and had an average plateau production of 110–120.000 Sm3/d. Total oil reserves are estimated to be 620 × 10 6 Sm3. The field has been on declining production since 1993 and to date almost 80% of the recoverable reserves have been produced. The structural elements of the Statfjord field could, very simplified, be described as a row of several major fault blocks dipping to the west by 5 to 8 degrees. From the top of the structure and eastwards, the reservoirs are broken apart by a complex pattern of listric faults. (figure 1 & 1B). The main oil-producing reservoirs of the field are sandstones of the middle Jurassic Brent Group and the Lower Jurassic/Upper Triassic Statfjord formation. The Brent Group is divided into the Upper(Tarbert and Ness) and Lower (Etive, Rannoch and Broom) Brent formations. The Statfjord reservoir is divided into three producing formations, from the top Nansen, Erikson and Raude.
This paper reviews the experience with the original completion of the Statfjord wells. A brief description of the reservoirs and geology is given and the drainage strategy for each reservoir is reviewed.The workovers' performed due to reservoir requirements, corrosion, sand production and mechanical failures are summarized.The design basis for an optimized completion is given and the benefdts of the monobore completion are reviewed. A typical Statfjord well life sequence is described and finally some production~esults are given.-
This paper gives a short introduction to the Statfjord field and background for extended-reach-drilled (ERD) and horizontal wells. We reviewed experiences with completion and workovers of horizontal and ERD wells on Statfjord. Ten horizontal wells with horizontal sections of up to 2150 m and four ERD wells with a horizontal reach of up to 7290 m were completed. Several wells were recompleted, and we performed interventions for logging purposes. We describe the development of the completion and workover techniques since the first horizontal well was drilled in 1990 to April 1994.
To achieve the goals of maximum lifecycle value of wells in the Stafjord field, continuous improvements in well design, completion and well intervention techniques have been made over the past 10 years, A major challenge has been to simultaneously optimise reservoir penetration, drilling and completion operations and later well interventions, This paper will review the development in the well design and completion techniques from the low angle « 60°) wells with cemented liner and step down nipple profile completion to the horizontal and extended reach wells with monobore completions, This includes the lessons learned from the numerous workovers performed and how they lead to a change in completion design to ensure reliability, redundancy and optimised production. The impact of the well profile and how it should be optimised for future light interventions, i.e. coiled tubing, or wireline tractor will also be discussed.Finally, the advantages of working in multi-disciplinary teams from the early planning stage to completing the well will be addressed.
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