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.