KOSTOL, PETTER, and HELGE TJOTTA, Statoil, Stavanger, Norway

ABSTRACT: Extended Reach and Horizontal Wells Experienced on the Statfjord Field

Statfjord field, the largest producing field in Europe, is located 200 km northwest of Bergen, Norway, on the United Kingdom/Norwegian boundary. Statfjord field is being developed with three fully integrated platforms of concrete gravity based on Condeep design. Three platforms have an oil production capacity of 132,500 standard cu m/day (830,000 bbl/day) and a water injection capacity of 193,800 standard cu m/day (1.2 x 10{6} bbl/day). The Statfjord field, which is approximately 24 km long and averages 4 km in width, consists of four reservoirs: Upper Brent, Lower Brent, Dunlin, and Statfjord, which are developed separately.

The overall objective for the horizontal and extended reach wells on Statfjord is to maximize the field recovery and accelerate production at a minimal cost. This is done by drilling extended reach wells to the far-away flanks of the field, and drilling horizontal wells to drain fault blocks and erosion zones in the Brent reservoir and wedge zones in the Statfjord reservoir.

To date, a total of 11 horizontal and extended reach wells have been drilled and completed on Statfjord field. The longest horizontal section drilled is 2146 m and the longest horizontal reach is 6086 m, with a total length of 7250 m. Presently (January 1993), a well is being drilled to reach 7140 m horizontally, with a total depth of 8550 m.

The following have been key factors in drilling the horizontal and extended reach wells: well profile, torque and drag, equipment limitations, hole cleaning, hole stability, mud and cement programs, and surveying.

To optimize the well profiles, extensive work has been put into simulating torque, drag, and ECDs. The well profiles are optimized with regards to drilling, completion, and workover, in addition to the reservoir targets.

The completion is designed to be able to perform all future work through tubing. Factors like zone isolation requirements, well profile, casing program, logging/testing/perforating requirements, and sand production are considered when planning the completion. A 7 in. monobore completion string together with a 7 in. cemented liner is used to meet the completion objective.

Several production logging tool, bridge plug, and perforation jobs have been performed on coiled tubing in horizontal wells on Statfjord field.

Problems related to hole cleaning, well killing, fishing, and packer setting have been experienced during drilling and completion of the wells.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.