This paper discusses the systematic approach adopted by Amoco (UK) Exploration Co. Ltd. (AMOEX) in order to achieve its project objectives during a recent platform well abandonment campaign. An integrated team, comprised of key service company personnel working in conjunction with the oil company operations and cementing research staff, developed and implemented innovative procedures and cement slurry designs to support the deployment of coiled tubing. This facilitated the subsequent timely and cost effective field operation to abandon 13 wells in a safe and environmentally sensitive manner. INTRODUCTION AMOEX operate an offshore oil production platform located in Block 211 of the United Kingdom Continental Shelf. The field began producing from the Brent formation in April 1983, with peak production reaching 86,500 barrels of oil per day (BOPD). Output has since declined to about 12,000 BOPD, which has been maintained since mid 1992. The arrest in the field's decline is attributed to improved waterflood response and optimized production operations, which have pushed back the anticipated cessation of production till 1995 or beyond. The disposition of the platform or its conversion to an alternative use is currently being assessed under a separate engineering initiative. When these evaluations are complete, a final plan will be submitted for approval to the Department of Trade and Industry (DTI). The reservoir top has a true vertical depth of 11,500 ft, with temperatures in excess of 270° F. The program for reservoir and well abandonment has been planned in three distinct operational phases, the first of which utilizes 1-1/2" coiled tubing (CT) through the existing completion string to set cement plugs across the perforation intervals at measured depths from 12000 to 20000 ft. During this phase anticipated problems included instances of leaking completions or casing strings, junk or fill, and high cross flows or loss of circulation associated with the mature multilayered reservoir. The second phase employs the existing two platform drilling rigs in order to recover a practicable quantity of tubing and casing prior to setting surface cement plugs. The last phase involves the removal of conductors, which will not occur until after production has ceased. Close liaison between personnel from the operator and the relevant service companies was fostered by regular team meetings, which explored and developed various innovative options. Two engineers with experience in platform drilling, workover, CT and wireline operations were dedicated to the project. The primary objective of their initial studies was to determine the most cost effective method of abandoning the wells, consistent with Amoco's own standards and satisfying the DTI and Health and Safety Executive (HSE). Initial tasks included the following:-Review of experience gained in well abandonments from within Amoco Production Co. and other operators.Compilation of data packs for all 40 well slots, collating information on casing, cement tops, completion details, drilling problems, and production wireline history.Identification of major issues pertinent to developing a conductor removal technique.Discussions with potential vendors about the optimization of procedures associated with CT, casing cutting, milling, bridge plugs, wireline tools, etc.

Summary This paper discusses Amoco U.K. Exploration Co.'s unsuccessful attempt to drill an extended-reach well in Arbroath field (U.K. Block 22/17) and how problems encountered were resolved on subsequent high-angle and extended-reach drilling operations in the field. The resolution of these problems over the course of drilling four high-angle wells and one extended-reach well involved (1) determining mud weight by use of rock mechanics principles, (2) evaluating hole conditions with a wellsite torque-and-drag program, (3) optimizing BHA performance, and (4) developing techniques for effective high-angle hole cleaning. By use of the methods outlined in this paper, improved drilling performance and significant cost savings are demonstrated. Introduction The initial attempt to drill Arbroath Well T14, an extended-reach well with a maximum 70° inclination, was suspended because of caving shale formation and inadequate hole cleaning. In this field, shale can be mechanically unstable at high wellbore inclinations. Earlier field experience by an offset operator had indicated that wells in this area were limited to 65° inclination because of the in-situ stress found in the shale. After suspension of work on Well T14, an evaluation of problems encountered and possible solutions was conducted. The unstable nature of the shale as the wellbore inclination increased was confirmed to be the primary problem. Kwakwa et al. had previously demonstrated the importance of mud weight as a means to stabilize the Tertiary period shale in this area. Another major problem was the difficulty in determining how well the hole was being cleaned during drilling. Johancsik et al. had previously developed a drillstring torque-and-drag model and Brett et al. had demonstrated the use of this model as a means of monitoring hole cleaning. Kwakwa et al.'s mud weight recommendations and Brett et al.'s hole-cleaning monitoring recommendations were successfully applied during the drilling of four high-angle wells and one extended-reach well together with (1) a back reaming program to clean the wellbore, (2) use of a variable gauge stabilizer to improve steerable bottomhole assembly (BHA) performance, (3) drilling of a 16-in. intermediate hole instead of a 17 1/2-in. intermediate hole, and (4) use of 6 5/8-in. drillpipe to improve hydraulics and hole cleaning. These methods resulted in improved drilling performance and significant cost savings. Arbroath Field Arbroath field is an oil development in North Sea U.K. Block 22/17. Its sandstone reservoir, which is normally pressured, is at 8,300 ft TVD. Fig. 1 shows that the reservoir is overlain by a massive section of Tertiary shale with a maximum 12.8-lbm/gal pore pressure. The shale requires both chemical inhibition to prevent it from swelling and a mud weight significantly higher than pore pressure to stabilize it mechanically. To drain the reservoir, development of the field outer edges was necessary. This required wells with a horizontal displacement of up to 15,000 ft and tangent angles of up to 74 . All well paths would pass through the overpressured Tertiary shale.