in 1989 BP formed a world wide task force to focus on lowering its stuck pipe costs. In its campaign to reduce this cost,the task force gathered together key personnel from each of its three operating companies and its research centers. This paper reports on the methods used to produce a substantial reduction in its. stuck pipe costs.

This paper overviews critical technologies for extended-reach drilling (ERD). ERD is a pivotal industry activity because it enables optimisation of field development through the reduction of drilling sites and structures and provides access to otherwise unavailable reserves. These efficiencies increase profit margins on viable projects and can make marginal prospects financially viable. ERD technologies to be reviewed include torque/drag, drillstring design, wellbore stability, hole cleaning, casing considerations, directional drilling optimisation, drilling dynamics, and rig sizing. These technologies have been found critical to the success of ERD. The paper is based on experience gained in the pursuit of world record ERD objectives in BP Exploration’s Wytch Farm oilfield, and as a result combines current technology assessments with practical field knowledge.

Summary This paper discusses the novel application of technology in the cementing and bond evaluation from the world-record breaking ERD (Extended Reach Drilling) wells in Wytch Farm, where horizontal liners of the order of 800m to 1300m at TvD of ca 1600m have been successfully cemented and perforated. Detailed analysis of the conditions by a multi-disciplinary team provided some practical procedures which enabled us to achieve our objectives of zonal isolation and cement bond evaluation successfully. Important aspects of zonal isolation, such as the use of spiral-blade centraisers, rotating the liner, and trials of the ECPs (External Casing Packer) are discussed in detail. Cement bond evaluation is also detailed, involving CT (Coiled Tubing) deployment and various bond logging tools, including ultrasonic tools. The CBL was found to be surprisingly reliable if used correctly. Introduction Cementing horizontal wells and evaluating the cement integrity encounter new challenges when the horizontal section of the well becomes longer and longer, i.e. in the ERD (Extended Reach Drilling) wells. How to face up to these challenges is the subject of this paper. Cementing and its integrity evaluation of the horizontal liners in several Wytch Farm ERD wells have provided us with some good lessons and experiences. These are discussed and presented with case studies. Some brief background information is provided first. Techniques used in cementing the horizontal liners are then presented in detail, followed by discussion on the cementing evaluation including CT (Coiled Tubing) operations, logging tool selection and centralisation, and log interpretation. Case studies are then presented before the conclusions. Background Wytch Farm is the largest onshore oil field in Western Europe, and is situated on the southern coast of England, about 100 miles south-west of London. The discovery and development history of this field is briefed in paper SPE 28558. Briefly, a second reservoir (the Sherwood Triassic sandstone) was discovered in 1978 at the time the Bridport Jurassic sandstone reservoir was being developed. The Sherwood reservoir formations, at ca. 1600 m TVD, extend offshore into Poole bay, up to ca. 9 km from the existing onshore drilling sites.

Drilling oil wells on the North Slope of Alaska is not a new endeavor. Thousands of wells have been drilled over the past two decades in order to fill the Trans Alaska Pipeline. The majority of these wells have been drilled from a number of large drilling pads connected via a road network. Some of the newer developments have been drilled from remote pads accessible by fixed wing aircraft and ice road during the winter. So what is it that makes the Northstar Development stand out among all other drilling operations on the North Slope? It is the first Arctic Offshore Development that is not accessible by road for most of the year and does not have fixed wing air support. The implications of limited access to a 400' by 400' island are enormous. Successful completion of the first drilling season at Northstar is a significant milestone marked by detailed design and execution as well as pure determination. Many of the challenges were anticipated and accounted for while many others were not. The first Arctic Offshore Development delivered its first barrels of oil as per schedule on 2nd November 2001. Now comes the next challenge- drilling more for less to improve the profitability of this unique Alaskan project. Introduction Drilling oil wells on the North Slope of Alaska is not a new endeavor. Thousands of wells have been drilled over the past 2 decades in order to fill the Trans Alaska Pipeline. The majority of these wells have been drilled from a number of large drilling pads connected via a road network. Some of the newer developments have been drilled from remote pads accessible by fixed wing aircraft and ice road during the winter. So what is it that makes the Northstar Development stand out among all other drilling operations on the North Slope? It is the first Arctic Offshore Development that is not accessible by road for most of the year, and does not have fixed wing air support. The implications of limited access to a 400' by 400' island are enormous. Successful completion of the first drilling season at Northstar is a significant milestone marked by detailed design and execution, as well as pure determination. Many of the challenges were anticipated and accounted for while many others were not. The first Arctic Offshore Development is well on its way to delivery, but at a price. Northstar is BP's newest field development on Alaska's North Slope. The field is currently being drilled and production has just commenced from the man made Seal Island. Northstar is approximately 6 miles north of Prudhoe Bay in the Beaufort Sea (Figure 1). The island was built in approximately 40 feet of water on the remains of Seal Island, which was used for the original discovery/appraisal wells. The field encompasses roughly 60 square miles and contains an estimated 176 million barrels of recoverable reserves. Northstar will be the first development in Alaska that will be produced from both State and Federal Leases, with oversight from both the Alaska Oil and Gas Conservation Commission and the Mineral Management Service.

BP Exploration, operator of the Wytch Farm Oil Field, has since April 1993 been developing the offshore extension of the Sherwood Reservoir using extended reach drilling (ERD) techniques. Over that time new drilling technology has become available, drilling strategies and methods modified, and many difficulties overcome. Wells are now being drilled to record breaking departures utilizing geosteering, casing floatation and torque reduction techniques. Horizontal reservoir sections in excess of 2.5km are being drilled, cased, successfully cemented and selectively perforated to boost accessible reserves. Increasingly, the conventional limits of directional drilling and completion are being pushed back. This paper will summarize the many ERD achievements to date at Wytch Farm. It will describe the technology, tools, techniques and strategies currently being applied to drill and complete the more recent extended reach wells in Western Europe's largest onshore oilfield. Introduction BP's Wytch Farm oilfield, located on the south coast of Britain, is currently being developed through the drilling of extended reach (ER) wells into the offshore part of the Sherwood sandstone reservoir. As has been well documented in previous papers, the development drilling of the offshore extension of the reservoir was originally planned to be accomplished from an artificial island to be constructed in Poole Bay. In December 1991, based on advances being made within the industry, this plan was abandoned in favour of extended reach drilling from the mainland. The cancellation of the Island project in favour of ERD assumed that 6km step-out wells could be drilled into the shallow (1,550m TVDss) Sherwood reservoir. In fact, 5 years on, over 8km step-out has been achieved, (Fig. 1). SPE paper no. 28293 referred to four Wytch Farm wells (F18 to F21) which attained a maximum step-out of 5.5km. This paper deals initially with experience on wells M1, M2, M3 and M5, each of which have reached ever increasing departures (Fig. 2). M5 attained a step-out of 8,035m, claiming the world record departure at any vertical depth. The paper also discusses wells M6 to M9 where new equipment and techniques were employed to improve ERD efficiency and provide the means to reach targets which exist at even greater departure in the near future. Trajectory Design The last three wells on F site had been drilled with a tangent of 80 – 82. This was continued on the M site wells, utilizing higher tangent angles as the departure increased. On M2 the tangent was increased to 830 to achieve the largest departure at that time of 6.7km. Through the build the maximum planned build rate was 2.5 /30m. The increasing tangent angle was minimizing torque during the drilling phase, but on M2 it became apparent that drag was becoming more of a limitation. The ability to slide a drillstring at depth was limited, and achievable reach with coiled tubing was being compromised. Comprehensive modeling indicated that the tangent angle should be reduced to 81 for M3 and M5 to improve sliding reach. This resulted in the build rate being increased to a maximum of 2.75 /30m on M5. This all appears like very fine tuning, but a 1 change in angle over a 5km tangent section does have a significant effect on ultimate torque and drag at 8.5km total depth. Once the reservoir was encountered, the inclination was immediately increased to 85 - 95 as required for the long geosteered 8 1/2" section. Drilling Operations Top Hole. Since moving to the newly constructed M-Site where near surface anti-collision problems were less severe, 24" hole was directionally drilled in one pass without the need for a pilot hole to 60 inclination by 220m. The 17.1/2" section attained 600 by casing point at circa 860m MDbrt. After running and cementing the 13.3/8" casing, the water based mud was displaced to oil based mud (OBM) before drilling the long,, 12.1/4" hole section. The build rate established in the 17.1/2 hole section was maintained at the start of the 12.1/4" hole section until the tangent angle of 800 to 830 was attained. 12.1/4" Hole Section. The length and tangent angle of the 12.1/4" hole section obviously depended on the step-out desired at the 9.5/8" shoe which was typically set at top reservoir. MS was drilled with an 81 12.1/4" hole section some 5,163m in length, 4,014m of which was drilled in one bit run. Steerable assemblies were used throughout, although the amount of sliding in the tangent section has with each well been steadily reduced to as little as 3%. Towards the end of the M5 12.1/4" section, an extended power section positive displacement motor (PDM) was run. P. 371^