British Petroleum has continuously been at the forefront of ERD (Extended-Reach Drilling) achievements, with its operations at Wytch Farm in Southern England, Pompano in the Gulf of Mexico, numerous fields in the North Sea and the Niakuk and Milne Point developments off the North Slope in Alaska. In order to access reserves and extend the life of mature fields, a strong demand for cost effective ERD has now materialised. As the ERD envelope has rapidly evolved during the 1990s, many operators are now reassessing field opportunities previously considered uneconomic, when an onerous capital investment in new equipment was necessary. A now common question is "Using ERD, how far can we drill using an existing rig and what is the impact of upgrading various rig components?" This paper attempts to address this question by exploring a number of recent case studies where offset field data and advanced analysis techniques are utilised. Increased emphasis is being placed on data collection and analysis, both of which are necessary in understanding critical ERD operations. With this improved learning, predicting future performance in higher step-out wells is more manageable. For future ERD campaigns it has been determined that drilling hole is not necessarily the most limiting operation in significantly extending reach. The "drilling" constraint that is now emerging is more often associated with excessive drag levels when running long casing strings or sliding drilling in high angle, high step-out wells. Most of this recent experience relates to shallow reservoirs where the highest step-out wells have been drilled. This however is where the most productive engineering advances have been made. The paper will also provide a vision of the future and highlight areas where technological breakthroughs will be required in order to drill and complete ultra-reach ERD wells of the future. P. 87

TX 75083 -3836 U.S.A., fax 1 .972. 952.9435. AbstractTorque and drag (T&D) modeling is regarded as an invaluable process to assist in well planning and to predict and prevent drilling problems. Although T&D software has existed for over 20 years, some confusion still exists over the validity of the models used to characterize drilling and completion operations. This paper provides an assessment of current limitations of the various T&D models (soft-string and stiffstring) and appraises their validity. Field data from various operations is used to illustrate certain limitations. The paper defines future requirements for what is considered to be the next generation of T&D models . Probably the most important technical requirement is a more realistic stiff-string model to correctly account for the impact of tubular stiffness, hole clearance and tortuosity effects.

This paper discusses the planning and preparation process for drilling and completing a 10km departure well at the Wytch Farm Oilfield in Southern England. An 8km departure well was drilled at Wytch Farm during 1995. At the time, this was at the limit of drilling operations. Some fundamental changes involving new technology, operational practices and techniques have been necessary to enable this well to be drilled. More specifically, the paper will describe the directional drilling techniques necessary to enable the reservoir interval to be accessed. Research and development work performed by the drilling team to identify mechanical limitations in drilling operations at this departure are also examined. This includes a comprehensive review of offset well data to determine friction factors for all operations and concomitant measures adopted to limit rotary torques and drags to workable levels. The other major focus of this paper is to appreciate the mechanism by which drilling muds are lost to the permeable reservoir and describe methodologies employed to overcome this problem. The paper will also discuss recent experience with the application of partially floating casing, rotary steerable drilling systems and running and cementing long liners. Completion and intervention challenges are also examined with an analysis of future requirements. Introduction The development of the offshore extension of the BP operated Wytch Farm Oilfield, located on the South coast of Britain, utilising extended reach (ER) wells into the offshore part of the Sherwood sandstone reservoir has been extensively documented in a series of technical papers [1], [2] and [3]. (Figure 1). The current phase of the development is to tap into significant reserves located at reservoir departures in excess of 10km. The Drilling Challenge. The section of the reservoir targeted by this Ultra-Reach well (Measured Depth : True Vertical Depth ratio >5), M-11, lies between 8km and 10km departure from the 'M Wellsite' where the Deutag T-47 rig is located. This site, specially constructed to access the offshore portion of the reservoir currently contains 10 extended reach wells and yields over half of the total 110,000 bopd production at Wytch Farm. The challenge is to safely and efficiently drill and complete a 10km departure well into the target area to access oil in place of 24mm STB. A single horizontal well into this target is expected to recover some 25–35% of these reserves. Although this is likely to be the most expensive well drilled at Wytch Farm, the significant reserves that it will access are critical to the long term profitability of the field. The well design is the culmination of over a year's evaluation, design and planning, providing an excellent test of the industry's capabilities. Successful delivery of this well will have a significant impact on the industry to access reserves that a decade ago would have required major capital expenditure, in the shape of new facilities, to recover. P. 191^

Running long production casing strings in extended-reach wells is usually recognised as one of the most critical of all well operations. Failure to reach target depth often has a profound consequence on well deliverability and overall cost. In this paper, an overview on the status of current casing running tools and techniques is given. This is complemented with an assessment of the impact of drilling technology on the ability to run casing. The systematic collection of quality data and application of consistent analysis techniques can help identify common factors associated with both casing running success and failure. Results are given, where this approach has been applied to two current extended-reach developments. Introduction During the planning phase for drilling and completing an extended-reach well, casing running is frequently identified as a challenging operation. This is not necessarily due to lack of available running weight, but often due to the consequences of setting casing high. The subsequent knock-on effect of a leaner casing design and often substantial additional capital cost, must to be factored into the overall risk assessment and cost estimate. The drilling team is usually faced with designing the casing running operation to ensure success. There are potentially a large number of design variables and each of these has their own associated degree of uncertainty. All too often the impact of each design parameter is not well understood and both under-design and over-design frequently occurs. Usually this has a low impact on success, however occasionally the outcome of a wrong decision can be disastrous. For example, a common issue is the use of centralisers: are they needed, if so, how many, what type, and what should the installation frequency be? During ERD (Extended-Reach Drilling) well planning, torque and drag analysis is recognised as an essential part of the risk management process. For modelling purposes, careful consideration has to be given to choice of friction factors. Ideally, casing running data from offset wells should be collected, analysed and friction factors calculated. All too often this is not done and a large degree of uncertainty exists as to what values should be used. Another misconception is that friction factors calculated for the drilling phase of the well, can be directly applied to the ensuing casing run. This is not usually the case. In this paper, findings from BP's friction factor database are summarised, where results from over fifty ERD casing runs have been analysed. In the absence of good offset data, the database provides a valuable reference point for drag analysis. The latest BP drilling envelope is illustrated in Figure 1 and reflects many of the challenging ERD casing runs included the database. Recent advances in technology have also blurred the casing running decision process. These include the impact of rotary steerable tools in ERD wells; the increasing use of underreaming while drilling practices; the emergence of ad-hoc casing sizes; the deployment of flush casing strings; the applicability of SET (solid expandable tubulars); the relevance of casing drilling technology; casing floatation techniques and drag efficient casing centralisers. The potential impact of each technology is discussed and where appropriate, examined further in the two field case studies. Data collection and analysis are fundamental to a better understanding of how wells are drilled and the impact this has on the subsequent casing running operation. This topic is a common theme of this paper and best practice based on recent experience given. Frequent data sampling also gives new insights into both casing sticking detection and how changes to running techniques can help mitigate against this. The two case studies from the BP operated Harding and Chirag fields are used to highlight the benefits of data collection, modelling and the application of technology.

This paper was prepared for presentation at the 1999 SPE/IADC Drilling Conference held in Amsterdam, Holland, 9-11 March 1999.