Today's increasingly complex and crowded drilling environments have placed a greater emphasis on wellbore collision avoidance. The safety and financial implications of shutting in production on platforms or repairing damaged wells have established a need for the industry to evaluate the potential for collision with a producing well. This paper will describe an effective approach to evaluating, minimizing and mitigating these hazards, and will include a number of case studies illustrating the successful application of this approach in the field. This paper, the latest in a progressive series will detail the importance of gathering appropriate data—such as completion type, offset surveys, well pressures, casing depths, reservoir fluids and mud densities—and analyzing this data to accurately assess potential collision risks. Each well and field poses different challenges; not all data is available and wells can vary from simple vertical land wells to crowded offshore and fishbone designs. The well position uncertainties are determined by using survey error models from the Industry Steering Committee on Wellbore Survey Accuracy. This method was chosen because it is an industry-recognized standard of defining the magnitude of survey uncertainty. Recommendations for minimizing risk are based on the status and conditions of the adjacent wells and the nature and severity of the risks associated with a collision. These recommendations are formulated to minimize the risk while ensuring that production is disturbed as little as possible. Introduction With the worldwide growth in drilling activity, operators are encountering increasingly complex and crowded drilling environments, especially in previously developed fields where existing well density is high and legacy positional data often unreliable. The safety, environmental and financial consequences of a wellbore collision can range from minor to catastrophic, and the cost of shutting in nearby producing wells during drilling or repairs can be prohibitive, causing producers to bypass otherwise viable opportunities. As part of an international drilling and services provider (the Company), the authors have worked in close collaboration with client organizations to understand and meet these challenges. Because no industry-wide anti-collision (AC) standard exists, the Company has established its own standard and a comprehensive anti-collision AC process for meeting it. To comply with the AC standard when any new well is drilled, the drilling engineers must analyze each of the offset wells within a certain radius of the proposed subject well. This can be a relatively quick and simple process in a new field where only a few wells are involved. In such situations, the AC process might take no more than a few hours and be solved at the location level. But in highly developed brownfield locations, the AC process becomes much more complex, requiring the analysis of hundreds of adjacent wells before finalizing a new trajectory. This paper will illustrate the design and application of the Company's AC process, including a number of success stories from real-world drilling assignments. Lessons learned from these experiences feed back into the development process to achieve a continuous improvement in its effectiveness and breadth of application. The Challenge of Avoiding Well Collisions A number of recent trends contribute to an ever-increasing complexity in the AC process. In land drilling activities, new production in older, established fields can pose an increased hazard of collisions with existing wells. In some parts of the United States, for example, rules concerning well density have been relaxed to facilitate more domestic production. From a former spacing limit of one well per 25 acres, new regulations have reduced that to a 20-acre limit and then a 10-acre limit, with proposals for a 5-acre limit in the future. The same trend worldwide has opened opportunities for producers to return to established fields with an infill drilling campaign, placing new wells between and in relatively close proximity to existing wells, which are often still producing.
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^
The past year has experienced dramatic changes in industry activities. Despite the downturn, it has been encouraging to see that there has remained an active interest through various industry events and discussions in improvement in the delivery of complex wells.I had the opportunity to participate in several SPE Advanced Technology Workshops (ATWs) and Forums related to this topic, and it was great to see record attendances, which provided for a diverse, yet high-quality, discussion and interaction. Design factors, improving drilling execution, and complex-well design, along with maximizing reservoir contact for horizontal and complex wells, are still major industry drivers, even though the industry has already drilled and completed many thousands of these wells.Every year, new technology enters the market place providing potential for improvement of all aspects of horizontal-well operations, but on the basis of excellent and open discussions at SPE events, there still are further challenges to overcome. Conclusions from several meetings included positive reactions to the introduction of new technologies in helping drive performance to new levels, but it was highlighted that the repeatability depended upon good knowledge capture and transfer of learning.Development of the structured approach, focused on continuous improvement, is as relevant today as it was 20 years ago. This message was echoed at all ATWs and Forums. The reduction in nonproductive time and overcoming operational challenges through better planning, although well known, are still a required focus.As the industry adapts to a constantly evolving horizontal-and complex-well environment, positional accuracy and placement of the well trajectory are critical to better reservoir contact and production.One interesting conclusion was that the successful drilling of many highly challenging wells appears to have been taken for granted. However, delivering the completion phase on long-stepout wells and management of the reservoir remain challenges for the future. Horizontal and Complex-TrajectoryWells additional reading available at OnePetro: www.onepetro.org SPE JPT Greg Conran, SPE, is Drilling Advisor of Drilling and Measurements for Schlumberger. With more than 29 years' experience, he has worked globally with expertise in measurements, directional drilling, and drilling engineering specializing in extended-reach drilling. Conran has held many field positions in addition to management and technical positions as extended-reach-drilling projects manager, drilling-engineering manager, drilling-business-development manager, and head of domain for drilling engineering and optimization. He has published several SPE and industry papers on extended-reach drilling, downhole-drilling systems, and surveying. Conran has served on SPE/IADC advisory, technical, and program committees for national, Middle East, and Asia regions, and he serves on the JPT Editorial Committee. He holds a BSc Honors degree in geology from Cardiff University in Wales.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWell-collision avoidance has gained greater importance as fields become more crowded and well paths increasingly complex. The safety and financial implications of shutting in production wells on platforms or repairing damaged wells have established a need for the industry to evaluate the potential for collision with a producing well. This paper will cover three main topics related to minimizing the risk of well collisions:• Evaluating the risk • Managing the risk • Demonstrating the results of the new riskminimization process The paper will detail the processes of gathering appropriate data such as completion type, offset surveys, well pressures, casing depths, reservoir fluids and mud densities. Each well and field poses different challenges; not all data is available and wells can vary from simple vertical land wells to crowded offshore and fishbone multilateral designs.The well position uncertainties are determined by using survey error models from the Industry Steering Committee on Wellbore Survey Accuracy. This method was chosen because it is an industry-recognized standard of defining the magnitude of survey uncertainty.Recommendations for minimizing risk are based on the status and conditions of the adjacent wells and the nature and severity of the risks associated with a collision. These recommendations are formulated to minimize the risk while ensuring that production is disturbed as little as possible.
fax 01-972-952-9435. AbstractA steerable rotary drilling system (SRD system) has been used on several extended reach wells at the Wytch Farm oilfield in southern England.Recently the SRD system successfully drilled the 8½" hole section of the first well ever to have a step out of more than 10km. The record breaking well, M11SPZ/SPY, has a measured depth of 34,967ft [10,658m] and a horizontal departure of 33,181ft [10,113m]. The reservoir section required rotary drilling techniques to be used. Improvements in drilling operations and reductions in cost were made in drilling the reservoir section. This section was geosteered throughout the reservoir with the SRD system giving control of both the inclination and azimuth.The 9 5 / 8 " casing was set from surface to 28,986ft. The SRD system drilled from 29,337ft (MD) to TD at 34,967ft (MD). The SRD system drilled a total of 7,680ft in 44 days (this included a side-track for geological reasons) against the plan of 5,548ft in 49 days. This improvement against the plan was achieved largely by the elimination of the requirement to slide a steerable motor in order to steer the well. Continuous rotation of the drillstring helped reduce drillstring torque and drag and improved hole cleaning. This led to more efficient weight transfer to the bit and allowed higher average penetration rates.
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