Minimizing the Risk of Well Collisions in Land and Offshore Drilling

Abstract

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.

The Risk of Using Risk Matrices

“…Rather than refer to expected downside consequence as "risk," we will use the more precise term expected loss (EL). Pritchard et al (2010) gave an example of using RMs to assess the risk of a drilling hazard. This paper was one of three in a special issue of World Oil devoted to advances in drilling.…”

“…This paper was one of three in a special issue of World Oil devoted to advances in drilling. Pritchard et al (2010) note the example as a "typical industry risk assessment matrix." We have adopted this example as Fig.…”

“…The problem context presented in Pritchard et al (2010) is the loss of fluid during drilling in a particular section of a well. There is a need to identify the possible outcomes and consequences arising from this event and to prioritize these risks.…”

Development of Static Magnetic Detection Anti-Collision System While Drilling

“…Benny Poedjono and his colleagues [3,4] proposed the concept of oriented separation factor and the calculating method of oriented separation factor. However, these methods cannot prevent the accumulated error in well trajectory calculation and thus fail to meet the actual needs of cluster well drilling engineering.…”

Application of Spatial Analytic Geometry in the Calculation of Adjacent Well Separation Factors

“…For the past few years, the foreign drilling circles have proposed many explanations for separation factors, among which the one obtained by pedal curve method has been widely applied [8]. In 2009, Benny Poedjono raised the new concept of oriented separation factor (OSF) and presented method for calculating the oriented separation factor [9][10][11].…”