Summary Subsurface separation criteria have evolved empirically over the years. They still are based largely on untested assumptions about safety factors, comfort values, and survey tool accuracy. A mathematical analysis of the probability of collision combined with a decision tree describing the consequences provides a method of risk evaluation. The mathematics can be simplified under certain special assumptions, allowing key features of the problem to he illustrated. A flow chart of the directional-drilling tolerance setting procedure shows how the methods described can be used in daily well-planning operations. Introduction Formal methods for planning deviated wells, determining safe interwell separations, and executing drilling programs are poorly described in the literature. Basic geometrical calculations are covered in textbooks, but the more detailed procedures for operating on multiwell platforms have evolved gradually over the years and are largely undocumented. Two approaches commonly are used to establish safe well separations. 1. A set of fixed separation guidelines is defined as a function of depth. This method has the major advantage of simplicity. The rules may be empirical or may have been derived from an analysis of survey errors. The principal difficulty with this method is that there is no way to assess whether the values are conservative. 2. Ellipses of uncertainty can be calculated and separation criteria can be based on a minimum allowable distance between ellipses. While appearing to be more "scientific," many uncertainty models are not formally validated, and the use of confidence intervals appears to be quite arbitrary. Consequently, users are again unable to assess whether the predictions are conservative. In the face of the twin pressures of safety and cost-effectiveness, neither procedure allows the planner to balance the sizes of tolerances, costs of surveying, efficiency of drilling, loss of production, and probability of collision against the consequences of a production, and probability of collision against the consequences of a collision. Therefore, there is good justification for developing Procedures that enable engineers to demonstrate the optimum Procedures that enable engineers to demonstrate the optimum operational plan when the consequences of undetected errors have been minimized. This problem has five solution components:a set of formally validated models of instrument behavior;a mathematical estimate of probability of intersection between two wells at a specified separation for a given level of survey uncertainty;a method establish maximum tolerable probability of intersection between two wells;a procedure for defining subsurface tolerances based on the intersection criteria; anda management structure for plan execution at the wellsite. The purpose of this paper is to describe a risk-analysis-based solution to the well-collision problem embodying three new ideas: a method to derive maximum tolerable intersection criteria, calculation of intersection probability between wells, and a method to integrate these solutions into the directional-well planning process. Risk Analysis The process of risk analysis involves three steps: devising an event/outcome tree, quantifying the consequences of different branches, and assessing whether the resulting risks are tolerable. Inspection of the well-intersection problem indicates that the most important considerations are fluids in the well, the flowing characteristics of the well and its pressure regime; the nature of any barriers to the blowout, such as a blowout preventer (BOP) or subsurface safety valve (SSSV); properties of the drilling well, including mud weight and fracture gradient; and probability of ignition of the blowout. The problem may be analyzed by means of an event/outcome tree (Fig. 1 and Tables 1 and 2).
As every motorist knows, a vehicle’s dashboard is an important interface that alerts the driver of real-time changes regarding certain car engine "health?? metrics and alerts the driver that the engine may need to be serviced. While not a diagnostic tool in and of itself, the dashboard serves to alert the driver that a performance or health issue may exist. Blowout Preventer (BOP) equipment is designed to secure the well and a BOP’s health is critical to ensuring that it works as designed. A realtime BOP dashboard can improve communication between operations personnel, rig contractor subsea engineers and the Original Equipment Manufacturer (OEM) to assess potential BOP health issues. This paper describes a development process for a BOP dashboard and discusses the potential benefits, challenges, and lessons learned associated with implementing a BOP monitoring system.
SPE Members @t 1=. IAMPE OtiW conhrawe. TM PKW w PWXIMCI for preeentewm al me 1S95 lACCiSPE Ofillmg cenferenca held m Amstwditrn. 2S Fe4ru&y+Aerch 2. 1S9S This WYW w sdected fu pt'esenmem by w IAOUSPE Program Cc#nmdfea fdbwmg -of mhrmdm wntmned m an~sdmntld by the author(s). The meiend, as pre5mted. 00es ncd nemswity Mecf any pcekm of me IACC u SPE. tfwr ofkem, w memters PV psunfed af IACG5PE meeorv ere s@@~~~n -by E-Cam-of the (Afx w SPE. Pwwon m UVY IS mdmaecl toantbstmct ofnotmuetian 300wxds, wstra0ns nuy d be cqxed. me *WKI should -n consw.wus dmcwk3dwM enf of wtwe and by WIWM me w IS -ted. AbstractA 'J'-shaped directional well was successfully drilled in record time without problems to total depth (TD) in the Cusiana Field in Colombia.
SPE Members Abstract While some extended reach wells appear to be drilled with comparative ease, others to deeper targets and lower departures can present all sorts of difficulties. A simple two dimensional model is present all sorts of difficulties. A simple two dimensional model is presented specifically to illustrate the interaction between the key presented specifically to illustrate the interaction between the key variables associated with an extended reach well: kick-off point, locked-in inclination, build-up rate and tortuousity. The analysis indicates that the maximum achievable drillable depth depends upon inclination and has a minimum in the region of 45-55 degrees. Maximum reach may he obtained by, wherever possible, adjusting the kick-off depth to achieve a locked-in inclination of 70-75 degrees. Drillable depth is not very sensitive to initial build-up rate. Excessive tortuousity can severely limit drillable depth and should therefore he used as an objective measure of directional drilling contractor performance. Introduction Extended reach wells are regularly drilled in a wide range of situations. However, some wells turn out to be remarkably problematic. For example, high torque loads, together with severe problematic. For example, high torque loads, together with severe drillstring and casing wear, may be encountered in a 50 degree inclination well to 13,000 ft TVD and displacement of 16,000 ft. Yet, it appears that other operators can drill to departures of 20,000 ft with little obvious difficulty. This apparent contradiction indicates that the interaction between borehole shape and drillstring mechanics may not be widely appreciated and the knowledge not applied to the planning of this class of well. planning of this class of well. In 1986 Sheppard et al proposed a theoretical explanation of why drillstring loads were sensitive to trajectory shape and showed why an under-section well should offer significant advantages from a drag and torque standpoint. However, their analysis concentrated on devising a more practical trajectory than the catenary proposed by McClendon et al. They called it the Continuous Build and focussed primarily on drag rather than torque loads. They did not explore the application of their method to the question of maximising reach. At the time they wrote their paper, they quite correctly qualified their findings by expressing concern over the contingent problems, such as borehole stability, hole cleaning and differential sticking. Recent work in these areas, combined with the extensive experience of horizontal drilling built up by the industry in the intervening years, may have allayed the worst of their fears. In particular, cuttings transport studies have shown that hole cleaning is poor in the 30-50 degree inclination range but conditions improve at higher inclinations. The purpose of this paper is to examine further the problem of torque in extended reach wells in order to resolve the apparent contradiction and provide guidelines for the design of future extended reach wells. Genesis of Torque in Deviated Wells Following Johancsik et al, numerous other authors have described the theoretical basis and application of drillstring torque-drag models. A number of case studies have specifically addressed the problems of high angle and extended reach wells. The following analysis is intended to illustrate the dependency of torque on build-up rate, locked-in inclination and borehole tortuousity. The problem is deliberately simplified so that its essential characteristics can be captured in relationships that are amenable to hand calculation (on a spreadsheet) and their interaction understood intuitively. First, assume that the borehole trajectory lies in a single vertical plane and that it consists of a vertical section to a kick-off point followed by a uniform build to a locked-in inclination which is then maintained until TD. When considering a rotating drillstring, it is assumed that the ratio of rotational to axial velocity is sufficiently high that the axial component of the friction may be neglected. Neglecting self-weight, the wall contact force per unit length in a curved section of hole is the drillstring tension divided by the locat radius of curvature. This assumption is justified by the small length of hole concerned (the end of the build-up section) and the fact that the self-weight induced reduction of the wall contact force, for representative tensions and curvatures, is only about 10%. P. 85
SPE/IADC Members Abstract This is a study of BPX Colombia's initial experience introducing under balanced drilling technology to their Piedemonte licence. The intention was to prove that a step change in performance could be achieved by application of this technology. Thus significantly reducing traditionally very high operational costs due to the faulted and over thrust nature of this developing mountain region. The occurrence of over thrust sheets which contain very hard sandstone and shale sequences have in the past proven particularly difficult to drill, slow and therefore very expensive. BPX Colombia researched the options available in this developing technique considering, proven and developing technology in order to prepare a strategy leading to the evaluation of under balanced drilling on two wells in the Piedemonte Licence. Introduction BP Exploration Colombia in the past few years has made significant discoveries in the Colombian foothills. Building upon these discoveries, exploration has successfully continued North into the Piedemonte licence (figure 1). In order to develop the Cusiana and Cupiagua fields, BPX Colombia and it's Partners conducted significant research to provide solutions to the difficult drilling problems. However even with the application of that knowledge Piedemonte wells are significantly more difficult to drill due to the more complex geology. This is characterised by high horizontal stresses, steeply dipping beds, numerous faults and alternating sand shale sequences combined with the El Morro thrust structure containing the very hard Mirador and Barco sandstone which has proven particularly difficult to drill using optimised conventional techniques. The El Morro thrust sheet is not present in the Cusiana and Cupiagua fields. Traditionally drilling the El Morro thrust sheet alone has taken upwards of 72 bits and 100 days per well. Under balanced drilling was identified as a technology which had the potential to deliver significant performance improvements, even by solely doubling the ROP which has been currently achieved. The decision was taken to investigate the potential for it on two wells which were in the planning stage. Initial planning consisted of a literature review and site visits to operations in South and Central America where various aspects of under balanced drilling operations were ongoing. In parallel with this effort all the contractors associated with BPX Colombia reviewed their own immediate in house experience in under balanced drilling. The net was then cast further to identify as much experience and technology as possible prior to determining what aspects of the technologies would be evaluated on these two wells. At a series of open meetings with all the contractors, they outlined the knowledge and technology which existed within their organisations. Each technology and technique was examined in order to identify where it could contribute towards a step change in performance in the Piedemonte licence. This identified at an early stage that only a few companies had specific knowledge in a narrow sphere, but no one company had all the experience. The air drilling Service Contractor had an overall perspective, however the Colombian Llanos foothills and specifically the Piedemonte licence was a new area to them, hence operational experience still had to be developed. It was recognised and acknowledged by BPX Colombia that the limited experience available indicated that under balanced drilling operations required a period of time to tailor it to a specific area, as experienced in other geological regions of the world. As this initial planning process progressed it confirmed the magnitude of the possible prize. It was decided to evaluate under balanced drilling techniques using Foam, Aerated Water Based Mud (WBM) and Nitrified Oil Based Mud (OBM) on two Piedemonte wells which were at the planning stage. Several options identified other than the selected under balanced drilling techniques are still being monitored or pursued by BPX Colombia in order to provide additional step changes in performance. P. 891^
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