Fully-Rotating Rotary Steerable and Concentric Reamers Technology Combination Eliminate Wellbore Threading in Deepwater
Abstract: Improving hole quality is a major factor for accurate formation evaluation and reduced well construction costs in deepwater. Further optimization of the borehole quality using new generation drilling assemblies is now possible. Not only to improve formation evaluation, increase penetration rates, and reduce the risk of drill string failure, but also to reduce the load points of salt formations on completions. Concurrent drilling and reaming techniques have been successfully used to mitigate the effect of non-u… Show more
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Cited by 6 publications
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Detailed analysis of downhole weight-on-bit, torque, bending moment and vibration signals measured between bit and hole opener have provided clear insight into the dynamic response of hole opening BHAs in interbedded formations. Based on transmitted real-time information from an advanced downhole multi-sensor data acquisition and processing system, application-specific drilling procedures and guidelines have been developed to avoid or to identify and overcome critical dynamic situations downhole. Applying the new procedures, several hole sections in the GOM were drilled for the first time in one run from casing shoe to casing shoe. Here previous attempts had resulted in failures of the drilling equipment or even in twist-offs. The paper starts with a list of observations made with the downhole multi-sensor tool placed between bit and hole opening device. Log examples with downhole and surface drilling data demonstrate the dynamic response of hole opening BHAs. For the first time, the paper presents downhole measurements showing the changes in weight on bit versus weight on reamer when drilling interbedded formations. Again, log examples are used to document the effect of the drilling procedures that were applied to successfully resolve critical downhole situations. The paper concludes with a summary of the lessons learned in planning and executing hole opening applications with shoe to shoe performance. Introduction Driven by a variety of technical and economic reasons, more and more drilling programs include hole enlargement operations while drilling. In deepwater applications, the ability to enlarge the hole below the last casing shoe allows for tighter tolerance intermediate casings to be run. Figure 1 shows a typically deepwater casing and drilling program, where the intermediate casing strings are instrumental to reach the reservoir with an economically viable production string size. In other applications, hole opening or underreaming techniques are applied to address ECD limitations or to deal with swelling shale or salt formations. Earlier, hole enlargement operations were carried out by first drilling a pilot hole through the interval of interest and then opening it up with a second pass. Today, several enlargement options while drilling are available to eliminate the second pass: Bicenter PDC bits, eccentric reaming-whiledrilling (RWD) or concentric reaming devices1–10. In particular references 3, 9 and 10 discuss at some length the benefits and limitations of the three options for various applications with respect to dynamic stability, reliability, steerability and hole quality. Over the past years, the concentric reaming devices have gained significant market share, in particular in rotary steerable (RSS) applications. Concentric reamers include expandable arms, ribs or blocks, which are mechanically or hydraulically activated, after passing e.g. the last casing shoe8,9. All examples except one presented in this paper feature concentric reaming devices. In general, drilling with a reaming device in the bottom hole assembly (BHA) with the associated lack of stabilization in the BHA in the enlarged borehole above the reamer significantly increases the risk of the drilling operation. In particular, dangerous backward whirl situations with high lateral vibrations can develop and result in failures of BHA components, and subsequently in costly trips or even more costly fishing operations. Several deepwater projects in the GOM suffered significant cost overruns as a result of vibration problems during hole enlargement operations while drilling. In some cases in the GOM and other areas, operators decided to go back to a second run for the hole enlargement operation.
Detailed analysis of downhole weight-on-bit, torque, bending moment and vibration signals measured between bit and hole opener have provided clear insight into the dynamic response of hole opening BHAs in interbedded formations. Based on transmitted real-time information from an advanced downhole multi-sensor data acquisition and processing system, application-specific drilling procedures and guidelines have been developed to avoid or to identify and overcome critical dynamic situations downhole. Applying the new procedures, several hole sections in the GOM were drilled for the first time in one run from casing shoe to casing shoe. Here previous attempts had resulted in failures of the drilling equipment or even in twist-offs. The paper starts with a list of observations made with the downhole multi-sensor tool placed between bit and hole opening device. Log examples with downhole and surface drilling data demonstrate the dynamic response of hole opening BHAs. For the first time, the paper presents downhole measurements showing the changes in weight on bit versus weight on reamer when drilling interbedded formations. Again, log examples are used to document the effect of the drilling procedures that were applied to successfully resolve critical downhole situations. The paper concludes with a summary of the lessons learned in planning and executing hole opening applications with shoe to shoe performance. Introduction Driven by a variety of technical and economic reasons, more and more drilling programs include hole enlargement operations while drilling. In deepwater applications, the ability to enlarge the hole below the last casing shoe allows for tighter tolerance intermediate casings to be run. Figure 1 shows a typically deepwater casing and drilling program, where the intermediate casing strings are instrumental to reach the reservoir with an economically viable production string size. In other applications, hole opening or underreaming techniques are applied to address ECD limitations or to deal with swelling shale or salt formations. Earlier, hole enlargement operations were carried out by first drilling a pilot hole through the interval of interest and then opening it up with a second pass. Today, several enlargement options while drilling are available to eliminate the second pass: Bicenter PDC bits, eccentric reaming-whiledrilling (RWD) or concentric reaming devices1–10. In particular references 3, 9 and 10 discuss at some length the benefits and limitations of the three options for various applications with respect to dynamic stability, reliability, steerability and hole quality. Over the past years, the concentric reaming devices have gained significant market share, in particular in rotary steerable (RSS) applications. Concentric reamers include expandable arms, ribs or blocks, which are mechanically or hydraulically activated, after passing e.g. the last casing shoe8,9. All examples except one presented in this paper feature concentric reaming devices. In general, drilling with a reaming device in the bottom hole assembly (BHA) with the associated lack of stabilization in the BHA in the enlarged borehole above the reamer significantly increases the risk of the drilling operation. In particular, dangerous backward whirl situations with high lateral vibrations can develop and result in failures of BHA components, and subsequently in costly trips or even more costly fishing operations. Several deepwater projects in the GOM suffered significant cost overruns as a result of vibration problems during hole enlargement operations while drilling. In some cases in the GOM and other areas, operators decided to go back to a second run for the hole enlargement operation.
Concurrent rotary-steerable directional drilling and hole enlargement utilizing concentric underreamers is becoming more commonplace. Significant cost savings can be obtained enlarging the hole while drilling with a rotary-steerable system (RSS) as opposed to using a designated hole-opener run after the pilot has been drilled. However, RSS underreamer assemblies are often challenged with BHA instability, excessive vibration and stick-slip problems when the two different cutting structures (bit and underreamer) interact with significantly different formations. This paper describes case histories of directional wells that have been drilled with both point-the-bit and push-the-bit RSS underreamer assemblies in the North Sea, Mediterranean Sea and Nile Delta (Egypt). In particular, RSS underreamer assemblies opening from 13" to as large as 17 ½", using 12 ¼" pilot holes will be discussed. A unique sensor system, integrated into this specific RSS provides measurements of near-bit borehole caliper, stick-slip and vibration. While drilling, borehole quality and downhole vibrations were monitored in real-time at the rig site and from a remote operating center. The real-time data was used to optimize drilling parameters and provide enhanced performance from the RSS underreamer assembly. The RSS solution to simultaneous wellbore enlargement has been analyzed in terms of vibration, efficiency, performance, directional objectives and cost. The physical components, operational aspects and limitations of RSS underreamer technology will be discussed. The combination of a specific RSS and underreamer with a balanced cutting structure has resulted in excellent ROP and directional control, while reducing reaming-related vibration and potential failures. Further, an automated directional drilling feature and real-time drilling process monitor have enabled optimum directional drilling performance. Introduction Hole enlargement while drilling using RSS and underreamers is becoming widely accepted on directional projects worldwide. Conventionally, steerable motors with bi-center bits were the only practical option for directional hole enlargement where casing pass-through was a restriction. Today, BHAs utilizing a combination of RSS and underreamers are commonly used on wells that require directional hole enlargement. Slim well casing programs, casing whipstocks or re-drilling around a fish all commonly use RSS underreamer technology. Common problems associated with bi-center bits are: poor directional control, inconsistent directional results in soft formations, low ROP, excessive vibration, and irregular and/or spiraled holes1–3. All these problems lead to the need for an alternative method of hole enlargement, with the ability to enlarge the hole beyond the size of existing casing. The RSS underreamer BHA has become the obvious solution to this problem.
Multi-Diameter String Tools Deliver Lower Cost-Per-Foot in Demanding Rotary Steerable Applications
The use of hole opening tools in conjunction with Rotary Steerable Systems (RSS) has increased dramatically in the past few years. Although excellent performance has been delivered with the mainstream commercial tools, alternate options have been developed to enable an RSS to drill the pilot hole in conjunction with a string tool to open the hole in a single run. The most popular current option involves a weight or hydraulic activated underreamer. However, fixed blade, multi-diameter reaming tools have recently been developed for use within Rotary Steerable (RS) assemblies:An eccentric string reamer that will pass through a small pilot hole but then drill and produce a larger hole. This provides a significantly lower-cost hole opening option.A concentric string reamer that utilizes a tapered design incorporating a mid and main reamer section. This innovative design uses a mid-reamer that enlarges the pilot hole to an intermediate size and stabilizes the main reamer above it on its gauge pads. Because of its unique design, the mid reamer is able to stabilize the tool even if the pilot hole is of poor quality or is overgauge. This is particularly beneficial with RS tools in soft formations, leading to improved borehole quality and BHA stabilization. It also enables the use of smaller RS tools, thus providing greater directional potential. Additionally, a single RSS can be used to drill multiple hole size intervals, minimizing BHA changes, which in turn increases rig floor safety and lowers costs. Several distinct applications are documented where these fixed bladed solutions, in combination with both Push and Point RS tools, have proven extremely successful. This has provided greater flexibility with regard to tool selection and well planning options, delivering lower cost per foot in RS projects. Case studies are presented from the Far East, Norway, and the Gulf of Mexico. Introduction Hole opening tools fall into two main categories; Eccentric and Concentric. Eccentric reamers are fixed reamers that are dominated by bicenter drill bits or 'wing-like' string reamer tools using PDC cutters. They are developed for applications where hole enlargement is required but the tool has to pass through a smaller diameter restriction than the required final hole size. The concentric tools are more diverse and consist of fixed designs such as concentric drill bits and string tools (that could be either PDC or roller cone cutting structures), to more complex tools that open on demand by either mechanical or hydraulic control. The growth in the use of hole opening devices over the last few years was driven predominantly by the growth of deepwater drilling. The lessons learned from innovations in the deepwater have extended those applications to shallower waters and even to selected land wells. Hole opening while drilling devices have enabled operators to set larger strings of casing deeper in holes where hole stability, lost circulation and high-pressure zones are a constant problem. This has the obvious advantage of eliminating trips while leaving sections of open-hole exposed over shorter durations, as well as providing a larger annulus for better cement jobs. The ability to reach extremely deep reservoirs with 12 1/4", 10–5/8", and 8 ½" well bores enables operators to run larger and more complex production strings, and this in turn has had an enormous impact on exploration and production economics.
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