Using a concentric underreamer is a widely used technique for efficient wellbore construction. Most underreamers are fitted with lock-out systems to provide a means of drilling out the shoe-track with the cutters closed before enlarging the tool below casing. Several underreamers also provide a system to lock the tool closed after reaching TD to enable full flow while POOH for best possible cleaning. However, a major limitation these systems have in common is the underreamer cannot be reactivated once closed and the tool must be placed at top BHA due to the activation method. To increase reamer efficiency/BHA flexibility, a new hydro-mechanical system has been developed that makes it possible to perform multiple activation/deactivation of the underreamer by manipulating the flow rate in a short sequence allowing infinite open/close cycling for selective underreaming and more flexible placement opportunities within the BHA. The concept does not require any form of device to be pumped down the drill string. The system also increases the potential to save rig time on the activation/deactivation sequence. Through the field testing stage, it has been proven that the system works as designed under difficult drilling conditions. It delivers operator value by having the flexibility to selectively activate/deactivate and save rig time. The majority of runs have been on complex rotary steerable BHAs together with MWD/LWD systems and does not interfere with those tools’ operating range. All criteria set in the comprehensive field testing plan have been met to qualify the reamer as a viable downhole tool system. Several case studies will be presented to document successful operation of the on-demand surface controlled system with details about operator benefits including downhole flexibility, cost savings and increased safety.
Reentry wells are drilled routinely in mature fields. On some occasions, drilling the reentry well is complicated by unexpected casing wear in the motherbore or restrictions above the planned kickoff point, which might be due to junk in the hole, sagging, casing collapse, or ovality. In this paper, we present an actual case where a reentry well design was affected by such a restriction and how this challenging situation was overcome efficiently. This paper will: Present the consequences of the restriction on the reentry well design, initially planned with its 12 ¼-in. section and 9 5/8-in. liner.Describe the solution designed to pass through the restriction and deliver a reentry well design as near to the initial plan as possible, including an innovative undersized whipstock design, 10 5/8×12¼-in. hole section with a dual-reamer assembly, leaving a marginal 10 5/8-in. rathole and a little 11¾-in. rathole, and real-time near-bit directional data sent across the lower reamer.Summarize the risks and compensating measures associated with the designed solution, including shocks and vibrations leading to tool failure and trip, limited record of directional work available with such a design; i.e., a section longer than the vendor’s world record for this dual-reamer size and running 9 5/8-in. liner in the 11¾-in. rathole.Present the successful operation results obtained by using the dual-reamer assembly, fit-for-purpose directional capability, and successful casing run to total depth. This was the longest 10 5/8×12¼-in. run with a dual-reamer assembly, also known as rathole elimination assembly, performed by the vendor worldwide and the section was drilled and completed ahead of schedule and below budget.Highlight the main drivers that make this custom-made solution portable for applications in other situations. This case study demonstrates how close collaboration between the operator and wellbore departure and directional drilling vendors led to an innovative whipstock and an aggressive drillstring design delivering a proper sidetrack and a fit-for-purpose borehole in one run. This collaboration turned a challenging situation into a successful drilling operation by minimizing the effects of a potentially harmful restriction.
Hole Enlargement While Drilling (HEWD) using a concentric underreamer is a widely used technique for efficient wellbore construction. Most underreamers are fitted with lock-out systems to provide a means of drilling out the shoe-track with the cutters close before enlarging the borehole below casing. Several vendors also provide a system to lock the tool closed after reaching total depth (TD) to enable full flow while pulling out of the hole for best possible wellbore cleaning. However, most available underreamers cannot be reactivated after deactivation. Another limiting factor is that the tools must be placed on top of the Bottom Hole Assembly (BHA) due to the ball drop activation method. To solve the problem, a new system has been developed that makes it possible to perform multiple activation/deactivation of the underreamer. The most obvious advantages are infinite open/close cycles for selective underreaming and the more flexible placement opportunities within the BHA due to the activation method. Other advantages are time saving through the elimination of several runs, shorter activation time and higher flow rate capabilities. Several successful tests in realistic drilling environments were performed prior to starting the field testing program. Through the field testing stage the system has performed as planned under normal drilling conditions and has a significant cost saving potential for the operator. The authors will discuss the application challenges, benefits, features and engineering efforts including field testing, that led to a commercial Ream on Demand (ROD) system.
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