Automated Wireline Milling System
Abstract: An automated wireline milling solution targeted for removal of wellbore obstructions of a varying type, from scale to metal, with built-in capabilities of autonomous cruise navigation between consecutive obstacles, is presented. This paper highlights design features that made a step change in the efficiency and usability of milling services. Control challenges are still common in downhole milling technology. Changes in milling target composition, cuttings accumulation around the target, drag for… Show more
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Cited by 9 publications
References 8 publications
Coiled tubing (CT) milling of downhole plugs in large monobore completions is considered one of the most challenging CT workover operations, especially when conducted in offshore environments where intervention workflows are driven by efficiency gains for operators and service companies alike. Experience gained from milling operations using CT instrumented with real-time data enabled measurable improvements in efficiency. Post-job data analysis offered additional insights to improve methodologies and further unleash untapped efficiencies. Real-time bottomhole assembly data were collected during plug milling operations using a positive displacement motor. Critical downhole readings, such as CT internal and annular pressure, axial force (thrust), and torque were monitored during the operation to identify tagging of isolation plug targets, onset of milling, and stalls. The real-time data not only added confidence to event confirmation, but also increased the accuracy in estimating efficiency metrics such as rate of penetration (ROP) and stall recovery duration. Post-job analysis calculated the error and shortcomings associated with estimating event detection based on surface measurements. Additionally, error in event detection was tied back to inaccuracies in estimating efficiency metrics when relying on surface measurements alone. Analysis of downhole measurements in CT milling improves the precision of event detection and enables rapid reactions. Target tagging reflects instantly in thrust, and motor activation reflects synchronously in downhole differential pressures and torque, which together provide certainty of motor engagement on the target. Stalls reflect in differential pressure and torque spikes that coincide with motor specifications. ROP more than doubled by leveraging these event detection techniques throughout milling operations. New torque-thrust signatures were also identified to detect material interfaces. Changes in signature behavior indicated when the bit milled through one target and reached the next. This is particularly useful when the operator must mill through a target but stop at a subsequent, contiguous one. Post-job data also suggested that some events may have been mistaken as stalls during the operation, with downhole data confirming they were false positives. Finally, at operating conditions in the case study, a 7-second lead-time window was identified to anticipate and react to stalls. This highlights the importance of access to real-time downhole information, such as differential pressure, to avoid both stalls and false positives, and ultimately, to make breakthroughs in operational efficiency. Integrated analysis of downhole measurements during CT milling lent visibility to actual ROP, stall rates, and stall recoveries. These constitute important baselines against which any improvement in efficiency must be compared. The methodologies proposed here for event detection, with special attention to stall anticipation and milling interface detection, pave the way for smarter, more efficient operations.
Coiled tubing (CT) milling of downhole plugs in large monobore completions is considered one of the most challenging CT workover operations, especially when conducted in offshore environments where intervention workflows are driven by efficiency gains for operators and service companies alike. Experience gained from milling operations using CT instrumented with real-time data enabled measurable improvements in efficiency. Post-job data analysis offered additional insights to improve methodologies and further unleash untapped efficiencies. Real-time bottomhole assembly data were collected during plug milling operations using a positive displacement motor. Critical downhole readings, such as CT internal and annular pressure, axial force (thrust), and torque were monitored during the operation to identify tagging of isolation plug targets, onset of milling, and stalls. The real-time data not only added confidence to event confirmation, but also increased the accuracy in estimating efficiency metrics such as rate of penetration (ROP) and stall recovery duration. Post-job analysis calculated the error and shortcomings associated with estimating event detection based on surface measurements. Additionally, error in event detection was tied back to inaccuracies in estimating efficiency metrics when relying on surface measurements alone. Analysis of downhole measurements in CT milling improves the precision of event detection and enables rapid reactions. Target tagging reflects instantly in thrust, and motor activation reflects synchronously in downhole differential pressures and torque, which together provide certainty of motor engagement on the target. Stalls reflect in differential pressure and torque spikes that coincide with motor specifications. ROP more than doubled by leveraging these event detection techniques throughout milling operations. New torque-thrust signatures were also identified to detect material interfaces. Changes in signature behavior indicated when the bit milled through one target and reached the next. This is particularly useful when the operator must mill through a target but stop at a subsequent, contiguous one. Post-job data also suggested that some events may have been mistaken as stalls during the operation, with downhole data confirming they were false positives. Finally, at operating conditions in the case study, a 7-second lead-time window was identified to anticipate and react to stalls. This highlights the importance of access to real-time downhole information, such as differential pressure, to avoid both stalls and false positives, and ultimately, to make breakthroughs in operational efficiency. Integrated analysis of downhole measurements during CT milling lent visibility to actual ROP, stall rates, and stall recoveries. These constitute important baselines against which any improvement in efficiency must be compared. The methodologies proposed here for event detection, with special attention to stall anticipation and milling interface detection, pave the way for smarter, more efficient operations.
A new downhole machining system has been developed for lightweight intervention applications to remove wellbore obstructions and stuck valves, combining the precision of real-time bit position measurement with the power of push-pull forces up to 40,000 lbf. This tool builds on existing hardware from proven milling and shifting services, with added software features for advanced automation and control. This paper describes the new machining system and benefits for the operator to enable a reliable and robust contingency machining service. Conventional wireline milling tools use a tractor tool for weight-on-bit and torque reaction. These tractor-based milling systems can be efficient for removing obstructions over a long interval, but they are not ideal for milling hard metal targets. For example, a nipple milling operation might require many hours to mill, during which time the operator has no indication that the milling operation is progressing as planned since the tractor does not provide any measurement of milling progress. The new machining system provides the operator with a real-time measurement of milling progress with resolution down to 1/100-in. to quickly diagnose and correct any problems due to bit damage, engagement with the target, or cuttings accumulation. For known targets of multiple materials or interrupted geometry, or for bits with staged cutting features, the direct measurement of bit position enables automatic machining programs that can autonomously execute a predefined sequence of cutting parameters (weight, speed, and torque) that change with measured bit position. The machining progress and quality indicators are displayed in real time at surface using a graphic interface showing the machining target and current bit position. The machining tool uses the same anchor and linear actuator modules from wireline shifting service tools, combined with the same rotary motor and gearing modules from wireline milling service tools. Torque from the bit is transferred across the linear actuator module using a sleeve that is keyed above and below the piston. Both the linear actuator hydraulic motor and the rotary motor are equipped with rotor position and torque feedback and powered by a downhole inverter for maximum power efficiency, precise control of hydraulic pressure and bit position, and reverse operation for stall prevention and recovery. Test data are shared in this paper to compare the performance of the new machining tool with a high-performing tractor-based milling service tool. Examples are given for both isolation valve machining and nipple machining.
Wireline Tractor System with User Programmable Behaviors for Semi-Autonomous Restriction Navigation
A semi-autonomous wireline tractor solution for casedhole applications enabling navigation through complex restrictions with minimal operator interaction in absence of digital telemetry is presented. The robotic conveyance technology provides a foundation for applications where programming of tractoring behaviors is available to field personnel as a part of the job design. Digital telemetry may not be available for wireline tractor tools. A conveyance system with programmable behaviors allows downhole navigation when conventional telemetry is nonexistent or has prohibitively low bandwidth or a protocol conflict, which is relevant in configurations with third-party tools. The presented control technology utilizes downhole on-board measurements with tracking and decoding of head voltage waveforms where electrical power is supplied by the surface system. Voltage is set by an operator to fall into one of several predefined bands representing specific tool commands that trigger a set of robotic sequences. The logging cable can be freed to carry a high-frequency communication signal to payload tools while powering both the tractor and its payload. Although the tractor does not have feedback through its telemetry data, tractor operational condition can be derived from the variations of electrical current measured at surface. A head voltage stabilization system along with a load calibration method compensates voltage fluctuations due to load changes and losses in the logging cable. An advanced signal-processing algorithm implemented in downhole embedded software quantizes denoised voltage and reliably maps it to operational bands, effectively eliminating transient processes resulting from high-power jobs. The voltage estimation technique supports a finite set of commands to be interpreted by the downhole tools and to activate control logic implemented as scripted state machines with a core based on the deterministic finite automaton concept. Behaviors scripted and parametrized by an operator in custom metalanguage use a dictionary of actions and conditions provided by the embedded software that runs the tools. Controllers may be designed and put into action by nonprogrammers to solve restriction navigation needs for a known well completion. The availability of design and simulation software aids job planning. Multiple tractor configurations with individually controlled arms were successfully tested at locations in the USA and Eurasia, with and without third-party tools with their own telemetry. Reliable restriction navigation using preprogrammed behaviors controlled by voltage levels has been demonstrated. The design opens development opportunities for other semi-autonomous downhole applications. Run-time pattern recognition of electrical current in the software enables further automation of the surface power system to drive the downhole navigation, detect and respond to anomalies, and reliably manipulate voltage transitions. The presented technology removes the compatibility barrier between different telemetry systems and elevates flexibility of systems lacking telemetry while preserving their usability and robustness.
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