Turbine Driven Reaming Bit Torque Fluctuation Control
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Solution Overview
Problem
High-speed, low-torque turbines or motors attached to casing or liner strings experience inconsistent performance and torque fluctuations when used with conventional reaming bits, leading to stalling and unreliable reaming results due to the limited torque capacity and unpredictable weight-on-bit variations in heterogeneous formations.
Innovation Solution
A reaming bit design featuring an arcuate profile from the gage dimension to the nose with a profile length to bit size ratio under 0.75, asymmetrical blade spacing, blades extending into a concave cone section, and additional features like smooth spiraled gage pads and protrusions to control depth of cut and stabilize the bit at high speeds, reducing torque fluctuations and enhancing drilling efficiency in obstructed or tortuous boreholes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional reaming bits are used with high-speed turbines, then rotational speed increases, but torque capacity decreases causing stalling and unreliable performance
Solution Approach 1:
The patent modifies the reaming bit profile parameters, specifically reducing the profile length to bit size ratio to less than 0.75 and changing the taper angle to greater than 30 degrees. These parameter changes optimize the bit for high-speed operation by reducing mechanical advantage, which prevents stalling and improves reliability when used with high-speed turbines
Solution Approach 2:
The patent employs asymmetrical blade spacing where blades are not uniformly distributed around the bit circumference. This asymmetric configuration reduces torsional vibrations and torque fluctuations during rotation, allowing the bit to maintain stable operation at high speeds without stalling, thereby improving performance reliability
2Force
If conventional reaming bits with long tapered sections are used, then mechanical advantage increases for cutting, but torque fluctuations increase due to unpredictable weight-on-bit variations
Solution Approach 1:
The patent changes the critical profile parameters by reducing the profile length to bit size ratio to less than 0.75 and increasing the taper angle to greater than 30 degrees. These modifications reduce the mechanical advantage of the bit, which directly decreases torque fluctuations and weight-on-bit variations, resulting in more stable torque delivery while maintaining adequate cutting capability
Solution Approach 2:
The asymmetrical blade spacing configuration distributes cutting forces more evenly throughout the rotation cycle, preventing the concentrated loading that causes torque fluctuations. This asymmetric design smooths out the weight-on-bit variations and reduces torsional vibrations, improving torque stability without sacrificing cutting effectiveness
3Force
If reaming bits are designed for high torque capacity, then cutting capability improves, but compatibility with low-torque turbines is reduced causing stalling
Solution Approach 1:
The patent optimizes the profile parameters by reducing the profile length to bit size ratio to less than 0.75 and increasing the taper angle to greater than 30 degrees. These changes reduce the bit's torque requirements, making it compatible with low-torque turbines while still providing adequate cutting capability through optimized blade geometry and asymmetric spacing
Solution Approach 2:
The asymmetrical blade spacing reduces the peak torque demands on the drive system by distributing cutting loads more evenly during rotation. This asymmetric configuration allows the bit to operate reliably with low-torque turbines at high speeds, improving adaptability to different drive systems while maintaining cutting effectiveness
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design significantly reduces torque fluctuations and stalling, enabling reliable and efficient reaming at high speeds by minimizing mechanical advantage and stabilizing the bit, even in challenging formations, and ensuring continuous drilling through obstructions.
Implementation Method 1
More recent projects use a hollow turbine or motor at the leading end of the casing string which are driven by drilling fluid pumped from the surface
Implementation Method 2
The mechanical advantage is proportional to 1/tan α and therefore is quite significant for smaller angles. This is desirable in applications where it is difficult to deliver sufficient WOB to advance the reamer but becomes the source of high torsional oscillations in applications where WOB control is difficult or erratic
Implementation Method 3
The reaming tool further comprises a cutting structure for enlarging, also termed 'reaming,' of a bore hole through contact with the side wall thereof
Data Source
AI summary
A reaming bit designed to operate with low torque fluctuation when driven with a turbine at speeds in the order of 300-600 RPM and above features a profile that is arcuate from the gauge dimension to the nose area or alternatively has a blunt straight taper section but with a ratio of profile length (PL) to bit size (BS) of under 0.75. The blades extend into a concave cone and the cutting structure continues along the blades towards the center. The blades have a step near the gauge section to increase the exposure of the blade cutting structure. An array of protrusions are disposed parallel to and behind the cutting structure to increase high speed stability and adjacent the blade step transition to protect outer casing on run in.