Hybrid Ovoid Cutting Elements for Rotary Drag Bit Stability
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Solution Overview
Problem
Rotary drag bits with PDC cutting elements face issues of overloading and aggressiveness, particularly in formations with varying compressive strengths, leading to torque fluctuations, stick-slip, and potential damage to the bit and cutting elements, especially when drilling through interbedded formations.
Innovation Solution
The use of hybrid ovoids with a cylindrical base and domed upper portion, featuring a planar cutting surface extending through 180°, mounted axially on the bit blades to control depth of cut and reduce aggressiveness, providing a shear-type cutting action and core out protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If aggressive cutting structures with high torque to WOB ratio are employed to achieve high ROP, then productivity is improved, but the cutting elements become overloaded and suffer damage
Solution Approach 1:
The patent changes the geometric parameters of cutting elements by providing a range of exposure heights (0.010 to 0.040 inches) and different configurations (blade-mounted vs. crown-mounted). This parameter adjustment allows optimization of the torque to WOB ratio to achieve high ROP while preventing cutter overload and damage in varying formation conditions
Solution Approach 2:
The patent implements dynamic adjustment capabilities through interchangeable cutting elements with different exposure heights and configurations. This allows the drilling system to adapt to varying formation conditions, maintaining optimal cutting aggressiveness while preventing overload during transitions between hard and soft formations
2Productivity
If high exposure cutting elements are used to increase depth of cut and ROP, then productivity is improved, but the bits become more aggressive and cause torque fluctuations and stick-slip
Solution Approach 1:
The patent provides specific exposure height parameters (0.010 to 0.040 inches) and different mounting configurations that can be selected based on formation conditions. This parameter control allows maintaining stable drilling operations while achieving high ROP by preventing excessive aggressiveness that causes stick-slip and torque fluctuations
Solution Approach 2:
The interchangeable cutting element system allows dynamic adjustment of exposure heights and configurations during drilling operations. This enables adaptation to varying formation conditions, maintaining operational stability while preventing the stick-slip phenomenon associated with overly aggressive cutting elements
3Productivity
If PDC cutting elements drill into softer formation material without changing WOB, then penetration and ROP increase, but torque increases substantially causing damage and operational interruptions
Solution Approach 1:
The patent implements preliminary action by providing depth of cut control features and using cutting elements with controlled exposure heights before drilling into softer formations. This prevents excessive penetration and torque spikes when transitioning from hard to soft formations, avoiding cutter overload and operational interruptions
Solution Approach 2:
The patent applies preliminary anti-action through depth of cut control features and controlled exposure heights that counteract the tendency for excessive penetration into softer formations. This preemptive control prevents torque fluctuations and potential damage before they occur during formation transitions
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
This design enhances bit control and durability by maintaining stable weight-on-bit across formation transitions, reducing torque fluctuations, and preventing core outs, while allowing for efficient cutting in both hard and soft formations.
Implementation Method 1
an at least substantially planar cutting surface formed in at least the domed upper portion and defining a cutting edge extending angularly through an angle of at least 180°, the at least substantially planar cutting surface configured for a shear-type cutting action, oriented substantially in the direction of intended bit rotation
Data Source
AI summary
An earth-boring tool includes a body, at least one blade extending axially from the body, at least one cutting element mounted at a leading face of the at least one blade and at least one hybrid ovoid mounted at an axial end of the at least one blade and rotationally trailing the at least one cutting element. The at least one hybrid ovoid includes a cylindrical base portion, a domed upper portion extending from a top of the cylindrical base portion, and an at least substantially planar cutting surface formed in at least the domed upper portion and defining a cutting edge extending angularly through an angle of at least 180°, the at least substantially planar cutting surface is configured for a shear-type cutting action, oriented substantially in the direction of intended bit rotation, and exhibits a lesser aggressiveness than the aggressiveness of the at least one cutting element.