Bearing Elements for Rotary Drag Bit Cutter Exposure Control
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Solution Overview
Problem
Rotary earth boring drag bits face issues with cutter overloading and bit balling due to excessive exposure of cutters, leading to instability and damage during drilling, especially when transitioning from harder to softer formations, and existing wear knots fail to provide consistent stability and accurate force distribution.
Innovation Solution
Incorporating bearing elements with uniform thickness behind cutters on the bit crown to reduce cutter exposure and distribute weight evenly, limiting the depth-of-cut and preventing overloading, while allowing for precise control of the bearing elements' design and placement based on formation compressive strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cutters are placed in cavities with standard cutter displacements to achieve high rates of penetration, then productivity is improved, but cutter overloading occurs leading to bit balling and instability
Solution Approach 1:
A bearing element is introduced as an intermediary component between the cutter and the formation. This bearing element has a bearing surface that contacts the formation and limits the depth-of-cut, preventing cutter overloading while allowing the cutter to maintain its aggressive exposure for high productivity. The bearing element mediates the interaction between cutter and formation to achieve both high ROP and drilling stability.
2Productivity
If cutters are exposed aggressively to increase depth-of-cut and productivity, then productivity is improved, but cutter overloading and bit balling occur
Solution Approach 1:
The cutting function is segmented into two distinct components: the cutter which provides aggressive exposure for high depth-of-cut capability, and the bearing element which limits the actual penetration depth. This segmentation allows the cutter to be positioned aggressively without causing overloading, as the bearing element controls the effective depth-of-cut by contacting the formation first.
3Productivity
If weight-on-bit is increased to improve penetration rate, then productivity is improved, but cutter overloading and tool face loss occur
Solution Approach 1:
The bearing element acts as a mediator that distributes the weight-on-bit force through its bearing surface area. By increasing the surface area in contact with the formation, the bearing element reduces the force per unit area on individual cutters, preventing cutter overloading even when high weight-on-bit is applied to maintain penetration rate.
4Reliability
If conventional wear knots are used to provide stability, then drilling stability is improved, but consistent stability and accurate force distribution are not achieved
Solution Approach 1:
The bearing element is designed with controlled parameters including bearing surface area, thickness, and material properties that can be precisely manufactured. By controlling these parameters, consistent force distribution and reliable drilling stability are achieved. The bearing surface area is specifically designed to provide adequate support while maintaining cutter exposure, and the thickness is controlled to ensure proper load distribution.
Data Source
AI summary
A bearing element for a rotary, earth boring drag bit effectively reduces an exposure of at least one adjacent cutting element by a readily predictable amount, as well as a depth-of-cut (DOC) of the cutter. The bearing element has a substantially uniform thickness across substantially an entire area thereof. The bearing element also limits the amount of unit force applied to a formation so that the formation does not fail. The bearing element may prevent damage to cutters associated therewith, as well as possibly limit problems associated with bit balling, motor stalling and related drilling difficulties. Bits including the bearing elements, molds for forming the bearing elements and portions of bodies of bits that carry the bearing elements, methods for designing and fabricating the bearing elements and bits including the same, and methods for drilling subterranean formations are also disclosed.