Rotary Steerable Drill String with Closed-Center Bit
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Solution Overview
Problem
Current rotary steerable drill strings for directional drilling face challenges in efficiently creating and controlling underpressure in specific azimuthal segments of a borehole, which affects the trajectory of the drilled path.
Innovation Solution
A rotary steerable drill string design featuring a drill bit with a fully closed center and converging junk slots to enhance drilling fluid flow velocity, directing fluid preferentially into preselected azimuthal segments, and a flow diverter that maintains drilling fluid flow in a geostationary configuration to create localized underpressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If drilling fluid is diverted into a selected azimuthal segment to create underpressure for directional drilling, then the borehole trajectory can be controlled, but the underpressure effect is insufficient to achieve precise steering control
Solution Approach 1:
The drill bit design features a closed center region that concentrates drilling fluid flow into specific azimuthal segments rather than distributing it uniformly. This localized flow concentration creates pronounced underpressure in targeted segments, enabling precise directional control. The junk slots are strategically positioned and sized to control fluid distribution patterns, ensuring that underpressure is generated exactly where needed for steering.
Solution Approach 2:
The patent modifies the physical parameters of the drill bit structure, specifically implementing a closed center design and varying junk slot dimensions. These parameter changes affect the drilling fluid flow dynamics, increasing flow velocity in selected azimuthal segments and enhancing the underpressure effect. The closed center configuration changes the flow distribution pattern from uniform to concentrated, directly improving the steering force magnitude.
2Quantity of substance
If a conventional open-center drill bit is used, then drilling fluid flows freely through the center, but underpressure cannot be effectively concentrated in specific azimuthal segments
Solution Approach 1:
The closed-center drill bit design creates distinct flow zones: a closed center region that restricts fluid flow and azimuthal segments with junk slots that control fluid ejection. This local differentiation allows drilling fluid to be concentrated and directed into specific azimuthal segments, creating the necessary underpressure for effective trajectory steering control.
Solution Approach 2:
The junk slots act as intermediary structures that mediate between the closed center and the external formation. These slots control the transition of drilling fluid from the high-pressure closed center region into the azimuthal segments, enabling precise regulation of fluid flow concentration and underpressure generation in targeted directions.
3Force
If drilling fluid flow velocity is increased to enhance underpressure effect, then steering force improves, but energy consumption and fluid requirements increase
Solution Approach 1:
The closed-center design with controlled junk slots creates localized high-velocity flow zones only in the azimuthal segments where steering is needed, rather than increasing flow velocity throughout the entire drill bit. This localized approach enhances steering force while minimizing overall energy consumption, as energy is concentrated only where it produces useful steering effect.
Solution Approach 2:
The patent optimizes the parameters of the junk slots (size, position, orientation) to maximize flow velocity in specific azimuthal segments while maintaining efficient overall fluid circulation. By carefully controlling the geometric parameters of the flow path, the system achieves high steering force with minimal additional energy input, as the closed center configuration naturally channels fluid through the most efficient paths.
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 achieves a more pronounced underpressure in targeted segments, allowing for precise control over the borehole trajectory and increased steering forces, enabling efficient directional drilling with tailored build rates.
Implementation Method 1
a flow diverter configured in a lower end of the drill string in the drilling fluid passage, which flow diverter is configured rotatable about the drill string longitudinal axis relative to the drill string, to preferentially direct the drilling fluid from the drilling fluid passage into an azimuth segment which is stationary relative to the flow diverter
Implementation Method 2
at least one junk slot is provided on the barrel surface to provide a flow channel having an effective aperture for upward flow of drilling fluid that has been expelled from the at least one nozzle, which effective aperture decreases along the upward flow direction of the drilling fluid
Implementation Method 3
a drill string rotates in an azimuthal direction about a drill string longitudinal axis... The flow diverter can direct the drilling fluid from the drilling fluid passage into an azimuth segment which is stationary relative to the flow diverter
Implementation Method 4
This creates an underpressure resulting in a curve in the trajectory of the borehole being drilled
Data Source
AI summary
A rotary steerable drill string (16) employs a drill bit (10) selected to positively contribute to underpressure in a preselected azimuthal segment of the borehole relative to an opposing azimuthal section. Generally, a high flow velocity of drilling fluid in the selected azimuthal segment relative to in other segments will result in a more pronounced underpressure in the selected azimuthal segment. Drill bit designs which locally enhance the drilling fluid flow velocity are proposed to be employed in the present rotary steerable drill string.