Annular Flow Restrictor for Drilling BHA Pressure Control
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Solution Overview
Problem
In directional drilling, especially in Motor-Assisted Rotary Steerable Systems (MARSS), the radial bearing wear causes excessive leakage of drilling fluid, leading to insufficient hydraulic pressure for steering the drill bit and potential erosion issues.
Innovation Solution
The implementation of an annular flow restrictor within the bearing assembly, which uses an annular gap to control the bypass flow of drilling fluid, thereby maintaining sufficient hydraulic pressure and reducing erosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radial bearing gaps are used to control mud flow leakage, then initial flow restriction is achieved, but flow restriction degrades over time due to bearing wear
Solution Approach 1:
The flow control function is segmented into two independent components: radial bearings for mechanical support and an annular flow restrictor for fluid control. This separation ensures that bearing wear does not affect flow restriction, as the restrictor is a dedicated component with a fixed annular gap that maintains consistent flow control throughout the bearing's service life.
Solution Approach 2:
The annular flow restrictor acts as an intermediary element between the driveshaft bore and the annulus. It provides a controlled pathway for drilling fluid bypass flow, maintaining a consistent annular gap that restricts flow independently of bearing condition. This intermediary component decouples the flow control function from the mechanical support function.
2Reliability
If bypass flow rate is increased to lubricate bearings, then bearing lubrication is improved, but drilling fluid loss to annulus increases
Solution Approach 1:
The annular gap dimensions of the flow restrictor are carefully designed to control the bypass flow rate within an optimal range. This parameter optimization ensures sufficient flow for bearing lubrication while minimizing excessive fluid loss to the annulus. The restrictor maintains this optimized flow rate consistently throughout operation.
Solution Approach 2:
The flow restrictor creates a localized flow control zone with a specific annular gap geometry. This localized restriction ensures that bypass flow remains controlled at the bearing section, providing adequate lubrication without allowing excessive flow to escape to the annulus. The local quality of the restrictor's annular gap provides precise flow management.
3Reliability
If choke is used to control bypass flow, then radial bearing wear issue is solved, but metal-to-metal face seal degrades due to abrasion and high pressure
Solution Approach 1:
The flow control function is extracted from the choke assembly with its metal-to-metal face seal and placed into a dedicated annular flow restrictor. This extraction eliminates the harmful metal-to-metal sealing interface that was subject to abrasion degradation from high-velocity bypass flow and high pressure. The annular restrictor uses a non-contacting gap between rotating and stationary components, avoiding seal degradation entirely.
Solution Approach 2:
The mechanical face seal system is replaced with a fluid dynamic flow restriction system. Instead of using a metal-to-metal choke seal to control bypass flow, the invention uses an annular gap flow restrictor that controls flow through viscous effects and pressure gradient in the annular space. This substitution eliminates the mechanical contact and associated wear problems.
4Ease of manufacture
If material options are limited for high pressure/volume loading, then manufacturing is simplified, but flow control reliability deteriorates
Solution Approach 1:
The annular flow restrictor employs composite construction combining a rotating inner component attached to the driveshaft with a stationary outer component. This composite structure distributes high pressure and velocity loads across different materials and components, with each optimized for its specific loading conditions. The composite design enhances reliability under high PV loading while maintaining manufacturability.
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 annular flow restrictor effectively controls the bypass flow, ensuring consistent hydraulic pressure for steering the drill bit and reducing the risk of erosion, thus enhancing the reliability and efficiency of directional drilling operations.
Implementation Method 1
The flow restrictor includes an annular gap to control the bypass flow of drilling fluid
Data Source
AI summary
A bottom hole assembly (“BHA”) includes a driveshaft including a bore through which the drilling fluid is flowable. The BHA also includes a bearing assembly configured to rotatably support the driveshaft that includes a radial bearing with an internal radial gap; an annular flow restrictor with an inner sleeve and an outer sleeve separated by a restrictor clearance; and a bypass fluid flow path open to the bore and extending through the radial gap and the restrictor clearance such that at least some drilling fluid is diverted from the bore into the bypass fluid flow path. The restrictor clearance is sized to restrict flow of the drilling fluid diverted through the bypass fluid flow path to control a pressure of the drilling fluid in the driveshaft. The outer sleeve is dynamically radially supported such that a radial load absorbed by the annular flow restrictor is below a selected threshold.