Downhole Shock Tool Axial Oscillation Friction Reduction
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Solution Overview
Problem
Current downhole oscillation systems face inefficiencies in converting cyclical pressure pulses into axial oscillations, leading to increased friction and reduced rate of penetration during drilling operations due to frictional engagement between the drillstring and the borehole formation.
Innovation Solution
A shock tool design featuring an outer housing with intermeshing splines and a mandrel assembly, along with a biasing member and annular flow passages, that axially extends and retracts in response to pressure pulses, reducing friction by inducing axial reciprocation in the drillstring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional shock tool design is used to convert pressure pulses into axial oscillations, then axial reciprocation is achieved, but friction between the drillstring and borehole sidewall remains high due to inefficiencies in pressure pulse conversion
Solution Approach 1:
The shock tool employs a dynamic mandrel assembly that moves axially relative to the outer housing in response to pressure pulses. The mandrel can extend and retract, creating variable displacement that enhances the efficiency of converting pressure pulses into axial oscillations, thereby reducing friction and improving rate of penetration
Solution Approach 2:
The shock tool is divided into distinct functional segments: an outer housing, a movable mandrel assembly with internal components, and intermeshing splines. This segmentation allows each component to be optimized for its specific function - the splines for torque transmission, the mandrel for axial movement, and the overall structure for pressure pulse conversion efficiency
2Productivity
If weight-on-bit is increased to maintain drilling performance, then rate of penetration can be maintained, but frictional engagement increases leading to stick-slip conditions
Solution Approach 1:
The shock tool generates controlled mechanical vibrations and axial oscillations in the drillstring through pressure pulse conversion. These vibrations reduce the effective friction between the drillstring and borehole sidewall, allowing maintenance of drilling performance with reduced weight-on-bit and preventing stick-slip conditions
3Device complexity
If a simple shock tool design is used, then device complexity is low, but conversion efficiency of pressure pulses to axial oscillations is insufficient
Solution Approach 1:
The shock tool features a nested structure with the mandrel assembly positioned inside the outer housing. The mandrel contains internal components including splines and flow passages that are nested within each other. This nested design achieves high conversion efficiency through sophisticated internal mechanics while maintaining a compact overall form factor
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 shock tool effectively reduces friction between the drillstring and the borehole sidewall, enhancing the rate of penetration and reducing the necessary weight-on-bit by efficiently converting pressure pulses into axial oscillations.
Implementation Method 1
a biasing member disposed about the mandrel assembly in a first annulus radially positioned between the mandrel assembly and the outer housing. The biasing member is configured to generate an axial biasing force that resists axial movement of the mandrel assembly relative to the outer housing.
Implementation Method 2
The pressure pulses created by the pressure pulse generator are cyclic in nature. The continuous stream of pressure peaks and troughs in the drilling fluid cause the shock tool to cyclically extend and retract telescopically at the pressure peak and pressure trough, respectively.
Data Source
AI summary
A shock tool for reciprocating a drillstring includes an outer housing and a mandrel assembly coaxially disposed in the outer housing. The outer housing has a radially inner surface including a plurality of circumferentially-spaced splines. The mandrel assembly includes a mandrel having a radially outer surface including a plurality of circumferentially-spaced splines and a plurality of circumferentially-spaced troughs. Each spline of the outer housing is disposed in one trough of the mandrel. Each spline of the mandrel includes a top surface, a first lateral side surface extending radially from the top surface, a second lateral side surface oriented parallel to the first lateral side surface, and a bevel extending from the top surface to the second lateral side surface. Each spline of the mandrel also includes a pocket in the second lateral side surface extending radially from a bottom surface of a trough to the bevel.