Cable Head Piston Balance for Petroleum Logging
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Solution Overview
Problem
Conventional cable heads for petroleum logging require excessive tension force to break the tension rod when stuck in a well, leading to potential damage or discard of the logging cable due to the high forces applied by well fluids, especially at greater depths.
Innovation Solution
A cable head design featuring a first connector with three pistons of varying diameters, where the second piston's axial projected area equals the cross-sectional area of the first piston, allowing for fluid pressure balance and enabling the tension force from the logging cable to be directly applied to the tension rod without being influenced by well fluid pressure, eliminating the need for silicone grease and simplifying assembly and maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cable head is filled with silicone grease for sealing, then the sealing performance is improved, but the assembly and disassembly difficulty increases
Solution Approach 1:
The invention removes the silicone grease filling requirement by extracting the sealing function from the cable head interior. The fully-sealed structure achieves sealing through mechanical design of the joint and housing components rather than relying on grease filling, thereby eliminating the trouble of assembly and disassembly associated with grease application.
2Reliability
If the tension rod breaking force is designed based on safe tension force, then the cable head reliability is improved, but the cable damage risk increases when stuck in deep wells
Solution Approach 1:
The invention applies the counterweight principle by designing the tension rod breaking force to counterbalance the harmful fluid pressure forces. The tension rod is designed with a breaking force that specifically compensates for the hydrostatic pressure at operating depths (1-1.5 km), allowing the cable to break the tension rod at the intended safe tension force without being hindered by fluid pressure forces.
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
Ensures the logging cable can be disconnected under a set tension force without damage, maintaining cable integrity and simplifying operations by balancing fluid pressures, thus preventing cable damage and facilitating easier maintenance.
Implementation Method 1
the axial projected area of the lower end face of the second piston of the first connector is equal to a cross section area of the first piston, allowing for fluid pressure balance
Data Source
AI summary
A cable head for petroleum logging includes a first connector and a second connector; there is a tension rod between the first connector and the second connector; a first piston, a second piston and a third piston are successively provided on the upper part, the middle part and the lower part of the first connector; the diameter of the second piston is greater than the diameters of the first and third piston respectively; the first and second piston are sealed and mounted inside a first cylinder; the third piston is sealed and mounted inside a second cylinder; the lower part of the second cylinder is fixedly connected with the second connector; a balance cavity is formed between the lower end face of the second piston and the upper end face of the second cylinder when the lower end face of the first cylinder is contacted with the upper end face of second cylinder; the balance cavity communicates with the external by a passage on the first or second cylinder; an axial projected area of the lower end face of the second piston is equal to a cross section area of the first piston. When the cable head is stuck in the well in use, the logging cable can be disconnected by breaking the tension rod, thus it is no need to overcome the pressure of fluid in the deep well.