Downhole tools are used for operations inside boreholes of oil and gas wells. Downhole tools operate in a very harsh environment and must be able to withstand inter alia corrosive fluids, very high temperatures and pressure.
To avoid unnecessary and expensive disturbances in the production of oil and gas, the tools deployed downhole have to be reliable and easy to remove from the well in case of a breakdown. Tools are often deployed at great depths several kilometers down the well, and removing jammed tools are therefore a costly and time-consuming operation.
Well tools are often part of a larger tool string containing tools with different functionalities. A tool string may comprise both transportation tools for propelling the tool string in the well and operational tools for performing various operations downhole.
Well tools often utilise hydraulics for performing operations or providing propulsion in transportation tools, also denoted well tractors. Supplying pressurised hydraulic fluid to various parts of a downhole tool requires a reliable and robust hydraulic system, as tools in the well cannot be accessed easily.
Especially the supply of hydraulic fluid into moving parts of a downhole tool is challenging. In regular machines, this is often accomplished by utilising external, flexible hydraulic hoses, which provide great freedom of design. In downhole tools the use of external hoses is undesirable due to the risk of hoses getting torn or the tool getting stuck due to entangled hoses.