Stefano cools sensitive electronics to a refreshing 175°C working environment in high temperature oil-wells

Tuesday 08 Nov 16

Stefano Soprani from DTU Energy has successfully defended his Industrial PhD thesis "Active Cooling of a Down Hole Well Tractor”.

Oil drilling has changed. It used to be that wells were drilled straight down and if reparations were needed, gravity helped the maintainance equipment down to the place needing fixing. Nowadays oil wells also go sideways, and gravity and oil producers need a helping hand from companies like Danish Welltec to drive intervention tools down the well pipes. Welltech uses a so-called well tractor to make repairs, open valves, replace pipes, and remove clogging in wells.

Read about the technologies and services of Welltech here

Stefano Soprani from DTU Energy did an Industrial PhD at Welltec. He has just defended his thesis "Active Cooling of a Down Hole Well Tractor”, in which he presented a cooling system for the heat-sensitive equipment in well tractors using thermoelectric cooling devices and a hull-integrated sensor.

"We have devised a cooling system able to maintain a working temperature inside the well-tractor below 175 °C while operating in wells up to 200 °C"
Stefano Soprani, DTU Energy

Most wireline interventions are done using small remote-controlled well tractors bristling with electronic and robotic equipment. The tractor moves through the flowing oil and down into the pipes on small wheels. Interventions in high temperature oil wells represent a very big challenge for the oil and gas industry.

Local cooling spots

“Several electronic components contained in the wireline robotic tools are very likely to fail at temperatures higher than 175 °C, and no replacements for higher operating temperatures are available on the market.  We have devised a cooling system able to maintain a working temperature inside the well-tractor below 175 °C while operating in wells up to 200 °C”, says Stefano Soprani, who as part of his PhD studied a lot of cooling techniques before choosing thermoelectric devices.

“Thermoelectric devices can be used either to generate electricity from a heat source, or for cooling using an electric current. In our work, we used thermoelectric coolers to lower the inside temperature of the well-tractor. The only drawback of thermoelectric devices is a low efficiency, but they are very reliable as they do not have moving parts” says Stefano Soprani.

The heat removed by the cooled electronics needs to be transferred to the well and the small dimensions of the tool (inner diameter of ~6 cm) make this process complex, so Stefano Soprani and his colleagues at DTU Energy had to limit the use of cooling to the most heat sensitive parts, placing the very small thermoelectric coolers, no more than 4x4 cm2 with a thickness of approx. 4 mm, right on top of the exact groups of electronics needing cooling.

“The majority of the sensitive equipment is clustered together, so by creating very local cooling zones we are able to maintain those critical components below 175 °C and allow the entire well-tractor to function properly.”

Heat vented out in oil

The unwelcome heat from the interior of the well-tractor is transferred through the thermoelectric devices to the outer housing of the tractor, where oil or gas flows by, cooling the hull and absorbing the heat like a stream of water can cool its surroundings, but the process is sensitive to changes in the flow of oil and gas.

“Fast flow gives high heat rejection, but if the flow slows down the cooling effect lessens, the temperatures inside the hull rise and we risk a breakdown. So we also had to develop and design an integrated sensor to monitor the outside fluid flow to be able to regulate the amount of current we can supply to the cooling system without risk of overheating”, says Stefano Soprani.

The sensor can be integrated into the housing of the well-tractor and the research group at DTU Energy has proven the entire concept and made a prototype.

Welltec, where Stefano took his Industrial PhD, is interested in the design and, despite the low oil prices which have slowed down the research and development process, will implement the active cooling concept in 2017. With Stefano’s Industrial PhD successfully defended, he has now accepted a position as postdoc in DTU Energy and continues his research into energy conversion devices.

Read more about DTU Energy’s research into thermoelectric devices here