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The GeoCam is around 2.4 metres long and weighs 60 kilos. For the first functional prototype, the components of the camera unit were produced from heavy stainless steel at a high cost.
© KIT
Camera for deep geothermal energy
24.08.2016

The housing of the camera head with ceramic window will be extended after a pressure test of 500 bar from the autoclave.
© KIT

This is what live images from drilling holes can look like: this sample photograph was taken in the Altdorf geothermal well at a depth of 231 metres.
© BRG

Video inspection tool brings light into the darkness

Scientists in Karlsruhe are developing a camera inspection system for deep geothermal drilling holes. The device must be able to withstand strong pressure and high temperatures. This presents a particular challenge for the electronic components. A first draft design for the system has now been completed.

In order to assess the state of geothermal drilling holes, drilling engineers and geologists are reliant on the values displayed on their measurement instruments and on their experience. Despite the high degree of reliability of images, cameras are only rarely used when constructing and modifying drilling holes. The reasons for this are that existing systems are expensive and do not permit a more precise view onto sections that are of interest due to the lack of live transmission. Scientists from the Karlsruhe Institute of Technology (KIT) are working with cooperation partners to develop a camera inspection tool for geothermal drilling holes. With the aid of the device, operators will in future be able for example to inspect the degree of corrosion and wear of the pipes and geological obstacles via live image transmission.

Pressure-resistant and thermally insulated housing

The camera inspection tool consists of several vessels which lie in layers on top of each other like an onion and which consist of different materials. The electronic camera unit is located inside Dewar vessels. These are double-walled vessels made of glass or stainless steel, between which there is a vacuum. They are to be found in everyday objects such as Thermos flasks. These Dewar vessels shield the temperature-sensitive electronic components against the high ambient temperatures. However, this thermal insulation is not entirely sufficient to enable operation over several hours. For this reason, the temperature inside the tool is further lowered by cooling using phase change materials (PCM). The Dewar vessels are inserted inside a pipe made of a nickel-based alloy and are affixed there with a Teflon plug. The camera unit, which consists of a frontal camera and two lateral cameras, can be pivoted and films through a frontal window and six lateral windows. These consist of a special ceramic material. For all lenses, the focus and aperture can be individually adjusted during use according to current requirements. A large number of integrated LED diodes ensure that the necessary brightness and variation options are provided. It is difficult to pass on image data over several kilometres since the transmission rate decreases rapidly as the distance increases. For this reason, the data from the images shot at depth is compressed using software and transferred to the surface via a cable.

Further development work is currently being planned

During the course of the three-year research period, it was possible to solve a large number of problems related to the detail, the structure and the design, such as the materials used, the cooling concept, the image transmission and the control and lighting of the camera. A prototype that is ready for use in the field, which could be tested in a real-life geothermal system, is currently not yet available. Dr Jörg Isele, project head at KIT, explains the further need for development: “In recent years, we have already succeeded in finding innovative solutions to key details. Currently, we are being assisted in the completion of the slim steel Dewar by colleagues who usually work on the vacuum technology of the ITER fusion reactor. More work is needed on the development of reliable connection technology between the transparent ceramic windows and the nickel-based alloy, and the data transmission via cable over long distances still needs to be brought to conclusion and tested.” In 2016, the KIT will continue to test the functional prototype of the camera inspection tool under more realistic conditions in the autoclave.

The depth is not as easy to overcome as it looks

In deep drilling holes at depths of up to 4,000 meters, the conditions for a camera inspection tool with temperature-sensitive electronics are harsh. At this depth, the ambient temperature in Central Europe is up to 165 degrees Celsius, with pressure levels of up to 600 bar. The device usually also operates in corrosive thermal water. It therefore needs to be watertight and be made of corrosion-proof materials. To enable it to be used in narrow drilling holes, the outer diameter should not exceed 95 millimetres.

The highest temperature in the interior for the electronic components may not exceed 70 degrees Celsius. The PCM cooling elements must be easy to replace. To enable the operating team to react to details at depth above ground, and to ensure that the device is in reality not too far from the site of the image currently being transmitted on the monitor, the data transfer from the depth must reach up to 25 colour images per second as far as possible.

(mi)

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Project coordination
KIT-IAI

Design and concept
Fraunhofer IKTS

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Video on the drilling hole
A video made by the BRG Brunnen-Regenerierungs GmbH well testing company from the geothermal well in Altdorf (open hole and casing). The photographs were taken at lesser depths than those set for the camera inspection tool in the research project.