Geothermal wells use underground loops to extract hot water and transfer it to heat pumps in homes or buildings.
High-temperature drilling can require special mud additives to reduce the erosion of downhole tools and equipment.
Reputation
Geothermal system contractors must have extensive experience installing geothermal systems, several solid references, and a certification. They should also be licensed to build in your area, have adequate insurance, and be willing to comply with a background check.
Geothermal drilling requires larger hole sizes and volumes than oil wells, requiring different rigs and mud pumps. It is also expected to drill geothermal wells into production intervals producing steam or hot brine, requiring special techniques to control the flow and avoid lost circulation and messy cleanup.
High-quality bentonite clay is the principal product used in geothermal drilling to control viscosity. There are several polymers and proprietary blends that are effective both in thickening the mud and inhibiting gelation. In addition, new continuous-correction drilling tools have been developed for the geothermal industry and are more efficient than the bent housing motor tools used in oil and gas.
Experience
The most crucial factor to consider when choosing a geothermal drilling contractor is their experience level. Those with extensive experience in the field can provide superior service and ensure your project is completed correctly and within budget.
Having experience in the geothermal industry can also help you save money on equipment and supplies. For example, you may not need to purchase the most expensive geothermal drill rig if your business only offers drilling services for small residential projects. Instead, you can rent or buy a more affordable model with the necessary functionality.
Attending regional workshops is another way to learn about geothermal technology and build connections with contractors in your area. These seminars often feature presentations on topics such as utility funding for geothermal projects, new drilling techniques, and hybrid systems.
Equipment
Geothermal wells have unique requirements. Although drilling equipment used for oil and gas can be modified for geothermal wells, the rig design and crew are also critical to success.
For example, directional drilling may be required to intersect specific formation targets and lease boundaries, which can add cost. Also, because of the high temperatures, mud systems must be designed to handle water loss and maintain lubricity.
Likewise, the mud pits must be large enough to hold cooling water, and the pumping capacity should be sufficient for the planned hole size and possible downhole motor use. Because of the lower specific gravity, additives are often needed to increase the weight of the mud for proper fluid pressure control in geothermal wells. Differentially stuck pipes can also be a problem in geothermal wells because the pore pressure is lower than the drilling fluid pressure. To overcome this, geothermal muds are typically designed with low viscosity and good lubricity.
Safety
As with all drilling operations, safety is paramount. Geothermal wells have specific challenges that the drilling contractor must consider.
Lost circulation is a significant cost in geothermal drilling, especially when the fluid is expensive (steam or hot water). The larger diameters of production intervals in geothermal wells require more casing strings to the same depth than in oil and gas wells.
An excellent geothermal drilling contractor will have a plan to mitigate lost circulation issues before they become significant problems. Conventional lost-circulation treatment involves withdrawing the drill string, injecting cement into the fractures to seal them, and then resuming drilling. This is often difficult in a geothermal borehole because the fractures are often too large to be sealed by conventional lost-circulation treatment techniques.
In addition, geothermal wells often encounter corrosive brines. In these cases, the use of titanium casing is required. This is costly, and it can be challenging to design a well where the corrosive brine can be cased out.