Technology from differing fields is being adopted by the geothermal industry as ever deeper wells are being drilled. However, due to the extreme conditions created within deep geothermal wells lining them requires new solutions. As geothermal operators go deeper and encounter more extreme pressure, temperature, drilling and environmental conditions, cement and casing integrity challenges multiply
For Halliburton, the solutions start with the elimination of cement carbonation. Carbon dioxide (CO2) is a common element in downhole fluids, whether naturally occurring in groundwaters or the result of CO2 injection processes. When CO2 comes into contact with the Portland cement that is used to cement well casings, it produces a deterioration phenomenon in the cement called carbonation. Over time, the loss of cement due to carbonation can cause serious damage to downhole tubulars and destroy zonal isolation integrity, resulting in costly remedial services or even abandonment of a well.
In order to overcome such issues, Halliburton has created a CO2 resistant formulation - ThermaLock. ThermaLock cement is a specially formulated calcium phosphate cement that is both CO2 and acid resistant. The result of a joint development project for high-temperature, geothermal wells, the unique cement is now being promoted as an alternative for Portland cement wherever CO2 may be encountered. It has been laboratory tested and proven at temperatures as low as 140°F and as high as 700°F. As a result of this resistance to extremes, Halliburton's proven HPHT cementing solutions are helping extend the productive life of wells that tap geothermal reservoirs for energy power generation.
ThermaLock is not the only development Halliburton has in place for use in geothermal wells. The company utilises its reverse-cementing method when required to help achieve and retain a reliable annular seal for the life of geothermal wells.
With reverse cementing Halliburton is able to overcome major pressure challenges. Conventional cementing methods involve pumping cement through the casing to come up the annulus. Reverse-cementing involves pumping the slurry down the annulus directly and taking returns through the casing. This requires specially designed casing equipment and monitoring capabilities to determine the top of cement inside the casing. This method is used to lower bottom hole circulating pressure to avoid damaging or breaking down weak formations.
Wells that require the method of reverse cement benefit from reduced equivalent circulating densities, improved mud displacement, shorter slurry thickening times, improved compressive strength development, improved safety and environmental management, flexible cement slurry selection, and improved production due to less risk of cement invasion into the producing zone.
Alongside the introduction of Thermalock and its reverse-cementing method, Halliburton also offers electromagnetic telemetry technology that works without fluid, making it ideal for use at geothermal sites.
In geothermal drilling operations, lost circulation of drilling fluid is a huge issue. Because the downhole rocks are so brittle, their natural fractures alone cause significant fluid loss. This affects mud pulse technology (where data signals are sent from the bottom of the hole to the surface with the help of a continuous fluid column). If telemetry signals disappear because of a fluid loss, the operator is suddenly working "blind" since drilling data signals have been interrupted.
Halliburton's EMT MWD/LWD service allows for uninterrupted data transmission without a continuous fluid column. The EMT service establishes a two-way communications link between the surface and the tool downhole. Using low-frequency electromagnetic wave propagation, this service facilitates high-speed data transmission to and from the surface through any formation. Data formats can be readily customised to suit the drilling needs of the particular well. This service provides a cost-effective alternative to pulse systems - a key differentiator from other services on the market.
Halliburton's EMT technology has many applications, including making drilling more cost-effective, especially when drilling with air or gasified drilling fluids—an environment in which conventional mud pulse telemetry systems cannot function.