Background
Dr. Eric van Oort and his team have developed a deep, closed-loop geothermal well design to improve upon traditional enhanced geothermal systems (EGS). Dr. van Oort is the Joe J. King Chair of Engineering No. 2 and B. J. Lancaster Professorship in Petroleum Engineering and a professor at UT Austin, with primary interests in drilling/completion fluids, hydraulic fracturing/reservoir geomechanics, and unconventional resource development. Dr. van Oort has received numerous SPE publication awards as well as distinguished SPE lecturer awards and has published numerous technical articles over the past three decades. The focus of his work has broad applicability in drilling technology, production optimization, and the developing field of data analytics as applied to oil/gas reservoir production applications.
Invention
The developed closed-loop geothermal well design uses steam turbines to convert geothermal energy to electricity with application in wells at depths ranging from 5-10 km true vertical depth that have encountered subsurface steam/geothermal resources with a temperature of 200°C/400°F or higher. Unlike traditional EGS wells, which are limited to specific geographic locations with “hot spot” indications (e.g., thin crust layers, active fault systems, heightened volcanic activity), the closed-loop geothermal technology provides the capability to access subsurface geothermal energy at any location, provided the well is drilled to an appropriate depth.
The drilled well used in the developed design has a vertical portion, a deviated angle build portion, and a lateral section. Once drilled, the well/system can be constructed in a variety of configurations; an internal closed loop system with the returning fluid flow path being the annular section (conventional pumping applications) of the well or through production tubing (reverse circulation technique), or an external closed-loop system using a U-shaped wellbore with separate inlet and outlet wellbores. Depending on the well configuration, the fluid heat loss of the returning geothermal fluid is minimized by thermally insulating the casing/cement or the tubing (e.g., vacuum insulated tubing, or VIT).
After drilling, the well is completed using a cased hole or an open hole completion technique. Return fluid flow is controlled using a manual or automatic surface choke, and the circulating well fluid can be either water, brine, or another thermally efficient fluid. Well temperature simulations on a 7km inlet section, a 7km lateral section, and a 7km return section indicated good power production performance (30 MW/minute) and temperature control of the returned fluid from a formation with a reservoir temperature of 300°C.
