Abstract
A scientific injection campaign was conducted at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) site in 2017 and 2019. The testing included pump-in/shut-in, pump-in/flowback, and step rate tests. Various methods have been employed to interpret the in-situ stress from the test dataset. This study focuses on methods to interpret the minimum in-situ stress from step rate, pump-in/extended shut-in tests data obtained during the stimulation of two zones in Well 58-32. This well was drilled in low-permeability granitoid. A temperature of 199 °C was recorded at the well’s total depth of 2297 m relative to the rotary Kelly bushing (RKB). The lower zone (Zone 1) consisted of 46 m of the openhole at the toe of the well. Fractures in the upper zone (Zone 2) were stimulated between 2123–2126 m measured depths (MD) behind the casing. The closure stress gradient variation depended on the depth and the injection chronology. The closure stress was found to increase with the pumping rate/volume. This stress variation could indicate that poroelastic effects (“back stress”) and the presence of adjacent natural fractures may play an important role in the interpretation of fracture closure stress. Further, progressively increasing local total stresses may, consequently, have practical applications when moderate volumes of fluid are injected in a naturally fractured or high-temperature reservoir. The alternative techniques that use pump-in/flowback tests and temperature signatures provide a valuable perspective view of the in-situ stress measurements.
Highlights
Enhanced geothermal systems (EGS) offer the potential to bring low-cost geothermal energy to locations that lack natural permeability
The estimated closure stress for Zone 2 determined from flowback tests is 14.7–15.4 MPa/km, which is much lower than the values of 17.2–21.5 MPa/km estimated from step rate and extended shut-in tests
Closure stress interpretations are presented for the injection activities in FORGE Well 58-32
Summary
Enhanced geothermal systems (EGS) offer the potential to bring low-cost geothermal energy to locations that lack natural permeability. In 2017 and 2019, a suite of injection activities was conducted in a pilot well, Well 58-32, at the FORGE site to assess the in-situ stress and other reservoir properties. These injection activities included pump-in/shut-in, pump-in/flowback, Energies 2020, 13, 5842; doi:10.3390/en13215842 www.mdpi.com/journal/energies. Pump-in/flowback tests [7] and temperature signatures [8] provide alternative methods to infer the in-situ stresses, which is beyond the scope of this investigation. Issues related to the in-situ stress interpretation are discussed, and a brief description of alternative methods of analysis, such as flowback tests and temperature signatures, are presented
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
