Subsidence and Stress Change in the Cerro Prieto Geothermal Field, B. C., Mexico

Abstract

Previous works have shown that ground deformation and seismicity in the Cerro Prieto geothermal field (CPGF) are due to both tectonics and field exploitation. Here, we use information about current tectonics and data from precision leveling surveys, to model tectonic and anthropogenic subsidence. Our results show that tectonic subsidence constitutes only $4% of the measured subsidence. Anthropogenic subsidence was evaluated using a model of rectangular tensional cracks, based on the hydrological model of the field, together with the Coulomb 2.0 program. From the resulting values of the fissure parameters and from extraction and injection data, we calculate that the volume changes caused by closure of the geothermal and cold water reservoirs account for only $3% and $7%, respectively, of the volume change which should occur due to extraction. Since 18% of the extracted fluids are reinjected, external recharge must compensate for about 72% of the expected volume reduction. An analysis of the changes in Coulomb stress caused by exploitation of the geothermal field suggest that even though the anthropogenic stresses account for only a fraction of tectonic stresses, they are large enough to trigger seismicity.

Subsidence monitoring with geotechnical instruments in the Mexicali Valley, Baja California, Mexico

“…Moreover large earthquakes concentrate along the major, Imperial and Cerro Prieto faults, while scattered seismicity, (mainly swarms), and deformation are observed in the Pull-apart Cerro Prieto Basin (Lomnitz et al, 1970;Nava and Glowacka, 1994;Suárez-Vidal et al, 2008). Fluid extraction began in the Cerro Prieto Geothermal Field (CPGF) in 1973, and brine injection therein began in 1989; these processes have been influencing deformation, stress, and seismicity of the area (Majer and McEvilly, 1981;Glowacka and Nava, 1996;Fabriol and Munguía, 1997;Glowacka et al, 1999Glowacka et al, , 2005Trugman et al, 2014).…”

“…This zone, also known as Cerro Prieto basin, is larger than the extraction zone, suggesting the existence of a recharging region. Since the sunken area is limited by tectonic faults, Glowacka et al (1999Glowacka et al ( , 2005Glowacka et al ( , 2010a, suggest that these faults constitute a boundary of the subsiding region, due to differential compaction and/or due to poor permeability in the direction perpendicular to the faults that acts as a groundwater barrier.…”

Aplicación de DInSAR a los estudios de subsidencia en el Valle de Mexicali

“…Desde los años ochentas, Majer y McEvilly (1982), Glowacka y Nava (1996), Fabriol y Munguía (1997), Glowacka et al ( , 2005Glowacka et al ( , 2010, Carnec y Fabriol (1999) y Hanssen (2001 han relacionado sismicidad y/o deformación con el proceso de extracción, y/o inyección de fluidos geotermales en el campo geotér-mico Cerro Prieto. En el período de 1973 a 1997 la tasa de subsidencia aumentó después de cada aumento grande y sostenido de extracción .…”

“…En el período de 1973 a 1997 la tasa de subsidencia aumentó después de cada aumento grande y sostenido de extracción . Con datos de la nivelación realizada en los años 1994 a 1997 (Figura 2) en el Valle de Mexicali, se hizo la modelación de la componente tectónica y antropogénica de la subsidencia (Sarychikhina, 2003, Glowacka et al, 2005 y se encontró que la subsidencia antropogénica es responsable del 94% al 96% de la subsidencia observada. La zona que presenta subsidencia de origen antropogénico coincide en posición, extensión y forma con la región de la subsidencia tectó-nica.…”

“…En la Figura 6a y 6b, también se comparan los resultados de esta publicación con los resultados de nivelación para los años 1994-1997 (Glowacka et al, , 2005. Para eso, sobrepusimos los datos de nivelación 1994-1997 (en forma de isolíneas) a los mapas de tasa de subsidencia obtenidos usando la técnica de DInSAR (Figura 6a y 6b).…”