Iterative Development of Stress Models for Deep Geothermal Reservoirs

Modern geothermal technology, especially EGS (Engineered Geothermal System) technology involves reservoir stimulation to enhance a geothermal reservoir from initially non-commercial to commercial status by increasing reservoir permeability, hence well productivity. These technologies require the quantification of the regional and local stress field. Moreover, exploitation of geothermal systems differs to hydrocarbon systems because production and injection rates from geothermal wells are much larger than from oil and gas wells. This specific operation in geothermal reservoirs has significant effects on the in situ stresses. Therefore, the understanding of the stress field is a key element in geothermal field development, and ultimately the acceptance of overall geothermal projects is affected if stress changes evoke fault reactivation and induced seismicity as an effect of massive reservoir stimulation or large injection rates. This article shows how the stress field of deep geothermal reservoirs can be derived by iterative steps, adapted to the specific data generated by the typical project phases of geothermal plays. Methods are described, and an iterative concept of stress field determination is developed based on the lessons learned from the prominent EGS site Gro Schnebeck in the NE German Basin.