Performance optimization of pinnate horizontal well in geothermal energy utilization with orthogonal test

Abstract

• Enhanced geothermal system (EGS) with pinnate horizontal wells is proposed. • Geostress balance is taken into account in numerical model. • Multifactor and multilevel optimization is presented. • Effects of human-made parameters on the heat extraction performance are discussed. Aiming at efficiently utilizing the hot dry rock resources, a potential enhanced geothermal system (EGS) with pinnate horizontal well (PHW) is investigated in present work. The multifactor and multilevel orthogonal tests are performed to probe the combined effect of human-made parameters on the reservoir properties, and to find the optimum operation strategy of PHW EGS. To evaluate the heat extraction performance of PHW EGS, geostress balance method is taken into account in the thermo-hydro-mechanical (THM) coupling model. The main factors of different human-made parameters that affect the heat extraction performance have been ranked based on their effect level, which are injection temperature, injection mass rate, production pressure, well spacing and length. In addition, Enthalpy-exergy is employed to evaluate the maximum available work of the extracted thermal energy. The present results demonstrate that the heat extraction performance of doublet EGS can be significantly improved by 12.57 MW ∼ 13.60 MW when the branch wells are introduced. The fractured region is mainly affected by the tensile stress, and the compressive stress predominates in reservoir margin. The production temperature is significantly affected by the well spacing, while the water loss rate has a strong correlation with production pressure. Under the recommended operation scheme, the maximum available work of PHW EGS ranges from 20.18 MW to 17.31 MW can be obtained, which accounts for from 23.76 % to 26.12 % of the extraction of thermal energy.