Stratified rock hydraulic fracturing for enhanced geothermal system and fracture geometry evaluation via effective length

Rock stratification and anisotropy extensively exist in geothermal reservoir, and have great effects on the results of hot dry rock hydraulic fracturing. Therefore, the understanding of fracturing mechanism is critical to successfully building an engineered reservoir with high permeability for enhanced geothermal system. Some previous researchers have attempted to reveal hydraulic fracturing process of stratified rock, but the rock hydraulic fracturing propagation and fracture quality evaluation are still not clear enough. We established a numerical model to study the propagation of non-planar fractures in stratified rock by using extended finite element method. For fracture quality evaluation, we proposed fracture effective length as an index, which is the length of the segment where fracture width greater than 1 mm, considering the volume of sand within injected proppant. It is found that fractures generated from stratified rock is more conducive to heat extraction process. A large in-situ stress difference is more conducive to an increase in the fracture effective length. The methodology and results would guide the perforation location selection for stractified rock hydraulic fracturing process to achieve a reasonable fracture morphology. (C) 2020 Elsevier Ltd. All rights reserved.