Présentations Colloques

Hydraulic transmissivity enhancement of natural fractures has become one of the common practices during the last two decades in various disciplines such as shale gas development in oil industry, block caving in mining and enhanced geothermal systems (EGS). The main concept is based on the pressure increment (usually less than fracture pressure) and hydraulic shearing of the existing fractures in order to enhance the fracture transmissivity permanently known as hydraulic stimulation. In order to quantify the efficiency of hydraulic stimulation, hydraulic characterization methods such as hydraulic packer testing can be conducted before and after the stimulation process.**In-situ hydraulic stimulation and circulation (ISC) experiment has been initiated at the Grimsel Test Site (GTS) to study and address a wide-range of EGS related objectives in Switzerland. One of the main objectives of this multi-disciplinary experiment is to provide a high resolution pre- and post-stimulation characterization of fracture conductivity and connectivity in order to investigate patterns of preferential flow paths. A series of hydraulic fracturing (HF) and hydraulic tests in pre-existing fractures (HTPF) were conducted to characterize the in-situ local stress. The hydraulic response of the rock mass under hydro-mechanical perturbations was investigated by conducting various hydraulic packer tests (e.g. pulse, constant rate and head) in multiple hydraulically isolated borehole sections before and after the stress measurements.**Detailed analysis of the transient pressure responses of the hydraulic packer tests show that HF in the packed intervals with no presence of natural fractures does not affect the hydraulic conductivity of the rock mass significantly, as the implemented pressure for hydraulic characterization was not sufficient to re-open the tensile hydraulic fractures. Contrarily, HTPF in the intervals with the presence of brittle fractures was associated with more than two orders of magnitude hydraulic transmissivity increment by two orders due to shear dilation of fractures and permanent hydraulic transmissivity enhancement. Considering the injection volume during the main stimulation phase, even more significant hydraulic transmissivity enhancement is expected.