Abstract

The current study presents a numerical modeling approach for three-dimensional simulation of hydro-shearing in jointed rocks for the generation of a man-made, multi-fracture heat exchanger in Hot Dry Rock (HDR) Geothermal reservoir. Various literatures have suggested the presence of in-situ fractured rock mass even in massive granite formations. Thereby, 3D numerical modelling is essential, since the prediction of fracture growth in 3D is key to investigation of different fracture designs and furthermore various operational parameters in order to optimize the heat exchanger design and the resulting energy production. The numerical approach incorporates the Dynardo's approach of homogenized continuum method to simulate the hydro-shearing process in jointed rocks unlike vast majority of commercial and scientific approaches which use the discrete modelling technique. The main motivation of the continuum approach is the numerical efficiency of the 3D coupled hydraulic- mechanical simulations of hydraulic fracturing process in comparison to other alternatives. The input parameters of the numerical model from the best available well log and reservoir data are calibrated from diagnostics measurements such as Micro-seismic events, Bottom Hole Pressure, etc to assign the correct level of forecast quality to the important mechanisms of hydraulic fracturing. The numerical procedure is applied to a prospective Granite reservoir in Thuringen, Germany within the purview of a German joint research project - optiRiss. The integrated approach involves ANSYS as a pre-processor and solver, Dynardo's fracturing simulator on top of ANSYS, Tamino - a post-processing tool and optiSLang - an environment for optimization and uncertainty quantification.

Energy consumption in the world has seen an ever increasing upward trend since the early part of the 20th century. Still a major chunk of the total energy supply comes from non-renewable energy resources with approximately 66 % supplied only by crude oil, natural gas and coal reserves. The large share of these resources are not just restricted to developing economies such as China, Brazil, etc. but also economic powerhouses such as USA and the European Union [1]. Geothermal Energy provides tremendous benefits in terms of reducing dependence on fossil fuels, reducing greenhouse emissions and generating new economic and employment opportunities. Geothermal Power systems aim to extract the inexhaustible heat available beneath the earth's surface. Natural Geothermal springs are rare to find and hard to locate and in order to reduce dependence on naturally occurring hydrothermal reservoirs, Hot Dry Rock/Enhanced Geothermal Systems (EGS) provide a suitable alternative. EGS reservoirs are set-up by drilling wells beneath the earth's surface and creating a man-made permeable fracture network between the wells. In the process, Hydraulic Fracturing is a well-stimulation technique used for creating artificial heat exchanger by creating a network of permeable fractures between injection and production wells.

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