Numerical evaluation of hot dry rock reservoir through stimulation and heat extraction using a three-dimensional anisotropic coupled THM model

J. Liao, M. Haris, Y. Tao, Y. Xie, Y. Yue, Z. Hou
HDR, Heat extraction, Hydraulic fracturing, Numerical mode, THM, THOUGH2MP-FLAC3D

Geothermal energy attracts extensive attention for its excellent features like large capacity and lack of dependency on weather conditions. This paper presents a development of numerical model to study the hydraulic fracturing and heat extraction from geothermal reservoir, especially from brittle hot dry rock (HDR) reservoir. In this numerical model, an anisotropic damage model has been introduced based on Thermal-Hydraulic-Mechanical (THM) coupling code THOUGH2MP-FLAC3D and this damage-permeability model has also been integrated to demonstrate the enhancement in permeability of stimulated fracture network. Furthermore, numerical studies on planed Dikili enhanced geothermal system (EGS) were carried out by using newly developed model. As the simulated results show, a roughly circular fracture network is created, wherein simulated reservoir volume and area reaches to 49 million m3 and 1.41 million m2, respectively. The maximum permeability increases from initial permeability of 4 × 10−18 m2 to 7.52 × 10−14 m2 in z-direction. Based on these results, heat extraction calculations are performed for 10-years at different injection rates. The accumulated amount of produced net energy increases with the rising injection rate, while growth rate of the average thermal capacity over 10-year slows down. The production results suggest that an injection rate of 100 L/s can recover approximately 1.00 × 1016 J of thermal energy of over a 10-year period, with an average thermal capacity of 31.75 MWth.

Keywords: HDR, Hydraulic fracturing, Heat extraction, THM, THOUGH2MP-FLAC3D, Numerical mode