HEAT TRANSFER CHARACTERISTICS OF A SINGLE FRACTURE WITH DIFFERENT FRACTURE SURFACE ROUGHNESS LEVELS AND APERTURE VARIATIONS

Understanding the flow pattern along a fracture plane is essential to achieving efficient heat extraction in enhanced geothermal systems (EGSs). The nature of surface roughness and aperture variation in fractures influences the heat extraction and performance of geothermal reservoirs due to flow disparity. In this study, aperture pattern and fracture surface roughness are derived from statistical distribution parameters to investigate the heat transfer characteristics of a single fracture. A geometric variation of thermal and mechanical (TM) parameters of the rock matrix is randomly distributed in three-dimensional space, and a fully-coupled thermo-hydro-mechanical (THM) model is presented. The result shows that rough fracture surfaces with small constant aperture, and varying apertures with higher standard deviation in their distribution, exhibit slower production temperature decline and improved heat and power generation during the extraction period as reduced fracture flow occurs within them. For the same aperture pattern, higher roughness levels of the fracture surface have improved power output and less decline in production temperature than smooth fracture. A small production temperature decline and improved power generation was observed considering a varying TM parameter model. Large values of constant and varying apertures exhibit high stress across the fracture and on the matrix block, evident by the fracture permeability evolution and matrix stress distribution.