Numerical Simulation of Mineral Composition Effect on Thermal Cracking of Rock

Abstract

Many geo-engineering applications, such as geothermal energy extraction and underground nuclear waste storage, lead to significant temperature variations. When rock is undergone through temperature increase, many cracks would be generated due to the thermal cracking process as shown in literature and laboratory experiments. These micro-cracks can have beneficial or detrimental impacts depending on specific application. Different thermal expansion coefficients of various mineral particles are considered as the key factor affecting the thermal cracking of rocks. In order to understand the thermal cracking process and evaluate and se1ect the potential site for different applications, numerical simulations on thermal cracking of rocks were conducted with discrete element method. The variations of elastic modulus, tensile strength and thermal expansion coefficient with temperature were considered in the simulation. Based on the mineral analysis of granite sample from a hot dry rock well in Lijin of China, three main mineral particles, namely quartz, K-feldspar and plagioclase feldspar, were included in the numerical simulation. The simulation shows that the ratio of mineral composition plays an important role in thermal cracking besides the thermal expansion coefficient difference. When the proportion of quartz, K-feldspar and plagioclase feldspar changes from 1:1:8 to 4:4:2, the statistical cracks increase approximate ten-fold. The more one of mineral compositions is, the less the thermally produced micro-cracks are. The more the two minerals with the largest difference of thermal expansion coefficients are, the more the thermally produced micro-cracks are. It means that the rock with more complex mineral compositions has a high probability of thermal cracking.