## 1 Introduction  
The utilization of fossil energy sustains the rapid development of the world economy but also brings about an increasingly serious world energy crisis and environmental pollution [1, 2]. Therefore, searching for renewable and clean energy that can replace fossil one has become an important task for governments and research institutions. Renewable energy sources mainly include wind, solar, hydraulic power, and geothermal energy. As for the aforementioned renewable energy sources, their reserves are huge. However, the large-scale application of solar energy is limited by natural conditions such as diurnal, latitude, and altitude. And wind energy is heavily dependent on climatic conditions, where unstable wind speed will result in a discontinuous generation of power. Additionally, the development of hydraulic power is restricted by geographical and seasonal conditions and is not suitable for regions with water shortages. Due to the independence of seasonal, climatic, and diurnal as well as other factors, geothermal energy turns out to be a stable and uninterrupted energy supplies [3]. Considering its many advantages, geothermal energy has received widespread attention at home and abroad [4]. According to their depth in the earth's strata and production conditions, geothermal resources can be divided into three categories: shallow geothermal energy, hydrothermal resource, and hot, dry rocks (HDR) [5]. In particular, due to its huge reserves, HDR is expected to play a key role in solving the aforementioned societal problems [6]. According to conservative estimation, in China, the amount of geothermal energy reserved inside HDR reaches over 2.09 \(\times\) 10\({}^{7}\) EJ, which is about 100,000 times more than other categories [7]. Consequently, how to achieve large-scale exploitation with regards to HDR is becoming a prospective but promising direction among the studies of geothermal developments. HDR is characterized by its extremely low natural permeability, so developing HDR requires establishing Enhanced Geothermal System (EGS) [8]. In 1970, the concept of EGS was first introduced by Los Alamos National Laboratory. It typically consists of injection wells, production wells, and heat reservoirs created by artificial enhancement techniques [9; 10]. Generally, hydraulic fracturing techniques are used to create fracture networks to connect these wells and make more heat transfer areas. However, hydraulic fracturing is still immature, and its many inherent flaws are seriously bottleneck heat energy reserved inside HDR from being extracted at a large industrial scale. It is so far improbable to credibly control fracture extension and precisely predict the structural distribution of reservoir morphology. This results in the reservoir volumes being limited up to pilot testing scales, and the field designs are tentative [11; 12]. Although project Fenton Hill had achieved satisfactory fracturing outcomes, its reservoir volume was only 0.035 km\({}^{3}\) as estimated, which is far from the required 0.2 km\({}^{3}\), which is the minimum for commercial development [13]. Furthermore, in order to improve the stimulating effects of fracturing, the fracturing fluids to be adopted usually contain chemicals that can seriously contaminate groundwater environments [14]. In addition, fracturing activity disturbs the crude balance existing among in-situ stresses, which might trigger an accidental earthquake. In Basel, Switzerland, 3500 micro seismic events occurred between 2006 and 2007 as a result of hydraulic fracturing activity [15]. In 2007, an earthquake of magnitude 5.4, the highest magnitude estimated to be related to EGS, struck the northern part of Pohang city. Then the local project of geothermal power generation was suspended, causing a direct economic loss of more than USD $47 M [16]. Similar lessons have told many times that stability and safety need pre-requisitely guaranteed.