Formation of Superaitical Geothermal Resevoirs by Means of Supercritical Water-Induced Cracking

该研究项目确定了利用超临界水与造岩矿物之间的相互作用在温度和压力条件超过水临界点的深层岩体中建立人工地下地热储层的可行性。主要研究结果如下：1.通过超声波速度测量，证实了围压在高温试验中的应用，可以有效地缓解由于成岩矿物热膨胀失配而引起的热应力诱发的微裂纹; 2.采用厚壁圆筒试样对几种类型的花岗岩进行了渗透率测量。岩石样本包括取自实际地热田现场深层高温岩体的岩心。结果表明，当含水条件超过临界渗透率时，测得的渗透率有明显的跃变 ...更多信息 无论本研究中使用的岩石类型如何，渗透率的显着增加被证明是由于超临界水和成岩矿物之间的相互作用引起的颗粒尺度的微裂纹。从深层岩体中获取的岩石样品的渗透率增加的程度小于从露头中获得的岩石类型的渗透率增加的程度。3.进行了三轴压缩试验，以检查应力对上述超临界水诱导开裂现象的影响。结果表明，当温度高于临界温度时，最终断裂面附近的微裂纹密度明显大于远场。微裂纹密度的增加表明应力的作用加速了超临界水诱导的开裂。超临界水加速应力腐蚀开裂新称之为超临界水强化应力腐蚀开裂。实验观察表明，超临界水强化应力腐蚀开裂在水力诱发地热膨胀中具有潜在的应用价值。e.循环水）和围岩中的热传递。考虑了超临界流体的温度、压力以及流体的密度、粘度等因素的影响，通过数值计算，指出了存在一个最佳的注入速度，以便从超临界油藏和亚临界温度岩体中提取热能。少

The research project determined the feasibility of utilizing the interactions between supercritical water and rock-forming minerals in the creation of an artificial subsurface geothermal reservoir in a deep-seated rock mass, in which temperature and pressure conditions exceed the critical point for water. The main results obtained in this study are summarized below.1.Application of confining pressures in high temperature testing was shown tot be effective in order to mitigate the thermal stress induced micro-cracking due to thermal expansion mismatch of the rock-forming minerals by conducting ultrasonic wave velocity measurements.2.Permeability measurements were made for several types of granitic rocks using thick-walled cylindrical specimens. The rock specimens included cores taken from the deep-seated high temperature rock mass at an actual geothermal field site. It has been shown that the permeability measured jumped significantly when the condition of water exceeded the critical po … More int for water regardless of the rock types used in this study. The significant increase in permeability was shown to be due to grain-scale microcracking induced from the interaction between the supercritical water and rock-forming minerals. The extent of the permeability increase was less for the rock specimens taken from the deep-seated rock masses than that for the rock types obtained from outcrops.3.Tri-axial compression tests were conducted in order to examine the effect of stress on the above-mentioned supercritical water induced cracking phenomenon. It has been demonstrated that the microcrack density at the vicinity of the final fracture plane was signifcantly larger than that at the far-field when the temperature was greater than the critical temperature. The increase in the microcrack density points out that the supercritical water induced cracking was accelerated by the effect of stress. The accelerated cracking is newty named as supercritical water enhanced stress corrosion cracking. The experimental observation may suggest the potential use of the supercritical water enhanced stress corrosion cracking the expansion of hydraulically-induced geothermal reservoirs.4.We undertook long-term thermal extraction numerical modeling analysis, for a supercritical rock mass, which incorporated fluid flow characteristics (i. e. circulating water) and thermal transfer in the surrounding rock mass. We considered the effects of temperacure and pressure in the supercritical fluid regime, as well as fluid density, viscosity etc. Based on the numerical results, it has been shown that there is an optimum injection rate to extract the heat energy from the supercritical reservoir combined with subcritical temperacure rock mass. Less