Development of a Fractured Geothermal Reservoir Simulator in terms of Mechanical and Chemical Water/Rock Interactions.

热干岩(HDR)/热湿岩（HWR）地热能源开采系统是利用天然和人工地下裂缝进行水与热岩之间的热交换，作为一种新的能源获取技术受到广泛关注。为了评价裂缝性地热储层的热采性能，需要对裂缝性地热储层的水流和传热进行数值分析。本研究首先对HDR/HWR地热储层进行了基于分形几何的裂缝网络表征。利用裂缝网络地热储层模型，建立了分析储层水流传热的方法。裂缝孔径的变化对流体流动有重要影响，对水循环过程中裂缝行为的预测具有重要意义。水和岩石之间的机械和化学相互作用也包括在程序中。根据岩石力学理论计算了水压作用下各裂缝的份额扩张。在高压和高温下进行了岩石溶解和沉淀实验。水/岩相互作用速率是温度和地表水流速的函数。在日本HDR/HWR试验场之一的Ogachi油田进行了短期水循环试验。利用所编制的程序对生产温度曲线进行了分析，结果与实际数据吻合较好。此外，该分析还可以对大垣水库的长期动态进行随机估计。

Hot Dry Rock (HDR)/Hot Wet Rock (HWR) geothermal energy extraction systems, which attract a great deal of attention as one of new technologies to obtain energy, are designed to utilize natural and artificial subsurface fractures for the heat exchange between water and hot rock. Numerical analysis of water flow and heat transfer in fractured geothermal reservoir is strongly needed to estimate the heat mining performance of these systems.In this study, first of all, HDR/HWR geothermal reservoirs were characterized by fracture network based on fractal geometry which is getting popular to assess subsurface fractures. By using fracture network geothermal reservoir model, the mithodology to analyze water flow and heat transfer in reservoirs has been established. The changes of fracture apertures has significant influence on fluid flow, and it is important to estimate fracture behavior during water circulation. The mechanical and chemical interaction between water and rock was included into the program. Share dilation of each fracture caused by water pressure was calculated based on rock mechanics theory. Rock dissolution and precipitation experiments in high pressure and temperatures have been performed. Water/Rock interaction rate was obtained as a function of temperature and surface water velocity.Short-term water circulation test was conducted at Ogachi field, one of HDR/HWR test sites in Japan. The profile of production temperature was analyzed by the program developed in this study, and the results has shown good agreement with the actual data. Furthermore this analysis could give a stochastic estimation of long-term performance of Ogachi reservoir.