Optimization of Heat Extraction Performance from Multiple Borehole Reservoir Systems-Towards the Enlargement of Geothermal Reservoirs and Enhancement of Heat Extraction-

建立了裂缝性热干岩（HDR）地热储层的改进三维模拟模型（FRACSIM-3D）。它结合了水力增产过程中岩石-流体的力学相互作用，并定量预测了储层的三维生长行为。在该模型中，预先存在的裂缝是随机产生的。假设随机定向的便士形裂缝的分形尺寸分布。在注入压力恒定的条件下，通过将裂隙岩石的连通性映射为规则的立方网格来模拟流体在离散裂缝网络中的流动。流体流动用达西定律方程近似。由于裂缝剪切偏置，注入井的流体压力诱导裂缝的孔径增大。裂缝扩展的计算需要多次迭代，每次都要重新求解模拟裂缝系统的完整流动模型，并重新计算剪切位移，更多的是在前一次迭代的基础上计算裂缝内压力。数值模型是根据Hijiori HDR油藏现有的现场数据进行校准的。例如，对储层内不同随机播种的裂缝及其孔径初始分布进行了一系列数值计算。数值模拟结果与实验检测结果吻合较好，选择该分布作为模拟天然裂缝介质的合适分布。由于不同实验技术获得的相关现场数据不太可靠，因此将该模型用于评价Hijiory储层的适当应力状态。最新版本的FRACSIM-3D集成了注入井和生产井的多井眼系统。通过对模型的改进，可以分析不同井系布置对储层产能的影响。对不同几何形状的钻孔进行了数值试验。在此基础上，提出了生产和注水井的最佳布置方案，以保证相应的油藏采收率和较少的活动井眼数量。少

An improved three-dimensional simulation model (FRACSIM-3D) for the fractured hot-dry-rock (HDR) geothermal reservoir is developed. It incorporates the mechanical rock-fluid interaction during hydraulic stimulation and quantitatively predicts the 3D reservoir growth behavior. In this model the pre-existing fractures are generated stochastically. The fractal size distribution of the penny-shaped fractures with random orientation is assumed. The fluid flow through the discrete fracture network is simulated by mapping the connectivity of the fractured rock to a regular cubic grid under condition of constant injection pressure. The fluid flow is approximated by the Darcy law equation. The fluid pressure from the injection well induces the growth of the fractures' apertures due to the fracture shear offset. Computation of the fracture dilation requires several iterations: solving the complete flow model simulating the fracture system anew each time and recalculating the shear displacement u … More sing the inner fracture pressure from the previous iteration. The numerical model is calibrated on the basis of the field data available for the Hijiori HDR reservoir. For instance, the series of numerical computations was carried for the different randomly seeded initial distributions of fractures and their apertures within the reservoir. The distribution, which leads to a good agreement of the numerically obtained and experimentally detected Hijiori reservoir's volume and growth direction, was chosen as an appropriate one for simulating the natural fractured media. The model was used for the assessment of the adequate stress regime of the Hijiory reservoir since the related field data obtained by the different experimental technique are not very reliable. The latest version of FRACSIM-3D incorporates the multi-borehole system of injection and production wells. This improvement of the model makes possible to analyze the effect of different borehole system arrangement on the reservoir productivity. A number of numerical experiments for the different geometrical boreholes configurations have been conducted. As a result, the optimal arrangements of the production and injection wells, which provide the relevant reservoir recovery rate with lesser amount of active boreholes, are proposed. Less