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

提出了一种改进的裂缝性干热岩(HDR)地热储三维模拟模型(FRACSIM-3D)。该方法考虑了水力吞吐过程中岩石-流体的力学相互作用，定量预测了三维油藏的生长动态。在该模型中，预先存在的裂缝是随机产生的。假设了具有随机取向的硬币状裂缝的分维尺寸分布。在注水压力恒定的条件下，通过将裂隙岩石的连通性映射到规则的立方体网格来模拟流体在离散裂隙网络中的流动。流体流动可用达西定律方程近似。由于裂缝的剪切偏移，注入井的流体压力会导致裂缝开度的增长。裂缝扩张的计算需要几次迭代：求解完整的流动模型，每次重新模拟裂缝系统，重新计算剪切位移u…。更多的是从上一次迭代中得到的内部破裂压力。根据Hijiori HDR油藏的现场资料对数值模型进行了标定。例如，对储集层内不同随机播种的裂缝及其孔隙度的初始分布进行了一系列的数值计算。数值模拟结果与实验测得的Hijiori储集层体积和发育方向吻合较好，是模拟天然裂缝性介质的较好分布。由于不同实验技术获得的相关现场数据不太可靠，该模型被用于评价Hijiory油层的充分应力状态。最新版本的FRACSIM-3D结合了注水井和生产井的多井系统。该模型的改进使分析不同井系布置对油藏产能的影响成为可能。针对不同的井眼几何构型进行了大量的数值实验。提出了以较少的活跃井数获得相应的油藏采收率的生产井和注水井的优化布置方案。较少

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