Fault damage zones potentially represent native permeable channels within otherwise ultra-tight igneous formations that may be used to promote fluid circulation for convective heat recovery. The United Downs Deep Geothermal Power (UDDGP) project aims to recover geothermal energy by directly injecting, circulating then recovering fluids from such a fault. The UDDGP project injects fluid into the fault at 2500 m where rock temperature is ~75 °C – 80 °C and recovers the injectate from 4500 m, where the bottom hole temperature is predicted to be 190 °C. We explore such down-dip circulation through numerical modeling to determine the anticipated temperature and longevity of the thermal recovery and the potential for induced seismicity (fault reactivation) by contrasting response for up-dip circulation. The results reveal that down-dip circulation not only maximizes water temperature and flow rate at the outlet but also simultaneously suppresses fault reactivation over the long term. In down-dip circulation, fault permeability in the critically stressed shallow fault damage zone is more greatly enhanced than that of the deep fault as a result of the strong injection-induced thermal stress. Fault sealing is breached as a result of reactivation in the shallow fault, prompting transverse fluid penetration and subsequent fluid circulation in the footwall. Switching the injection scheme from down-dip circulation to up-dip circulation, while maintaining an identical injection rate, leads to a drastic increase in the cumulative number of seismic events, with the average magnitude increasing from 1 to 2. This reversed well configuration (circulation bottom to top) also reduces power output from 6 to 7 MW_thermal to 2 MW_thermal, due to reduced enthalpy and flow rate in the production well. The outcomes from this study confirm the preferred design of the well pattern as circulating top to bottom, to both maximize heat recovery and limit induced seismicity. A lower production pressure is necessary to avoid pressure build-up inside the fault . Production pressure at 15–20 MPa could ensure both high cumulative power generation and a stable fault state.

断层破坏区可能代表超致密火成岩地层内的天然可渗透通道，可用于促进流体循环以进行对流热回收。United Downs Deep Geothermal Power (UDDGP) 项目旨在通过直接注入、循环然后从此类断层中回收流体来回收地热能。UDDGP 项目在 2500 m 处向断层注入流体，其中岩石温度约为 75 °C – 80 °C，并从 4500 m 处回收注入液，其中井底温度预计为 190 °C。我们通过数值模拟探索这种下倾环流，通过对比上倾环流的响应来确定热恢复的预期温度和寿命以及诱发地震活动（断层再激活）的潜力。结果表明，下倾循环不仅使出口处的水温和流速最大化，而且同时长期抑制断层再激活。在下倾环流中，由于强烈的注入热应力，浅层断层受临界应力破坏带的断层渗透率比深层断层渗透率提高得更多。由于浅层断层的再活化，断层封闭被破坏，促使流体横向渗透并随后在下盘进行流体循环。将注入方案从下倾环流切换到上倾环流，同时保持相同的注入速率，导致地震事件的累积数量急剧增加，平均震级从 1 增加到 2。_热到2兆瓦_热，由于减少了热焓和流速在生产井。这项研究的结果证实了井网的首选设计为从上到下循环，以最大限度地提高热回收率并限制诱发地震活动。需要较低的生产压力以避免断层内压力积聚。15-20 MPa的生产压力可以保证高累积发电量和稳定的故障状态。