Knowledge Resource Center for Ecological Environment in Arid Area
| 增强型地热系统采热开发数值模拟研究 | |
| 其他题名 | Numerical Simulation of Heat Extraction Development of the Enhanced Geothermal System |
| 翟海珍 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 江雷 ; 田野 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 增强型地热系统(Enhanced Geothermal System，EGS)是采用人工形成地热储层的方法，从低渗透性岩体中经济地采出相当数量深层地热能的人工地热系统，是开发深层高温地热资源的有效途径。EGS运行的地下过程是复杂的传热-流动-力学-化学（thermal-hydraulic-mechanical-chemical，THMC）多场耦合过程，其中热流耦合过程是复杂的THMC多场耦合过程的基础和核心。理解EGS运行过程中地下裂隙储层中流体的流动与岩体的热交换及流岩温度场的演化规律对于制定、优化EGS采热策略、建设高效EGS电站有重要指导意义。由于EGS场地试验资金投入高、技术难度大、试验周期长，本研究采用数值模拟方法开展EGS的研究。论文针对EGS裂隙储层特点，通过分析当前常用的数值模型，选取离散裂隙模型开展EGS采热开发数学模拟研究。深层热储层垂直裂隙模型是研究EGS开采过程的基本模型。本文指出了垂直单裂隙模型(single vertical fracture model，SVFM)解析解的局限性及适用范围，并在此基础上构建了平行多裂隙模型(multi-parallel fracture model，MPFM)，对比验证了模型的可靠性和优越性，可通过灵活调整模型参数研究热储激发程度对采热的影响。在此基础上引入上、下层围岩体，构建了引入围岩的平行多裂隙模型更接近真实地质情况。本文采用引入围岩的平行多裂隙模型，基于法国苏尔士（Soultz）和美国沙漠峰（Desert Peak）的地质资料和试验数据，开展了EGS热开采和热恢复数值模拟研究，评估了系统的采热性能，给出了热开采和热恢复过程中流岩温度场的演化特征，探讨了EGS采热开发的影响因素，为EGS注采策略的制定提供了重要的参考和借鉴。采用引入围岩的平行多裂隙模型对法国苏尔士地热田进行采热潜力评估，可为注采策略的制定提供数值参考依据。系统流体注入流量为30kg/s，HTU厚度为100m时，采热前15年，流体产出温度为200℃，热功率为18.9MW，电功率为2.3MW，符合商业EGS产能要求，热开采50年产出温度仅下降6.8%。EGS储层激发程度与流体产出温度、储层热采率及储层寿命呈正相关性。热恢复是保证EGS长期稳定运行的有效措施，采用引入围岩的平行多裂隙模型对美国沙漠峰地热田进行EGS热开采和热恢复数值模拟研究。结果表明，采用此模型开发沙漠峰地热田目标储层是可行的，当系统流体注入流量为100 kg/s，HTU厚度为40 m时，连续采热前20年流体产出温度为210 ℃，电功率为7.6 MW，50年内流体产出温度仅下降约6.2 %，产出温度和产能均符合EGS商业开发的要求。热恢复初期温升迅速梯度大，后期明显减缓。热恢复的主要影响因素是热恢复初始温度场及采热-热恢复时间周期。EGS储层的激发程度与系统循环流量共同作用决定了热恢复初始温度场，二者对热开采和热恢复过程的影响效应相一致。其中，HTU厚度、流体流量和热开采-热恢复周期均与流体产出温度和储层寿命呈负相关性。裂隙宽度对流体产出温度的影响不大。储层岩体的导热系数与流体产出温度和储层寿命呈正相关性。增强型地热系统储层的激发程度决定了热开采的效果，EGS储层激发呈现出较强的不均匀性。以平行多裂隙模型为基础构建平行多裂隙非均匀展布模型，研究储层不均匀激发对EGS釆热的影响。结果表明：热储层的裂隙数目是热开采的最主要影响因素，流体产出温度与裂隙数目呈不严格的正相关性，还受到裂隙及换热单元体展布特征的影响；流体产出温度与储层裂隙的优势流动比及换热单元体的优势厚度比均呈负相关性。综合而言，裂隙数目越多，裂隙宽度和换热单元体厚度分布越均匀，流体产出温度越高，采热效果越好。本研究对EGS地热田的储层激发，和人工热储层的构建有一定的指导意义。 |
| 英文摘要 | Enhanced geothermal systems (EGS) is artificial engineered reservoirs that is created to extract economical amounts of heat from deep located hot dry rock of low permeability and/or porosity. It is an effective way to explore deep geothermal energy. There undergoes a complex thermal-hydraulic-mechanical-chemical coupling process underground during EGS running, in which the most basic and important component of the multi-field coupling is the thermal-hydraulic (T-H) coupling process. Understanding the fluid flow, heat exchange and temperature filed evolution of fluid and rock within the underground heat reservoir is of great significance for EGS heat extracting strategy setting and optimizing and efficient EGS pilot development. Due to the high investment of EGS field test, the large technical difficulty and the long test period, the numerical simulation method is used to carry out EGS research. Based on the characteristics of EGS subsurface reservoir, the discrete fracture is selected to carry out the study of EGS heat extraction development by analyzing the current numerical model. Deep geothermal vertical fracture model is the basic model in the study of EGS heat extraction process. Based on the knowledge of single vertical fracture model (SVFM), the limitations and the applicable scopes of the analytical solution of SVFM is pointed out. Multi-parallel fracture model (MPFM) is built up and validated. Through adjusting the parameters of the model, MPFM can be used to study the reservoir stimulation effect on EGS heat extraction. Based on MPFM, the upper and underlying layer of surrounding rock is introduced to make the reservoir model more close to real reservoir geology. In this paper, based on the geological background and circulation data of Soultz field (France) and Desert peak field (USA), the MPFM with surrounding rock is applied to the simulation study of EGS heat extraction and recovery. The heat extraction performance is evaluated, and the evolution characteristics of the temperature field of fluid and rock are studied, and the affecting factors of EGS heat extraction are discussed. Theses researches will play an important role on guiding EGS project on injection-production strategy setting.Evaluation of heat extraction potential at Soultz field with the MPFM with surrounding rock can provide references in injection-production strategy settings. The system with a circulation fluid flow of 30kg/s, thickness of HTU of 40m, has an outlet temperature of 200℃, thermal power of 18.9MW, electric power of 2.3MW in the first 15 years. After fifty-year extraction, the outlet temperature is modeled to decreases only by 6.8%. The production temperature and power can meet the requirements of EGS commercial development. The stimulation degree of the reservoir has a positive effect on outlet temperature, heat extraction rate and lifetime when the width of fracture is constant.Heat recovery is an effective way to ensure the long-term stable operation of EGS. Based on the geological background of American Desert Peak field, we studied the heat extraction and heat recovery process with the MPFM with surrounding rock. The results suggest that, it is feasible to extract geothermal energy at Desert Peak field with this model. The system with a circulation fluid flow of 100kg/s, thickness of HTU of 40m, has an outlet temperature of 210℃, electric power of 7.6MW in the first 20 years. After fifty-year extraction, the outlet temperature is modeled to decreases only by 6.2%. The production temperature and power can meet the application demand of EGS. In the initial period of heat recovery process, temperature rises rapidly in a large gradient, while slows down in the latter period. Two main affecting factors of the recovery process are the initial temperature field and the recovery time period. For affecting the initial temperature of the recovery process together, the property of the reservoir (i.e. the stimulation degree of the reservoir and the heat conductivity of the rock) and the fluid flow has the same impact on the heat recovery process as on the heat extraction process. The thickness of HTU, fluid flow, and the heat extraction and recovery period are negatively correlated with outlet temperature and lifetime. The width of the fracture has a lesser impact on outlet temperature. The heat conductivity of the rock is positively associated with outlet temperature and lifetime. The heat extraction effect of EGS strongly depends on the reservoir stimulation degree, while the heat reservoir of EGS appeared to be strongly unevenly stimulated with differently distributed fracture networks. Based on the multi-parallel fracture model, the multi-parallel fracture non-uniformly distributed model is built to study the impact of unevenly stimulated reservoir on EGS extraction. The results reveal that the number of the fracture is the dominant factor and is not strictly positive related to the production temperature, which will also be affected by the distribution characteristics of the fracture and heat transfer unit. The production temperature is in negative correlation to the preference flow ratio and the preference thickness ratio. In conclusion, it is favorable for production from the heat reservoir by the conditions of a large number of fractures, evenly distributed fracture width and HTU thickness. This research has instructional significance for the heat reservoir stimulation and construction of artificial reservoir of other EGS geothermal fields. |
| 中文关键词 | 增强型地热系统 ; 平行多裂隙模型 ; 围岩 ; 储层激发 ; 热恢复 |
| 英文关键词 | Enhanced Geothermal System (EGS) Multi-Parallel Fracture Model (MPFM) Surrounding Rock Reservoir Stimulation Heat Recovery |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 热能工程 |
| 来源机构 | 中国科学院广州能源研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287889 |
| 推荐引用方式 GB/T 7714 | 翟海珍. 增强型地热系统采热开发数值模拟研究[D]. 中国科学院大学,2017. |
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