Knowledge Resource Center for Ecological Environment in Arid Area
| 裂隙岩体中高温地热开采数值模拟研究 | |
| 其他题名 | Numerical Simulation of Heat Production Potential from Fractured Hot Rocks |
| 曾玉超 | |
| 出版年 | 2014 |
| 学位类型 | 博士 |
| 导师 | 吴能友 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 干热岩地热能是地热资源的主体，具有储量大、分布集中、连续性强和可提供基础电力负荷等优点。近30多年的增强型地热系统 (Enhanced geothermal system, EGS) 现场试验已经证实通过工程方法开发干热岩资源是可行的，尽管高效地开发资源还面临着不少难题。进行干热岩开发试验资金要求高、技术难度大，因此数值模拟是研究干热岩开发的重要手段，特别是研究长周期(20~30年)循环的产能和效率特征时。 本文在前人数值模拟研究的基础上，根据美国沙漠峰地热田和中国羊八井地热田的实际地质资料，重点开展了以下四个方面的研究，这能为未来开发干热岩资源提供重要的参考和借鉴。 (1)在前人研究的单竖直裂隙采热模型的基础上，建立和完善了单竖直裂隙开发沙漠峰高温岩体地热的概念模型和数值模型，利用TOUGH2求解了数值模型，获得了20年开采期内系统产热发电的能效特征；获得了裂隙温度场、压力场和水流密度场的演化规律；分析了影响系统性能的主要因素；首次推导出了水泵功率和能量效率的计算公式。结果表明在参考条件下，单竖直裂隙系统的电能功率是0.81~0.36MW，消耗的水泵功率是0.05~0.10MW，获得的能量效率是17.93~3.61。在开采期内，水泵功率逐渐增大，而能量效率逐渐降低。当裂隙渗透率在一定的范围内增大时，产出的电能功率可能改变很小，但会显著地降低水泵功率，从而显著地提高能量效率；较高的岩石热传导系数将会改善系统的生产性能，因为它提高了围岩向裂隙壁面导热的速度。通常，较高的岩石热传导系数将会提高电能功率，降低水流阻抗，从而提高系统的能量效率。采用合理的循环流量将会获得更好的电能功率曲线和合适的水流阻抗，从而非常有利于提高系统的性能。提高注入温度将会降低电能功率和水流阻抗，但对能量效率的影响可能非常有限。 (2)提出了利用双水平井开发沙漠峰高温岩体地热的方案，建立和完善了双水平井开采热能的概念模型和数值模型，利用TOUGH2求解了数值模型，获得了系统在20年内产热发电的能效特征，获得了储层温度场、压力场和水流密度场的演化规律，分析了影响系统性能的主要因素。结果表明参考条件下，该系统在20年内的电功率是8.6~6.2MW，储层水流阻抗是0.10~0.13MPa/(kg/s)，能量效率是30.6~10.8。在产能稳定阶段，岩石中的热能被稳定的汲取出来，产出温度和电功率保持不变；在产能衰减阶段，储层中的热能不断减低，产出温度和电功率逐渐降低。由于生产井维持定压生产，注入压力和储层压力在生产期内不断升高。系统的能量效率在生产开始时达到最大值，之后不断下降，这是因为产出温度维持不变或不断降低，而注入压力不断升高造成的。开采期内，注入井周围形成低温度区域、高压力区域和高密度区域，且该区域不断从注入井扩大至整个储层。决定双水平井增强型地热系统性能的主要参数是储层的渗透率，水流产量和注入温度；提高系统性能的措施是适当地提高储层渗透率，或采取合理的水流产量和注入温度。 (3)提出了单水平井开采羊八井热田裂隙基岩热能的方案，建立了单水平井开采羊八井热田裂隙基岩热能的概念模型和数值模型，利用TOUGH2求解了数值模型，获得了系统在20年采热期内采热发电的能效特征，获得了储层温度场、压力场和蒸汽饱和度场分布演化的规律，分析了影响系统性能的主要参数。结果表明在参考条件下，系统的井底压力介于8.76~3.58MPa，水泵功率介于0.04~0.20MW，发电功率介于3.23~3.48MW，能量效率介于50.00~17.16。较大的孔隙度含有较多的热流体，使得井底压力降低较慢，降低了水泵的功率，从而提高了系统的能量效率，还能够消除汽化阶段。较大的储层渗透率能够改善储层传导水流的能力，减缓井底压力下降的速度，从而降低水泵功率、提高系统的能量效率，还能消除汽化阶段。降低流体产量能减缓井底压力的降低速度，降低水泵功率和电功率，但能提高系统的能量效率。 (4)以沙漠峰地热田DP23-1井资料为依据，采用双竖直井EGS研究了井距、循环流量和储层渗透率对产能和阻抗的影响。在定流量循环条件下，开采期内由于生产井井底压力和产出温度逐渐降低，电能功率也逐渐降低。较大的井距和较低的循环流量能够减缓电能功率的衰减，而在一定范围内储层渗透率的变化对电能功率的影响不大。开采期内由于储层温度逐渐降低，使得水流的粘度/密度比逐渐变大，导致水流阻抗逐渐增大。较大的井距和较高的循环流量将增大水流阻抗，但效应不明显；而在一定范围内提高储层渗透率将显著地降低储层水流阻抗。 |
| 英文摘要 | Deep geothermal resource or hot dry rock (HDR) geothermal resource is main part of the total geothermal resource. The reserves of the HDR geothermal resource is very big, and the resource is constantly available and thus can be used to generate base-load power with no need for storage and virtually no emissions. The enhanced geothermal system (EGS) field tests for the past 30 years have shown that it is feasible to develop the HDR resource by engineering approaches, though there are still many big problems for exploiting the resource of high efficiency. How to exploit the deep geothermal resource with effective method and analyze the production performance and efficiency during long-term circulations is the most important key problem for EGS field project. It is very hard and expensive to conduct the field tests of EGS, so numerical simulation is important way to research the EGS, especially to research the capacity and efficiency during long-term (20~30years) circulations. Based on previous numerical studies, this work has conducted the following studies from four aspects according to the geological data from Desert Peak geothermal field and Yangbajing geothermal field. These researches will paly an important role for expanding research and development of HDR resource in the future. (1) According to previous heat mining models of single vertical fracture, this work has established a new conceptual and numerical heat mining model of single vertical fracture based on the geological and engineering data from the Desert Peak geothermal field; the numerical model is solved with the TOUGH2 codes. Based on these, the capacity and efficiency characteristics during a period of 20 years have been obtained, and the evolutions of temperature distribution, pressure distribution and water density distribution are displayed. Main influencing factors of system performance are also analysed. The computational formulas of pump power and energy efficiency are deduced for the first time. Under reference conditions, the single fracture system obtains an electric power of 0.81~0.36MW, with a pump power of 0.05~0.10MW and an energy efficiency of 17.93~3.61. The pump power gradually increases while the energy efficiency continuously declines during the heat mining period. When the fracture permeability increases within a certain range, the electric power may change very slightly, but the pump power will obviously decrease, thus the energy efficiency will improve obviously. A higher rock heat conductivity will improve the electric power, decrease the water flow impedance, and finally increase the energy efficiency. A reasonable water production rate will improve the electric power and decrease the water flow impedance, thus will greatly improve the system performance. Increasing the injection temperature will decrease the electric power and water flow impedance, but may only slightly influence the energy efficiency. (2) This paper proposed a scheme of heat mining through two horizontal wells at Desert Peak site, and established the conceptual and numerical model of heat production by water circulating through two horizontal wells. We have solved the numerical model with TOUGH2 codes. The results show that the two horizontal well system obtains an electric power of 8.6~6.2MW, with a water flow impedance of 0.10~0.13MPa/(kg/s) and an energy efficiency of 30.6~10.8 during the 20 years. During the stable stage, the production temperature and electric power maintain unchanged; during the declining stage, the production temperature and electric power gradually decline. Because the bottomhole pressure of production well is maintained as constant, the reservoir pressure along with the injection pressure gradually increases. The energy efficiency decreases with time as the injection pressure continuously goes up. During the heat mining period, there forms cold temperature zone, high pressure zone and high water density zone around the injection well, and t |
| 中文关键词 | 干热岩 ; 增强型地热系统 ; 单竖直裂隙 ; 双水平井 ; 单水平井 |
| 英文关键词 | hot dry rock enhanced geothermal system single vertical fracture two horizontal wells single horizontal well |
| 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/2XILL650/287330 |
| 推荐引用方式 GB/T 7714 | 曾玉超. 裂隙岩体中高温地热开采数值模拟研究[D]. 中国科学院大学,2014. |
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