Wellbore–reservoir coupled simulation to study thermal and fluid processes in a CO2-based geothermal system: identifying favorable and unfavorable conditions in comparison with water
Wellbore–reservoir coupled simulation to study thermal and fluid processes in a CO2-based geothermal system: identifying favorable and unfavorable conditions in comparison with water
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DOI：
10.1007/s12665-015-4293-y
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发表时间：
2015-03
影响因子：
2.8
通讯作者：
Tianfu Xu;Guanhong Feng;Z. Hou;H. Tian;Yan Shi;Hongwu Lei
中科院分区：
文献类型：
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作者：
Tianfu Xu;Guanhong Feng;Z. Hou;H. Tian;Yan Shi;Hongwu Lei
利用CO2作为传热流体提取地热能是目前被认为是实现CO2资源化和地质封存的一种途径。CO2作为一种新型的传热流体，其热物理性质与水有很大的不同。CO2具有许多优点，如密度和粘度较低，因而具有较大的流动性和浮力。这将减少驱动循环的压力消耗，并节省外部设备的能量。在负循环压差条件下，甚至可以利用虹吸现象实现循环。然而，CO2作为传热流体仍存在一些缺点，如热容小，导致在相同质量流量下热量较少。同时，由于CO2具有较大的膨胀和压缩系数，温度和压力的变化可能会引起更复杂的流动和热力学过程。较大的压缩系数使注入井底部温度较高，而较大的膨胀系数使温度沿生产井沿着迅速下降。因此，如何科学地控制生产压力，保证生产井口有足够的高温，从而提高热采效率，是需要进一步解决的关键问题。地质和地热条件与松辽盆地中央坳陷相对应。该凹陷具有较高的地热梯度和热流。在本文中，一个经典的理想化的“五点”油藏模型与井筒耦合用于模拟和分析。研究目的是：（1）研究超临界CO2在井筒和储层中的流动和热过程;（2）了解超临界CO2的排热机理;（3）分析CO2作为传热流体的优缺点;（4）为传热流体的选择提供理论依据。
Using CO2as a heat transmission fluid to extract geothermal energy is currently considered as a way to achieve CO2resource utilization and geological sequestration. As a novel heat transmission fluid, the thermophysical properties of CO2are quite different from those of water. CO2has many advantages, such as larger mobility and buoyancy resulted from the lower density and viscosity. This will reduce the consumption of pressure driving the circulation, and save the energy of external equipment. The cycle even can be achieved by siphon phenomenon under a negative circulating pressure difference. However, there are still some disadvantages for CO2as the heat transmission fluid, such as small heat capacity, leading to a less heat at the same mass flow rate. At the same time, because of the lager expansion and compression coefficient for CO2, changes in temperature and pressure may cause a more complex flow and thermodynamic processes. The lager compressibility makes it possible to get high temperature at the bottom of the injection well, whereas the lager expansion coefficient makes the temperature drop rapidly along the production well. Therefore, how to scientifically control the production pressure to guarantee sufficient high temperatures at the head of production well and, thereby, improve the efficiency of heat extraction are the key issues needed to be further addressed. The geological and geothermal conditions correspond to the central depression of the Songliao Basin located in the Northest of China. This depression has a high geothermal gradient and heat flow. In this article, a classic idealized “five-spot” reservoir model coupled with wellbores is used for simulations and analyses. The objectives of the present work are: (1) to investigate the fluid flow and thermal processes of supercritical CO2along the wellbore and in the reservoir, (2) to understand the heat-extracting mechanism, (3) to identify advantages and disadvantages of using CO2as the heat transmission fluid, and (4) to provide a theoretical basis for the selection of heat transmission fluid.