The influence of complicated fluid-rock interactions on the geothermal exploitation in the CO2 plume geothermal system
The influence of complicated fluid-rock interactions on the geothermal exploitation in the CO2 plume geothermal system
复制标题
CO2羽流地热系统中复杂的流体-岩石相互作用对地热开发的影响
DOI：
10.1016/j.apenergy.2017.10.114
复制
发表时间：
2018-10-01
期刊：
影响因子：
11.2
通讯作者：
Wang, Hongsheng
中科院分区：
文献类型：
--
作者：
Cui, Guodong;Ren, Shaoran;Wang, Hongsheng
无处不在的天然沉积储层及其高渗透性使得CO2羽流地热系统越来越受到关注。然而，地热开发过程中复杂的流体-岩石相互作用会造成严重的储层损害，制约了CO2良好的热采性能，降低了CO2羽流地热系统的应用前景。为了分析和解决这一影响地热开发的能源问题，建立了综合考虑CO2羽流地热（CPG）系统中地层水蒸发、盐分沉淀、CO2-水-岩石地球化学反应以及储层孔隙度和渗透率变化的数值模拟模型。利用该模型，分析了地热开采过程中的地球化学反应和盐沉淀作用及其对地热开采的影响，并提出了减小流体-岩石相互作用对地热开采率影响的措施。模拟结果表明，重力和蒸发引起的负的气液毛管压力梯度可以使地层水向注入器流动。地层水的回流导致盐沉淀在注入井区域中积聚，这可导致严重的储层损害和随之而来的热采率的降低。CO_2-水-岩石地球化学反应可导致某些矿物的溶解和其他矿物的沉淀，但其对热采率的影响很小，可以忽略不计。而盐沉降则通过影响CO2的流动和分布来影响地球化学反应，使热采率降低到原来的2/5。敏感性研究表明，储层条件会影响盐沉淀和热采率，因此，CPG应用应选择高温、高孔渗、低矿化度的沉积储层，并具有适当的高注采压差。在注CO2前先注低矿化度水以及CO2和水蒸气联合注气可以减少CPG系统中的盐沉淀，提高热采率。
The ubiquitous natural sedimentary reservoirs and their high permeability have made the CO2 plume geothermal system increasingly attractive. However, the complicated fluid-rock interactions during the geothermal exploitation can cause severe reservoir damage, constraining the excellent heat mining performance of the CO2 and decreasing the possible applications of the CO2 plume geothermal system. In order to analyze and solve this energy issue affecting the geothermal exploitation, in this study, a comprehensive numerical simulation model was established, which can consider formation water evaporation, salt precipitation, CO2-water-rock geochemical reactions, and the changes in reservoir porosity and permeability in the CO2 plume geothermal (CPG) system. Using this model, the geochemical reactions and salt precipitation and their effects on the geothermal exploitation were analyzed, and some measures were proposed to reduce the influence of fluid-rock interactions on the heat mining rate. The simulation results show that the gravity and the negative gas-liquid capillary pressure gradient induced by evaporation can cause the formation water to flow toward the injector. The back flow of the formation water results in salt precipitation accumulation in the injection well region, which can cause severe reservoir damage and consequent reductions to the heat mining rate. The CO2-water-rock geochemical reactions could result in the dissolution of certain minerals and precipitation of others, but its minimal influence on the heat mining rate can be ignored. However, salt precipitation can affect the geochemical reactions by influencing the CO2 flow and distribution, which can reduce the heat mining rate up to 2/5 of the original. Sensitivity studies show that the reservoir condition can affect the salt precipitation and heat mining rate, so a sedimentary reservoir with high temperature, high porosity and permeability, and low salinity should be selected for CPG application, with an appropriately high injection-production pressure difference. The injection of low salinity water before CO2 injection and the combined injection of CO2 and water vapor can be applied to reduce the salt precipitation and increase the heat mining rate in the CPG system.