超临界地热资源的地球物理分析--以鲜水河高温水热系统为例

Geophysical analysis of supercritical geothermal resources: a case study of Xianshuihe high-temperature hydrothermal system

鲜水河高温水热系统位于川西地热区,是我国重要的“水热型”地热资源区和高温地热发电工程建设选区,其深层超临界地热资源可以大幅提高热-功转换效率和地热发电能力,具有极大的应用价值.超临界地热资源是地热学的全新研究方向,研究深层超临界地热资源促进地热学拓宽研究领域,具有重要的科学意义.本文利用地球物理资料、地热地质资料,对鲜水河高温水热系统超临界水热流体构造条件、有利赋存部位、热结构与热状态开展计算分析.结果表明:鲜水河断裂带浅源小震群与深层超压热流体层相关,热泉群串珠状负重力异常圈闭之下超厚沉积地层是赋存深层超临界地热流体储层的有利构造部位;康定中谷-二道桥-榆林宫热水区的水源补给、热源补给、水热循环通道等地热地质条件优良,其下方存在酸性岩浆活动,是形成高温水热系统浅层热储、深层超临界热液区的重要热源条件.我们认为:鲜水河断裂带是深部热流体上升至浅表产生强烈水热活动的通道,沿此通道,在160~250℃温度区间,是鲜水河水热系统地热储层的赋存区域;在350~400℃温度区间,是深层超临界流体(H2O、CO_(2))的赋存区域;随温泉水大量溢出的高浓度CO_(2)地热气体,伴随出现pH值略小于7的弱酸性热水,其下方是形成深层超临界地热资源的有利区域.

Xianshuihe high-temperature hydrothermal system, located in the geothermal area of Western Sichuan, is an important construction area of high temperature geothermal power generation project in China. It contains deep supercritical geothermal resources, which can greatly improve the geothermal power generation capacity. It is of great interest to study deep supercritical geothermal resources. Supercritical geothermal resources is a new research direction of geothermal science and will broaden the research fields of geothermal geology. The study of deep supercritical geothermal resources has important scientific significance. Based on geophysical data and geothermal geological data, this paper calculates and analyzes the structural condition, favorable location, thermal structure and state of supercritical hydrothermal in Xianshuihe hydrothermal system. The results show that the shallow source small earthquake in Xianshuihe fault zone is related to the deep overpressure hot fluid layer, and the ultra thick sedimentary stratum under the beaded negative gravity anomaly trap corresponding to hot spring group is a favorable structural position for the occurrence of deep supercritical geothermal fluid reservoir. The geothermal geological conditions such as water supply, heat source supply and hydrothermal circulation channel are excellent in Kangding Zhonggu-Erdaoqiao-Yulingong hot water area. There is acidic magmatism below the hot water area, which is an important heat source for the shallow thermal reservoir and deep supercritical hydrothermal area. We argue that Xianshuihe fault zone is a channel that produce strong hydrothermal activity from deep thermal fluid to shallow surface. Along this channel, in the temperature range of 160~250 ℃, it is the occurrence area of geothermal reservoir. In the temperature range of 350~400 ℃, it is the occurrence area of deep supercritical fluid(H2O, CO_(2)). A large amount of high concentration CO_(2) geothermal gas overflowed with warm spring water is accompanied by weak acidic hot water with pH value slightly less than 7, below which is a favorable area for the formation of deep supercritical geothermal resources in Xianshuihe thermal system.