Geothermal fluid circulation in the Guide Basin of the northeastern Tibetan Plateau: Isotopic analysis and numerical modeling
Geothermal fluid circulation in the Guide Basin of the northeastern Tibetan Plateau: Isotopic analysis and numerical modeling
复制标题
青藏高原东北部贵德盆地地热流体循环：同位素分析与数值模拟
DOI：
10.1016/j.geothermics.2017.10.007
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
Zhang Yu
中科院分区：
文献类型：
--
作者：
Jiang Zhenjiao;Xu Tianfu;Owen D. Des R.;Jia Xiaofeng;Feng Bo;Zhang Yu
位于青藏高原东北部贵德盆地的扎仓地热田被认为是建设地热发电厂的潜在目标。本研究通过同位素分析(~3H、D、~(18)O、~3He、~4He)和流体-热-氦输运数值模拟相结合的方法，研究了该地区地热资源的形成机制。δD和δ18O表明，大气降水是扎仓地热水最可能的来源，深层水中δD和δ18O的贫化指示了积雪融化和/或较凉爽的气候的补给。一条东西走向的导电断裂作为一条管道，将上覆河流和第四系含水层中的大气降水输送到扎仓油田的裂隙花岗岩中。该导水断裂的地下水向下运动受重力的驱动，水温随深度增加而升高。不均匀的温度分布会引起浮力，导致热水在导电断层与不透水的南北走向断层相交的位置向上输送到陆地表面。补放率之间的水质量平衡和氦比的数值模拟表明，扎仓油田不存在来自深层的外部流体输入，从而导致异常高温。相反，热是由断裂活动的摩擦和/或形成于三叠纪的花岗岩中的剩余热产生的。热流运移的数值模拟结果表明，断裂带呈环流流态，出现了地下水滞留时间较长的滞流区。在重力和浮力的共同作用下，断层内的流速和温度分布不均匀，从未达到稳定状态。
The Zhacang geothermal field in the Guide Basin, in the northeast of the Tibetan Plateau, is considered a potential target for establishing a geothermal power plant. This study investigated the formation mechanisms of geothermal resources in this field by combining isotopic analysis (3H, D,18O,3He and4He) and numerical modeling of fluid-heat-helium transport. δD and δ18O indicated that the meteoric water is the most likely source of the geothermal water in the Zhacang field, with depleted δD and δ18O in deeper water indicative of recharge via snow melt and/or from cooler climates. A west-east trending conductive fault acts as a conduit that transports this meteoric water from an overlying stream and the Quaternary aquifer to the fractured granites in the Zhacang field. The downward groundwater movement in this conductive fault is driven by gravity force, and water temperature increases with depth. An uneven temperature distribution induces buoyancy force which results in heated water being transported upward to the land surface at positions where the conductive fault intersects an impermeable north-south trending fault. The water mass balance between recharge and discharge rates and the numerical modeling of the helium ratio imply that there is no external fluid input from the deep subsurface to induce the abnormally high temperature in the Zhacang field. Instead, the heat is generated by the friction of fault activity and/or the remaining heat in granite formed in the Triassic. The numerical modeling of heat and flow transport yields a circumfluence flow pattern in the fault zone, where a stagnant flow zone with high groundwater residence time appears. Both flow velocity and temperature distribute unevenly in the fault and never reach a steady state under the joint influence of gravity force and buoyancy force.