综合物探方法在佛坪穹隆地热勘探中的应用

    Application of comprehensive geophysical exploration technology in geothermal exploration of the Foping dome

    • 摘要: 陕南佛坪地区为地热空白区,为探测穹隆深部构造特征、地层结构,初步圈定地热水富集范围,布置了广域电磁测深(WFEM)和土壤氡气测量剖面,通过野外数据采集、处理和反演,获得了工作区内4000 m以浅的电性结构特征,提出了佛坪地区新的认识:由NW向SE方向多重推覆,北段逆冲,南段下滑,总体构造样式为以佛坪县城为中心的背形构造;深部存在连续分布的低阻异常带,这与底板滑脱断裂、岩体侵入时中边部形成的断裂破碎带相关,这些断裂为地下水的向下运移和储存创造了条件,推覆岩片叠加过程中,岩片间裂隙较为发育,大理岩、石英岩等脆性岩石形成的孔、洞、裂隙等形成了地热水赋存的空间。结合当地产业规划、经济发展、道路条件等客观因素,在佛坪县城以北2.5 km椒溪河西岸的长角坝镇教场坝村布设钻探工作,完钻井深2 002 m,成功打出了水温35 ℃、392 m3/d的地热水。打破了佛坪穹隆不含水或含水量少的传统理念,为该地区地质构造特征、水文地质条件研究获得了切实的实物资料,也为基础地质理论研究提供了可靠的依据。

       

      Abstract: The Foping area, a geological dome in southern Shaanxi Province, has long been a geothermal blank zone. To explore the deep structural characteristics and stratigraphic configurations of the dome and preliminarily delineate the accumulation range of geothermal water, this study arranged the wide-field electromagnetic method (WFEM) and soil radon measurement profiles in the Foping area. Through field data collection, processing, and inversion, the electrical structural characteristics of the Foping area within a burial depth of 4 000 m were obtained. A new understanding was proposed accordingly: the Foping area develops multiple nappes from northwest to southeast, with the northern and southern sections dominated by thrusting and gliding, respectively. Its overall structural style is manifested as an antiform centered around Foping County. A continuous low-resistivity anomaly zone, occurring in the deep part, is associated with the roof detachment fault and the fracture zones formed in the central and lateral parts during rock intrusion. These faults create conditions for the downward migration and storage of groundwater. The superposition of thrusting rock fragments has led to well-developed fractures between rock fragments and pores, vugs, and fractures in brittle rocks such as marbles and quartzites, constituting the space for the occurrence of geothermal water. Based on objective factors such as local industrial planning, economic development, and road conditions, drilling work was conducted in Jiaochangba Village, Changjiaoba Town, 2.5 km north of Foping County, along the west bank of the Jiaoxi River. The completed well reached a depth of 2 002 m, producing geothermal water with a temperature of 35 ℃ at a flow rate of 392 m3/d. This achievement breaks through the traditional concept that the Foping dome contains no or little water. Therefore, this study provides actual data for exploring the geological structural characteristics and hydrogeological conditions in the Foping area, as well as a reliable basis for basic geological theory research.

       

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