四川广安铜锣山背斜热储性质及地热成因模式

A study of the characteristics of geothermal reservoir and genesis of thermal groundwater in the Tongluoshan anticline near Guang’an in east Sichuan

岩溶热储赋存丰富的中-低温地热水,是广安市地热资源勘探和开发的主要目的层。通过地热地质、地球物理、地球化学和环境同位素等方法和手段对广安地区铜锣山背斜热储性质及成因模式进行了探讨。研究结果表明:①区内地温梯度值每百米为1.8~2.0℃,水温为26~42℃,水化学类型为SO4—Ca·Mg型,属于低温中性热矿水。②氢氧同位素显示地热水的主要补给来源为大气降水,补给高程超过1100 m,位于区域北部的大巴山一带,具有较远的补给来源及较长的径流途径。③音频大地电磁测深解译成果和2503 m地热钻井测温曲线揭示,牟家镇刘家沟村地下800~1100 m存在低阻层和温度拐点,推测为导水断裂带。基于地热钻探认识、物探解译成果、水文地球化学和同位素分析结果,概化其地热成因模式为:大气降水在高隆起背斜槽谷区渗入地下,沿溶隙、管道和构造通道自北向南形成深部径流,吸收岩石热量后成为热水,并于河流深切峡谷地段以天然温泉出露或以地热井形式被人工揭露。此项研究可为广安市地热勘探、开发和利用提供科学依据。

Abundant geothermal water of low-medium temperature occurs in the karstic geothermal reservoirs,which are the major target strata for the exploration and exploitation of geothermal resources in the city of Guang’an.In this paper,methods and means of geothermal geology,geophysics,geochemistry and environmental isotopes are used and the characteristics and genesis of the geothermal reservoirs in the Tongluoshan anticline are discussed.The comparative studies of regional geology,geological structure and geothermal wells suggests that(1)the regional geothermal gradients,water temperatures,and hydrochemical type are 18~20℃/km,26~42℃and SO4—Ca·Mg type,suggesting a neutral and low-temperature thermal mineral water.(2)The thermal groundwater is of meteoric origin,and the recharge area is located in the Daba Mountain area to the north with an elevation of more than 1100 m,indicating a deep groundwater circulation and a long flow path indicated by oxygen and hydrogen isotopes.(3)Results of the audio frequency magnetotelluric method and measured temperature curve of a geothermal well drilled to a depth of 2503 m suggest a water conducted zone at depth of 800~1100 m,since there is an area with low resistance belt and remarkable inflexion.Based on the results of geothermal drilling,the audio frequency magnetotelluric method,hydrogeochemistry and environmental isotopes,the genetic model of thermal groundwater in the Tongluoshan anticline are summarized.Groundwater receives recharge from precipitation in valley areas of the high-ridge anticline,flows from north to south through dissolved-fissure,karst conduit,and structural channels.Thermal groundwater receives heat from heat flow and discharges naturally in the deep section of the canyon and/or tapped artificially by geothermal wells.This study may provide a scientific basis for geothermal exploration,development and utilization for the local government in the city of Guang’an.