贵州省毕节市米底河地热特征及形成机理

Geothermal characteristics and formation mechanism of the Medi River in Bijie City,Guizhou Province

研究地热资源形成机理及水化学特征可为资源综合利用与开发提供参考。通过采集贵州省毕节市米底河水样进行水化学特征分析,采用Piper三线图、地温温标法和音频大地电磁等手段对米底河地下热水水化学和形成机理进行了研究。研究表明,该地区受平寨穹窿构造影响穹窿内节理构造极其发育,利于深部热水向穹窿内承压相对低区域运移,形成褶皱穹起构造对流型地下热水资源;通过区域断层探测,推断该区域存在5条断层破碎带(或者裂隙),其中F4与F13断层产状较陡,向下延伸较浅;F9比较明显,倾向北西;F1走向近似南北向,倾向北西,延伸较深;F17与F18反映较为明显,但是延伸较浅,推断F1断层具有良好的控热性,是地下热水上涌的有利位置;在平寨穹窿边部环带接受大气降水入渗补给后径流至2500 m深度内获得围岩的加热,并在上覆寒武系碎屑岩隔水、保温盖层的作用下,于震旦系灯影组白云岩中形成深部承压热储;水化学特征分析得出地热水属低矿化度水,地热井水源中Na^(+)为主要阳离子,占45%左右,其次为Ca^(2+)与Mg^(2+),占49%左右。阴离子中HCO_(3)^(-)占主体,SO_(4)^(2-)占39%,Cl^(-)几乎没有,因此地下热水水化学类型为HCO_(3)^(-)·SO_(4)^(2-)-Na·Ca型;根据玉髓温标得出地热井地下热水热储温度为53.98℃,地温梯度为2.85℃/100m,地下热水循环深度在2500 m左右。研究结果对贵州毕节地区地热资源开发利用具有较好的指导意义。

To study the formation mechanism and hydration characteristics of geothermal resources and provide a reference for the comprehensive utilization and development of resources.Collect the water samples from Midi River in Bijie City,Guizhou Province,analyze the hydrochemical characteristics,and adopt the Piper trilinear diagram,geothermal and landmark method and audio magnetotelluric method to study the geothermal hydration and formation mechanism of Midi River.The research indicates:affected by Pingzhai dome structure,the internal joint structure in the dome is very developed in this region,which is conducive to the migration of deep thermal water to the relatively low area in the dome,forming the convective underground thermal water resources of the fold dome structure.Through regional fault detection,it is inferred that there are five shattered fault zones(or fissures)in this region,among which F 4 and F 13 faults have steep occurrence and shallow downward extension;F 9 is more pronounced and tends to be northwest;F 1 has a nearly northsouth trend,tends to northwest,and extends deeper;F 17 and F 18 are more obvious,but the extension is shallow.It is inferred that the F 1 fault has good thermal control lability and is a favorable position for underground thermal water upwelling.Heating of the surrounding rock is obtained within 2500 m depth of runoff after receiving infiltration recharge water from atmospheric precipitation in the rim of Pingzhai dome,and a deep pressure-bearing thermal reservoir is formed in the dolomite of Dengying Formation of Sinian System under the action of overlying Cambrian clastic rock water-resisting and heat-preservation overburden.The analysis of hydrochemical characteristics shows that geothermal water is low-salinity water.Na^(+)is the main positive ion in geothermal well water,accounting for approximately 45%,followed by Ca^(2+)and Mg^(2+),accounting for approximately 49%.HCO_(3)^(-)accounts for the main negative ion,SO_(4)^(2-)accounts for 39%,and Cl^(-)accounts for almost no,so the chemical type of geothermal water is HCO_(3)^(-)·SO_(4)^(2-)-Na·Ca;the geothermal reservoir temperature of the geothermal well is 53.98℃,the geothermal gradient is 2.85℃/100 m,and the circulation depth of the geothermal water is approximately 2500 m.The research results have a good guiding significance for the exploitation and utilization of geothermal resources in Bijie City,Guizhou Province.