青海共和盆地存在干热岩可能性探讨

Exploration of the possibility of hot dry rock occurring in the Qinghai Gonghe Basin

青海共和盆地地处"秦昆岔口"的新生代断陷盆地,盆缘构造岩浆岩带发育,活动断裂、温泉密集,超过60℃的温泉6处,最高可达93.5℃;盆地内温泉成群分布,地热钻井揭露温度高,1203m钻孔(R1)实测孔底温度可达83℃,969m钻孔(QR1)实测孔底温度为70℃,地温梯度高达6～7℃/100m,是正常地温梯度的2倍,地热增温随深度增大而升高,推测3000m温度可达200℃,并在(QR1)孔底见36m花岗岩;地震反射波和可控源音频大地电磁测深推断基底斜坡界面对应重力低异常,可认为重力低异常为花岗岩引起,作为盆地热源可能存在干热岩。

The Qinghai Gonghe Basin is located in the＂Qin Kun Fork＂Cenozoic fault basin.Oil-drilling data show that the Cenozoic overburden thickness is greater than 5000 m.The basin margin structure-magma belt is well developed;active faults and hot springs are intensive.There are 6 hot springs with temperature ranging from 60℃ to 93.5℃.The hot springs occur in groups in the inner basin.Geothermal drilling data reveal that the temperature in depth is quite high.In the 1203 m borehole（R1）,the measured bottom hole temperature is as high as 83℃,and in the 969 m borehole（QR1）,the temperature can reach 70℃.The geothermal gradient is as high as 6 ～ 7℃ /100 m and is twice the normal value.Geothermal temperature increases with the decreasing depth.The temperature at a depth of 3000 m is expected to reach 200℃.At the borehole（QR1） granite of 36 m thick can be found.Seismis reflection indicates that the slope of the basement corresponds to gravity low anomaly.Gravity low anomaly is thought to be caused by granite and the basin heat source may indicate the existence of hot dry rock.