西藏羊八井地热田热水的化学组成

羊八井地热田深、浅层热水都是Cl-Na类型,具有相同的B/Cl比值,说明深层热水在上升通道中与冷水相混合形成了浅层热水。浅层流体自西北向东南流动,温度逐渐降低。浅层热储内普遍存在着水岩交换反应,对热水的化学组成有一定的影响。石英和玉髓地热温度计分别适用于计算深、浅层的热储温度。纳木错(湖)不是羊八井地热田的补给区。深层热水在井筒内绝热汽化时不会出现SiO₂结垢,CaCO₃是否会在井筒壁沉淀需要放喷较长时间来检验。文中还阐述了对热水的化学组分进行监测的必要性。

CHEMICAL COMPOSITION OF THERMAL WATER IN THE YANGBAJING GEOTHERMAL FIELD, TIBET

The cold and hot waters in the Yangbajing geothermal field could be classified into Ca-HCO₃,Na-HCO₃-Cl,(Ca,Mg)SO₄ and Na-Cl types.Thermal waters in the shallow and deep reservoirs are of Na-Cl types both with the same B/Cl ratio.There is distinct difference on chemical and isotopic compositions between the thermal waters and the water of Lake Nam Co.It suggests that Lake Nam Co is not a recharge area of the Yangbajing geothermal field.The shallow thermal water is a mixture of the deep thermal fluid and the shallow cold ground water.Its movement is controlled mainly by faults in the region.It flows with a decreasing in temperature from northwest to southeast.Exploitation of the deep thermal water would accelerate the shallow resource exhaustion.Some minerals reach or approach chemical equilibrium in the shallow reservoir.Water-rock interaction results in the Na/K ratio increasing in the shallow thermal water.The calculated temperatures of Na/K geothermometer are between those in the deep and shallow reservoirs.Quartz and chalcedony geothermometers are applicable for the deep and shallow reservoirs respectively in the Yangbajing geothermal field.The CO₂ and H_{2S contents in the steam of well ZK4001 are much higher than that of the shallow fluid.Anticorrosive measures should be paid attentiosubn to during exploitation of the deep geothermal resources.When the deep thermal water adiabatically boils down to 125℃,silica scaling will become very serious.The tail water could not be used to inject directly in order to prevent silica deposit lowering rock permeability.The CaCO3 saturation index of the deep thermal water is lower than that of the shallow one and its calcite scaling is not serious.it needs a long-term discharge to verify,whether there is no calcite deposit on the wellbore.The chemical monitoring of the thermal water is of benefit to understand the state of the reservoirs.}