Tidally Modulated Temperature Observed Atop a Drillsite at the Noho Hydrothermal Site, Mid‐Okinawa Trough
Tidally Modulated Temperature Observed Atop a Drillsite at the Noho Hydrothermal Site, Mid‐Okinawa Trough
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DOI：
10.1029/2021jb023923
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发表时间：
2022-01
期刊：
影响因子：
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通讯作者：
M. Kinoshita;K. Kitada;T. Nozaki
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文献类型：
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作者：
M. Kinoshita;K. Kitada;T. Nozaki
我们在日本西南部冲绳海槽中部的Noho热液系统中钻了一个50 m深的钻孔，在安装在该钻孔顶部的Kuroko矿石（热液硫化物）培养装置中观察了10个月的温度变化，以监测热液流体和原位矿物沉淀实验。装置安装后，温度和压力立即随潮汐周期波动。最初，平均温度为75 - 76 ° C，半日潮温调制的幅度为10.3 ° C。四个月后，潮汐温度调制的幅度逐渐增加到4 ° C，与平均温度下降到1.40 ° C同步。数值模拟结果表明，潮汐振幅的增加和平均温度的降低都是由于流入装置的流量逐渐减少，这促进了通过管壁的传导冷却。流入量减少可能是由于设备内部堵塞造成的，但我们不能排除自然原因，因为钻井会显著减少储层中热流体的体积。温度波动相位滞后于压力波动相位约150 °。假设波动起源于流入从水库，我们进行了二维数值热液模拟的多孔弹性介质。为了产生150 °的相位滞后，储层中的渗透率需要超过周围地层中的渗透率103个数量级。潮汐变化相可以作为评估水热系统水文状态和响应的有用工具。
We observed temperature variations over 10 months within a Kuroko ore (hydrothermal sulfide) cultivation apparatus installed atop a 50‐m‐deep borehole drilled in the Noho hydrothermal system in the mid‐Okinawa Trough, southwestern Japan, for monitoring of hydrothermal fluids and in situ mineral precipitation experiments. Temperature and pressure in the apparatus fluctuated with the tidal period immediately after its installation. Initially, the average temperature was 75–76°C and the amplitude of the semidiurnal tidal temperature modulation was ∼0.3°C. Four months later, the amplitude of tidal temperature modulation had gradually increased to 4°C in synchrony with an average temperature decrease to ∼40°C. Numerical modeling showed that both the increase in tidal amplitude and the decrease in average temperature were attributable to a gradual decrease in inflow to the apparatus, which promoted conductive cooling through the pipe wall. The reduced inflow was probably caused by clogging inside the apparatus, but we cannot rule out a natural cause, because the drilling would have significantly decreased the volume of hot fluid in the reservoir. The temperature fluctuation phase lagged the pressure fluctuation phase by ∼150°. Assuming that the fluctuations originated from inflow from the reservoir, we conducted 2D numerical hydrothermal modeling for a poroelastic medium. To generate the 150° phase lag, the permeability in the reservoir needed to exceed that in the ambient formation by ∼three orders of magnitude. The tidal variation phase can be a useful tool for assessing the hydrological state and response of a hydrothermal system.