synonymGeothermal heating rate(Below the normal temperature layer, it is controlled by the heat energy generated by the transformation of radioactive elements inside the earth) Generally, it refers to the geothermal gradient
Geothermal gradientAlso called“Geothermal gradient”、Geothermal heating rate。It refers to the growth rate of the earth's stratum temperature, which is not affected by the atmospheric temperature, increasing with the depth.A parameter indicating the degree of uneven distribution of temperature in the earth's interior.Generally, the deeper the burial depth is, the higher the temperature value is, which is expressed by the increased number of ℃ per 100 meters of vertical depth.The geothermal gradient value is different in different locations, usually (1-3) ℃/100m, and the volcanic activity area is relatively high.
Chinese name
Geothermal gradient
Foreign name
geothermal gradient
Alias
Geothermal gradient、Geothermal heating rate
Definition
Parameter of uneven distribution degree of temperature in the earth's interior
measuring method
Direct measurement, artificial ground temperature and geothermal flow measurement
Special area
Geothermal anomaly zone
Special area representatives
Huanren County, eastern mountainous area of Liaoning Province
In practical work, it is usually expressed by the temperature increase value per 100 meters or 1 kilometer of depthGeothermal gradient；In the geothermal anomaly area, the geothermal gradient is often expressed by the temperature increase value per 10m or 1m depth.The approximate average geothermal gradient of the earth's crust is 25 ℃ per kilometer. If it is greater than this number, it is called geothermal gradient anomaly.The geothermal gradient near the surface varies from place to place, and its size is proportional to the large geothermal flow in the areaThermal conductivityInversely.Therefore, the regional variation of geothermal gradient may come fromHeat flowThe change of the thermal conductivity of the near surface rock mass may also be the source of the change of the thermal conductivity of the near surface rock mass.In the whole earth interior, the geothermal gradient gradually decreases with the increase of depth.[1]
The reciprocal of the geothermal gradient is called geothermal gradient, or geothermal degree, and its physical meaning can be understood as two when the temperature differs by 1 ℃Isothermal surfaceDistance between.
Positive and negative gradients
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The direction of geothermal gradient points to the direction of temperature increase, which is called positive gradient.
If the temperature goes down, that is, it decreases with the increase of depth, it is called negative gradient.Negative gradients often occur after hot field drilling penetrates the thermal reservoir.[1]
Measurement of geothermal gradient
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direct measurement
The direct measurement of ground temperature is carried out in underground conditions such as tunnels, drilling wells or seabed.The shallowest is to measure the ground temperature at a depth of 1 meter underground, which is a simple method of measuring ground temperature. The data of this ground temperature field can be used to find geothermal fields with large abnormal amplitude and shallow burial depth.Direct detection of concealed underground thermal storage structures, often conducted in shallow wells of 10~30m or 50~100mtemperature gradient measurement 。The geothermal field data at this depth can reflect the thermal reservoir structures with different abnormal amplitudes and burial depths.The deeper geothermal field (such as 300~1000m) is used to study regional structure, deep geothermal resources and oil and gas fields.For example, the geothermal anomaly on the contour map of geothermal gradient in the northern North China Plain reflects the deep geothermal resources and oil and gas fields.[2]
Artificial ground temperature method
Geothermal prospectingIt mainly measures the natural temperature field of the surface and crust.Like electrical method and seismic exploration, geothermal method can also artificially create a local temperature field to study certain geological problems.The borehole temperature diffusion method is a commonly used artificial geothermal method.After quantitative hot (or cold) water is injected into the well, the temperature change of the whole well can be repeatedly measured after a certain period of time to study the aquifer.This method is more effective when the salinity of underground aquifer is high and the conventional salt diffusion method cannot be used.Inject hot (or cold) water into a well, and observe the temperature change of the surrounding wells, you can calculate the water conductivity of the aquifer, study the energy storage space and efficiency of the aquifer, and study the development life of the geothermal field's thermal storage.
Geothermal flow measurement
The temperature field of the crust is affected by many disturbing factors.The geothermal gradient is related toThermal conductivity of rockTherefore, the application of these data is limited by region and time, which is not conducive to national or global comparison.Geothermal flow value is an ideal parameter.
Geothermal gradient anomaly zone
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Geothermal gradient anomaly can be used to studygeological structure At the same time, it also plays an important role in studying the formation and distribution of minerals (gold, oil, etc.).
The temperature change in nature depends on the light and heat of the sun,Due to the existence of the declination angle, the annual change of the movement of the solar direct point between the north and south latitudes of 23 ° 26 'on the earth is caused, which causes the seasonal change of the noon solar height and the length of day and night, and causes the seasonal change of the amount of solar energy obtained by various places, so the revolution of the sun forms the replacement of the four seasons.[3]However, some strange lands have broken this natural law, and a magical phenomenon - warm in winter and cool in summer has appeared. Such zones are called geothermal anomaly zones.
