Definition - What does Geothermal Gradient mean?
Geothermal Gradient is the rate of change of temperature as the depth of an oil well or a gas well increases. It is a physical quantity denoted by temperature per unit length. The commonly used units to represent Geothermal Gradient are Degree Fahrenheit per 100 feet or Degree Celsius per meter. The SI unit for Geothermal Gradient is Kelvin per Meter (K/m).
Petropedia explains Geothermal Gradient
As the depth of drilling increases, the temperature and Geothermal Gradient of the well also increases. It is also known as "Temperature gradient" or simply "Thermal Gradient". Average Temperature Gradient ranges from 25 to 30 degree Celsius per km or 15 degree Fahrenheit per 1000 feet. Geothermal Gradient (dT) can be expressed as dt/dL.
Geothermal Gradient is a vector quantity and is given by the formula:
dT = dt/dL
dT = (dt/dx, dt/dy, dt/dz)
L = x, y and z the three coordinates of location of interest under the ground.