Formation Temperature for a Given Gradient is the estimated temperature of a geologic formation at a specified depth, calculated from a known geothermal gradient and a reference surface temperature. It is a basic concept in petroleum engineering, geothermal engineering, hydrogeology, and subsurface geoscience because the temperature of underground formations influences fluid properties, rock behavior, drilling operations, well design, cement selection, logging interpretation, reservoir performance, and geothermal energy potential.
Formation Temperature for a Given Gradient Formula |
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\( T_f \;=\; T_s \cdot g_g \cdot \left( \dfrac{ D }{ 100 } \right) \) (Formation Temperature for a Given Gradient) \( T_s \;=\; \dfrac{ T_f \cdot 100 }{ g_g \cdot D } \) \( g_g \;=\; \dfrac{ T_f \cdot 100 }{ T_s \cdot D } \) \( D \;=\; \dfrac{ T_f \cdot 100 }{ T_s \cdot g_g } \) |
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| Symbol | English | Metric |
| \( T_f \) = Formation Temperature | \(^\circ F\) | - |
| \( T_s \) = Temperature Near Surface | \(^\circ F\) | - |
| \( g_g \) = Geothermal Gradient | \(F \;/\; 100\;ft\) | - |
| \( D \) = Total Depth | \(ft\) | - |
The Earth's temperature generally increases with depth due to heat flowing from the Earth's interior. This increase is described by the geothermal gradient, which is the average rate of temperature increase per unit depth. Assuming the gradient remains constant over the depth interval of interest, the formation temperature can be estimated by adding the temperature increase due to depth to the surface or reference temperature.
