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Geothermal Gradient and Formation Temperature Calculator

Geothermal gradient describes temperature change per unit increase in depth. For a reference temperature T1 at positive-down depth z1 and a constant interval gradient G, a simple linear estimate is T2 = T1 + G times the difference between target depth z2 and reference depth z1. Rearranging solves reference temperature as T1 = T2 minus G times the depth interval, average gradient as G = the temperature difference divided by the depth difference, or target depth as z2 = z1 + the temperature difference divided by G. GeoMiner solves all four directions. Temperature inputs and outputs support degrees Celsius and Fahrenheit. Depth supports metres, feet, kilometres, and miles. Gradient supports degrees Celsius per kilometre, degrees Celsius per 100 metres, and degrees Fahrenheit per 100 feet. Unit conversion normalizes temperatures to Celsius, depths to metres, and gradient to degrees Celsius per kilometre before calculation. Both depths must use one declared vertical datum. In a deviated borehole, measured hole depth is longer than true vertical depth and cannot be substituted into a vertical geothermal gradient without justified geometry. Reference temperature and reference depth must describe the same physical point and condition. Land-surface air temperature, mean annual ground temperature, shallow groundwater temperature, seafloor or mudline temperature, and a temperature logged within a borehole are not interchangeable. Solving a gradient from two points returns one straight-line interval average. It does not prove that the local derivative is constant between, above, or below those points. Temperature gradients can change with rock thermal conductivity, lithology, layering, heat flow, radioactive heat production, sedimentation and erosion, topography, climate history, faults, intrusions, groundwater and hydrothermal advection, borehole flow, and measurement disturbance. Heat flow is not temperature gradient under another name. Conductive heat flow also requires representative thermal conductivity and a stated sign convention, while advective or transient conditions require a broader thermal model. Bottom-hole temperatures measured soon after drilling or fluid circulation commonly do not represent equilibrium formation temperatures. Correction validity depends on measurement method, shut-in and circulation history, basin calibration, data quality, and thermal

Verification resources

Cross-check terminology, classification, methods, and safety with these authoritative external resources.

  • undefined. Defines geothermal gradient as the rate of temperature increase with depth and provides a broad U.S. educational average.
  • undefined. Maps measured drill-hole gradients, documents wide regional variation, and distinguishes temperature gradient from heat flow through rock thermal conductivity.
  • undefined. Explains why wireline bottom-hole temperatures require corrections calibrated to the relevant basin before representing in-situ reservoir temperature.
  • undefined. Explains thermal-equilibrium and bottom-hole correction issues and why linear temperature-depth extrapolation can be inaccurate across changing lithology, fluids, and flow.
  • undefined. Defines integral geothermal gradient from temperature difference and depth and discusses local effects from lithology, conductivity, heat flow, and formation-water movement.

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Common questions

How do I calculate temperature from geothermal gradient?
For a stated reference temperature T1 at depth z1 and constant gradient G, the linear estimate is T2 = T1 + G times (z2 minus z1). Depth is positive downward and units must be compatible.
How do I calculate geothermal gradient from two temperatures?
Subtract the shallower reference temperature from the target temperature, then divide by the positive-down depth interval. State both depths, the common datum, temperature conditions, and units.
Is geothermal gradient the same as heat flow?
No. Temperature gradient describes temperature change with depth. Conductive heat flow also depends on thermal conductivity and sign convention, while groundwater flow and other processes can alter the profile.
Can an uncorrected bottom-hole temperature define the gradient?
Not reliably. Drilling and fluid circulation disturb borehole temperature. Equilibrium measurements or basin- and method-specific corrections may be required before estimating in-situ formation temperature.
Can this estimate design a well, tool, cement job, or geothermal project?
No. It is transparent linear arithmetic, not a thermal model, BHT correction, tool-rating approval, cement or mud design temperature, geothermal resource estimate, or professional design.

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