Formation Temperature Calculator: Geothermal Gradient at Depth

How It Works

1. Enter Surface or Mudline Temperature

   Input the mean annual surface temperature, mudline temperature, or project datum temperature. Replace generic values with NOAA, measured, or project-specific data when available.

2. Enter Geothermal Gradient

   Input the local gradient in degF per 100 ft or degC per 100 m. Use corrected offset wells, heat-flow maps, or geothermal data rather than the local presets for decisions.

3. Enter Target TVD

   Input true vertical depth from the selected temperature datum. Do not use measured depth unless it has been converted for the well trajectory.

4. Review Source Warnings

   Use the static temperature, local below-static BHT screen, and optional tool-rating margin as preliminary flags only. Confirm with corrected temperatures, manufacturer derates, and qualified review.

Built For

• Drilling teams performing a first-pass temperature screen before gathering offset BHT and well-program data
• Cementing and mud specialists flagging whether a well may need project-specific temperature validation
• Logging and MWD/LWD planners checking whether a user-entered tool rating deserves vendor review
• Geothermal teams making an early depth-temperature sensitivity table before resource modeling
• Geoscientists comparing local gradient assumptions against corrected temperature or heat-flow data
• Completion teams flagging elastomer, electronics, and material-temperature questions for manufacturer review
• Well planners documenting preliminary temperature assumptions for later validation

Features & Capabilities

Linear Gradient Screen

Computes T = T_surface + gradient x TVD as a transparent local arithmetic screen, not a calibrated thermal model.

Local Preset Table

Includes regional starting points that are explicitly labeled as assumptions and should be replaced by local data.

Gradient Sensitivity

Shows plus/minus 10 and 20 percent sensitivity so users can see how much the assumption moves the result.

Tool Rating Flag

Compares the estimate against a user-entered rating while warning that manufacturer derates and job conditions control.

Unit Conversion

Switches between degF, degC, degF/100 ft, degC/100 m, feet, and meters.

PDF Export

Exports the preliminary screen with source warnings, assumptions, and source pointers.

Assumptions

• Geothermal gradient is constant from the selected datum to the depth of interest.
• Surface or mudline temperature is entered by the user and has not been independently validated.
• Default regional gradients are local source-gap planning assumptions only.
• No transient drilling, production, injection, salt, lithology, or fluid-flow thermal effects are modeled.

Limitations

• Does not apply Horner or other BHT correction methods to wireline, DST, or production temperature data.
• Does not validate cement, mud, elastomer, electronics, logging, MWD/LWD, or completion equipment suitability.
• Does not model non-linear gradients, layered thermal conductivity, salt, hydrothermal circulation, or geothermal reservoir flow.
• Does not replace NOAA climate normals, mudline data, offset wells, heat-flow maps, or project thermal modeling.
• Not suitable as a final geothermal resource, HPHT, well-control, cement, or tool-run decision.

References

• USGS source pointers for geothermal-gradient and bottom-hole-temperature correction context.
• NOAA NCEI climate normals source pointer for site temperature context.
• DOE geothermal basics source pointer for general geothermal-energy context.
• Current offset well data, corrected BHT, product data sheets, manufacturer derates, and qualified review.

Frequently Asked Questions