drilling · temperature
Bottom Hole Temperature (BHT)
BHT = Ts + (G × TVD / 100)
click formula to derive ↑
Inputs
°F
°F/100ft
ft
Description
Estimates bottom hole temperature from a linear geothermal gradient applied to true vertical depth. BHT is a critical input for Rw temperature corrections, mud and cement design, and identifying HPHT well conditions.
Variables
| Symbol | Unit | Description |
|---|---|---|
| BHT | °F | Bottom Hole Temperature |
| Ts | °F | Mean annual surface (or mudline) temperature at the wellsite — typically 50-70°F for onshore US, lower for arctic or deepwater locations. |
| G | °F/100ft | Geothermal gradient for the area. Typically 1.0-1.5°F/100ft onshore; higher gradients (1.5-1.8°F/100ft) are common in Gulf of Mexico salt-withdrawal basins. |
| TVD | ft | True vertical depth to the point of interest. For a deviated well, use TVD, not measured depth (MD). |
Assumptions
- Geothermal gradient is approximately linear over the depth range of interest (no major lithology-driven gradient changes, e.g., across a salt body)
- Surface/mudline temperature value is representative of the long-term average, not a single day's reading
- TVD is accurate — for deviated or horizontal wells, MD must first be converted to TVD
Limitations
- Real gradients are rarely perfectly linear — salt, igneous intrusions, and basement rock change thermal conductivity and bend the gradient
- Static BHT differs from the circulating temperatures measured during logging; allow time for thermal recovery before treating a logged temperature as static BHT
- Single-gradient models break down across major unconformities or where deep aquifer flow redistributes heat
Use Cases
- → Rw temperature correction: Use BHT as the target temperature when correcting a water resistivity measured at a different (e.g., surface) temperature for Archie Sw calculations.
- → HPHT well planning: Screen whether a planned well will encounter HPHT conditions (commonly >300°F / 150°C) requiring specialized mud, cement, and completion equipment.
- → Mud and cement design: Provide the design temperature for mud rheology programs and cement slurry thickening time calculations.
Related Calculations
Region Notes
Permian Basin
Geothermal gradient is relatively low, around 1.1-1.2 °F/100ft; a 10,000 ft TVD well with Ts≈65°F typically reaches BHT≈175-185°F.
Gulf of Mexico
Salt-withdrawal basins commonly show elevated gradients of 1.5-1.8 °F/100ft above and around salt bodies, with cooler gradients directly beneath thick salt.
Haynesville
High-temperature shale gas play with gradients often exceeding 1.5°F/100ft, producing BHT >300°F at typical 12,000-14,000 ft depths — routinely HPHT.
North Sea
Central Graben gradients average ~1.0-1.2°F/100ft (≈30°C/km); mudline temperature for water depths >100m is close to 4°C and should be used instead of land surface temperature.
References
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