Inputs
Formula Used
How to Use This Calculator
- Enter TVD and choose the depth unit.
- Set surface pressure in your preferred unit.
- Select a fluid input method and enter its value.
- Choose friction as total loss or gradient × length.
- Optionally add a safety margin and formation pressure.
- Press Calculate to view results above the form.
- Use Download CSV or Download PDF for reporting.
Example Data Table
| Case | TVD (ft) | Mud Weight (ppg) | Surface Pressure (psi) | Friction (psi) | Safety (%) | Computed BHP (psi) |
|---|---|---|---|---|---|---|
| A | 8,500 | 10.2 | 250 | 150 | 2.0 | 5,006.6 |
| B | 10,500 | 9.6 | 300 | 220 | 0.0 | 5,761.6 |
| C | 7,000 | 11.5 | 0 | 90 | 1.5 | 4,340.1 |
| D | 9,200 | 12.1 | 180 | 140 | 3.0 | 6,291.9 |
| E | 6,000 | 8.9 | 120 | 60 | 0.5 | 2,971.6 |
Pressure Components in the Wellbore
Bottomhole pressure is the sum of surface pressure, hydrostatic head, and any signed friction term, with an optional safety margin. Hydrostatic head dominates in static conditions, while friction becomes important during circulation, production, or injection. Use consistent reference points: surface pressure should match the wellhead datum used in your procedures, and depth should be true vertical for hydrostatics. The result supports quick checks, not a transient model.
Choosing an Accurate Hydrostatic Gradient
Hydrostatic pressure depends on fluid density and true vertical depth. For drilling fluids, a shortcut is G = 0.052 × mud weight(ppg) in psi/ft; for water-based references, G = 0.433 × specific gravity in psi/ft. For example, 10.0 ppg gives a gradient of 0.520 psi/ft. When density is entered as kg/m³ or SG, verify it reflects downhole temperature and gas cut.
Accounting for Friction and Flow Direction
Friction losses represent pressure change along the flow path and can be added or subtracted depending on your sign convention. During upward flow, higher friction usually requires higher surface pressure to achieve the same bottomhole pressure, so adding friction is common. If you know total loss from a hydraulics report, enter it directly. If you have a friction gradient, multiply by the chosen length; measured depth is often better for deviated wells.
Equivalent Mud Weight and Gradient Checks
Equivalent mud weight (EMW) translates the computed bottomhole pressure into an “as-if” density for comparison with pore pressure and fracture limits. EMW(ppg) = BHP ÷ (0.052 × TVDft). Review the implied bottomhole gradient, BHP ÷ TVDft, to detect unrealistic inputs. When formation pressure is provided, overbalance highlights whether the well is underbalanced, balanced, or overbalanced for stability and influx control.
Using Results for Operations and Reporting
Use calculated bottomhole pressure to screen mud programs, verify well control targets, and communicate expected pressures across teams. Compare scenarios by varying density, friction, and safety margin rather than changing multiple inputs at once. If you export results, include the input set, depth basis, and friction method to preserve traceability. Always reconcile this estimate with measured pressures, temperature-corrected densities, and detailed hydraulics before making operational decisions.
FAQs
1) What is bottomhole pressure in this calculator?
Bottomhole pressure is the estimated pressure at the specified depth. It combines surface pressure, hydrostatic head from the fluid column, and an optional friction term, then applies any selected safety margin.
2) Why does the tool use TVD and also allow MD?
Hydrostatic pressure depends on true vertical depth, so TVD is used for the fluid column. Measured depth can be used for friction length in deviated wells where flow path length exceeds TVD.
3) Which fluid input method should I pick?
Use the method that matches your trusted data source. Mud weight (ppg) and SG are common field entries, while kg/m³ suits lab density. If you already know a gradient, enter it directly.
4) How should I set the friction sign?
Choose “Add” when friction requires extra surface pressure to achieve the same bottomhole pressure, common in upward flow. Choose “Subtract” only if your workflow defines friction as reducing bottomhole pressure under your sign convention.
5) What does the safety margin percentage do?
It increases the computed base pressure by the chosen percentage to cover uncertainty in density, depth, or losses. Keep it small and documented, and avoid using it to replace proper hydraulics or measurement.
6) How do I interpret overbalance versus formation pressure?
If formation pressure is entered, overbalance equals bottomhole pressure minus formation pressure. Positive values indicate overbalance, near-zero suggests balance, and negative values suggest underbalance, which may increase influx risk depending on conditions.