Calculator Inputs
Example Data Table
| Scenario | Pore Pressure (psi) | TVD (ft) | Overbalance (%) | Safety (psi) | Computed MW (ppg) |
|---|---|---|---|---|---|
| Conservative well control | 6,500 | 10,000 | 3 | 150 | ~13.25 |
| Standard planning estimate | 4,800 | 8,500 | 2 | 100 | ~11.22 |
| Gradient-based check | — | — | — | — | 0.465 psi/ft → ~8.94 ppg |
Formula Used
- Hydrostatic pressure: P = 0.052 × MW(ppg) × TVD(ft)
- Mud weight from pressure: MW = P ÷ (0.052 × TVD)
- Mud weight from gradient: MW = Gradient(psi/ft) ÷ 0.052
- Target pressure: Pᵗ = Pᵖ × (1 + OB%) + Safety
Units shown are field-standard. Conversions to SG and kg/m³ are included.
How to Use
- Select a calculation mode for your task.
- Enter depth, pressure, or gradient values.
- Add overbalance and safety margin if required.
- Press Submit to view results above the form.
- Download CSV or PDF for documentation.
Engineering Notes
- Use true vertical depth for hydrostatic calculations in vertical wells.
- For deviated wells, consider using TVD at the pressure point of interest.
- Overbalance and safety margin should reflect the drilling program and uncertainty.
- Always validate against local procedures and real-time measurements.
Mud weight as a primary well control variable
Mud weight is the simplest field control for maintaining bottomhole pressure above formation pore pressure while staying below fracture limits. A small change in density can shift hydrostatic pressure by hundreds of psi across deep intervals, affecting kick tolerance, trip margins, and equivalent circulating density planning.
How depth and gradient drive hydrostatic pressure
The calculator uses true vertical depth to translate density into pressure through a standard conversion constant. This links the pressure gradient in psi/ft to mud weight in ppg and allows quick checks against offset data. When a measured gradient is available, converting it directly to density reduces transcription errors. For directional wells, use TVD at the point of interest because measured depth does not represent hydrostatic height.
Applying overbalance and safety margin inputs
Operational practice often requires holding an intentional overbalance to accommodate uncertainties in pore pressure, temperature, cuttings loading, and measurement noise. The percentage overbalance and fixed safety margin in this tool build a target pressure. The resulting mud weight represents a planned minimum for static conditions.
During execution, circulating conditions may raise equivalent density due to frictional losses. Use the computed static density as a baseline, then compare to circulating models and fracture gradient limits to keep the operating envelope intact across pumps on, connections, and trips.
Unit conversions for consistent reporting
Field teams may communicate in ppg, while engineering reports may require specific gravity or metric density. The tool outputs SG and kg/m³ from the same computed mud weight so daily logs, drilling programs, and management summaries remain consistent. Pressure gradient is also shown in kPa/m for metric workflows. Consistent units also help compare mud checks, pit volume trends, and laboratory reports without manual rework.
Using exports for audits and daily documentation
Well control calculations are frequently reviewed during pre-spud, handovers, and incident investigations. Exporting results as CSV supports quick inclusion in spreadsheets, while PDF provides a print-ready record with the inputs and computed outputs. Keeping these snapshots with the daily drilling report improves traceability and decision clarity. Standardized exports also support training, peer review, and verification when conditions change.
FAQs
1) What mud weight unit does the calculator use?
The primary output is pounds per gallon (ppg). The same result is automatically converted to specific gravity (SG) and kilograms per cubic meter (kg/m³) for consistent reporting across field and office teams.
2) Which depth should I enter for deviated wells?
Use true vertical depth (TVD) at the point where you need pressure control. Measured depth can overstate hydrostatic height in deviated sections and can misrepresent the static pressure you are trying to balance.
3) How are overbalance and safety margin applied?
The tool builds a target pressure by adding a percentage overbalance to pore pressure, then adding a fixed safety margin in psi. It then computes the minimum static mud weight needed to meet that target at TVD.
4) Can I calculate pressure from an existing mud weight?
Yes. Select the hydrostatic pressure mode, enter mud weight and TVD, and the calculator returns hydrostatic pressure and equivalent gradients. This is useful for quick checks during planning and operations.
5) Why do my results differ from an ECD model?
This calculator is for static hydrostatic relationships. ECD adds annular friction while circulating, and it depends on rheology, flow rate, hole geometry, and cuttings. Use this result as a baseline, then compare to circulating limits.
6) What do the CSV and PDF exports contain?
Exports include the key outputs and their units, plus the calculation mode label. CSV is best for spreadsheets and trend tracking, while PDF is useful for printing, sign-off, and attaching to daily reports.