Live Engineering Dashboard

Well Testing Toolbox

Interactive Tools

Engineering calculators and conversion utilities for field work.

How to Use this Calculator

This tool provides two methods to calculate the Static Bottom Hole Pressure (Pws) and the initial Gas Gradient.

1. Exponential Method (Precise)

Uses the full barometric formula: $$P_{ws} = P_{wh} \cdot e^{\frac{0.01875 \cdot \gamma_g \cdot D}{Z_{avg} \cdot T_{avg}}}$$ Requires SG, Temp, and Z-factor for higher accuracy.

2. Simplified Method (Rule of Thumb)

A field approximation: $$P_{ws} = P_{wh} + 0.25 \left(\frac{P_{wh}}{100}\right) \left(\frac{D}{100}\right)$$ Useful for quick estimates when gas properties are unknown.

✅ Step 1: Enter Gas Gravity (SG) and Wellhead Pressure (psia).
✅ Step 2: Input Depth and Average Reservoir Temperature in Rankine (°R).
✅ Step 3: Results update automatically. Compare the green (Precise) vs yellow (Simplified) cards.

Gas Gradient & Static BHP

* Enter values in fields and find results in the cards below.

Gas Gravity (SG)

Wellhead Press (psia)

Depth (ft)

Avg Temp (°R)

Avg Z-Factor

Gas Gradient (psi/ft)

Pws (Exponential) psia

Pws (Simplified) psia

Scientific Basis (Static BHP)

1. Gas Gradient ($G$)

$$G = \frac{0.01875 \cdot \gamma_g \cdot P_{wh}}{Z_{avg} \cdot T_{avg}}$$

2. Static BHP (Exponential)

$$P_{ws} = P_{wh} \cdot e^{\left(\frac{0.01875 \cdot \gamma_g \cdot D}{Z_{avg} \cdot T_{avg}}\right)}$$

3. Static BHP (Simplified)

$$P_{ws} = P_{wh} + 0.25 \left(\frac{P_{wh}}{100}\right) \left(\frac{D}{100}\right)$$