You have learned how to estimate the gas migration rate. Today, I would like to show you how to figure out the **actual gas migration rate after** you shut the well in due to well control.

The concept of this topic is to measure the pressure increment in a hour and divided by gradient of mud weight that you have in the well.

Let’s look at the formula:

**Actual gas migration rate = Increase in casing pressure ÷ Pressure gradient of drilling mud**

Where;

Actual gas migration rate in ft/hr

Increase in casing pressure in psi/hr

Pressure gradient of drilling mud in psi/ft

**Let’s try to determine the actual gas migration rate with this following information:**

Initial shut in casing pressure = 450 psi

Shut in casing pressure after half an hour shut in = 650 psi

Current mud weight = 12.5 ppg

**Solution:**

Pressure increase in half an hour = 650 – 450 = 200 psi

It means that pressure increase in an hour is 400 psi. Therefore, you get the increase in casing pressure = 400 psi/hr.

You need to calculate your mud weight in to ppg with this formula:

Mud gradient = 0.052 x mud weight

Mud gradient = 0.052 x 12.5 = 0.65 psi/ft

**Note: **you can read more about it via this link: how to convert mud weight to pressure gradient.

Actual gas migration rate = 400 (psi/hr) ÷ 0.65 (psi/ft) = 616 ft/hr

**Ref book: ** **Formulas and Calculations for Drilling, Production and Workover, Second Edition**