Maximum initial shut-in casing pressure, abbreviated as \(MISICP\), based on the original mud weight before you start drilling ahead. It represents the maximum surface pressure that can be safely applied to the casing annulus (shut-in casing pressure) without fracturing the formation at the casing shoe, after accounting for an increase in mud weight from the original value used during the leak-off test (LOT). This adjustment is necessary because drilling deeper typically requires heavier mud weights, which add hydrostatic pressure in the annulus and thereby reduce the allowable additional surface pressure before reaching the formation's fracture limit.
Adjusted Maximum Allowable Shut-in Casing Pressure Formula
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| \( MASICP \;=\; LOP - [\; STVD \cdot (MW2 - MW1)\;] \cdot 0.052 \) | ||
| Symbol | English | Metric |
| \( MASICP \) = adjusted maximum allowable shut-in casing pressure (psi) | \(lbf\;/\;in^2\) | - |
| \( LOP \) = leak off pressure (pressure you get when you perform leak off test) (psi) | \(lbf\;/\;in^2\) | - |
| \( STVD \) = true vertical depth of casing shoe | \(ft\) | - |
| \( MW2 \) = current mud weight (ppg) | \(lbs\;/\;gal\) | - |
| \( MW1 \) = origional mud weight (ppg) | \(lbs\;/\;gal\) | - |
