When pulling out of hole, volume of steel will be out of hole and mud volume will replace the steel volume. If we don’t fill hole, hydrostatic pressure will decrease. There are 2 cases of pulling pipe which are pull dry and pull wet. Each condition is different in calculation concept because mud volume to displace pipe volume is different.

This topic shows you how to calculate hydrostatic pressure loss for both cases of pulling pipe, pull dry and pull wet. Moreover, there is the Excel sheet for calculating pressure decrease due to pulling out of hole.

**Case#1: When pulling DRY pipe**

When pulling dry, we will consider volume of steel out of hole only.

**Step 1: Determine Total Pipe Volume**

**Step 2: Determine Hydrostatic Pressure Decrease**

**Example:** Determine the hydrostatic pressure decrease when pulling DRY pipe out of the hole:

Number of stands pulled = 10

Pipe displacement = 0.0055 bbl/ft

Average length per stand = 91 ft

Casing capacity = 0.0873 bbl/ft

Mud weight = 12.0 ppg

**Step 1:** Determine of pipe displacement in Barrels = 10 stands x 91 ft/std x 0.0055 bbl/ft displaced

Barrels displaced = 5.01 bbl

**Step 2:** Determine HP, psi decrease = 5.01 barrels x 0.052 x 12.0 ppg ÷ (0.0873 bbl/ft – 0.0055 bbl/ft)

Hydrostatic pressure decrease = 38.2 psi

**Case#2: When pulling WET pipe**

When pulling wet, we will consider volume of steel out of hole and volume of mud in drillpipe as well. Therefore, pulling wet will decrease hydrostatic more than pulling dry pipe.

**Step 1:** Barrels displaced = number of stands pulled per stand in ft

x average length x {pipe disp inbbl/ft + {(% volume in drill pipe out of hole ÷ 100) x pipe cap in bbl/ft)}

**Step 2: **Determine hydrostatic pressure in psi decrease = barrels displaced x 0.052 x mud weight, ppg ÷ ((casing capacity in bbl/ft) – (Pipe disp in bbl/ft + pipe cap in bbl/ft))

**Example:** Determine the hydrostatic pressure decrease when pulling WET pipe out of the

hole:

% of volume in drill pipe out of hole = 100

Number of stands pulled = 10

Pipe displacement = 0.0055 bbl/ft

Average length per stand = 91 ft

Pipe capacity = 0.01876 bbl/ft

Mud weight = 12.0 ppg

Casing capacity = 0.0873 bbl/ft

**Step 1:** Barrels displaced = 10 stands x 91 ft/std x {(.0055 bbl/ft + (100 ÷ 100) x 0.01876 bbl/ft)}

Barrels displaced = 22.08 bbl

**Step 2:** hydrostatic pressure in psi decrease = 22.0766 barrels x 0.052 x 12.0 ppg ÷ ((0.0873 bbl/ft) – (0.0055 bbl/ft + 0.01876 bbl/ft))

HP decrease, psi = 218.52 psi

**Please find the ****Excel sheet for calculating pressure decrease due to pulling out of hole.**

**Ref books: **Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.