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. This topic shows you how to calculate hydrostatic pressure loss while pulling out of hole without filling the wellbore. Moreover, there is the Excel sheet for calculating pressure decrease due to pulling out of hole.

**Oilfield Unit**

**Step 1: Determine Total Volume of Steel Out of Hole**

Total Volume of Steel Out of Hole = Length of pipe pulled out × Pipe Displacement

Where,

Total Volume of Steel Out of Hole in bbl

Length of pipe pulled out in ft

Pipe Displacement in bbl/ft

**Step 2: Determine Hydrostatic Pressure Decrease**

Hydrostatic Pressure Decrease = (Total Volume of Steel Out of Hole × 0.052 × mud weight) ÷ (casing capacity – pipe displacement)

Where,

Hydrostatic Pressure Decrease in psi

Total Volume of Steel Out of Hole in bbl

mud weight in ppg

casing capacity in bbl/ft

pipe displacement in bbl/ft

**Example:** Determine the hydrostatic pressure decrease when pulling 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 × 91 ft/std × 0.0055 bbl/ft displaced

Total Volume of Steel Out of Hole = 5.01 bbl

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

Hydrostatic pressure decrease = 38.2 psi

**Metric Unit**

**Step 1: Determine Total Volume of Steel Out of Hole**

Total Volume of Steel Out of Hole = Length of pipe pulled out × Pipe Displacement

Where,

Total Volume of Steel Out of Hole in m^{3}

Length of pipe pulled out in m

Pipe Displacement in m^{3 }/m

**Step 2: Determine Hydrostatic Pressure Decrease**

Hydrostatic Pressure Decrease = (Total Volume of Steel Out of Hole × 0.00981 × mud weight) ÷ (casing capacity – pipe displacement)

Where,

Hydrostatic Pressure Decrease in KPa

Total Volume of Steel Out of Hole in m^{3}

mud weight in kg/m^{3}

casing capacity in m^{3 }/m

pipe displacement in m^{3 }/m

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

Number of stands pulled = 10

Pipe displacement = 0.00287 m^{3 }/m

Average length per stand = 30 m

Casing capacity = 0.04554 m^{3 }/m

Mud weight = 1440 kg/m^{3}

**Step 1:** Determine of pipe displacement in m^{3 } = 10 stands × 30 m/std × 0.00287 m^{3 }/m pipe displacement

Total Volume of Steel Out of Hole 0.86 m^{3
}

**Step 2:** Determine HP, psi decrease = 0.86 m^{3 }× 0.00981 × 1440 kg/m^{3} ÷ (0.04554 m^{3 }/m- 0.00287 m^{3 }/m)

Hydrostatic pressure decrease = 285 KPa

**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.