You can determine how much slug weight required in order to achieve desired length of dry pipe with certain slug volume that you will use.

**Oilfield Unit**

Please follow these steps of calculation below;

**Step 1 Determine Length of slug in drill pipe in ft:**

Length of slug in drill pipe in ft = slug volume in bbl ÷ drill pipe capacity in bbl/ft

**Step 2 Determine hydrostatic pressure required to give desired dry pipe drill pipe:**

Hydrostatic Pressure in psi = mud weight in ppg × 0.052 × desired length of dry pipe

**Step 3 Determine slug weight needed in ppg:**

Slug weight in ppg = (Hydrostatic Prำssure (from step 2) ÷ 0.052 ÷ Length of slug in ft (step1)) + mud weight, ppg, in hole

**Example: Determine slug weight required for the following data:**

Desired length of dry pipe = 200 ft

Mud weight in hole = 12.0 ppg

Drill pipe capacity = 0.016 bbl/ft

Volume of slug = 20 bbl

**Step 1 – Determine Length of slug inside drill pipe in ft:**

Slug length = 20 bbl ÷ 0.016 bbl/ft

Slug length = 1250 ft

**Step 2 – Determine hydrostatic pressure required to give desired dry pipe drill pipe**

Hydrostatic Pressure in psi = 12.0 × 0.052 × 200

Hydrostatic Pressure in psi = 124.8 psi

**Step 3 – Determine slug weight needed in ppg:**

Slug weight in ppg = (124.8 ÷ 0.052 ÷ 1250) + 12.0

**Slug weight in ppg = **13.9 **ppg**

**Metric Unit**

Please follow these steps of calculation below;

**Step 1 Determine Length of slug in drill pipe in meter (m):**

Length of slug in drill pipe in m = slug volume in m³ ÷ drill pipe capacity in m³/m

**Step 2 Determine hydrostatic pressure required to give desired dry pipe drill pipe:**

Hydrostatic Pressure in psi = mud weight in kg/m³ × 0.00981 × desired length of dry pipe in m

**Step 3 Determine slug weight needed in ppg:**

Slug weight in ppg = (Hydrostatic Pressure (from step 2) ÷ 0.00981÷ Length of slug in m (step1)) + mud weight, kg/m³, in hole

**Example: Determine slug weight required for the following data:**

Desired length of dry pipe = 120 m

Mud weight in hole = 1,400 kg/m³

Drill pipe capacity = 0.007824 m³/m

Volume of slug = 4.5 m³

**Step 1 – Determine Length of slug inside drill pipe in ft:**

Slug length = 4.5 m³÷ 0.007824 m³/m

Slug length = 575 m

**Step 2 – Determine hydrostatic pressure required to give desired dry pipe drill pipe**

Hydrostatic Pressure in psi = 1,400 × 0.00981 × 120

Hydrostatic Pressure in psi = 1,648 KPa

**Step 3 – Determine slug weight needed in ppg:**

Slug weight in ppg = (1,648 ÷ 0.00981 ÷ 575) + 1,400

**Slug weight in ppg = **1692 kg/m³

**Please find the excel sheet used to calculate Weight of slug required for a desired length of dry pipe with a set volume of slug.**

**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.

Thank you very much for these useful formulas and ideas