## How Does 1029.4 Come From?

1029.4 is used in several calculations in the oilfield and we’ve been asked about what is 1029.4, how it comes from, why it needs to be this figure so in this article, we will show you how 1029.4 comes from.

First of all, we would like to give someone about the background of this figure. The 1029.4 is widely used for capacity calculations. The following equations utilizing 1029.4 are listed below; Continue reading

## Drill pipe pulled to lose hydrostatic pressure

You previously learn about hydrostatic pressure lose due to pulling out of hole . This article will use the same concept but we will determine how many feet of drill pipe pulled to lose certain amount of hydrostatic pressure in well bore.

## Oilfield Unit

Pipe pulled, ft = (hydrostatic pressure loss in psi × (casing cap in bbl/ft – pipe displacement in bbl/ft)) ÷ (mud weight in ppg × 0.052 × pipe displacement in bbl/ft)

Example: Determine the FEET of drill pipe that must be pulled to lose 200 psi overbalance using the following data:

Hydrostatic pressure loss = 200 psi
Casing capacity = 0.0873 bbl/ft
Pipe displacement = 0.01876 bbl/ft
Mud weight = 12.0 ppg
Pipe pulled  = 200 psi × (0.0873 – 0.01876) ÷ (12.0 ppg × 0.052 × 0.01876)
Pipe pulled = 1171 ft
You need to pull 1171 ft of dry pipe to lose 200 psi hydrostatic pressure.

## Metric Unit

Pipe pulled, m = (hydrostatic pressure loss in KPa× (casing cap in m3/m- pipe displacement in m3/m-)) ÷ (mud weight in kg/m3 × 0.00981× pipe displacement in m3/m)

Example: Determine how many meters of drill pipe that must be pulled to lose 1400 KPa overbalance using the following data:

Hydrostatic pressure loss = 1400 KPa
Casing capacity = 0.04554 m3/m
Pipe displacement = 0.00979 m3/m
Mud weight = 1440 kg/m3
Pipe pulled  = 1400× (0.04554 – 0.00979 ) ÷ (1440 × 0.00981 × 0.00979 )
Pipe pulled = 362 m
You need to pull 362 m of dry pipe to lose 1400 KPa hydrostatic pressure.

Please find the Excel Spreadsheet to calculate how many feet  or meter of drill pipe pulled to lose certain amount of hydrostatic pressure in well bore.

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.

## Hydrostatic Pressure (HP) Decreases When POOH

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 m3

Length  of pipe pulled out in m

Pipe Displacement in m3 /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 m3

mud weight in kg/m3

casing capacity in m3 /m

pipe displacement in m3 /m

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

Number of stands pulled = 10
Pipe displacement = 0.00287 m3 /m
Average length per stand = 30 m
Casing capacity = 0.04554 m3 /m
Mud weight = 1440 kg/m3

Step 1: Determine of pipe displacement in m3 = 10 stands × 30 m/std × 0.00287 m3 /m pipe displacement

Total Volume of Steel Out of Hole 0.86  m3

Step 2: Determine HP, psi decrease = 0.86  m3 × 0.00981 × 1440 kg/m3 ÷ (0.04554 m3 /m- 0.00287 m3 /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.

## Calculate inner capacity of open hole/inside cylindrical objects (Internal Capacity Factor)

From the previous post, you learn how to calculate annular capacity and this article shows you how to use the same principle to calculate internal capacity factor of  open hole & inside cylindrical objects such as tubular, drill pipe, drill collars, tubing, casing, etc.

There are several formulas to calculate inner capacity depending on unit of inner capacity required. The formula are listed below;

## Calculate Internal Capacity Factor in bbl/ft

Inner Capacity in bbl/ft = (ID)2 ÷1029.4

Where;
Internal Diameter (ID) in inch

Example:

Determine Internal Capacity Factor in bbl/ft of a 6-1/8 in. hole:
Internal Capacity Factor in bbl/ft = 6.1252÷1029.4
Internal Capacity Factor in bbl/ft = 0. 0364 bbl/ft

## Calculate Internal Capacity Factor in gal/ft

Inner Capacity in gal/ft = (ID in.)2 ÷24.51
Where;
Internal Diameter (ID) in inch

Example:

Determine Inner Capacity Factor in gal/ft of 6-1/8 in. hole:
Internal Capacity Factor in gal/ft = 6.1252÷ 24.51
Internal Capacity Factor in gal/ft = 1.53 gal/ft

## Calculate Internal Capacity Factorin cu-meter/meter (m3/m)

Annular capacity in m3/m =  (ID2) ÷1,273,240

Where;
Internal Diameter (ID) in mm

Example:

Hole size (ID) = 155.56  mm.
Internal Capacity Factor in m3/m = (155.562 ) ÷1,273,240
Internal Capacity Factor in m3/m = 0.0190 m3/m

## Calculate Internal Capacity Factorin liter/meter (l/m)

Annular capacity in m3/m =  (ID2) ÷1,273.24

Where;
Internal Diameter (ID) in mm

Example:

Hole size (ID) = 155.56  mm.
Internal Capacity Factor in l/m = (155.562 ) ÷1,273.24
Internal Capacity Factor in l/m = 19.0 l/m

Volume can be determined by this following formula;

## Oilfield Unit

Volume = Internal Capacity Factor x Length

Where;

Volume in bbl

Internal Capacity Factor in bbl/ft

Length in ft

Example:

Internal Capacity Factor =  0. 0364 bbl/ft

Hole Length = 3,000 ft

Volume = 0. 0364 x 3,000 = 109.2 bbl.

## Metric Unit

Volume = Internal Capacity Factor x Length

Where;

Volume in cu.meter

Internal Capacity Factor in cu.meter/meter

Length in meter

Example:

Internal Capacity Factor in m3/m = 0.0190 m3/m

Hole Length = 3,000 m

Volume = 0. 0190 x 3,000 = 57 m3