Basic Drilling Formulas
Drill Pipe/Drill Collar Calculations

Drill Pipe/Drill Collar Calculations

Using basic drilling formula to calculate drill collar and drill pipe calculation for drilling projects.

Capacities, bbl/ft, displacement, bbl/ft, and weight, bbl/ft,
can be calculated from the following formulas:

Capacity, bbl/ft = ID, in.² / 1029.4
Displacement, bbl/ft = OD, in.² - ID, in.² / 1029.4

Weight, Ib/ft = displacement, bbl/ft x 2747Ib/bbl

Example:

Determine the capacity,bbl/ft,displacement,bbl/ft,
and weight, bbl/ft, for the following:

Drill collar OD = 8.0in.
Drill collar ID = 2 13/16 in.

Convert 13/16 to decimal equivalent:

13 + 16 = 0.8125

a) Capacity, bbl/ft = 2.8125² /1029.4
Capacity = 0.007684 bbl/ft

b) Displacement, bbl/ft = 8.0² - 2.8125² / 1029.4

Displacement, bbl/ft = 56.089844 / 1029.4
Displacement = 0.0544879 bbl/ft.

c) Weight, lb/ft = 0.0544879bbl/ft x 2747 lb/bbl.
Weight = 149.678 lb/ft

Rule of thumb formulas

Weight, lb/ft, for REGULAR DRILL COLLARS can be approximated using the following formula:

Weight, lb/ft = (OD, in² - ID, in²) x 2.66

Example: Regular drill collars

Drill collar OD = 8.0 in.
Drill collar ID = 2-13/16 in.
Decimal equivalent = 2.8125 in.

Weight, lb/ft = (8.0² - 2.8125²) x 2.66
Weight, lb/lft = 56.089844 x 2.66
Weight = 149.198981 lb/ft

Weight, lb/ft, for SPIRAL DRILL COLLARS can be approximated using the following formula:

Weight, ib/ft = (OD, in² - ID, in²) x 2.56
Exarnple: Spiral drill collars

Drill collar OD = 8.0 in.
Drill collar ID = 2 13/16 in.
Decimal equivalent = 2.8125 in.
Weight, lb/ft = (8.0² - 2.8125²) x 2.56
Weight, Ib/ft = 56.089844 x 2.56
Weight = 143.591 lb/ft

Drilling

Clean formation refers to a homogenous formation that is
not interbedded and is 100% one lithology type.

These types of formations are rare as some shales for example include a certain sand and limestone content.

However, selecting parameters that suit the primary lithology will generally optimise drilling performance.

* Soft clean shales
- Increasing rotary speed generally improves penetration rate,(usually RPM has a greater effect on RoP than WoB).
- There is minimal risk of damaging the cutting structure in this lithology.

* Hard clean chalk/limestones
- Penetration rate is maximised by increasing cutter point loading to fracture the formation. High weight is recommended with low rotary speed to allow the cutters to bite into the formation.
- Bits may suffer impact damage. If the formation is clean (ie: no sand content) the cutters should suffer minimal abrasive wear.

* Hard sandstones o Penetration rate is maximised by increasing cutter point loading so high weight is recommended.
- To ensure the cutters can get a bite, low rotary speeds are preferred.
- Bits may suffer both impact damage and abrasive wear. Low RPMs will reduce abrasive wear.
- Low rotary speeds will also reduce penetration rates so a reasonable compromise must be reached.