Drilling Calculations Course

Common Units and symbols

parameter Unit Symbol

length Feet,inches or Mtr Ft ,inor M

Area Square feet, Square inches or square meters

Volume Cubic feett, cubic centimeters cubic meters or

Cuft. Cu In or Meters cube

Capacity US barrels,US gallons, Cubic ft

bbl, gal(US), cuft

Mass Pounds,Short tons lbs, Sh tn

Force (weight) Pounds-force lbf

Presure Ppounds –force per square inch

psi

Density (mudweight) Pounds per gallon, pounds per cubic ft

Ppg ,pcf

torque Foot pounds ftlbs

AREAS

Areas

• Area of a square

Len

gth

breadth

Area of a Square = length X breadth

This same expression is applicable to a rectangle and parallelogram

breadth

Len

gth

Area of a Triangle

base

Hei

ght

Area of a triangle = Base x Height 2

Hei

ght

base

Area of a CircleDiameter Radius

Area of a circle = Π x radius x radius

Where r= radius of the circle Π = 3.142Since diameter= 2 x radius

Area of circle= Π x Diameter x Diamater 4

VOLUMES

Annular area

d

D

Annular or cross sectional area = Π {(D x D)-(d x d)} 4

This can be used to calculate annular areas of the wellbore or Cross sectional areas of tubulars

Volume of a cube

Volumes

length

hie

ght

bread

th

Volume of a cube = length x breadth x height

Cylindrical Capacities

Hei

ght

Area

Volume of a cylinder = Area x Height = Π x Diameter x Diameter x Height

4This is the basis for all volume the capaciy calculations in well control

Capacity Calculations

Rule of thumb: Capacity of a cylinder in bbls/ft= Diamater x Diameter

1029.4Multiply this by the Height of the cylinder ( or length of the hole) gives the volumetric capacity in barrels

HVolume = Diameter x Diameter x height(or length) 1029.4

This expression is generally used on the rig for volume and capacity calculations

Annular volume calculationsTop view

Annular Volume in bbls

{(D x D)-(d x d)}xlenght 1029.4

d

D

ANNULAR VOLUME AROUND DP =

[( D3² - D1² ) / 1029.4] x L1

ANNULAR VOLUME AROUND DC =

[( D3² - D2² ) / 1029.4] x L2

Hole volume calculations

Using the following data, calculate the total annular volume.

L1 = 4000 ft

L2 = 800 ft

D1 = 5 in

D2 = 6.5 in

D3 = 8.5 in

Hole volume calculations example

ANNULAR VOLUME AROUND DP =

[( 8.5² - 5² ) / 1029.4] x 4000 = 183.6 bbls

ANNULAR VOLUME AROUND DC =

[( 8.5² - 6.5² ) / 1029.4] x 800 = 23.31 bbls

Total Annular Volume =183.6 + 23.31 = 206.91 bbl

Hole volume calculations

Pump displacement volumes

The same expression for calculation od hole volumes can also be used for the calculation of mud pump displacementsTriplex Pump displacement in bbls/ft = D² x L x e x3

1029.4 x 12 x100Where D= liner size in inches L= Stroke length in inches

e= Volumetric efficiency in %

L

D

Pump displacement volumes example

Where D= 7 inches L= 11 inches

e = 97% Pump displacement= 7 x 7 x 97 x 11 x 3

1029.4 x 12 x 100= 0.127 bbls/ stroke

L

D

Weight on bit

• Drill collars and/or heavy wall drill pipes are uses to put weight on the bit

• Drill collars are also used to keep the string in tension and prevent it from buckling

• There is a point in the drill collars where compression stops and tension starts this point is called the neutral point

• Weight on bit is usually about 75-90%of the buoyed drill collar weight