[h=1]Block and Drilling Line Calculation[/h]
This article will focus on block and drilling line calculations as block efficiency, drilling power input/output, etc. Additionally, there are some examples which will help you understand how the formulas work.
This article will focus on block and drilling line calculations as block efficiency, drilling power input/output, etc. Additionally, there are some examples which will help you understand how the formulas work.
Block and drilling line efficiency formula is described below;
Power Output (Po) = F[SUB]h[/SUB] x V[SUB]tb[/SUB]
Power Output (Pi) = F[SUB]f[/SUB] x V[SUB]f[/SUB]
Where;
F[SUB]h[/SUB] is the hook load in lb.
V[SUB]tb [/SUB]is the velocity of the travelling block in feet per minute (fpm).
F[SUB]f[/SUB] is the fast line load in lb.
V[SUB]f [/SUB]is the velocity of the fast line in feet per minute (fpm).
The relationship between the fast line speed and the travelling block speed is listed below;
V[SUB]f [/SUB]= n x V[SUB]tb[/SUB]
Where;
n is number of lines strung between the travelling block and the crown block.
We can describe the hoisting efficiency into the following form.
Example#1: The maximum anticipated hook load is 500,000 and the travelling block velocity is 200 ft/minute. Hoisting efficiency is 85% and the drawworks efficiency is 75%. Based on the given information, what is the required horsepower for the drawworks for this situation?
Pi = 58,832,529 ft-lb/min
1 horsepower = 33,000 ft-lb/min
Pi = 58,832,529 ÷ 33,000 = 1,783 hp
We need to look at the drawworks. The drawworks output is the hoisting system output therefore we can figure out the horse power of the drawworks.
Pi = 2,377 hp
You need input horsepower of the drawworks of 2,377 hp.
Example#2: The string will be pulled out from 15,000 ft. The rig information is listed below;
Drilling lines: 12 lines
Hoisting efficiency: 70%
Drawworks: 1,200 hp
Drawworks efficiency: 80%
Expected hookload at 15,000 ft: 350,000 lb
What is the speed at which the first stand (90 ft stand) can be pulled out of hole based on the drawworks technical limit?
F[SUB]f [/SUB]= 41,667 lb
Fast line velocity (V[SUB]f[/SUB]) = Power Input (Pi) ÷ Fast line Load (F[SUB]f[/SUB])
Power Input (Pi) comes from the drawworks and we can determine it from the drawworks efficiency.
Power Input (Pi) = 0.8 x 1,200 = 960 hp
1 horsepower = 33,000 ft-lb/min
Power Input (Pi) = 960 x 33,000 = 31,680,000 ft-lb/min
Fast line velocity (V[SUB]f[/SUB]) = 31,680,000 ÷ 41,667 = 760 fpm
Travelling block velocity can be calculated by the following equation.
V[SUB]f [/SUB]= n x V[SUB]tb[/SUB]
V[SUB]tb [/SUB]= V[SUB]f [/SUB]÷ n
V[SUB]tb [/SUB]= 760÷ 12 = 63.3 fpm
The travelling block speed = 90 ÷ 63.3 = 1.42 minute.
The pulling speed for the first stand is 1.42 minutes.
Reference book => Formulas and Calculations for Drilling Operations
