Hoisting System

Drilling Engineering 1 Course
3rd Ed. , 3rd Experience

1.
Hoisting System:
A.
Introduction
B.
The Block & Tackle
a.
Mechanical advantage and Efficiency
b.
Hook Power
C.
Load Applied to the Derrick

Typical hoisting system

The hoisting system is used to raise, lower, and suspend equipment in the well

(e.g., drillstring, casing, etc).

It is consists of:

derrick (not shown)

draw works

the block-tackle system

fast line (braided steel cable)

crown block

traveling block

dead line (1” to 13/4=3.25”)

deal line anchor,

storage reel,

hook.
Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 4

The Derrick

The derrick provides

the necessary height and support to lift loads in and out of the well.

The derrick must be strong enough to support

the hook load, deadline and fastline loads, pipe setback load and wind loads.

Derricks are rated by the API according

to their height (to handle 2, 3, or 4 joints) and

their ability to withstand wind and compressive loads. Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 5

The Derrick

The derrick stands above the derrick floor.

It is the stage where several surface drilling operations occur.

At the derrick floor are located

the drawworks, the driller’s console, the driller’s house (or “doghouse”), the rotary table, the drilling fluid manifold, and several other tools to operate the drillstring.

The space below the derrick floor is the substructure.

The height of the substructure should be enough to accommodate the wellhead and BOPs.
doghouse

Substructure and Monkey Board

At about 3/4 of the height of the derrick is located a platform called “monkey board”.

This platform is used to operate the drillstring stands during trip operations.

During drillstring trips, the stands are kept stood in in the mast, held by “fingers” in the derrick rack near the monkey board.

drawworks

The drawworks provides hoisting and braking power required to handle the heavy equipment in the borehole.

It is composed of

a wire rope drum,

mechanical and hydraulic brakes,

the transmission,

and the cathead

(small winches operated by hand or remotely to provide hoisting and pulling power to operate small loads and tools in the derrick area).
a typical onshore rig drawworks

Reeling in and out

The reeling–in of the drilling line

is powered by an electric motor or Diesel engine

the reeling–out

is powered by gravity

To control the reeling out,

mechanical brakes and

auxiliary hydraulic or magnetic brakes

are used, which dissipates the energy required to reduce the speed and/or stop the downward movement of the suspended equipment.

The Block & Tackle

Fast line

The drilling line coming from the drawworks, called fast line, goes over a pulley system mounted at the top of the derrick,

called the crown block,

and down to another pulley system

called the traveling block.

block-tackle

The assembly of crown block, traveling block and drilling line

The number of lines n of a tackle

is twice the number of (active) pulleys in the traveling block.

The last line of the tackle

is called dead line

and is anchored to the derrick floor, close to one of its legs.

Below and connected to the traveling block is a hook to which drilling equipment can be hung. Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 11

block-tackle system calculations

The block-tackle system

provides a mechanical advantage to the drawworks, and

reduces the total load applied to the derrick.

We will be interested in calculating

the fast line force Ff (provided by the drawworks) required to raise a weight W in the hook, and

the total load applied to the rig and

its distribution on the derrick floor.

Forces acting in the block–tackle

Dead Line Anchor

This allows new lengths of line to be fed into the system to replace the worn parts of the line that have been moving on the pulleys of the crown block or the travelling block.

The worn parts are regularly cut and removed by a process called: Slip and Cut Practice.

Slipping the line, then cutting it off helps to increase the lifetime of the drilling line.

Drilling Line

The drilling is basically a wire rope made up of strands wound around a steel core.

Each strand contains a number of small wires wound around a central core.

The drilling line is of the round strand type with Lang’s lay.

The drilling line has a 6x19 construction with Independent Wire Rope Core (IWRC).

6 strands and each strand containing 19 filler wires.

The size of the drilling line varies from ½ "to 2 ".

Ideal Mechanical advantage

The mechanical advantage AM of the block–tackle

is defined as the ratio of the load W in the hook

to the tensile force on the fast line Ff :

For an ideal, frictionless system,

the tension in the drilling line is the same throughout the system, so that W = n Ff .

Therefore, the ideal mechanical advantage is equal to the number of lines strung through the traveling block:

efficiency of a real pulley

Friction between the wire rope and sheaves reduce the efficiency of the hoisting system.

In a real pulley, however, the tensile forces in the cable or rope in a pulley are not identical.

If Fi and Fo are the input and output tensile forces of the rope in the pulley, the efficiency of a real pulley is:

We will assume that all pulleys in the hoisting system have the same efficiency, and we want to calculate the mechanical advantage of a real pulley system. Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 18

Efficiency Of The Hoisting Systems (Hoisting Operations)

during hoisting (pulling out of hole) operations If Ff is the force in the fast line,

the force F1 in the line over the first pulley (in the crown block) is

The force in the line over the second pulley (in the traveling block) is

Using the same reasoning over and over, the force in the ith line is

The total load W acting in the hook is equal to

the sum of the forces in each line of the traveling block. Fall 14 H. AlamiNia Drilling Engineering 1 Course (3rd Ed.) 19

Calculation of fast line load during hoisting

AM=the real mechanical advantage

The overall efficiency E of the system of pulleys is defined as the ratio of the real mechanical advantage to the ideal mechanical advantage

A typical value for the efficiency of ball–bearing pulleys is = 0.96.

Table shows the calculated and industry average overall efficiency for the usual number of lines.

if E is known, the fast line force Ff required to rise a load W can be calculated

Calculations of minor loads

Using the same reasoning Deadline-load is given by:

퐹퐹푑푑=퐹퐹푓푓∗휂휂푛푛=푊푊∗휂휂푛푛 푛푛∗퐸퐸

If the breaking strength of the drilling line is known, then a design factor, DF, may be calculated as follows: 퐷퐷퐷=푛푛푛푛푛푛푛푛푛푛푛푛푛푛푠푠푠푠푠푠푠푠푠푠푠푠푠ℎ표푤푤푤푟푟푟푟푙푙푙 푓푓푓푙푙푙푙

Lowering Operations:

During lowering of pipe,

the efficiency factor is: 퐸퐸푙=휂휂∗휂휂푛푛1−휂휂 1−휂휂푛푛

And fast-line load is: 퐹퐹푓푓푙=푊푊∗휂휂푛푛1−휂휂 1−휂휂푛푛

POWER REQUIREMENTS OF THE DRAWWORKS

As a rule of thumb, the drawwork should have 1 HP for every 10 ft to be drilled.

Hence for a 20,000 ft well, the drawwork should have 2000 HP.

A more rigorous way of calculating the horse power requirements is to carry out output power at drum:

푃푃d=Ff∗Vf=WnE∗n∗vb=W∗VbE

In the Imperial system, power is quoted in horse-power and the above equation becomes:퐷퐷퐷퐷퐷퐷퐷퐷표표표표표표표표표표=W∗vbE∗33000

The proof has mentioned in the following slides:

Input vs. output power

For an ideal block–tackle system,

the input power (provided by the drawworks) is equal to the output or hook power (available to move the borehole equipments).

In this case,

the power delivered by the drawworks is equal to the force in the fast line Ff times the velocity of the fast line vf , and

the power developed at the hook is equal to the force in the hook W times the velocity of the traveling block vb.

That is

relationship between the drawworks power and the hook power

Since for the ideal case n Ff = W, so

that is, the velocity of the block is n times slower than the velocity of the fast line, and

this is valid also for the real case.

For the real case, Ff=W/nE, and multiplying both sides by vf we obtain

which represents the real relationship between the power delivered by the drawworks and the power available in the hook,

where E is the overall efficiency of the block–tackle system.

The Block & Tackle

A rig must hoist a load of 300,000 lbf. The drawworks can provide a maximum input power to the block–tackle system of as 500 hp. Eight lines are strung between the crown block and traveling block.

Calculate

(1) the tension in the fast line when upward motion is impending,

(2) the maximum hook horsepower,

(3) the maximum hoisting speed.

The Block & Tackle

Using E = 0.841 (average efficiency for n = 8) we have:

Hook Loads

The following data refer to a 2 in block line with 12 lines of extra improved plough steel wire rope strung to the travelling block.

hole depth= 12,000 ft

drillpipe = 4.5 in OD/3.958 in ID, 13.75 lb/ft

drill collars= 800 ft, 8 in/2,825 in, 150 lb/ft

mud weight = 9 ppg

line and sheave efficiency coefficient = 0.9615

Calculate:

A: weight of drill string in air and in mud;

B: hook load, assuming weight of travelling block and hook to be 20,500 lb;

C: deadline and fast-line loads;

D: dynamic crown load;

E: wireline design factor during drilling if breaking strength of wire is 228,000 lb

F: design factor when running 7 in casing of 29 lb/ft.

Hook Loads

Clues:

Example 16.2: Hook Loads, WECPGO: 725

Weight of drillstring in air=weight of drillpipe + weight of drill collars

Weight of drillstring in mud =buoyancy factor x weight in air

Hook load= weight of string in mud+ weight of travelling block, etc.

Dynamic crown load = Fd + Ff + W

HOISTING DESIGN CONSIDERATIONS

The procedure for carrying out hoisting design calculations are as follows:

Determine the deepest hole to be drilled

Determine the worst drilling loads or casing loads

Use these values to select

the drilling line,

the derrick capacity and

in turn the derrick

The total load applied to the derrick

The total load applied to the derrick, FD is equal to

the load in the hook (Hook load)

plus the force acting in the dead line

plus the force acting in the fast line

for the force in the fast line

The worst scenario is that for the real case.

For the dead line, however,

the worst scenario (largest force) is that of ideal case.

Therefore, the total load applied to the derrick is:

static derrick loading (SDL) and wind load

Static derrick loading (SDL)=

fast-line load (where the efficiency is assumed equal 1) +

hook load +

dead-line load

So

SDL=HL/n+HL+HL/n

The wind load is given by: 0.004 V2 (units: lb/ft2)

V is wind speed in miles/hour

The wind load in lb/ft2 result must be multiplied by the WIND LOAD AREA which is given in API 4A for different derrick sizes in order to obtain the wind load in lb.

For offshore operations in windy areas, this load can be very significant.

Derrick floor plan

The total load FD,

however, is not evenly distributed over all legs of the derrick.

In a conventional derrick,

the drawworks is usually located between two of the legs

The dead line, however must be anchored close to one of the remaining two legs

The side of the derrick opposite to the drawworks is called V–gate.

This area must be kept free to allow pipe handling.

Therefore, the dead line cannot be anchored between legs A and B

the load in each leg

From this configuration the load in each leg is:

Evidently, the less loaded leg is leg B.

We can determine under which conditions the load in leg A is greater then the load in legs C and D:

Since the efficiency E is usually greater than 0.5,

leg A will be the most loaded leg, very likely it will be the first to fail in the event of an excessive load is applied to the hook.

The equivalent derrick load andThe derrick efficiency factor

If a derrick is designed to support a maximum nominal load Lmax, each leg can support Lmax 4 .

Therefore, the maximum hook load that the derrick can support is

The equivalent derrick load, FDE,

is defined as four times the load in the most loaded leg.

The equivalent derrick load

(which depends on the number of lines)

must be less than the nominal capacity of the derrick.

The derrick efficiency factor, ED

is defined as the ratio of the total load applied to the derrick to the equivalent derrick load:

derrick load

A rig must hoist a load of 300,000 lbf.

Eight lines are strung between the crown block and traveling block.

calculate

(1) the actual derrick load,

(2) the equivalent derrick load, and

(3) the derrick efficient factor.

derrick load

Solution:

Using E = 0.841 (average efficiency for n = 8) we have:

(1) The actual derrick load is given by

(2) The equivalent derrick load is given by

(3) The derrick efficiency factor is

TON-MILES OF A DRILLING LINE

The drilling line, like any other drilling equipment, does work at any time it is involved in moving equipment in or out of the hole.

The amount of work done varies depending the operation involved.

This work causes the wireline to wear and if the line is not replaced it will eventually break.

The reader should note that the drilling line can only contact a maximum of 50% of the sheaves at any one time, but the damage will be done on the contact area any way.

The amount of work done need to be calculated to determine when to change the drilling line.

Evaluation Of Total Service And Cut-off Practice

Portions of the drilling line on the crown and travelling blocks sheaves and on the hoisting drum carry the greatest amount of work and are subjected to a great deal of wear and tear.

These parts must be cut and removed at regular times other wise the drilling line will fail by fatigue.

The process is called "slip and cut practice".

The length of line to be cut is equal to

Length of drum laps = number of laps x drum circumference

1.(CDF) Jorge H.B. Sampaio Jr. “Drilling Engineering Fundamentals.” Master of Petroleum Engineering. Curtin University of Technology, 2007.
Chapter 2
2.(WEC) Rabia, Hussain. Well Engineering & Construction. Entrac Consulting Limited, 2002.
Chapter 16

Hoisting System

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