4 Rotary Drilling

7/26/2019 4 Rotary Drilling

1/13

ROTARY DRILLING

In the rotary method, the hole is drilled by a rotating bit to

which a downward force is applied. The bit is fastened to,

and rotated by, a drill string, composed of high quality drill

pipe and drill collars, with new sections or joints being

added as drilling progresses.

The cuttings are lifted from the hole by the drilling fluid

which continuously circulated down the inside of the drill

string through water courses or nozzles in the bit, and

upward in annular space between the drill pipe and bore

hole.

At the surface, the returning fluid (mud) is dierted

through shale sha!ers, desilters, desanders and series oftan!s or pits which treat the fluid. In the last of these pits

the mud is pic!ed up by the pump suction and repeats the

cycle. "igure # shows the basic components of a rotary

drilling rig.

1


2/13

2


3/13

$a!ing a connection, the process of adding a new joint of

pipe to the drill string is shown in "igure %. &eriodically the

pipe must be remoed from the hole in order to replace the

bit. The operation is illustrated in "igure '.

3


4/13

The basic drilling components are

#. erric!, mast and substructures

%. rawwor!s'. $ud pumps

*. &rime moers

+. The drill string

. -its

. rilling line

/. $iscellaneous and au0iliary equipment

erric!, mast and substructures

The function of a derric! is to proide the ertical

clearance necessary to the raising and lowering of the drill

string into and out of the hole during the drilling operations.

erric!s are rated according to their ability to withstand

two types of loading

#. 1ompressie loads%. 2ind loads

The allowable compressie load of a derric! is computed as

the sum of the strengths of the four legs. erric!s with

load capacities from appro0imately /,333 to #,*33,333 lb,

depending on steel grade and leg size are aailable.

4


5/13

Allowable wind loads for A&I derric!s are specified in two

ways, with or without pipe setbac!.

2ith pipe setbac!, the wind may be blowing perpendicular

to it, which is essentially a pipe wall. This is the worst

possible condition.

2ind loads are calculated by the formula

& 4 3.33*5%

where & 4 wind load, lb6ft%

5 4 wind elocity, mph

1alculation of )erric! 7oads

The bloc! and tac!le arrangement for a rotary rig is shown

in "igure *. Assuming that the system is frictionless, thefollowing relationship are apparent

2n

%n"d

+=

where "d 4 total compressie load on the deric!

5


6/13

n 4 number of lines through the traelling

bloc! (those supporting 2).

2 4 hoo! load

6


7/13

The derric! load is always greater than the hoo! load by

the the factor of (n8%)6% due to the two additional lines

(drawwor!s and anchor) e0erting a downward pull.

uring hoisting

74 nA

where 74 elocity of line being spooled (or

unspooled) at the drawwor!s during

hoisting.

A4 hoo! elocity

rawwor!s (hoist)

The drawwor!s or hoist is the !ey piece of equipment on a

rotary rig. The functions of the drawwor!s are

#. It is the control centre from which the drilleroperates the rig. It contains the clutches, chains,

sproc!ets, engine throttles and other controls wich

enable the rig pwer to be dierted to the particular

operation at hand.

7


8/13

%. It houses the drum which spools the drilling line during

hoisting operations and allows feed9off during drilling.

rawwor!s are commonly designated by a horsepower and

depth rating.

e

#0

'',333

2:& h=

where 2 4 :oo! load, lb

h4 hoisting elocity of traelling bloc!, ft6min

'',333 4 ft.lb6min per horsepower

e 4 :oo! to drawwor!s efficiency

:oo! to drawwor!s efficiencies are commonly between /3

to ;3 denotes that each

8


9/13

side of the piston does wor!, while =duple0> refers to the

number of pistons (two).

The superiority of the piston type pump for drilling serice

is due to the following features

#. Ability to handle fluids containing high percentages of

solids, many of which are abrasie.

%. 5ale clearance will allow passage of large solid

particles (typically lost circulation materials) without

damage.

'. ?ase and simplicity of operation and maintenance.

7iners, pistons and ales may be replaced in the field

by the rig crew.

*. 2ide range of olume and pressure aailable by using

different liner and piston sizes.

&rime $oers

The bul! of rig power is consumed by two operations

#. 1irculation of the drilling fluid

%. :oisting

9


10/13

"ortunately these requirements do not occur at the same

time and the same engine perform both jobs.

The prime moers used are the steam engines, electric

motors and internal combustion engines. The most

commonly used is the internal combustion engines such as

the automotie type (multicylinder, light flywheel) diesel

and gas engines capable of rapid acceleration.

The rill @tring

The rotary drill string includes the components as in "igure

+.

10


11/13

"ig. + @chematic diagram of drill

string components and bit. -it load isfurnished by heay walled large9

diameter drill collars.

otary bits

The bit is the part that drill the hole. -asically there are

three types of drill bits, these are the drag type, rolling

cutter type and the diamond bit. The most common is therolling cutter type. The diamond bit is commonly used in

hard formations.

rilling line

11


12/13

The rotary drilling line afford a means of handling the load

suspended from the hoo! during all drilling operations.

The ma0imum load occurs when running casing, although

fishing operations frequently require line pulls in e0cess of

the drill string weight.

Traelling -loc!, :oo! and @wiel

The traelling bloc! is the traelling pulley assembly that

connects the drilling line to the hoo! and swiel. The swiel

must suspend the drill string and allow rotation at the same

time.

-lowout &reenter (-B&)

The main function of a blowout preenter is to furnish a

means of closing off the annular space between the drill

pipe and casing.

12


13/13

It is not always possible to predict the e0act manitude of

pressures which will be encountered in the drilling of a well.

1onsequently it is not uncommon to encounter pressure

greater than those imposed by the drilling fluid, with the

result that formation fluids flow into the bore hole and

eentually to the surface.

This effect is called a blowout, and is one of the most

feared and e0pensie accidents which can occur in well

drilling.

$ost blowout preenters are either hydraulically or

pneumaticaly operated, with manual operation aailable as asafetry precaution.

13

4 Rotary Drilling

Documents