Drilling Engineering 1 Course3rd Ed. , 3rd Experience

1. The Rotary SystemA. IntroductionB. Kelly, Kelly Valves, and Kelly Saver SubC. Rotary Table and ComponentsD. The topdrive

IntroductionThe rotary system is the set of equipment

necessary to promote the rotation of the bit. The bit must be

mechanically and hydraulically connected to the rig.This connection is made by the drillstring.

The purpose of the drillstring is to transmit axial force, torque, and drilling fluid (hydraulic power) to the bit.

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Drillstring components The basic drillstring is

composed of the following components:Swivel,Kelly and accessories,Rotary table and components,Drillstring tubulars

(drill pipe, drill collars, etc.),BHADrill bit.

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The main components of rotating equipment

The main components are:Rotary tableKelly Top Drive

equivalent to the Kelly and rotary table, i.e. either top drive or Kelly/rotary table

Swivel Rotary hose

The rotary horse power requirement is usually between 1.5 to 2 times the rotary speed, depending on hole depth. Hence for rotary speed of 200 rpm,

the power requirement is about 400 HP.

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SwivelThe swivel

is suspended by the hook of the traveling block and

allows the drillstring to rotate as drilling fluid is pumped to within the drillstring.

supports the axial load of the drillstring.

Without the swivel, drilling fluid could not be

pumped downhole, or the drillstring could not

rotate.

A flexible hose connects to the gooseneck

which is hydraulically coupled to the top of the swivel stem by a stuffing box.

The stem shoulder rest on a large thrust tapered

roller bearing, which transmits the drillstring weight to the swivel body, and then to the bail.

The thread connector of the swivel is cut left–hand so that

it will not tend to disconnect when the drillstring is rotated by the kelly or by the top drive.

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cuts of a swivel showing the internal parts

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KELLY vs. TOP DRIVEStrictly speaking the Kelly or

top drive are not components of the drill string. The Kelly is

the rotating link between the rotary table and the drill string.

Its main functions are:transmits rotation and

weight-on-bit to the drillbitSupports the weight of the drillstringconnects the swivel to the uppermost

length of drillpipe; andconveys the drilling fluid from the

swivel into the drill string.

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kellyBelow and connected to the swivel is a long four-sided (square) or triangular orsix-sided (hexagon, the most common) steel bar

with a hole drilled through the middle for a fluid path called kelly.

The square or hexagonal section of the kelly allows it to be gripped and turned

by the kelly bushing and rotary table.

The Kelly comes in lengths ranging from 40 to 54 ft (12 to 16.5 m)

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The purpose of the kelly

The purpose of the kelly is to transmit rotary motion and torque to the drillstring (and consequently to the drill bit), while allowing the drillstring

to be lowered or raised during rotation.

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A square kelly and a hexagonal kelly

kelly bushingTorque is transmitted

to the kelly by the kelly bushing. It has an inside profile

matching the kelly’s outside profile (either square or hexagonal), but with slightly larger

dimensions so that the kelly

can freely move up and down inside it.

Kelly bushings

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Applications of the kelly valvesThe kelly valve consists of a ball valve which allows free

passage of drilling fluids without pressure loss.

This is a safety devicecan be closed to prevent flow from

inside the drillstring during critical operations like kick control.

It also isolates the drillstring

from the surface equipment and allows disconnecting the kelly during critical operations.

A kelly valve

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The Kelly cocks (the kelly valves)

The Kelly is usually provided with two safety valves,

one at the top and one at the bottom, called upper and lower Kelly cocks,

respectively.

The upper kelly valve has left–hand threads

The lower Kelly cock is always manual

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kelly saver subA kelly saver sub is simply a short length pipe with

has male threads on one end and female on the other. It is screwed onto the bottom of the lower kelly valve or

top drive and onto the rest of the drillstring.

When the hole must be deepened, and pipe added to the drillstring, the threads are unscrewed between

the kelly saver sub and the rest of the drillstring, as opposed to between the kelly valve or top drive and the saver sub.

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kelly saver sub (Cont.)This means that the connection between the kelly or

top drive and the saver sub rarely is used, and suffers minimal wear and tear, whereas the lower connection is used in almost all cases and

suffers the most wear and tear. The saver sub is expendable and

does not represent a major investment. However, the kelly or top drive component threads

are spared by use of a saver sub, and those components represent a significant capital cost and considerable downtime when replaced.

It is important that both lower kelly valve and kelly saver sub

be of the same diameter of the drill pipe tool-joints to allow stripping into the hole during control operations.

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master bushing and master casing bushingThe kelly bushing fits in

the master bushing,which, in turn, attach to

the rotary table. It connects to the master

bushing either by pins of by a squared link. The master bushing

transmit torque and rotation from the rotary table to the kelly bushing.

A master casing bushing is used to handle casings.

Master bushings, and casing bushing

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Kelly bushing and master bushingFigure shows

a kelly bushing, master bushing, and rotary table assembly.

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Drillpipe slip (detail when set in the master bushing)

The master bushing (and also the master casing bushing) has a tapered internal hole. The purpose of the tapered hole is to

receive the pipe slips. During pipe connection or

drillstring trip operations, this tapered hole receives either the drill pipe slips, or the drill collar slips, or the casing slips, which grips the tubular and frees the hook from its weight.

Because of the slick shape of most drill collars, a safety clamp is always used above the

drill collar slips (mandatory!) If the drill collars slides in the slips,

the safety clamp works as a stop to force the slips to grip the drill collar.

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DC slips, safety collar, casing slips and A rotary tableA drill collar slips (a),

a safety collar (b), and a casing slips (c) are shown in the Figure.The rotary table

receives power from the power system (either mechanical or

electric.) A gearbox allows

several combinations of torque and speed.

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Kelly set

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The top drive outlookThe top drive is basically a

combined rotary table and Kelly.The top drive consists of a DC drive motor that

connects directly to the drillstring without the need or a rotary table.

The top drive is mounted on the rig’s swivel,

the swivel attaches to the travelling block and supports the drillstring weight.

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The elevator and elevator links of a topdrive

The top drive has a pipe handler consisting of a

torque wrench and a conventional elevator to assist in pipe handling during connection and round trip operations.

The elevator and elevator links are supported on a shoulder

located on the extended swivel stem.

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Different positions of a topdrive

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Advantages of topdrive

The top drive functions is the same way as the Kelly. However, it has

many advantages over the Kelly system including circulating while back reaming, circulating while running in hole or pulling out of hole in stands.

The Kelly system can only do this in singles; i.e. 30 ft.

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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 and 10