drilling engineering – pe311 rotary system

Drilling Engineering – Fall 2012

Prepared by: Tan Nguyen

Drilling Engineering – PE311

Rotary System



The main parts of the rotary system (or the drill string) are:

1. Swivel

2. Kelley

3. Rotary table

4. Drillpipe

5. Drill collars

6. Heavy wall drill pipe

7. Stabilizer

8. Rotary reamers

Note: the bottomhole assembly (BHA) is that portion of the drill string between the drill pipe and the drill bit.

Introduction to Rotary System



The rotary system is the heart of the rotary drilling rig; its function involves

transmitting rotating function to the drillstring and consequently the bit.

As the drill string moves downhole, it is subjected to a variety of stresses, including

tension, compression, vibration, torsion, friction, formation pressure and circulating

fluid pressure. It is also exposed to abrasive solids and corrosive fluids.

The drill string not only must be sturdy enough to withstand this hostile

environment, but it must be lightweight and manageable enough to be efficiently

handled within the limits of the rig's hoisting system. At the same time, it must:

provide weight to the bit; allow control over wellbore deviation; and help ensure

that the hole stays "in gauge".

Introduction to Rotary System



The rotary swivel connects the circulating

system to the rotary system while providing a

fluid seal that must absorb rotational wear while

holding pressure. The swivel is hung under the

traveling block and directly above the Kelley. It

provides the ability for the Kelly to rotate while

the traveling block to remain in a stationary

rotational position while simultaneously allowing

the introduction of drilling fluid into the drill

string.

Swivel



The Kelley is of square or hexagonal cross-

section that screws into the drillstring while

providing a flat surface for applying torque to

rotate the pipe. The main function of a kelly is to

transfer energy from the rotary table to the rest

of the drill string.

Kelley



The longest portion of the drill string consists of

connected lengths of drill pipe. The primary

purposes of drill pipe are to provide length to the

drill string and transmit rotational energy from

the Kelly to the bottomhole assembly and the

drill bit. The drillpipe connects the rig surface

equipment with the bottomhole assembly and

the bit, both to pump drilling fluid to the bit and to

be able to raise, lower and rotate the bottomhole

assembly and bit.

Drillpipe



Hole size, well depth, casing and cementing requirements, subsurface pressures,

circulating system and drilling mud parameters, hoisting capacity, pipe availability and

contract provisions are among the factors that influence drill pipe selection.

The American Petroleum Institute has established standards for drill pipe

manufacturing practices, dimensions, strengths and performance properties. These

standards appear in the following publications:

• API Spec 5D: This American Petroleum Institute (API) specification covers seamless

steel drill pipe used in the oil and gas industry

• API Bul 5C2, Bulletin on Performance Properties of Casing, Tubing and Drill Pipe;

API-standard drill pipe is available in three length ranges: Range 1(18-22 ft), Range 2

(27-30 ft) and Range 3 (38-45 ft). Range 2 is the length most commonly used, making

the "average" length of a drill pipe joint about 30 feet.

Drillpipe



Drillpipe



The drill collars provide weight and

stability to the drill bit, maintain tension

on the drill pipe and help keep the hole

on a straight course. Drill collars are

thick-walled tubular pieces machined

from solid bars of steel. The bars of

steel are drilled from end to end to

provide a passage to pumping drilling

fluids through the collars.

Drill Collar



To accurately control the amount of force applied to the bit, the driller carefully

monitors the surface weight measured while the bit is just off the bottom of the

wellbore. Next, the drillstring (and the drill bit), is slowly and carefully lowered until

it touches bottom. After that point, as the driller continues to lower the top of the

drillstring, more and more weight is applied to the bit, and correspondingly less

weight is measured as hanging at the surface.

Downhole MWD sensors measure weight-on-bit more accurately and transmit the

data to the surface.

Drill Collar



To avoid fatigue failures, the drill

pipe and uppermost drill collars need

to be kept in tension at all times.

Tension can be maintained by

running an adequate number of

collars in the bottomhole assembly

to ensure that the neutral point (that

is, the point below which the drill

string is in compression, and above

which it is in tension) will always be

below the drill pipe

Drill Collar



Serves as an intermediate-weight drill string member between the drill pipe and

the much heavier drill collars, thereby reducing fatigue failures, providing

additional hole stability and aiding in directional control.

The most important drill string application for heavy wall drill pipe is in the so-

called zone of destruction — the area above the topmost drill collars where drill

pipe fatigue failure is most likely to occur. To reduce fatigue failures in this area of

the borehole, 18 to 21 joints of heavy wall drill pipe should be run above the drill

collars. This provides a gradual change in stiffness between drill collars and drill

pipe. Also, the ability of the heavy wall drill pipe to bend (unlike drill collars) serves

to relieve high stresses at the connections.

Heavy Wall Drill Pipe



Heavy wall drill pipe was first used in directional drilling, which generally requires

flexibility in the drill string. It is now widely used in vertical and horizontal drilling as

well. With less wall contact than would be experienced with drill collars, its usage

reduces torque and wall-sticking tendencies. Its smaller degree of wall contact,

together with its greater stiffness relative to regular drill pipe, results in increased

stability and better directional control. Heavy wall drill pipe is also useful in

reducing hook loads, making it ideal for smaller rigs drilling deeper holes.

Heavy Wall Drill Pipe



Centralize the drill collars, help maintain the hole at full-

gauge diameter and aid in directional control. Stabilizers,

by centralizing the drill string at selected points in the

borehole, can be used to:

•Ensure that the weight of the drill collars is concentrated

on the bit;

•Reduce torque and bending stresses in the drill string;

•Prevent wall-sticking or key-seating of the drill collars;

•Maintain constant bit direction in straight-hole drilling.

Stabilizer



The Rotary Reamer is designed for various reams in drilling operation. In very hard formations, the outside cutting structure of a bit gradually wears away if it is not protected. This results in a hole diameter that becomes smaller with increasing depth

When a hole is severely undergauge, it is necessary to ream each new bit back to bottom before drilling can resume. This not only costs rig time and reduces bit life, but it increases the possibility of sticking the drill string.

http://www.halliburton.com/ps/default.aspx?navid=1736&pageid=4000&prodgrpid=PRG%3A%3AKRMJK0LPT

Reamer

drilling engineering – pe311 rotary system

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