Q921 de1 lec 7 v1

Drilling Engineering 1 Course (1st Ed.)

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1. The Rotary SystemA. Introduction

B. Kelly, Kelly Valves, and Kelly Saver Sub

C. Rotary Table and Components

2. Well Control System

3. Well Monitoring System

1. Drillstring TubularsA. Drill Pipes

a. properties of drill pipes

B. Drill Pipe Elevator

C. Drill Collars & Heavy Wall Drill Pipes

D. Special Tools

Drillstring purpose & constitutes

The purpose of the drillstring is to transmit mechanical power (torque and rotation),

hydraulic power (pressure and flow rate), and weight to the bit.

The drillstring is composed mainly of the following elements:Drill pipes,

Heavy wall drill pipes,

Drill collars,

Several special elements and tools.

Fall 13 H. AlamiNia Drilling Engineering 1 Course (1st Ed.) 5

schematic of a typical rotary drillstring


Drill Pipe

Below the kelly assembly (upper kelly valve + kelly +lower kelly valve + kelly saver sub) is a length of drill pipes (DP).

Drill Pipe is a primary and important drillstring member.

Since the drill pipes are generally compose the upper and longest portion of the drillstring, they must be light and strong.

The drill pipe body is a seamless pipe with outside diameter (OD) varying from 2 3/8in to 6 5/8in.

The outside diameter and the wall thickness t determine the linear weight of the drill pipe. The inside diameter (ID) is equal to OD minus 2t.


Drill pipe material

Drill pipes are made of high grade steel

(there are also drill pipes made of aluminum, carbon fiber, etc).

API has standardized four steel grades: E–75, X–95, G–105, and S–135.

The figures represent the minimum yield strength Ys (in ksi) of the the steel.


Drill pipe specification and following basic parametersDrill pipes are specified with the following basic parameters:

1. Length range:Range I: 18ft to 22ft,Range II: 27ft to 30ft (most common),Range III: 38ft to 45 ft,

2. Nominal linear weight: in general 2 or 3 linear weight or wall thickness for each standard

OD

3. Wall upset: EU (external upset), IU (internal upset),

and IEU (internal & external upset). The wall upset is a length of extra thickness at both ends of the drill

pipe body to provide a smooth transition between the pipe body and the tool joint, in order to reduce the stress concentration,


Drill pipe specification and following basic parameters (Cont.)4. Tool joint OD, ID, and tong length,

5. Steel grade: (D-55), E-75, X-95, G-105, S-135,

6. Connection size and type: from 2 3/8in to 5 1/2in, type

IF (internal flush), EF (external flush), FH (full hole), XH (extra hole), SH (slim hole), DS (double streamline), and NC (numbered connection),

The API RP-7G contains the specification of all API standard drill pipes approved for oil and gas drilling use.


The tool joints

The tool joints are heavy coupling elements having coarse,

tapered threads and sealing shoulders designed

to sustain the weight and

to transmit torque along the drillstring.

The threads of the tool joints are specially designed to offer strength (axial and torsional), easy handling,

fast connections (number of turns to make the connection), and leak-proof sealing (metal to metal).

Tool joints might be welded or screwed to the ends of the drill pipe body.


Typical tool joint designs

(A) Internal upset DP with full–hole shrink–grip TJ,

(B) External upset DP with internal–flush shrink–grip TJ,

(C) External upset DP with flash–weld unitized TJ,

(D) External–internal upset DP with Hydrill™–pressure welded TJ.


common properties of drill pipes

Two other common properties of drill pipes are capacity and displacement.

Pipe Capacity: The capacity Ap of a drill pipe is a measure of

its internal area, expressed as volume/length, usually gal/ft or bbl/ft.Sometimes the capacity is expressed as the reversal of the area,

usually in ft/bbl. The reader should be attended to the units.

If Di is the inside diameter (ID) of a drill pipe in inches, then


common properties of drill pipes (Cont.)Pipe Displacement:

The displacement As of the drill pipe is the measure of its cross-section area, expressed as volume/length, normally bbl/ft.

If Do is the outside diameter (OD) of a drill pipe in inches,

Annulus Capacity: The annulus capacity Aa is not a property of the pipe because

it depends on the diameter of the hole opposite to the pipe.

DW is the diameter of the well, & the annulus capacity Aa in bbl/ft


Drill pipe nominal weight

The capacity and displacement formulas above do not take into account the tool joints,

and manufacturer tables must be consulted when more accurate values are required.

In particular, the nominal weight that specify a given drill pipe represents neither the pipe body linear weight,

nor the average linear weight (body plus tool joint divided by its length).

It is just a nominal value.


adjusted linear weight of the drill pipe

a typical 5in DP with 19.5 lb/ft has an internal diameter of 4.276in. The density of steel is 489.5 lb/ft3.

Therefore, one foot of pipe body weights

Considering a 30 ft long DP (Range II), the tool joints (pin and box) comprise about 2 1/2 ft of its length. Outside and inside diameters of the tool joints are 6in

and 3 1/2 in respectively.


adjusted linear weight of the drill pipe (Cont.)

Therefore, the linear weight of the tool joint is

The weight of the drill pipe (body plus TJ) is

Consequently, the adjusted linear weight of the drill pipe is


DP Classification according to wearing

Drill pipes are subjected to wear during operation. In particular,

reduction of tool joints OD and wall thickness reduce tensile and torsion capacity of the element.

Used drill pipes are classified as Premium or Class I

if the minimum wall thickness is at least 80% of the wall thickness of a new pipe, and A new pipe that for the first time is connected to a drillstring is

immediately re–classified to premium DP.

Class II when at least 70%.


New Drill Pipe Dimensional Data

The table presents dimensional data for new drill pipes.


drill pipe elevator

Drill pipes are handled during tripping using a drill pipe elevator. (The swivel and kelly are set aside in the rat hole.)

It is connected by two links to the hook body.

A hinge and latch allows opening and closing the bi–parted collar around the drill pipe.

The elevator is operated by the roughnecks at the rotary table level, and

by the derrick man at the monkey board.


A DP elevator and the links to the hook body


Drill pipes

Drill pipes extend across almost the whole length of the drillstring and,

although relatively light, they contribute with a significant part of the drillstring weight (50% or more).

However, drill pipes are, in general, used only under tension. They should not be subjected to compression

due to its low resistance to buckling. Therefore, they cannot be used to apply weight on the bit.

• In horizontal wells, drill pipes can be put under compression if located in a suitably curved section of the hole; in addition, compression service drill pipes (CSDP, S-135 grade DP with 2 or 3 wear knots) are specially designed to work under compression to drill short radius horizontal wells.


Drill collars role and specifications

Since drill pipes cannot be used to apply weight on bit, this role is played be the drill collars (and also by heavy weight drill pipes as shown next).

Drill collars (DC) are thick walled steel pipes

located normally right above the bit, and

purpose is to provide weight (axial force) to the bit.

are manufactured with carbon steel (AISI 4115), or some non-magnetic alloy (stainless steel, monel metal).


A spiraled and a slick drill collars

The outside of drill collars may be slick (small diameters) or spiral grooved (any size.).The purpose of the groves is to

reduce or avoid the risk of differential sticking opposite to permeable formations.

The depth of the grooves is made larger than the average thickness of a flocculated mud.

Average length of drill collars is 34 ft, but re–threading normally makes them shorter.


Drill collars elevators

The elevators for drill collars are very similar to the elevators for drill pipes. They differ in the shape of the internal hole that clamps

on the pipe.

Most drill collars are recessed so as to be handled with the elevator.

If the drill collar is not recessed (sometimes even if it is!), a special sub called lift sub is used. Lift subs have the shape of the upper end of a drill pipe, and

connects to the top of sections of drill collars during trips. • Then the drill pipe elevator can be used to lift or lower the

drillstring.


heavy wall drill pipes (HWDP)

In addition to drill pipes and drill collars, there are special pipes called heavy wall drill pipes (HWDP). They are intermediary pipes between drill pipes and drill

collars, being strong enough to be put under compression

(they contribute to the available weight to apply to the bit), and

they are flexible enough to be used in directional drilling (less torque and drag than drill collars.)

The use of HWDP also allow a gradual transition

between the flexible drill pipes and the stiff drill collars (less stress concentration, and therefore, less mechanical fatigue on the threads.)


Heavy wall drill pipes

HWDPs look very similar to regular drill pipes, being of the same length of Range II DP (27 to 30 ft),

but with longer tool joints (to permit re–threading).

HWDPs have a central external upset. it provides an additional third point of contact,

increasing the overall stiffness and protecting the pipe sections from excessive wearing in high inclination wells (normally the tool joints and central upset have a band of hard material to prevent/reduce wear).


Drillstring equipment

Several drilling equipment are used in the drillstring.

The most important are:stabilizers,

provide localized additional support points (localized larger diameter) in one or more positions along the drillstring.

reamers,

hole–openers.


Advantages of drillstring

For vertical wells, the stabilizer prevents low frequency vibration in the drillstring during rotation.

The advantages are:reduce wear (of both drillstring and casing),

reduce mechanical fatigue,

reduce mechanical instability of formation (caving),

reduce tortuous hole.

Stabilizers are essential equipment for directional drilling.


Stabilizer special characteristics and typesSuitable choice of

number and position of stabilizers in the drillstring lend to the bottom hole assembly (BHA, the lower part of

the drillstring composed of drill collars, stabilizers and HWDP)

special characteristics in terms of inclination control:angle build–up,

angle drop–off,angle hold.

Stabilizer may be of the following types:integral blade,interchangeable blade,non–rotating blades,replaceable blades,clamp–onnear-bit,


The diameter of stabilizers

The diameter of stabilizers can be in gauge or under gauge.

More recently, remote adjustable blade stabilizers were introduced. Changing suitably the diameter of the stabilizers provide

a level of control in the directional behavior of BHAs.


Some Stabilizers

(a) integral,

(b) interchangea

ble,

(c) non–

rotating,

(d)replaceable


Reamers

The purpose of the reamer is to keep the diameter of the open hole in gauge, that is, with the expected original diameter of the bit.

Two reasons may cause a decrease in the original diameter: formation swelling (hydrated shales,

moving salt),bit diameter reduction (hard and

abrasive formations).

The reamer also functions as a stabilizer since the rollers touch the borehole wall.

Different types of rollers can be selected to suit the formations being reamed.

A roller reamerFall 13 H. AlamiNia Drilling Engineering 1 Course (1st Ed.) 39

The hole–opener

The hole–opener is a tool designed to enlarge the diameter of a previously (or simultaneously drilled smaller borehole. Three situations (at least) are possible: to drill the borehole section with a smaller bit,

and later to enlarge to the final diameter (a special tool called bull nose is connected in the place of the bit, to guide the hole opener along the pre-drilled hole),

to drill the borehole section with a smaller bit and simultaneously enlarge to the final diameter,

to enlarge a section below a casing with a diameter larger than the internal diameter of the casing. In this case, a special hole opener (also caller

underreamer) with hinged arms actuated hydraulically is used (the drilling fluid pressure actuates in rams that open the arms forcing the cutters against the borehole wall).

A fixed hole–openerFall 13 H. AlamiNia Drilling Engineering 1 Course (1st Ed.) 40

1. Jorge H.B. Sampaio Jr. “Drilling Engineering Fundamentals.” Master of Petroleum Engineering. Curtin University of Technology, 2007. Chapter 3

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