IPM DPT
DPT Drill String and BHA design
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Drill String and BHA Design
References
DPT Drill String and BHA design
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• API RP 7G Drill Stem Design and Op Limits
• API SPEC 7 Specifications for Rotary Drilling
Elements
• API SPEC 5D Specifications for Drill Pipe
• SLB Drill String Design manual
• TH Hill DS-1 Drill String Design
Objectives
At the end of this lecture YOU will be able to describe:
Functions of Drill Pipe , Drill Collars and BHA selection
•
Grades of Drill Pipe and strength properties
•
Thread types and tool-joints
•
Drill collar weight and neutral point
•
Bending Stress Ratios and Stiffness Ratios
•
Margin Of Overpull
•
Basic design calculations based on depth to be drilled.
•
Functions of stabilizers and roller reamers.
DPT Drill String and BHA design
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•
Agenda
Introduction to Drill String Design: Overview
II.
Drill String Components
•
Drill Collars - Drill Pipe - HWDP
III. Drill String Design
•
Bottom Hole Assembly Design
•
Drill Pipe Selection
•
Buckling and max WOB
DPT Drill String and BHA design
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I.
Functions of the Drill String
The drill string is the mechanical linkage connecting the
drill bit on bottom to the rotary drive system on the
surface.
D
P
1. Transmit and support axial loads - WOB
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The drillstring serves the three main following functions :
2. Transmit and support torsional loads - rpm
3. Transmit hydraulics to clean the hole and cool the
bit.
DC
DPT Drill String and BHA design
WOB
Drill String Components
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The Drill String includes all tubular
equipment between the Kelly Swivel
and the bit
• Kelly
• Surface Safety Valves
• Drill Pipe
• Heavy Walled Drill Pipe
• Drill Collar
• Jars – Shock Subs – Bumper Subs
– Junk Baskets – Accelerators etc…
DPT Drill String and BHA design
The Kelly/Top Drive
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Strictly speaking, Kelly/ Topdrive
are not components of the drill
string; however, they provide the
essential requirements for drilling a
well:
1) Transmit rotation to the drillstring.
2) Provide access to the drilling fluid
into the drillstring.
3) Support the weight of the string.
DPT Drill String and BHA design
The Kelly
•
Supports the weight of the drillstring
•
Connects to the swivel and allow circulation thru
pipe.
The Kelly comes in lengths ranging from 40 to 54 ft with
cross sections such as hexagonal (most common), square
or triangular.
Connected to a Kelly Saver Sub
DPT Drill String and BHA design
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The Kelly is the rotating link between the rotary table and
the drill string.
• Transmits rotation and weight-on-bit to the drillbit
Kelly Cock
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The Kelly is usually provided with two safety
valves, one at the top and one at the bottom,
called Kelly cock.
The Kelly cock is used to close the inside
of the drillstring in the event of a kick.
The upper & lower Kelly cocks operate
manually.
IBOP / DPSV are not run in the drill string
but kept handy on the rig floor
DPT Drill String and BHA design
Top Drive
The top drive is basically a combined rotary table and kelly.
Advantages over the kelly system:
1. Efficient reaming and back reaming.
2. Circulating while running in
stands
hole or pulling out of hole in
3. The kelly system can only do this in singles; ie 30 ft.
DPT Drill String and BHA design
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It is powered by a separate motor and transmits rotation to the
drill string directly without the need for a rotary table.
Stabilizers
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DPT Drill String and BHA design
Stabilizers
Reasons for Using Stabilizers:
DPT Drill String and BHA design
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1. They are used as a fundamental method of controlling
the directional behavior of most BHAs.
2. Help concentrate the weight of the BHA on the bit.
3. Minimize bending and vibrations which cause tool joint
wear and damage to BHA components such as MWDs.
4. Reduce drilling torque by preventing collar contact with
the side of the hole and by keeping them concentric in
the hole. (FG!!)
5. Help preventing differential sticking and key seating.
Roller Reamers
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DPT Drill String and BHA design
Drill Pipe
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DPT Drill String and BHA design
Drill Pipe
Function
To serve as a conduit or conductor for drilling fluid
To transmit the rotation from surface to the bit on bottom
A pierced, seamless tube of forged steel or extruded
Aluminum
Tool joints attached to each end of the seamless tube
Tool Joints
Provide connections for the drill string
Separate pieces of metal welded to the seamless tube
Thick enough to have pin or box cut into them
DPT Drill String and BHA design
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Components
Drill Pipe Classification
2 3/8” to 6 5/8” – refers to OD of pipe body
2. Length
Range 1 18 to 22 ft, Range 2 27 to 30ft, Range 3
38 to 45 ft
3. Grade
E - 75, X – 95, G – 105, S – 135
the numbers denote 1000’s of psi minimum yield
strength
4. Weight
Depending upon the size of pipe different weight
ranges
5. Class
API classification for used pipe
For example a drill pipe could be - 5”, Range 2, G-105, 19.5ppf, New
DPT Drill String and BHA design
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1. Size
Drill Pipe Grades
There are four grades of pipe commonly used today.
Min Yield
Avg / MaxYield
E or E-75
75,000
85,000 / 105,000
X or X-95
95,000
110,000 / 125,000
G or G-105
105,000
120,000 / 135,000
S or S-135
135,000
145,000 / 165,000
DPT Drill String and BHA design
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Grade
Mechanical Properties of Steel
Young Modulus
E = Stress divided by Strain = 30,000,000
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Stress & Strength
Stress = Strength divided by Cross Section Area
Strain & stretch
Strain = Stretch divided by original length
DPT Drill String and BHA design
Mechanical Properties of Steel
Elastic Limit
Limit of stress beyond which, when the stress is removed, the
steel will have acquired a permanent stretch.
Ultimate Tensile Stress
The stress which will break the steel
DPT Drill String and BHA design
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Minimum Yield Stress
The stress which gives a stretch of 0.5% (0.005”). When the stress
is removed, the steel will have acquired 0.2% of permanent
deformation.
Exercise DP-00
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DPT Drill String and BHA design
Used Drill Pipe Classification
Unlike casing and tubing, which are normally run new, drill
pipe is normally used in a worn condition. It therefore has
Classes:
No wear, has never been used
Premium:
Remaining wall not less than 80%.
Class 2:
Class 3:
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New:
Remaining wall not less than 70%.
Remaining wall less than 70%.
Other details such as, dents and mashing, slip area mechanical
damage, stress induced diameter variations, corrosion cuts and
gouges, specified on Table 24 ( Classification of Used Drill Pipe ) of
API RP 7G.
DPT Drill String and BHA design
Drillpipe Upsets
Where the pipe joins the tooljoint, the pipe wall thickness is
increased or “upset”.
•The drill-pipe can have
• Internal upsets (IU), ( OD stays the same )
• External upsets (EU), ( ID stays the same )
• Internal and External Upsets (IEU).
DPT Drill String and BHA design
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•This increased thickness is used to decrease the frequency of
pipe failure at the point where the pipe meets the tool-joint.
Drill Pipe Weights
When referring to Drill Pipe Weights, there are four important ones:
Plain end Weight – Refers to the weight per foot of the pipe body.
Adjusted Weight – Refers to the weight per foot of pipe including the
upset but excluding the tool joint based on a length of 29.4 ft
Approximate Weight – The average weight per foot of pipe and tool
joints of Range II pipe. This approximate weight is the number to
use in Design calculations.
DPT Drill String and BHA design
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Nominal Weight - Refers to an obsolete standard. ( Weight of
Range I pipe with connections ) Is used today to refer a class of Drill
pipe.
Calculating Approximate Weights
Wt/ft =
Wt DP Adjusted ×29.4 + Wt ToolJt Approx
29.4 +L ToolJtAdj
DPT Drill String and BHA design
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Wt/ft =
approx. adj. wt.DP ×29.4 + approx. wt. tool jt
29.4 + tool jt adjusted length
Calculating Approximate Weights
Wt DP Adj
Nom upset Wt
=Tube Wt +
29 .4
….(1)
Data from Table 7API 5D
)
(
)
− 0 .501×d ×(D − DTE )
2
L= combined length of pin and box (in)
d= inside diameter of pin (in)
….(2)
D= outside diameter of pin (in)
DTE= diameter of box at elevator upset (in)
Data from Spec 7 Fig 6 Table 7
LTool Jt Adj =
L + 2 .253×(D − DTE )
ft
12
….(3)
Datat from Spec 7 Fig 6 Table 7
DPT Drill String and BHA design
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(
Wt Tool Jt Adj = 0 .222 × L D 2 − d 2 + 0 .167 × D 3 − D 3TE
Exercise DP-01
Compare the value against the one published on Table 9 of API
RP7G.
Tables 7API 5D and Table 7 of the Specification can be
found in handout # 1 of tables.
Table 9 of API RP7G can be found on handout # 2 of
tables.
DPT Drill String and BHA design
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Calculate the approximate weight of tool joint and drillpipe
assembly for 5 in OD, 19.5 lb/ft Drill Pipe having NC50 tool
joints with 6.625 in OD, 2.75 in ID and being internallyexternally upset. ( IEU ).
DP Data from Table 7 Spec 5d
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DPT Drill String and BHA design
DP Data from Table 7 Spec 7
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DPT Drill String and BHA design
API RP 7G
• Table 1-3 New Pipe Data
• Table 4-5 Premium Pipe Data
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• Table 6-7 Class Two Pipe Data
• Table 8-9 Tool-joint Data
• Table 10 Make-up Torque Data
• Table 12 Connection interchangeability
• Table 24 Classification of used DP
DPT Drill String and BHA design
Tool Joints
All API tool joints have a minimum yield strength of 120,000 psi
regardless of the grade of the drill pipe they are used on (E, X,
G, S) .
•
API sets tool joint torsional strength at minimum 80% of the
tube torsional strength.
•
Make up torque is determined by pin ID or box OD. The make
up torque is 60% of the tool joint torsional capacity. The
equation for determining make up can be obtained from the
appendix of API RPG7. ( Numeral A.8.2 ). This equation is
rather complex, so the API developed a series of charts to find
the recommended make up torque to any connection given the
tool jt OD of box and ID of pin. These charts can be found in
API RP 7G ( Figures 1 to 25 )
DPT Drill String and BHA design
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•
Exercise DP02
Using some tables (?) and some figures (?) of API RP7G
what should be the make up torque of NEW 19.5 ppf G105
and S135 drill pipe ?
DPT Drill String and BHA design
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How do these values compare to the ones reported on
Table 10 ?
Make-Up Torque Charts
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DPT Drill String and BHA design
Drillstring Connections
The most common thread style in drillpipe is NC
The thread has a V-shaped form and is identified by the pitch
diameter, measured at a point 5/8 inches from the shoulder
The size of a rotary shouldered connection
is fixed by its gauge point pitch diameter.
5/8”
GAUGE POINT PITCH DIAMETER
If the pitch diameter is 5.0417 in
Æ This is an NC50 connection
Multiply 5.0417 by 10 → 50.417
Choose first two digits → 50
Hence NC 50
DPT Drill String and BHA design
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Connection Number is Pitch dia*10 truncated to two digits
NC Drillstring Connections
• Seal is provided by shoulder not threads. A clearance
exists between the crest of one thread and the root of the
mating thread
• Use of Lead based dope vs Copper based dope for DCs.
Not for sealing but for lubrication, to help make-up and
prevent galling
DPT Drill String and BHA design
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• There are 17 NC’s in use : NC-10 (1 1/16”) through
NC-77 (7 3/4”)
• Typical sizes: NC 50 for tool joints with 6 1/2” OD for 5”
pipe and NC 38 for 4 3/4” tool joints and 3 1/2” pipe.
Connection Interchangeability
NC 38 NC 40 NC46
NC50
2-3/8
3-1/2
4
4-1/2
4-1/2
5
2-7/8
Int Flush
IF
Full Hole
Extra
Hole
FH
XH
2-7/8 3-1/2
Dbl
Streamline
DSL
3-1/2
Slim Hole SH 2-7/8
Ext Flush EF
4
3-1/2
4-1/2
4
5-1/2
4-1/2
4-1/2
DPT Drill String and BHA design
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NC 26 NC 31
Drill Collars
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DPT Drill String and BHA design
Drill Collars
Description
They are heavy walled metal tubes
The ends are threaded (box and pin)
Types
Comes in many OD and ID sizes
Typically 4 ¾” to 9 ½” OD
Most commonly in lengths of 30-31 feet
Square collars where the holes tend to be crooked
Spiral collars where there is chance of getting stuck
Collars with elevator and slip recesses
DPT Drill String and BHA design
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Functions
To put weight on bit (WOB)
To keep the drill string from buckling
More functions of Drill Collars
1. Protect the Drill string from Bending and Torsion
2. Control direction and inclination of wells
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3. Drill straighter holes or vertical holes
4. Provide Pendulum effect
5. Reduce dog legs, key seats and ledges
6. Improve the probabilities of getting casing in the hole.
7. Increase bit performance
8. Reduce rough drilling, sticking and jumping
9. As a tool in fishing, testing, completing
DPT Drill String and BHA design
More Types of Drill Collars
Slick Drill Collar
Spiral Drill Collar
2. In areas where differential
sticking is a possibility spiral drill
collars and spiral HWDP should
be used in order to minimize
contact area with the formation.
DPT Drill String and BHA design
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1. Both slick and spiral drill collars
are used .
Drill Collars Strapping
length
OD
slip
recess
Well#
Date:
Rig:
BHA#:
Hole Size
Item
Bit
Bit Sub
9 1/2" Drill Collar
Stab
9 1/2" Drill Collar
9 1/2" Drill Collar
9 1/2" Drill Collar
connection
TRG 1
28-Jul-03
IDPT
1
26"
Sl #
1234
SL 235
9546
237689
9503
9521
9520
Bit #
Sl #
Type
Manuf
Jets
ID
3 1/8"
3 1/8"
3 1/8"
3 1/8"
3 1/8"
3 1/8"
OD
26"
9 1/2"
9 1/2"
9 1/2"
9 1/2"
9 1/2"
9 1/2"
FN
0.67
0.93
0.78
0.95
1.03
Pin
7 5/8" R
7 5/8"
7 5/8"
7 5/8"
7 5/8"
7 5/8"
R
R
R
R
R
Box
7 5/8 R
7 5/8 R
7 5/8 R
7 5/8 R
7 5/8 R
7 5/8 R
Length
0.75
1.01
8.96
2.36
9.01
9.04
8.99
1
1234
atm 234
Hughes
20-20-20
Remarks
New
DPT Drill String and BHA design
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elevator
Fish neck
recess
I
D
API Drill Collar Sizes
ID Range
2 7/8
3
3 1/8
3 1/4
3 1/2
3 3/4
4
4 1/8
4 1/4
4 1/2
4 3/4
5
5 1/4
5 1/2
5 3/4
6
1 - 1.5
1 - 1.5
1 - 1.5
1 - 1.5
1 - 1.5
1 - 1.5
1 - 2.25
1 - 2.25
1 - 2.25
1 - 2.25
1.5 - 2.5
1.5 - 2.5
1.5 - 2.5
1.5 - 2.8125
1.5 - 3.25
1.5 - 3.25
Weight Range
ppf
16 - 19
18 - 21
20 - 22
22 - 26
27 - 30
32 - 35
29 - 40
32 - 43
35 - 46
41 - 51
44 - 54
50 - 61
57 - 68
60 - 75
60 - 82
68 - 90
OD
ID Range
6 1/4
6 1/2
6 3/4
7
7 1/4
7.5
7.75
8
8 1/4
8 1/2
9
9 1/2
9 3/4
10
11
12
1.5 - 3.5
1.5 - 3.5
1.5 - 3.5
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
1.5 - 4
Weight Range
ppf
72 - 98
80 - 107
89 - 116
84 - 125
93 - 134
102 - 144
112 - 154
122 - 165
133 - 176
150 - 187
174 - 210
198 - 234
211 - 248
225 - 261
281 - 317
342 - 379
DPT Drill String and BHA design
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OD
Drill Collar Connections
Characteristics
• DC connections are rotary shouldered connections and can mate
the various DP connections
• The lubricant is Copper based dope
• The connection is the weakest part of the entire BHA
• The DC connections go through cycles of tension-compression
and are subject to bending stresses
• Improper M/U torque, improper or insufficient lubricant, galling
can all lead to connection failure
DPT Drill String and BHA design
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• The shoulder provide the only positive seal against fluid leakage
Drill Collar Connections
Stress Relief Features
• Stresses in DC connections are concentrated at the base of the
pin and in the bottom of the box (stronger)
• DCs and other BHA components are however much stiffer than
the DPs and much of the bending stresses are transferred to the
connections.
• These bending stresses can cause fatigue failure at the
connections
Stress Relief Groove / Bore Back
DPT Drill String and BHA design
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• DP body bends easily and takes up the majority of the applied
bending stress, DP connections are therefore subjected to less
bending than the DP body.
Stress Relief Pin Feature
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DPT Drill String and BHA design
Stress Relief Pin & Box Features
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DPT Drill String and BHA design
Drill Collar Connections
• The stress relief groove is to mitigate the fatigue cracks
where the face and threads would have otherwise joined
• Stress relief features should be specified on all BHA
connections NC-38 or larger.
• Pin stress relief grooves are not recommended on
connections smaller than NC-38 because they may weaken
the connection’s tensile and torsional strength.
• Bore Back boxes could be used on smaller connections.
• The Low-Torque face is to increase the compressive stress at
normal M/U torque above that of a regular face
DPT Drill String and BHA design
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• The Bore Back serves the same purpose at the bottom of the
box
Lo-Torq Feature
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•The low torque feature
consists in removing part of
the shoulder area of the pin
and box.
•This allows for lower make up
torque maintaining adequate
shoulder loading.
•It is a common feature in
large OD connections.
DPT Drill String and BHA design
Torsion limits for DC
Torque is rarely limited by the DC connection because it is
usually higher in the DP at surface and lower in the DC.
DPT Drill String and BHA design
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• If DC make-up torque >Dp make-up torque you have no
routine problems.
• BH Torque at any point should not exceed 80% of makeup torque for the connections in the hole to avoid over
tightening connections which can lead to damage of seals.
Torque Limits for DC
PAC
H-90
API NC
DC< 7 in DC>7 in
79.5%
N/a
51.1%
56.2%
56.8%
62.5%
DPT Drill String and BHA design
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• API recommended makeup torque for connections
is a percentage of the total
torsional yield of the
connection
M/U Torque as % of total torque
Make Up Torque Tables for DCs
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DPT Drill String and BHA design
Heavy Weight Drill Pipe
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DPT Drill String and BHA design
Heavy Weight Drill Pipe
Function
Used in transition zones between DC and DP
This prevents the DP from buckling
Can be used in compression (?)
Used for directional drilling
Used in place of DC sometimes (?)
To keep Drill Pipe in tension
Not to be used for Weight on Bit in normal
circumstances
DPT Drill String and BHA design
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Design
Heavier wall and longer tool joints
Center wall pad
Also available in spiral design
Heavy Weight Drill Pipe
Characteristics
Has the same OD as a standard drill pipe but
with much reduced inside diameter (usually 3”
for 5” DP) and has an integral wear pad upset
in the middle.
•
It is used between standard Drill Pipe and Drill
Collars to provide a smooth transition between
the different sections of the drillstring
components.
•
Tool-Joint and Rotary shouldered connection
just like DP
•
HWDP, although stiffer than DP, can also
buckle
DPT Drill String and BHA design
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•
Heavy Weight Drill Pipe
HWDP in Compression?
•
HWDP can be run both in tension and in compression
•
Manufacturers recommend not to run HWDP in compression
in hole sizes larger than 12 ¼”
•
Experience shows that they should not be run in
compression in Vertical Holes
•
If run in compression, rules of thumb are:
• TJOD + 6” > OH diameter
• 2 x TJOD > OH diameter
DPT Drill String and BHA design
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BUT!!!
Agenda
Introduction to Drill String Design: Overview
II.
Drill String Components
•
Drill Collars - Drill Pipe - HWDP
III. Drill String Design
•
Bottom Hole Assembly Selection
•
Drill Pipe Selection
•
Buckling and max WOB
DPT Drill String and BHA design
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I.
Drill Collar Selection Principles
• Drill Collar selection is governed by two major factors:
Weight and Stiffness --- Size!
• Usually the largest OD collar that can be safely run is the best selection
• Usually Shortest BHA possible to
• Reduce handling time at surface
• Minimize # of Connections in the hole
• Minimize total DC in contact with the wall for differential sticking
exposure
DPT Drill String and BHA design
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• More weight available for WOB
• Greatest stiffness to resist buckling and smooth directional tendencies
• Cyclical movement is restricted due to tighter Clearances
Weight
DPT Drill String and BHA design
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• BHA Weight must be sufficient for the planned WOB
• BHA Weight must be sufficient to account for Buoyancy
• BHA Weight must be sufficient to account for hole
inclination
• BHA Weight must be sufficient so that the neutral point of
axial loads is within the BHA – with a safety factor of 15%
BHA Design
Drill Collar Weight & Neutral Point
Tension
Neutral
point
Compression
Design
WOB
Max Available Wt
= 1.15
Max Working Wt
Neutral Point (NP) to tension
should be in drill collars
WOB
DPT Drill String and BHA design
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DF for excess BHA=1.15
BHA Design
Procedure For Selecting Drill Collars:
1. Determine the buoyancy factor for the mud weight in use using
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the formula below:
BF = 1- (MW/65.5)
where
BF =Buoyancy Factor, dimensionless
MW =Mud weight in use, ppg
65.5 =Weight of a gallon of steel, ppg
DPT Drill String and BHA design
BHA Design
2. Calculate the required collar length to achieve the desired weight
on bit:
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DC Length = 1.15* WOB / (BF*Wdc)
where:
WOB=Desired weight on bit , lbf (x 1000)
BF =Buoyancy Factor, dimensionless
W dc =Drill collar weight in air, lb/ft
1.15 =15% safety factor.
The 15% safety factor ensures that the neutral point remains within
the collars when unforeseen forces (bounce, minor deviation and
hole friction) are present.
DPT Drill String and BHA design
BHA Design
3. For directional wells:
where: I= Well inclination
Note that for horizontal wells drill collars are not normally used and
BHA selection is based entirely on the prevention of buckling
DPT Drill String and BHA design
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DC Length = DC Length Vertical / Cos I
Exercise DP-03
Number And Size Of Drill Collars
Hole deviation = 0°
Mud density
= 12 ppg
DPT Drill String and BHA design
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Determine the number of 9 inch OD by 3 in ID drill collars
required to provide a weight-on-bit of 55,000 lbf assuming
Stiffness
• Stiffness Coefficient :
= Moment of Inertia x Young’s Modulus of Elasticity
= л (OD4 – ID4) / 64 x 30.000.000
DPT Drill String and BHA design
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• The BHA must have sufficient Stiffness to stabilize the
BHA, optimize ROP and prevent the formation of Key
Seats, ledges and doglegs
• The larger the DC, the stiffer the BHA
Exercise DP-04
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DPT Drill String and BHA design
Bending Strength Ratio
• BSR is the relative stiffness of the box to the pin of a given connection.
• Describes the Balance between two members of a connection and how they
are likely to behave in a rotational cyclical environment
Z box 32
D
BSR =
=
4
4
Z pin π ( R − d )
R
32
(D4 − b4 )
Z box
BSR =
= 4D 4
Z pin ( R − d )
R
Where:
Zbox = box section modulus
Zpin = pin section modulus
D = Outside diameter of pin and box
b = thread root diameter of box threads at
. end of pin.
R = Thread root diameter of pin threads ¾
. of an inch from shoulder of pin.
. d= inside diameter or bore.
DPT Drill String and BHA design
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π (D4 − b4 )
Section Modulus for Connections
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DPT Drill String and BHA design
BSR in DC Connections
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• A Connection is said to be balanced
if the BSR is 2.5
• When BSR is higher tend to see
pin failures
• When BSR is lower tend to see
more box failures
• However, field experience has
shown that:
• 8” Dc having BSR’s of 2.5
usually fail in the box
• 4-3/4” DC having BSR as low as
1.8 very rarely fail in the box.
DPT Drill String and BHA design
BSR in Connections
Schlumberger Private
This table is from T.H. Hill & Associates Inc. Standard DS-1.
DPT Drill String and BHA design
Additional BSR Guidelines
• High RPM, Soft Formation Small DC (8 in in 12.25 hole or
6 in in 8.25 hole) 2.25-2.75
2.5-3.2 (3.4 if using lo-torq connection)
• Abrasive formations 2.5-3.0
• New DCs 2.75 – more wear resistant
DPT Drill String and BHA design
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• Low RPM Hard Formations Large DC (10 in in 12-1/4 hole
API BSR Charts
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• Fortunately for you API
have worked the
problem!!!
• Pages 39-44 of Spec 7G
list the BSR of
Connections by OD and
ID of the collar
DPT Drill String and BHA design
T.H.Hill BSR Tables
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DPT Drill String and BHA design
Stiffness Ratio
(
(
4
4
ODupr ODlwr
− IDlwr
Z lwr
SR =
=
4
4
Z upr ODlwr ODupr
− IDupr
)
)
Note: Stiffness ratios are calculated using tube ODs & IDs, not connections.
DPT Drill String and BHA design
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• The SR measures the stiffness of a connection in a transition between 2
types of pipe
• Based on field experience, in a transition
from one collar or pipe to another the SR
should not exceed
• 5.5 for routine drilling
• 3.5 for severe or rough drilling
BHA Design Process
• Design the Collars
DPT Drill String and BHA design
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• Max OD DC which can be handled, fished and drilled with
• Excess BHA wt
• WOB
• Buoyancy
• Safety factor
• Connection Selection
• BSR
• SR
• Torque capability
• Stabilization and other directional requirements
Exercise DP-05
On Seeyoulater land rig we find the following collars:
9” OD x 3” ID – 6 5/8” FH connection
8” OD x 3” ID – 6 5/8” REG connection
6 ¼” OD x 2 ¼” ID – NC46 connection
What would your recommendation on BSR be for the connection chosen?
Check your recommended DCs with your recommended BSR
What would be the SR between the DC and 5” DP be?
Is it acceptable?
If not what would you do?
What would be your final BHA? Length? Buoyed Weight?
DPT Drill String and BHA design
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Given that we will drill a vertical 12 ¼” hole, with 9.5 ppg mud and 65000 pounds
in a relatively hard formations, what API collar would you recommend?
Agenda
Introduction to Drill String Design: Overview
II.
Drill String Components
•
Drill Collars - Drill Pipe - HWDP
III. Drill String Design
•
Bottom Hole Assembly Selection
•
Drill Pipe Selection
•
Buckling and max WOB
DPT Drill String and BHA design
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I.
Drill Pipe Selection Principles
• Drill Pipe selection is governed by two major factors:
Size+Weight and Strength
• Less pressure loss in the string
• More hydraulics available at the bit
• The Drill Pipe selection must address the following:
•
•
•
•
•
•
Drill Pipe must allow to drill to TD
Drill Pipe must support all weight below it (BHA+DP)
Drill Pipe must provide Overpull capacity
Drill Pipe must withstand slip crushing force
Drill Pipe must resist burst and collapse loads
Drill Pipe might have to work in H2S environment
DPT Drill String and BHA design
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• Usually the Drill Pipe with largest OD and ID is preferred
Axial Loads
P
Tension Design
Drillpipe
Ldp
Drillcollars
Ldc
DPT Drill String and BHA design
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The greatest tension (working
load Pw) on the drillstring occurs
at the top joint at the maximum
drilled depth
Working Strength
Drill Pipe Selection Parameters
Tension Design
Total weight, Tsurf, carried by the top joint of drillpipe
when the drill bit is just off bottom ;
]
….(1)
Drillpipe
Ld
p
Ldp = length of Drill Pipe
Wdp = weight of Drill Pipe per unit length
Drillcollars Ldc
Ldc = weight of Drill Collars
Wdc = weight of Drill Collars per unit length
DPT Drill String and BHA design
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[
Tsurf = (Ldp ×W dp + Ldc ×W dc ) × BF
P
Drill Pipe Selection Parameters
Tension Design
The drillstring is not designed according to the minimum yield strength!!!
If Drill Pipe reaches yield:
• Drill Pipe can have permanent deformation.
Tmax = 0.9 x Tyield
….(2)
Tmax = Max. allowable design load in tension , lb
Tyield = theoretical yield strength from API tables , lb
0.9 = a constant relating proportional limit to yield strength
IPM Defines a tension Design factor of 1.1 be applied to design loads. These
accomplish the same thing.
Do not double dip!
DPT Drill String and BHA design
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To prevent deformation damage to drillpipe, API recommends the use of
maximum allowable design load ( Pa)
Margin of Overpull
Margin of overpull is nominally 50-100k, or in the limit of
the difference between the maximum allowable load less
the actual load
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Choice of MOP should consider
• Overall drilling conditions
• Hole drag
• Likelihood of getting stuck
• Slip crushing
• Dynamic loading
DPT Drill String and BHA design
Drill Pipe Selection Parameters
Margin of Overpull
1.
Tmax = 0.9 x Minimum Yield Strength … lb
Class of pipe must be considered
DPT Drill String and BHA design
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Determine max design load (Tmax) :
(maximum load that drillstring should be designed
for)
Drill Pipe Selection Parameters
Margin of Overpull
2. Calculate total load at surface using
]
3. Margin Of Overpull : Minimum tension force above
expected working load to account for any drag or stuck pipe.
MOP = Tmax - Tsurf
….(3)
DPT Drill String and BHA design
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[
Tsurf = (Ldp ×W dp + Ldc ×W dc ) × BF
….(1)
Drill Pipe Selection Parameters
Margin of Overpull
Ldp =
T yield ×0 .9 − MOP
W dp × BF
W dc
−
× Ldc ….(4)
W dp
DPT Drill String and BHA design
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4. The maximum length of Drill Pipe that can be used is
obtained by combining equations 1 and 3 and solving for
the length of Drill Pipe
THINK OF STUCK PIPE!!!
When the Drill String is stuck, (and it most certainly is if
there is Overpull !) the buoyancy is lost!
W dp × BF
W dc
−
× Ldc
W dp
….(4)
When the Drill String is stuck, (and it most certainly is if
there is Overpull !) the buoyancy is lost!
DPT Drill String and BHA design
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Ldp =
T yield ×0 .9 − MOP
Exercise DP-06
DPT Drill String and BHA design
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• Drill Collars length : 600’ and weight in air is 150 lb/ft.
• MOP = 100,000 lbs.
• 5” / 19.5 lb/ft Premium G-105 DP with NC50 connections.
Calculate the maximum hole depth that can be drilled ?
Assume BF= 0.85
• Carry out calculations without MOP and with MOP of
100,000 lb
• Use API - RP7G Tables for the values of Approximate
Weight (Wdp) and for Minimum Yield Strength
Slip Crushing Force
• Slips because of the taper try to crush the Drill Pipe. This
hoop stress is resisted by the tube, and this increases the
overall stress in the steel
Schlumberger Private
2
Hoop Stress S h
DK  DK 

= 1+
+ 
Tensile Stress St
2 Ls  2 Ls 
D = Pipe OD (in) ; Ls = Slip length (in )
K = 1 / tan( y + z ) ; y = Slip Taper (9ο 27 ' 45'' )
z = ArcTan( µ ) ; µ = coeff Friction (0.08 for dope )
DPT Drill String and BHA design
Slip Crushing Force
• Generally expressed as a Factor
PLoad
Sh
= PAxial
St
Horz to Tang Stress Ratio
DP
SLIP LENGTH
TUBE
12 in
16 in
2 3/8
2 7/8
3 1/2
4
4 1/2
5
5 1/2
6 5/8
1.25
1.31
1.39
1.45
1.52
1.59
1.66
1.82
1.18
1.22
1.28
1.32
1.37
1.42
1.47
1.59
DPT Drill String and BHA design
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Hoop Stress
Working load *
= Equivalent Axial Load
Tensile Stress
Drill Pipe Selection Parameters
• You can only drill as far as you can set pipe in the slips.
• Different than overpull, this is based on working loads
DPT Drill String and BHA design
Schlumberger Private
L dp
T yield × 0 . 9
Sh
W dc
ST
=
−
× L dc
W dp × BF W dp
Exercise DP-07
A drill string consists of 600 ft of 8 ¼ in x 2 13/16 in drill collars and
the rest is a 5 in, 19.5 lbm/ft Grade X95 drill pipe with NC50
connections. If the required MOP is 100,000 lb and mud weight
is 10 ppg, calculate:
2) What is the maximum depth that can be drilled taking into
consideration slip crushing force for (a) and (b) above? To what
hook-load does this correspond? What is the MOP in this case?
DPT Drill String and BHA design
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1) The maximum depth of hole that can be drilled when using (a)
new and (b) Premium Drill Pipe. (MOP only)
Mixed String Design
• Step 1
• If we use different drill pipe, the weaker pipe goes on
bottom and stronger on top
Ldp
Pt ×0 .9 − MOP W dc
=
−
× Ldc
W dp
W dp
• Step 2
• Drill collars and bottom drillpipe act as the weight
carried by top section…effectively the drill collar
• Apply the equation for top drill pipe last
DPT Drill String and BHA design
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• Apply equation to bottom drill pipe first
Exercise DP - 09 Mixed Drill Pipe
An exploration rig has the following grades of DP to be run in a 15,000 ft
deep well :
•
•
Grade E : New 5” OD –19.5 # NC 50
Grade G : New 5” OD – 19.5# NC 50
Calculate :
1.
2.
3.
4.
Max. length of E pipe that can be used.
Length of G pipe to use.
MOP for the G and E pipe.
Max weight on slips for the G and E pipe.
DPT Drill String and BHA design
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It is desired to have an MOP of 50000 lbs on the grade E pipe. The total
length and weight of DCs plus HWDP are 984 ft and 101,000 lb
respectively. MW at 15,000’ = 13.4 ppg.
Other Loads
•
•
•
•
•
Schlumberger Private
• Collapse under Tension
• Burst
• Other loads not covered here
Shock Loads
Bending Loads
Buckling Loads
Torsion
Torsion with Simultaneous Tension
DPT Drill String and BHA design
Biaxial Collapse
PBiaxial Collapse
PNonimal Collapse
= K <1
DPT Drill String and BHA design
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• The DP will collapse if:
External Pressure Load > Collapse pressure rating
• A Design factor of 1.15 is used:
External Pressure Load < Collapse rating / 1.15
• When the string is in tension, the Collapse rating is further
de-rated:
Biaxial Collapse
• Collapse load is worst when For dry test work where pipe
is run in empty
PNo min al Collapse
4 − 3Z 2 − Z
=
2
Load
Z=
2
2
0.7854(OD − ID ) * Yp Average
• Note the use of the Average Yield Point not minimum
DPT Drill String and BHA design
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PBiaxial Collapse
Biaxial Collapse
Grade
E
X
G
S
YpAvg
85,000
110,000
120,000
145,000
DPT Drill String and BHA design
Schlumberger Private
• For nominal Collapse
• Use D/t and correct formula Spec 7G Appendix A 3
• Use the results found in Table 3-6 RP-7G
• For OD and ID, use Table 1 RP-7G
• For Avg Yp Use Table in section 12.8 RP 7G
Exercise DP-10
• New 5” Gr E 5” OD, 4.276” ID, Avg Yp= 85,000 psi
DPT Drill String and BHA design
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• We are going to dry test a liner lap at 9,000 ft. We will run in
with a packer set in tension with 50,000 lb. We will run the
packer in on 5 in 19.5 #/ft Grade E premium grade DP. At the
time of the test there will be nothing inside the drill pipe. The
annulus will have 12.0 ppg mud. What is the collapse load on
the bottom joint of DP?
DP-10
Schlumberger Private
• Premium has 80% wall remaining
• Wall will be 0.8*(5-4.276)/2=0.2896
• ID will be 4.276”
• OD will be 4.276+2*0.2896 =4.855”
Load
Z=
2
2
0.7854(OD − ID ) * Yp Average
50,000
Z=
2
2
0.7854(4.855 − 4.276 ) * 85,000
Z = 0.1417
DPT Drill String and BHA design
DP -10
PBiaxial Collapse
PNo min al Collapse
4 − 3Z 2 − Z
=
2
Schlumberger Private
4 − 3 * 0.14167 − 0.14167
=
2
PBiaxial Collapse
= 0.922
PNo min al Collapse
2
• Nominal Collapse is 7,041
• Biaxial reduced collapse is 6,489
DPT Drill String and BHA design
DP-10
Collapse load is 9,000*0.052*12= 5616 psi
Design load is 5616*1.15= 6,458
Derated collapse is 6489, so we are ok
Collapse design factor is 6489/5616=1.16
• IPM Specified Collapse design factor is 1.1-1.15
DPT Drill String and BHA design
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•
•
•
•
Burst
• Barlows formula applies
• Results are found in Spec 7G Table 3,5 & 7
• Burst will occur if internal pressure load > burst rating
DPT Drill String and BHA design
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PBurst
2 * Yp * t
=
D
Exercise DP11 - Burst Load Case
• In the last example assume we are performing a DST test
in the well at 9000 ft with BHP 200 psi less than the mud
wt. What is the burst DF on the top of the Premium Grade
E
DPT Drill String and BHA design
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• Worst load case happens during DST operations in a gas
well. Pressure at surface is BHP- gas gradient with no
backup
DP-11
• From last Example 5” 19.5# E Premium
• OD=5, Wall = 0.2896” Yp= 75,000
• Design factor = 8688/4516=1.92
DPT Drill String and BHA design
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• Burst = 8688 psi
• BHP= 12*0.052*9,000-200=5,416 psi
• P Surf= 5416-900=4516 psi
Drill String Design Process-2
DPT Drill String and BHA design
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After the BHA Design is performed:
• Slip Crushing forces on DP
• Overpull tensile design at surface
• Lengths of DP Sections
• Burst Design Check
• Collapse under tension Design check
Drill String Design Factors
Tension DFt Governs Max allowable tension on the system
SLB DFt is 1.1
Excess BHA Wt Dfbha Amount of BHA in terms of Wt in
excess of that used to drill to assure all Compressive and
torsional loads are kept in the Collars, SLB Dfbha is 1.15
DPT Drill String and BHA design
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Margin of OverPull MOP Desired excess tensile capacity
over an above the hanging weight of the string at Surface.
SLB MOP 50-100K
Drill String Design Factors
Collapse DFc Tube is de-rated to account for Biaxial
Tensile reduction and a design factor of is used SLB DFc
is 1.1-1.15
DPT Drill String and BHA design
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Torsion No Design Factor Required. Tool Joints are made
up to 60% of Torsional Capacity, and Tool joints are
designed to 80% of the tube Torsion Capacity. Thus if the
design limits to tool joint make-up there is an adequate
design factor built into the system
Drill String Design Factors
Burst DFb Simple burst is used with no allowance for axial
effects SLB DFB is 1.0
DPT Drill String and BHA design
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Buckling DFB In Highly deviated wells it is possible to use
DP in compression, provided it is not buckled.
Agenda
Introduction to Drill String Design: Overview
II.
Drill String Components
•
Drill Collars - Drill Pipe - HWDP
III. Drill String Design
•
Bottom Hole Assembly Selection
•
Drill Pipe Selection
•
Buckling and max WOB
DPT Drill String and BHA design
Schlumberger Private
I.
Buoyancy
Buoyancy is the weight of the displaced fluid
•
Buoyancy is usually accounted for via BF
•
Buoyancy is creating a hydrostatic effect: the
Pressure-Area Force
•
The forces acting on a drillstring are the self-weight
and the hydrostatic pressure of the drilling fluid
•
Buoyancy is creating a force acting at the bottom of
the drill string and placing the lower portion of the drill
string in compression and reducing the hook load by
HP x CSA
DPT Drill String and BHA design
Schlumberger Private
•
DP12 - Buoyancy
• What is the hook load with BF?
• What is the hook load with Pressure Area Force?
DPT Drill String and BHA design
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• We are running open ended DCs
9” x 3” – 192ppf
• The fluid in the well is 14 ppg
• The depth is 10000 ft
Bending & Buckling
A tube subjected to a load will bend
•
Bent is a condition in which the
bending increases proportionally with
load
•
When a little increase in load will
result in large displacements, the tube
is said to be buckling
•
The tube may not necessarily be
yielded as buckling does not
necessarily occurs plastically
•
The load which produces buckling is
called the Critical Buckling Load
Schlumberger Private
•
DPT Drill String and BHA design
Neutral Points
•
Neutral Point of Tension & Compression:
The point within a tube where the sum of the
axial forces are equal to zero
Schlumberger Private
•
Neutral Point of Bending:
The point within a tube where the sum of
moments are equal to zero
The point within a tube where the average of
the radial and tangential stress in the tube
equals the axial stress
The point within a tube where the buoyed
weight of the tube hanging below that point
is equal to an applied force at its bottom
end
DPT Drill String and BHA design
Forces in the Drill String
Neutral Point of Bending occurs where the effective hydrostatic force
equals the compressive force in the drillstring.
Schlumberger Private
DPT Drill String and BHA design
Buckling
Neutral point of bending is H = WOB / buoyed weight per foot of string
In vertical wells, buckling will occur only below the neutral point of
bending, hence the necessity to keep the buoyed weight of the BHA
exceeding the WOB
•
In deviated wells, buckling will not only occur below the neutral point
of bending but also above the neutral point of bending when the
compressive force in the drillstring exceeds a critical load
(OD 4 − ID 4 ) * BF * (OD 2 − ID 2 ) * sin(α )
Fcrit = 1617
Dhole − ODtooljt
DPT Drill String and BHA design
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•
DP13 – Max WOB in inclined holes
Schlumberger Private
DPT Drill String and BHA design
Drillstring Design
Now you should be able to describe:
Functions of Drill Pipe , Drill Collars and BHA selection
•
Grades of Drill Pipe and strength properties
•
Thread types and tool joints
•
Drill collar weight and neutral point
•
Bending Stress Ratios and Stiffness Ratios
•
Margin of overpull – Slip crushing force
•
Basic design calculations based on depth to be drilled.
•
Functions of stabilizers and roller reamers
•
Critical Buckling force and Neutral Point of Bending
DPT Drill String and BHA design
Schlumberger Private
•