1Rig Selection
2You should be able to:
List types of rigs
List selection criteria for various rig types
State site preparation requirement prior to mobilizing a rig onto a location
Rig sizing
Rig Selection
Learning Objectives
3Rig selection involves effort of many groups in the up
stream sector.
A typical scenario of actions performed leading to rig
selection are as follows :
Geologist develops a prospect and define the
desired well location(s)
Surveys or spots exact location of well on land or
coordinate of well location offshore
Land acquisition for land based operation/location
of well/site preparation
Rig Selection
Rig Selection
4 Water depth, seabed soil condition, near
seabed seismic results
Drilling engineer selects the rig
Drilling rig owner (Contractor) defines the rig
sizing requirements, rig weight, loads to be
handled, drilling fluid volumes, rig power
requirements depending upon type of well
i.e Exploratory well and development well
Rig Selection
Rig Selection
5Rig Selection
Rig Selection Process
6Rig Selection
Rig Selection Process
7Rig Selection
Rig Selection Process
8Drilling Rigs can be divided
into two main groups;
Marine Rigs used for drilling
on water
Land Rigs used for drilling on
land
Cable Tool Rigs no longer in
operation are used for drilling
shallow wells on land
CABLE TOOL RIGS
Rig Selection
Rig Types
9Drilling rigs used offshore are generally termed
marine rigs
Marine rigs are further grouped into:
Bottom supported rigs. Rigs rest on sea floor or on
pads built on the sea floor
Floating rigs where drilling operations are conducted
while the rig is in floating position
Drilling rig mounted on barge. Typically used for
drilling in 8-10 feet of water depth and self contained
Rig Selection
Marine Rigs
11
Land Rig
Swamp
Barge
10 ~ 30 ft
Tender
Assisted
30 ~ 400 ft
Semi-
submersable
7500 ft max
Jack-up
450 ft max
Drillship
10000 ft max
Rig Selection
Rig Selection Process
12
Rig Selection
Rig Selection Process ~ Land and Shallow Waters
Land
RigSwamp
Barge
Jack-up Tender
Assisted
13
Rig Selection
Rig Selection Process ~ Deep Water
Semi-
submersableDrillship
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Rig Selection
Rig Selection Process ~ Deep Water Installations
15
Major Rig selection criteria are as follows;
Water Depth rating
Rig capacity, bulk capacity, liquid and mud mixing
capacity
Derrick, sub structure, drilling envelope
Physical rig size and weight
Stability in rough water
Duration of drilling program
Type of drilling i.e Exploration or Development
Availability and cost
Rig Selection
Marine Rig Sizing and Selection
16
Water Depth rating
Primary consideration for Rig selection
Selection based on Bottom Supported Units and
Floating Rigs
Size of rig with respect to Drilling Equipment Set
(DES)
Commonly is never an issue of selection. Marine Rigs
are over-specified to meet a wide range of depth rating
Rig Selection
Marine Rig Sizing and Selection
17
Bottom Supported Units consists of
Jack Up rigs
Limited to 400 feet water depth. Typical water depth from minimum 25
feet to maximum 300ft
Most widely used marine rig for both stand alone drilling of exploratory
wells and multi-wells development drilling from jackets
Common used independent legs cantilever jack-ups which can cover 9 15 wells on a jacket or small platform depends upon the drilling envelop. The derrick and substructure is skidded out
on cantilever.
Individual legs penetrate into below sea bed Popular designs are Baker Marine 300C, Marathon Le Tourneau
116C and Friede Goldman L780 mod II
Rig Selection
Marine Rig Sizing and Selection
18
Bottom Supported Units consists of (continued)
Jack Up rigs
Mat type Jack up the drilling hull is supported by legs from large
mat/pontoon that rest on sea floor. Its used for very soft sea floor soil
condition
Slot type jack up rig where drilling of wells done through the slot in
the hull of the rig
Rig Selection
Marine Rig Sizing and Selection
19
Rig Selection
Marine Rig Sizing and Selection ~ Jack-up
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Bottom Supported Unit
consist of Jack Up rigs
Jack up rigs are self
contained and most are
for drilling depths of
25,000 feet
Rig Selection
Marine Rig Sizing and
Selection
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22
Rig Selection
Jack-up Positioning
23
Rig Selection
Jack-up Positioning
24
Rig Selection
Jack-up Risks
Punch Through Effect of RPD
(Rack Phase Differential)
25
Rig Selection
Jack-up Risks
26
Rig Selection
Jack-up Risks ~ Old Foot Prints
27
Rig Selection
Rig Specifications
28
Bottom Supported Units consist of
Platform rigs
Long term development drilling
projects from sufficiently large
platform (> 15 wells)
Self contained, complete rig with
facilities are installed on the
platform
Cost effective and limited only by
water depth limitation of the
platform
Rig Selection
Marine Rig Sizing and Selection
29
Bottom Supported Units consists of
Platform rigs
Variation is a Tender Assisted Platform Rig where
Drilling Equipment Set (DES) is positioned on the
platform. Prime movers, living quarters, rig pumps,
mud tanks on a floating tender anchored along side
Water depth limited by the anchoring capacity of the
tender
Rig Selection
Marine Rig Sizing and Selection
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Rig Selection
Tender Assisted Rig
31
Floating rigs (Floaters)
Water depth capability slowly increased to 7000 feet
Floating rigs do not rest on the sea floor
Not restricted by rigs leg length
Drillship and semi-submersible rigs
Different operating characteristics
Drillships are usually self propelled
Semi submersible have lower hull. Below sea level and ballasted
to maximize rig stability. More stable than drillship and some are
self propelled
Lower variable deck loading than drillship
Specially designed for petroleum operation hence more costly
Rig Selection
Marine Rig Sizing and Selection
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Rig Selection
Marine Rig Sizing and Selection
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Semi Submersible
Rig Selection
Marine Rig Sizing and Selection
34
Rig Selection
Marine Rig Sizing and Selection
Drill Ship
35
Floating rigs
1. Deepwater capability using dynamic positioning system
(DPS). Anchoring systems are not required
2. DPS maintains rig position by thruster and acoustic
beacons.
3. Power is provided by;
AC (alternating current) generator with silicon controlled
rectified (SCR) to provide DC to the drilling rig. [AC generator
SCR DC motor Rig component]
Rig Selection
Marine Rig Sizing and Selection
36
Rig Selection
Marine Rig Sizing and Selection
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Other Considerations for Offshore Location Are
Check for subsea pipelines, marine cables,
telephone lines, shipwreck
Usually sea bed features e.g slumping, steep
inclines, unusual debris at sea floor
Very soft sea bed soil condition, low anchor-
holding capability
Shallow gas
Rig Selection
Other Considerations
38
If problems cannot be resolved, alternate rig site should be selected site
survey studies proposed for Jack up leg investigation are as follows;
Side scan sonar for sea bed features, debris, boulder and pipeline
High resolution shallow seismic for shallow gas. Correlation with
soil bore data
Soil bore cores analysis to deepest expected penetration and for
platform installation
Penetrometer usually 3 feet in length to estimate undrained
strength of sea bed clays/formation for Jack up leg penetration
analysis
Echo sounder for water depth determination
Rig Selection
Marine Rig Sizing and Selection
39
Some common foundation problems are;
Punch through during preload
Inadequate leg length
Scouring due to strong seabed currents and soft soil
Seafloor instability
Unable to extract legs
Rig Selection
Common Foundation Problems
40
Most offshore rigs are rated /sized to drill well depth of 25000 ft. One rig can be used to drill various type
of well and well depths
Functionally, Offshore rigs becomes over specified and rig sizing is not an issue
Rig sizing are more pertinent to land drilling. Specifications are tailored to suit drilling well depths
and well condition
Rig Selection
Rig Sizing
41
Land Rigs are further categorized depending upon;
Conventional (unitised) rigs
Trailer mounted rigs
Helicopter transportable rigs (heli-rigs)
Desert rigs
Rig Selection
Land Rigs
42
Generally uses telescopic mast
Restricted to light work and medium depth drilling
to 10,000 feet
Generally mounted on a truck or large trailer.
Available in drive-in or back in unit
Low rig down, move and rig up time increase
efficiency and lower cost
Generally used, for land workover and well
servicing jobs
Usually limited in mast capacity (350 kips), limited
rig equipment capacities
Some rigs have doubles masts.
Limited height of rig floor require cellar to
accommodate height of higher rated BOP stack
Rig Selection
Land Rig ~ Trailer Mounted Rig
43
Largest land rigs are available with derricks or big jack
knife mast
Rated for drilling 10,000 to 35,000 feet well depths
Rig components are torn down and moved individually
on trucks due to size
Rig mounted on a sub-structure to allow use of tall, high
pressure rated BOP stacks, large pipe stand-back
capacity
Most rigs have 142 feet derrick or mast and able to pull
(3) joint stands of drill string
Rig Selection
Conventional Land rigs
44
After well site located, rig site preparation depends
upon;
Onshore : Marsh,terrain/topography
Offshore
Rig Selection
Rig Site Preparation
45
Onshore Rig site Preparation
Well location usually vertical on sub-surface target location
Land survey staking the well
Access road, land acquisition and land compensation, permits
Soil survey to check marshy or soft soil to take load of the rig
Require an area of 350 feet x 420 feet area to be cleared
Water source for drilling water well
Sometimes major civil engineering work is required
Barge rig for marshy location require dredging channel to bring
barge in
Filling up or small platform to take rig
Rig Selection
Rig Site Preparation
46
Main power requirements of a drilling rig are
the drawworks, rotating system, rig mud
pumps and power for rig ancilliaries
Modern rigs are designed to meet minimum
rig power requirements to run drawworks.
Both pumps running in parallel and the
topdrive/rotary table in operations. These are
driven by DC motors
Rig Selection
Rig Power Requirements
47
Rig ancilliaries consist of centrifugal mud pumps to run mud
treatment equipment, rig lighting, air compressor motors,
BOP accumulator and etc. Usually they require AC current
on land rigs and these power requirement are met by AC
generators from the utility house
Modern rigs offshore has prime movers driving AC
generators where the power is transmitted to the drilling
equipment DC generators via a AC-SCR system (SCR).
Alternating current silicon controlled rectifier system. Older
land rigs have mechanical engine compounds or have DC
generator driving the DC motors called a DC-DC system
Rig Selection
Rig Site Preparation
48
Mechanical Drive System
Commonly used for trailer-mounted rigs of medium
depth drilling range
Two and three prime movers (diesel engines) are
compounded by chain, gears and belts to drive
drawworks and pumps
Torque converters at the engine output are used to
reduce shock loading on engines. Provides torque
multiplication and constant power output
Rig Selection
Marine Rig Sizing and Selection
49
A TYPICAL AC-SCR-DC SYSTEM
As shown in schematically below :
Prime Mover (s) AC generator SCR system
Rig Ancilliaries
(AC motors)
Drawwork Drive
DC motor
Rig Pump Drive
DC motor
Top Drive
DC motor
Rig Selection
Marine Rig Sizing and Selection
50
Total Rig power required at the Prime Mover can be presented by ;
HP rig = HP H + 2 x HP P + HP RT
where
HP rig = Total rig power required at the SCR power outlet
HP H = Power required by the hoisting system at the input of the drawworks
HP P = Power required by each pump at the input
HP RT = Power required by the rotary table or top drive system input
Assuming the SCR and electrical transmission system efficiency at 0.90 (range
0.85 - 0.90)
HP RTHP engine = _
______ = 1.11 HP RT where = efficiency of the prime mover
0.90
Total HP required = HP engine x 1/
API standard 7B-11C defines
diesel engine performance
variation resulting from harsh
environment
Rig Selection
Marine Rig Sizing and Selection
51
Hoisting system provides the means for the vertical
movement of the pipe in the well
It consists of the drawworks, crown and travelling
blocks, wireline and ancilliary equipment such as hooks,
bails and elevators
The horse power required at the Travelling Blocks can
be computed by
HPTB = L x V
33,000 B
Where L = heaviest hook load (lbs)
V = hoisting rate (ft/min)
normally assumed 93ft/min
B=friction factor of the block
and tackle system
Rig Selection
Hoisting Power Requirements
52
As with all mechanical system, the block/tackle system is not friction
less i.e B < 1.0
Friction factor B = (0.98)n where n = number of sheave pulse
The following table indicates friction B for various pull system ;
No of lines B
6 0.886
8 0.850
10 0.817
12 0.785
Rig Selection
Marine Rig Sizing and Selection
53
Drawworks reels in wireline as the pipe is lifted and thus is made up of
drum to spool the wireline, shafts and chain driving the drum
A typical drawworks consists of four shafts and five chains and
efficiency is given by
D = (0.98)n where n = number of chains and shafts
Therefore D = (0.98)4+5 = 0.834
Therefore HP H horsepower required at the input of drawworks
HP H = HP TB = ____L x V_____
D 33,000 x B x D
Rig Selection
Marine Rig Sizing and Selection
54
The hook load L is normally taken as the heaviest casing load in
mud. Usually 9-5/8 casing represents the heaviest string. Therefore ;
L = buoyant unit weight of casing in mud x length of casing
Mud Buoyancy factor is calculated by
B F = 1 - m / 65.50 where m = mud weight in ppg
L = B F x W C x Hwhere B F = mud buoyancy factor
WC = unit weight of casing Ibs/ft
H = total length of casing run (feet)
Rig Selection
Marine Rig Sizing and Selection
55
Rotating system impacts rotating action to the drillstring and bit
Rotary system consists of the kelly, rotary table and drive bushing
Top Drive system consists of the top drive (DC motor and gear
box), drill string and bit
Rotating horse power requirements depend on speed of rotation,
hole friction, angle, depth straightness. Basically it can be given by
HP RT = T x N where HP RT = rotating system HP (BHP)
5250 T = rotary torque required (ft-lbs) N = rotary speed (rpm)
Rig Selection
Power Requirements for Rotary System
56
Power Requirements for Top Drive System
For modern day rigs drilling complex wells with top drive system. The horse power required can be calculated based on extreme
condition
HP RT = T x N where T = rotary torque. Assume maximum
5250 torque rating of a 5-1/2 drillpipe= 35,000 x 120 with 35,000 ft-lbs
5250 N = RPM. Assume at 120 rpm
= 800 BHP
Rig Selection
Power Requirements for Top Drive System
57
The mud pumps is the heart of a rig circulating system
Mud pumps are designed for pressure output, flowrate and horsepower requirements
Power required by rig pump can be calculated by
HHP (Hydraulic Horse Power) = P x Q
1714
Where HHP = pump output at fluid end in BHPP = total pressure drop in the system (psi)Q = pumping rate (GPM)
Rig Selection
Power Requirements for Pumps
58
Derrick or a mast provides the vertical height necessary for the
hoisting system to raise and lower the pipe
API standards 4A provides specs for derrick and API standard
4D provides specs for mast type structure
Derrick or Mast must be able to handle /support all loads,
including drilling load and weight of pipe set in the derrick
Derrick must be able to withstand wind loads acting horizontally
on the pipe racked in it
Selection for a derrick based on whether rig usage i.e drilling
activities or workover and servicing
Rig Selection
Derrick or Mast and Substructure
59
Drilling requires pipe to be handled in stands (3 joint
of connected pipe is about 90 feet in length)
Height of derrick is roughly ascertained by [pipe
length 90 feet + 25 feet for travelling block, hook, and
bails + 3 feet stick up above rotary table + 5 feet for
buffer below crown block] These will total at about
123 feet
Rig Selection
Derrick or Mast and Substructure
60
The schematic below shows API 4A Derrick size classification
Rig Selection
Derrick or Mast
61
Table 1 provides the General Dimension of Derrick size
Rig Selection
Derrick or Mast
62
Modern day Derrick or mast for drilling
activities require additional height to
accommodate Top Drive System
Most widely used Derrick size is API 19
which provides 146 feet height and 30 feet
square base with pipe racking capacity of
160 stands of 5 drill pipe
Rig Selection
Derrick or Mast
63
Derrick or Mast for workover or well servicing activities
handle tubings which are limber and tend to bend due to
its own weight. Pipe are handled in
Double (2 joints of connected pipe about 60 feet in
length)
Single (1 joint of pipe about 30 feet in length)
More time for pulling and running in pipes
Normal heights are 90 feet (for handling pipe in singles)
and 102 feet (for handling pipes in doubles)
Suitable for uneven terrains
Small rig site preparation required
Rig Selection
Derrick or Mast
64
Sub structure provides the height for the blowout preventer stack
required
Sub structure similar to the derrick must be able to support all
loads on rotary, weight of pipe set back racked in the derrick
Provides the derrick floor space for pipe set back and people to
work safely
On offshore rigs, especially for drilling from platform must have
sufficient longitudinal and traverse width to allow the drilling unit
to skid from one well to another over entire drilling envelope of
wells
Rig Selection
Substructure
65
Derrick load is defined by the heaviest hook load that can
be handled with proper safety factor
Effective derrick load can be evaluated by
F DE = 4L (N + 4)
4N
The heaviest hook load L is usually taken as the heaviest
casing load in mud as given in earlier section
Wind load is created by wind acting horizontally on the
pipe set back in the derrick and is calculated by
WhereF DE = Effective Derrick load, lbsN = number of lines string up
over the blockL = Heaviest hook load, lbs
Rig Selection
Derrick and Substructure Loading
66
Wind load is created by wind acting horizontally on the
pipe set back in the derrick and is calculated by
Lw = 0.004 V2 A
Please refer to Table for wind load areas
Where L w = wind load, lbsV = wind velocity, mphA = area of pipe set back
Rig Selection
Derrick and Sub structure loading