Rig Selection.pdf

Rig Selection

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Rig Selection Learning Objectives

You 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

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Rig Selection Rig Selection Rig 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 3

Rig Selection Rig Selection

 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 4

Rig Selection Rig Selection Process

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Rig Selection Rig Selection Process

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Rig Selection Rig Selection Process

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Rig Selection Rig Types

Drilling 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 8

Rig Selection Marine Rigs

Drilling 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

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Rig Selection Rig Selection Process Swamp Barge Land Rig

10 ~ 30 ft

Tender Assisted

Semisubmersable

Drillship

450 ft max 30 ~ 400 ft

7500 ft max

10000 ft max

Jack-up

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Rig Selection Rig Selection Process ~ Land and Shallow Waters Jack-up Land Rig

Tender Assisted

Swamp Barge

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Rig Selection Rig Selection Process ~ Deep Water

Semisubmersable

Drillship

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Rig Selection Rig Selection Process ~ Deep Water Installations

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Rig Selection Marine Rig Sizing and Selection 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 15

Rig Selection Marine Rig Sizing and Selection 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 16

Rig Selection Marine Rig Sizing and Selection 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 17

Rig Selection Marine Rig Sizing and Selection 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. It’s 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

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Rig Selection Marine Rig Sizing and Selection ~ Jack-up

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Rig Selection Marine Rig Sizing and Selection •

Bottom Supported Unit consist of Jack Up rigs

•

Jack up rigs are self contained and most are for drilling depths of 25,000 feet

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Rig Selection Jack-up Positioning

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Rig Selection Jack-up Positioning

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Rig Selection Jack-up Risks

Punch Through

Effect of RPD (Rack Phase Differential) 24

Rig Selection Jack-up Risks

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Rig Selection Jack-up Risks ~ Old Foot Prints

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Rig Selection Rig Specifications

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Rig Selection Marine Rig Sizing and Selection 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 28

Rig Selection Marine Rig Sizing and Selection

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

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Rig Selection Tender Assisted Rig

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Rig Selection Marine Rig Sizing and Selection 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

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Rig Selection Marine Rig Sizing and Selection

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Rig Selection Marine Rig Sizing and Selection Semi Submersible

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Rig Selection Marine Rig Sizing and Selection

Drill Ship

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Rig Selection Marine Rig Sizing and Selection 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]

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Rig Selection Marine Rig Sizing and Selection

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Rig Selection Other Considerations 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 anchorholding capability  Shallow gas

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Rig Selection Marine Rig Sizing and Selection 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 38

Rig Selection Common Foundation Problems

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

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Rig Selection Rig Sizing  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

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Rig Selection Land Rigs

Land Rigs are further categorized depending upon;

 Conventional (unitised) rigs  Trailer mounted rigs  Helicopter transportable rigs (heli-rigs)  Desert rigs

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Rig Selection Land Rig ~ Trailer Mounted Rig 

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 42

Rig Selection Conventional Land rigs  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 43

Rig Selection Rig Site Preparation

After well site located, rig site preparation depends upon;  Onshore : Marsh,terrain/topography

 Offshore

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Rig Selection Rig Site Preparation 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

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Rig Selection Rig Power Requirements  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

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Rig Selection Rig Site Preparation 

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

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Rig Selection Marine Rig Sizing and Selection 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 48

Rig Selection Marine Rig Sizing and Selection A TYPICAL AC-SCR-DC SYSTEM As shown in schematically below :

Prime Mover (s)

Rig Ancilliaries (AC motors)

AC generator

Drawwork Drive DC motor

SCR system

Rig Pump Drive DC motor

Top Drive DC motor

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Rig Selection Marine Rig Sizing and Selection 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 HP H HP P HP RT

= = = =

Total rig power required at the SCR power outlet Power required by the hoisting system at the input of the drawworks Power required by each pump at the input 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 RT

HP engine =

_

______

= 1.11 HP RT

0.90 Total HP required = HP engine x 1/

where

= efficiency of the prime mover API standard 7B-11C defines diesel engine performance variation resulting from harsh environment 50

Rig Selection Hoisting Power Requirements 





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 =

LxV 33,000

Where B

L = heaviest hook load (lbs) V = hoisting rate (ft/min) normally assumed 93ft/min B=friction factor of the block and tackle system

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Rig Selection Marine Rig Sizing and Selection 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

No of lines

B

6 8 10 12

0.886 0.850 0.817 0.785

B

for various pull system ;

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Rig Selection Marine Rig Sizing and Selection 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

Therefore

where n = number of chains and shafts D

= (0.98) 4+5 = 0.834

Therefore HP H horsepower required at the input of drawworks HP H = HP TB = D

____L x V_____ 33,000 x B x D 53

Rig Selection Marine Rig Sizing and Selection 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

L = B F x W C x H where

B

where F

m

= mud weight in ppg

= mud buoyancy factor

WC = unit weight of casing Ibs/ft

H = total length of casing run (feet)

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Rig Selection Power Requirements for Rotary System    

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 5250

where

HP RT = rotating system HP (BHP) T = rotary torque required (ft-lbs) N = rotary speed (rpm)

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Rig Selection Power Requirements for Top Drive System 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 5250 = 35,000 x 120 5250 = 800 BHP

where

T

= rotary torque. Assume maximum

torque rating of a 5-1/2” drillpipe with 35,000 ft-lbs N = RPM. Assume at 120 rpm

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Rig Selection Power Requirements for Pumps •

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 BHP P = total pressure drop in the system (psi) Q = pumping rate (GPM)

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Rig Selection Derrick or Mast and Substructure

 

  

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

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Rig Selection Derrick or Mast and Substructure

 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

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Rig Selection Derrick or Mast The schematic below shows API 4A Derrick size classification

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Rig Selection Derrick or Mast Table 1 provides the General Dimension of Derrick size

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Rig Selection Derrick or Mast

 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

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Rig Selection Derrick or Mast  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 63

Rig Selection Substructure 

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

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Rig Selection Derrick and Substructure Loading  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

Where F DE N

L

= Effective Derrick load, lbs = number of lines string up over the block = Heaviest hook load, lbs

 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

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Rig Selection Derrick and Sub structure loading

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 Where

L w = wind load, lbs V = wind velocity, mph A = area of pipe set back

Please refer to Table for wind load areas

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