01 - Rig Selection

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


7Rig Selection


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


12

Rig Selection

Rig Selection Process ~ Land and Shallow Waters

Land

RigSwamp

Barge

Jack-up Tender

Assisted

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Rig Selection

Rig Selection Process ~ Deep Water

Semi-

submersableDrillship

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Rig Selection

Rig Selection Process ~ Deep Water Installations

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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


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


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


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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

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

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Rig Selection

Jack-up Risks ~ Old Foot Prints

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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


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


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Rig Selection

Tender Assisted Rig

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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


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Rig Selection


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Semi Submersible

Rig Selection


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Rig 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


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Rig 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


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


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


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


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


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


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


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


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


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

Documents

01 - Rig Selection