29541844 6 motion compensation

7/29/2019 29541844 6 Motion Compensation

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1

TAMU - Pemex

Offshore Drilling

Lesson 6

Motion Compensation


2/39

2

Motion Compensation

Reentry

Tensioners

Heave Compensators

Passive Motion Compensation

Active and Semiactive Systems


3/39

3

Re-entry

It is possible to re-enter a borehole

without using guidelines!

1. Use land-based navigationequipment to get the vessel in

the vicinity of the well

or better still: Use GPS

(Global Positioning System)


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4

Re-entry, contd

2. Lower reentry string to a safe

distance above the wellhead

3.Use position location equipment

to complete the job:

(i) Television camera(ii) Acoustic device - pinger or transponder

(iii) ROV - Remote Operated Vehicle


5/39

5

Heave Compensation

How do you maintain a constant tension

on the marine riser - when the vesselheaves?

How do you maintain a constant weight

on the bit - when the vessel heaves?


6/39

6

Deadweight Riser Tensioning System

Dead Weight

(~constanttension)

Dead Weight

Slip Joint

Marine Riser

Early design - OK up to 100,000 lbf. Attached to lower half of telescoping joint. Adds weight & is bulky...


7/397

Pneumatic Riser

Tensioning System


8/398

Pneumatic/Hydraulic Heave

Compensation System

Pneumatic/Hydraulic Tensioners:

Take up much less room thandead weights

Facilitate changing the tension by

changing the air pressure Can be used for the marine riser,

the guidelines and the drill string


9/399


Compensation System

Passive Systemsare

the most popular Require essentially no energy input

Use an air spring with a variable

spring constant Can keep the tension within ~ 15%

or even less.


10/3910


Compensation System

Active Systems

Require external energy througheach load cycle

Provide a highly consistent force

But -- Have a high initial cost

Have a high operating cost


11/3911

Air reservoir

reduces

pressurechanges

F = PA

To support

larger load,increase the

pressure

An AIR spring ...

Passive

System


12/3912


13/3913

Consider Change from P1

and V1

to P2

and V2

P1 and P2 are absolute pressures

n = 1 for isothermal expansion or contraction

n = 1.41 for adiabatic expansion or contraction

1

2

1

2

P

P

F

F

n

V

V

P

P

and

=2

1

1

2


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14

Change in Volume

P1 and P2 are absolute pressures

Isothermal Volume Change: PV = const.

(slow; constant temperature)

Adiabatic Volume Change: PV1.41

= const.

(fast; no heat flow)


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15

V

V Relative

Change involume

37180

411

1

1

411

2

1

1

2 .V.

V

V

V

P

P.. =

=

=

Pres s

ur

eRatio,

P2

/P1

ADIABATIC

1.4

1.0

0.7

-0.1 +0.2

ISOTHERMAL

25.

8.

1

V0

V

V

V

P

P

1

1

2

1

1

2 =

=

=


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16

Theoretical reservoirsize vs. pressure

fluctuation.

Allowable Pressure Fluctuation, %Vo l.o fR

e s e rv

o ir

/Vo l .

o f C

y lind e r

15 300

15

30

Fig. 4-7


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17

Example

Consider a 14-inch piston with a 10-foot

stroke. We shall hook two units (cylinders)

to the reservoir. Determine reservoir size

for 15% force variation.

Reservoir Volume = R m A L

4)-7Figure(from5R

cylinderofvolumereservoirofvolumelTheoretica

=

=R = 5


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18

Example contd

Reservoir Volume = R m A L

= 5 * 2 * 10 * 1.07 = 107 ft3

m = 2 = number of cylinders

L = 10 ft = piston stroke

A = /4 (14/12)2

= 1.07 ft2 = piston area

VRES = R m A L


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19

Equation (on p. 170)

Theoretical force variations as a function ofpiston position and heave can be

determined by a modification of the

previous pressure - volume equation:

2

LL

2

L-and

1001LAmV

V1001

F

FE

n

1

2

=

=


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20

Where:

E = theoretical percentage error in forceapplied to the load

= force applied to the load relative to

the force with the piston centeredA = piston area, ft.2

L = full piston stroke, ft.

V = reservoir volume + L = length of the stroke from the

center of the piston, ft.

3

2 ft,

mAL

1

2

F

F

1001

1001

1

2

n

LAmV

V

F

FE

2

LL

2

L-


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21

Heave Down

PercentC

hangein

Load

0

15

-15-20 20

15

-15

0

010

Heave Up, ft

Reservoir Volume

= 5 * vol. swept by piston

Adiabatic


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22Lower sheaves are attached to the cylinder (and vessel), upper sheaves are attached to the piston rod

20 ft

5 ft1,500 psig WP

TypicalTensioner


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23

Motion

Compensator

Principles of

Operation

Purpose:

Keep bit on

bottomwith low bit

weight change

Air pressure can support entire weight of drillstring. e.g. 200,000 - 40,000 = 160,000lbf. Reduce air press.


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24

Rucker Heave

Compensator

Dual Pistons- on the

travelling

block

Large air

cylinders

below deck

Flexible hoses


25/39

25

Figure 7-9

Vetco dual

piston HeaveCompensator

L.P. hydraulic

fluid throttledfor damping

Piston

balancing

may be

problem


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26

Figure

7-10

Split travelling block

Hydraulicallyoperated pistons can

be locked in any

position with

remotely operated

valves.

Air operated units must be mechanically locked in position because of compressible fluid in cylinders.

Single

Piston Rod

Western Gear

Heave

Compensator


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27

Figure 7-13. Active Heave Compensator


28/39

28

Semiactive Heave Compensator


29/39

29

Bumper Subs

Fit into the drill collar string, but do

not have the ruggedness of drill

collars. To obtain a reasonableoperating life from bumper subs,

action has to be taken on the

following points of concern: 1. Always run the bumper subs at the

neutral point in the string.


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30

Bumper Subs, contd

2. Bumper subs are designed to

stroke, and if operated at a single

position, they will wear at that

position.

3. Running the subs in tension

minimizes the area through which

the torque will be transmitted, andwill cause excessive wear and fatigue.


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31

Bumper Subs

4. Running the joint in compression

increases torque reversals and fatigue

in the tool. It also increases bitchatter and instantaneous peak

torque, causing unnecessary wear to

the tool and the string. This is the fault

of the operation, not the sub.


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32

Bumper Subs

5. From items 3 and 4 above, it is

evident that once the string has

been run, the weight on the bit isfixed. This weight should not be

changed until the string has been

pulled and the number of drill collarsbelow the bumper sub changed.


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33

Bumper Subs

6.Do not separate the bumper subs in a

drillstring for heavy drilling operations.

7.Special care and maintenance are

required to obtain a reasonable

operating life.

*Remember: bumper subs fit into the same

part of the drillstring where drill collars and

stabilizers have been destroyed. This is a

severe test of workmanship & maintenance.


34/39

34

Unbalanced

BumperSubs


35/39

35

Buoyant Riser Module


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36

Cantilever

JackupRig

Float out to

location

Then lower

legs toseafloor

Then jack up


37/39

37

Jackup Rig

Side View


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38

Jackup

Rig

Deck

Plan


39/39

End of

Lesson 6

29541844 6 motion compensation

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