labo 9

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PETE 225-lab

© Copyright, 2005, TAMU

Lab#9Well Control



PETE 225-lab


Geology



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3

Sedimentation



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4

Pore Pressure

• Normal formation

pressure is equal to the

column of formation fluid.

• Abnormal pore pressure is

defined as a pore pressure

greater than normal

• Subnormal pore pressureis defined as pore pressure

less than normal.

C ol umn of

f or m a t i onf l ui d



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5

Normal Pore Pressure

MW Gradients Example area

Fresh water 8.3 ppg .433 psi/ft Rocky mountain

Brackish water 8.4 ppg .437 psi/ft

Salt water 8.5 ppg .442 psi/ft Most sedimentary basins

worldwide

Normal salt

water

8.7 ppg .452 psi/ft North sea

Salt water 8.9 ppg .465 psi/ft GOM

Salt water 9.2 ppg .478 psi/ft GOM



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Overburden Pressure

• Overburden pressure is

total pressure exerted

by the formation

weight (fluid + rock)

• Overburden pressure

usually is in the range

of 19 – 21 ppg.

C ol umn of f or m a t i on


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7

Example 1

• Assume Normal porepressure to calculateformation /overburdenpressure at the bottomhole

• Ppore

= 8.5 ppg

• Poverburden = 1 psi/ft

Ppore = 0.052 × 8.5 × 5500

= .442 × 5500

= 2430 psi

Poverburden = 1 psi/ft × 5500

= 5500 psi

5500 ft

Solution



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8

Fracture Pressure

• High bottomhole pressure can

fracture the formation.

•The amount of pressure needed tofracture the formation is equal to the

sum of downhole stress pressure and

tensile strength of rock.



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9

Example 2

• If the fracture gradient at the

bottomhole is 0.8 psi/ft

estimate the required

bottomhole pressure to

fracture the formation.

Pfracture = 0.8 psi/ft × 5500

= 4400 psi

5500 ft

Solution



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Basics of Well Control



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11

Equivalent Mud Weight

• Pressure usually is expressed in equivalent

mud weight (ppg) or gradient.

ppg0.052ftpsiGradientPressure

TVD0.052

HPppg

TVDppg0.052HP



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Example 3

• What is the equivalent mud weight for a

reservoir at the depth of 12000 ft with

8000 psi pressure? What is the minimum

mud weight to drill into the reservoir?

• Minimum mud weight = 12.9 ppg

weightmudlentEquiva82.12

200010.052

8000

TVD0.052

HPppg

ppg

Solution



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13

Pressure Calculation

• The general pressure calculation

equation considers pressure at the

surface.

• If surface pressure is 300 psi,

TVD = 9000 ft, mw = 12 ppg and

calculate the BHP.

TVDppg0.052PHP surface

Psurface

psi5920HP9000210.052003HP

Solution



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14

Example 4

• Calculate the surface pressure

– Formation pressure = 13730 psi

– MW = 17.6

– Depth = 14500 ft

?

psi604P1450017.60.05213730

TVDppg0.052HPP

TVDppg0.052PHP

surface

surface

surface

Solution



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15

U-Tube

• U-tube is a simple

schematic of the

well used for well

control purposes.• The simple concept

of u-tube is

consistent BHP from

drillstring and

annulus.

AnnulusDrill String

BHP



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16

Example 5

Calculate the mud weightin the left column to

balance the pressure at

the bottomhole.

BHP

350 psi

14 ppg

6 0 0 0 f

t

? ppg



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Example 5 - Solution

BHP

350 psi

14 ppg

6 0 0 0 f

t

? ppg

TVD0.052

PMWppg?

parametricRHSandLHSoutyou work If

15.2fluiddrillingof MW

15.12ppg?

6000ppg?0.0524720

psi4720

6000140.052350BHP

surfaceppg



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18

Frictional Pressure

• To circulate the mud in the well, energy is

needed to overcome frictional pressure in

the circulation system

– Drillstring – Nozzles

– Annulus

• In most cases during well control operation,

annular pressure drop can be ignored.



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Pressure Drop Estimation

• Killing is done using a heavier mud.

• Heavier mud has higher pressure drop

• If the rheological properties of mud stays

the same, the pressure loss in the system

estimated using

original

Kill

originalkill MW

MWPP

Slow Pump Rate



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Goal of Well Control

• Safely circulate out the kick with the

kill weight mud.

• Keep the BHP equal to or slightly

higher than the formation pressure.



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Kill Weight Mud

• Kill weight mud calculation is the same

as the one in Example 5.

• From Example 5

TVD0.052

PMWMW surface

originalkill



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Keep The BHP Constant

• To keep the BHP constant we have to

consider the following factor

– Gas expansion

– Pressure drop in the system

– Higher hydrostatic pressure due to the

heavier mud



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23

Initial Circulating Pressure

• Initial circulating pressure

is equal to the sum of

standpipe pressure and

system pressure drop

Pstandpipe

SPRstandpipeinitial PPP

S y s t e m

f

r i c t i on a l l o s s pr e s s u

r e



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Final Circulating Pressure

• The pressure required to circulate

the mud at the SPR, when the kill

mud passes the nozzles is called the

final circulating pressure.

• This pressure is maintained while

circulating the kill mud up the

annulus.

Pstandpipe

S y s t e m

f r i c t i on a l l o s s pr e s s ur e

originalMW

MWSPRFCP kill



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ICP - FCP

• Initial circulating pressure is greater thanFCP.

• As the kill mud displaces the original mudin the drillpipe

– Hydrostatic pressure increases. – Frictional pressure increases.

• The HP is greater than frictional pressureincrease.

• As the result of these two factorscirculating pressure drops.



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ICP – FCP (cont.)

• for operational purposes a linearbehavior between ICP and FCP vs.drillstring displacement stroke is

used.



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Drillpipe Pressure Schedule

ICP = 1100 psi

FCP = 830 psi

KWM to Bit KWM to Surface

Cum Volume of Mud Pumped, strokes

D

P

P

p

si



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Gas expansion

5000

5100

5100 5000

5100

2500

2500

BHP = 5100 psi BHP = 7600 psi BHP = 10100 psi

Psurface = 100 psi Psurface = 2600 psi Psurface = 5100 psi



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Casing Pressure



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Kill Sheet

• TVD=6000 ft

• Borehole = 9.875”

• Casing: – Length = 4000 ft

– 11.75”, 42 #/ft K55

• Drill pipe:

– Length = 6000 ft – 5”, 25.6 lb/ft

Mud weight=12.5 ppg

• Pump factor = 0.09 bbl/stk

• System pressure loss @ 30stks = 300 psi

• Shut-In Drillpipe pressure =350 psi

• Shut-In casing pressure = 500

psi

• Gain = 10 bbls



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Pre-recorded Information

31Kill sheet is courtesy of Well Control School

5 4.276 9500 19.5 10000

100009.875

8000 8000 42/k5511.75 11.084

0.1

14.0

0.0177

6 2500

.0049



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Kill Rates (Slow Pump Rate)

32

30 420 30 420



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Wait & Weight Worksheet

33

500 10000 14.0 15.0

Round up to the accuracy of 0.1 ppg

1 30 0.1 3.0 420

500 420 920

420 15.0 14.0 450



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Drill String Volume & Stroke Calculations

34

9500 0.01776

168.74 171.19 0.1 1712

Round up to a whole number

168.74 500 0.0049 2.45

2.45




Annular Volume & Stroke Calculations

36

105.6

0.1

1354.8

896.27 8962.7

8962.7 1712 10674.7

0.1 29.88




RECORDED KICK INFORMATION

37

1000010000

500

750

20

14.0

30

3.0

15.0

920

450

171.19

1712

896.27

8962.7

1354.8

10674.7

Pressure




Pressure

Chart

38

920

4501712

45010674.7

1712 171.2 920 450 47

873

826

779732

685

638

591

544497

171.2

342.4

513.6684.8

856

1027.2

1198.4

1369.61540.8



PETE 225 l b

Well Information

• TVD=10000 ft• Borehole = 9.875”

• Casing:

– Length = 8000 ft – 11.75”, 42 #/ft

• Drill pipe: – 5”, 19.5 lb/ft

• Drill collar: – Length = 500 ft

– 6×2

• Mud weight=14.0 ppg• Pump factor = 0.1 bbl/stk

• System pressure loss @ 30

stks= 420 psi

• Shut-In Drillpipe pressure =500 psi

• Shut-In casing pressure =750 psi

• Gain = 20 bbls

labo 9

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