tech drilling abnormalpress

8/20/2019 Tech Drilling AbnormalPress

1/41

1

PETE 411

Well Drilling

Lesson 20

Abnormal Pressure


2/41

2

Abnormal Pressure

Normal Pore Pressures

Abnormal Pore Pressure Gradients

Fracture Gradients Mud Weights

Casing Seat Depths

What Causes Abnormal Pressure? Detection of Abnormal Pressure

Quantification of Abnormal Pressure


3/41

3

HW #11

Slip Velocity

Due 10-28-02

Read:

Applied Drilling Engineering, Ch. 6


4/41

4

Abnormal

Pressure

Gradients

Normal Pressure Gradients

West Texas: 04!! "si#$t

Gul$ %oast: 04&' "si#$t

Normal and Abnormal Pore Pressure

Pore Pressure( "sig

D e " t ) (

$ t

10(000*? ?


5/41

5

Pore Pressure +s De"t)

0

'(000

10(000

1'(000

' 10 1' 20

Pore Pressure( lb#gal e,ui+alent

D e

" t ) (

$

Normal Abormal

Density of mud required to control this pore pressure

04!! "si#$t -!! lb#gal

04&' "si#$t .00 lb#gal


6/41

6

Pore Pressure

Gradient

/rature Gradient


7/417

Pore

PressureGradients

/rature

Gradients

%asing

etting

De"t)s


8/418

ome %auses o$ Abnormal Pressure

!" #ncomplete compaction of sediments

Fluids in sediments ha$e not

escaped and help support the

o$erburden"

%" &ectonic mo$ements

'plift

Faulting


9/419

ome %auses o$ Abnormal Pressure

(" A)uifers in Mountainous *egions

A)uifer recharge is at higher

ele$ation than drilling rig location"

+" Charged shallo, reser$oirs due to

nearb- underground blo,out"

." /arge structures"""


10/4110

3G3 PRE5RE

N6R7AL PRE5RE

T)i8( im"ermeable la9ers o$ s)ale or salt; restrit t)e mo+ement

o$


11/4111

3G3 PRE5RE

N6R7AL PRE5RE

Hydrostatic pressure gradient is lower in gas or oil than in water.


12/4112

When crossing faults it is possible to go from normal

pressure to abnormally high pressure in a short interval.


13/4113

Well >A? $ound onl9 Normal Pressure


14/4114

OB = p !

ob

" "


15/4115

?


16/4116

Abnormal Pressure ont*d

Detection of Abnormal Pore Pressures

Prediction of Abnormal Pore Pressures

D012ponent

DC012ponent

12ample #mportance of Shale Densit-


17/4117

ndiations o$ Abnormal Pore Pressures

7et)ods:

!" Seismic data

%" Drilling rate

(" Sloughing shale

+" Gas units in mud

." Shale densit-

3" Chloride content


18/4118

ndiations o$ Abnormal Pore Pressures

7et)ods( ont*d4

5" Change in Mud properties

6" &emperature of Mud *eturns

7" 8entonite content in shale

!9" Paleo information!!" Wire0line logs

!%" MWD0/WD


19/4119

Predition and Detetion o$ Abnormal

Pressure @ones

!" =e$ore drilling

Shallo, seismic sur$e-s Deep seismic sur$e-s

Comparison ,ith nearb- ,ells


20/4120


Pressure @ones

%" While drilling

Drilling rate: gas in mud: etc" etc" D 0 12ponent

DC 0 12ponent

MWD 0 /WD

Densit- of shale ;cuttings<


21/4121


Pressure @ones

(" After drilling

*esisti$it- log Conducti$it- log

Sonic log

Densit- log


22/4122

. – . SD99996."9e+!"9 −=φ


23/4123


24/4124

Decreasing *=P

What is d0

e2ponent?


25/4125

D Ex"onent

&hedrilling rate

e)uation4

Where * > drilling rate: fthr

@ > drillabilit- constant

N > rotar- speed: *PM 1 > rotar- speed e2pon"

W > bit ,eight: lbs

D8 > bit diameter: in

D > bit ,t" 12ponent

or D 0 e2ponent

D

8

1

D

WN@*

=


26/4126

D Ex"onent

#f ,e assume that @ > !

and 1 > !

&hen

D

8

1

D

WN@*

=

=

8D

Wlog

N

*log

D

D

8DW

N*

=


27/4127

D Ex"onent

A modified $ersion of this e)uation

follo,s4

=

8

3 D!9W!%log

N39

*log

d


28/41

28

Exam"le

Calculate the $alue of the d 0 e2ponent ifthe drilling rate is (. fthr : the rotar- *PM

is !99: and the ,eight on the !% !+ bit is

39:999 lbs"

=

8

3 D!9W!%log

N39

*log

d

%(96"!

%(+!"%

%."!%!9999:39B!%log

!99B39

(.log

3−

−=

=

d = #.$%


29/41

29

Exam"le

What happen to d i! " dou#le to $0 !t%hr&

Note that an increase in R resulted in a decrease in d"

Doubling R decreased d from !"6% to !".5

.5"!%(96"!

7((!"!

%."!%!9

999:39B!%log

!99B39

59log

d

3

=−−

=

=


30/41

30

Exam"le

d ma- be Corrected for densit- asfollo,s

=


31/41

31

Exam"le 2

Calculate d if4 * > %9 fthr N > !99 *PM

W > %.:999 lbf

D8

> 7 56 in

=

65."7B!9999:%.B!%log

!99B39

%9log

3

=

8

3 D!9W!%log

N39

*log

d

d > !"3(


32/41

32

Exam"le 2

#f the normal pore pressure gradient in the

area is 9"+(( psift: and the actual mud

,eight is !!"% gal: ,hat is dc?

=

=

%"!!

(("6B3("!


33/41

33


34/41

34

Proedure $or Determining Pore

Pressure /rom d Ex"onent

Calculate dc o$er !90(9 ft inter$als

Plot dc $s depth ;use onl- date from

%lean s)ale setions<

Determine the normal line for the

dc $s" depth plot"

1stablish ,here dc de$iates from the

normal line to determine abnormal

pressure Eone


35/41

35



d Ex"onent

D e " t ) Normal

Abnormal

N o r m

a

l & r e n d


36/41

36



#f possible: )uantif- the magnitude of the

abnormal pore pressure using

o+erla9s: or =en Eaton*s 7et)od

Pore

Pressure

Grad"=$erburden

Stress Grad"

Normal Pore

Pressure Grad

%"!

c

c

n normald

calculatedd

D

P

D

S

D

S

D

P

−−=


37/41

37

#n normall- pressured

shales: shale

compaction increases,ith depth


38/41

38

)ale Densit9 7ud %u" 7et)od

!" Fill mud cup ,ith shale until the ,eight is 6"(("%" Fill to top ,ith ,ater: and record the reading Wtot"

Note: Dr- sample carefull- ,ith to,el"

Do not appl- heat"

totW33"!3

(("6Gra$it-"Spec

−=

&l ' h d ) i bl d i l


39/41

39

&lternate 'ethod( )se variable density column.

ee " 2B0 in text


40/41

40

Pore Pressure $rom

Resisti+it9

Shale resisti$it- plots

ma- be de$eloped

from ;i< logs or

;ii< cuttings

What is the pore

pressure at the point

indicated on the plot?

Assume Gulf Coast"

Depth>!9:999 ft9"% 9". ! % (

!9:999H

D e "

t )


41/41

From plot: *n > !".. ohms

*obs > 9"69 ohms

From 1aton4

EAT6N

%"!

n

obs

n *

*

D

P

D

S

D

S

D

P

−−=

( )%"!

.."!

69"9+3."97."97."9

D

P

−−=

> 9"5(95 psift > !+"9. lbgal

P C 0B!0B 10(000 C B(!0B "si9"% 9". ! % (

!9:999H

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