3601-measurements of formation pressure from drilling data

8/11/2019 3601-Measurements of Formation Pressure From Drilling Data.

1/11

o?

P.IME

TliiS

IS A P?eHF3XT--- SUEJWT TO CO.RRXTION

Bill Rehm and

4 mer ican In st it ut e

of Forf f l ati m Pressure f rom

i l ri i l i ng Data

w

Ray McClendon,MembersAIME, Dresser-SWACO

@ Copyr igh t 1 9 71

of Mining Metallurgical and Petroleum Engineers. hic

This paper was preparedfor the ~th AnnualFall Meetingof the Societyof PetroleumEngineers

of AIME, to be held in Eew Orleans,La.,Oct. 3-6, 1971.

permissionto COpy is restrictedto an

abstractof not more than 300 words.

Illustrationsmay not be copied. The abst~actshouldcontain

conspicuousaclmowledgmentof where and by whom the paper is presented.

Publicationelsewhereafter

publicationin the JOURNALOF PETROLEUMTECHNOLOGYor the SOCIETYOF PETROLEUMENGR?ZERSJOURNiLis

t~~~~~ygranted~o~ requestto the Editorof the appropriatejound providedagreementtO give

-

prcpercreditis made.

Discussionofthis paper is invited.

Three copiesof any discussionshouldbe sentto the

Societyof ?

etroleumEngineersoffice. Sucn discussionmay be presentedat the abovemeetingand,

with the ~a?er,may be consideredfor publicationin one of the two SPE magazines.

ABSTRACT

tion.

A seriesof drLllingequationshave been

Sincevelocityis intimatelyrelatedto

proposedfor the measurementof formationpres-

rock density,the techniquesinvolvedin

sure. They appear to work well and are as

detemini.n

g pressurefrom velocityor density

accurateas log-derivedpressuretechniques.

shouldwork equallywell &th drillingrate

% fleit probablyis not possibleto develop one

insofar.as drilJingrate is relatedto d-asity

equationthat W work under W conditions?

or porosity.

one of the series shouldwork quitewell where

good dx5Jlxlg practices are used. Calculations

2.

The other drillingrate/pressurefacto

have been made US* these methods in dJ. major

involvedis the effectof differentialpressure

drilling=eas of the free world and accuracies

AS the differentialpressurebetweenthe

approaching0.2 lb/gsl have be=n attained.

wellboreand fonzationdecreases,drilhng rate

increases.

The increaseapproachesa hyperboli

INTRODUCTION

functionand often has an -inflectionoint at

about 500 psi overpressureagainstthe formatio

There are two reasons why adrfig/ (Fig. 1).

pressureequationshouldwork.

It may be noted that both phenomenawork i

1. The basic theom of abnormal.ressure

the samedirectionat the same time. Reduction

due to porosityor compactionindicatesthat as

in differentialpressuretends to come with the

the bit entersthe high pressurezone,the rock

entranceinto the overpressuredzone of greater

becomesmore porous and less dense than it was

porosityand botlnincreasethe drilliiigrate.

previously.

This has been provedby the methods

However,it appearsthat the differentialpree-

of detennini.n

pressuresfrom we~ logs, shale

sure phenomenonis the more sensitivefunction

densitiesand seism~cvelocities. The pficiple

of variationfrom normal was proposedby Hottman

I%eseobservationsled to the belief that

and Johnsonin 1965.12 They firmlyestablished not only was the determinationof overpressu.r

not only that variation from normal was an zones possible,but that it was possibleto

indicatorof high pressure,but that M@ pres-

detexmineformationpressuz-esfrom dx5Jlingrat

sure couldbe measured by the departureof the The main difficultyappearedto be resolvingth

velocityfrom what might be e~ected to be

sensitivitiesinvolvedin the drWLing rate

normalvelocityfor the depth under considera-

fmctiono

Referencesand illustrationsat end of paper.


2/11

MEASURINGFORMATIONPRE

~sIc c~i~~

Some basic fieldhvestigations,shortly

terpublicationof the paper by Jordanand

rley14furthercorKinnedthat the basic d

ationwas en excellentindicatorof differen-

pressure

~tl-,15+


3/11

~ 3601

BILL REHM and RAY McCLENDON

FTREH. IimZLOFI@YT

The difficultiesin keeptigdrillingand

mui iunctiansonstantduringdifferentialpres-

su7e calculationsin transitionzonesmake it

desirableto developan absolutepressurevalue.

As a resultof considerablefield work in

comparisonof the variousmethods,the d equa-

tion of Jordenand Shirleywas selectedas the

best possiblestartingpoint sincethe sensitiv-

ities and mechanicsappearedto be both accurate

and usable. Field correlationindicatedthat

the equationgave a ve~ reasonableappro=-

mation of differentialpressurebetweenthe

wellboreand fozmation.

It was postulatedthat if it was possible

to correctfor the effectof mud weight,the d

tem would then be an indicatorof formation

pressure. Ibis was attemptedon an empirical

basis on a number of differentmodels and

> :- A&. S.llmwirl

whirh g=y~ ~

resi i teu u uc ~ ~ u gt

excellentindicationof formationpressure.

dc~= %d, .0 **0****(4)

MW2

where dcs

= modifiede~onent ti general

drilfig equationto indicate

formationpressure

MWl

= noxmalmud weightgradientfor the

area

MN2 = equivalentcirculattigdensity or

mud weight in use

The plot of the dcs

l;te~ showeda Curve

that was similarto acousticlog shale plots ant

shaledensityplots (Fig.k).

THE SOLUTIONPIOT

Using the d and dcs terms,it is

possibleto plot two curvesthat relateto

differentialpressureand to fomation pressure

The comparisonof these two valuesprovidesa

valuabletool in dflli.ngrate/pressuresnalysi:

(Fig.5).

The similarityof the dcs and the shale

densityplotsled to the beliefthat a pressure

interpretationmight be made on the same depsr

ture from nozmdlbasis as on log plots.

The originalwork by Hottman and Johnson12

indicatedthat when dealingwith log~erived

values,the solutionof departurefrom normal v

pressuregradientwas a power functionclosely

approachingthe logarithmic.

This was further

redefinedby Combs (1967)in te~s of sh~e

arfllability. The discussionof shaledensity

by Boatman2definesthe same generalfunctioni

terms of shalebulk density.

3asedp~arily on the comparisonof the

acousticand the dc~

solutionfor departure

fromnormalvs pressuregradient,a term was

developedh the mode of the Combs work.

This was resolvedinto the following

expression.

Grad = mLog (Normal-Obsemed)+ B . (5)

w h ere Grad =

m=

Normal=

Observed=

B=

.

pressuregradient,psi/ft

slope constant

normal d

at depth for the dri1

tools i%olved

dcs at depth for driU tools in-

volved

offset

This was actuallyresolvedfor field use b

means of a standad overlayand plot paper (Fi

6).

When plottingon coordinategraph paper,

where 1 in. on the horizontalaxis is 0.5 dcs

units,the eq-uatioiiec.mes

Grad = .398Log (Normal-Obsened)+ .86

. . . . . ***** *.***

(54)

FIELDDATA COLLECTION

The collectionof accuraterig informatio

is the obviouskey to the accuratedeteminatio

of pressuresfrom drillingparameters. The

originalpremiseof the pressuresfrom driUing

rate projectwas that equipmemtto accurately

collectthe informationwas nekesssxyand woul

be designedas soon as the parameterswere

clearlyestablished. The equipmentwas desigd

and firstbecame availablein late 1969. The

personnelin the units were extensivelytraine

for the specificpurposeof pressuredetermina

tion and upon their enthusiasticeffortsreste

the successand

accuracyexperienced.

DriJ3ia

data was gatheredon over 90 wells throughout

the world ut~zing this equipmentand crews.

The collectionof the drillingdata has been

continuallyimprovedby e~erience and the int

ductionof newer and more rtiable eqyipment.

DATA COILEC~ONMETHOD

Whether the solutionto bottom-holepres-

sure is plottedby computeror by hand, the

variationsin the earth and the drilMng proce

must be taken into account. Iheimplest,yet

most importantcorrectionis for vtiations in

the foxmation. Since the equationsdo not tak

changesin lithologyinto account,a stand-

must be established. Shale is the most conven

ient standardbecauseit is relativelyeasy to

identifyand displaysthe greatestdegree of

compaction. It is also the standamiestablis

by earlierwork in pressuredetermination.

Other standards,suchas silts,redb+s, or

sands,may be used but they are proportionate


4/11

MEASURINGFORM4TIONPRESS~ FROM DRIIJZNGDATA

SPE 3601

I

:erto fiterpret.

In Gulf Coast-typearil.ltigthe difference

tt~eens~~ ad sh~e shows Up dramaticallyti

e drilltigrate.

The sand values can then be

noredon a

by tispection

1basis or CSIICeUSd

t oya dead beat band in the electronic

Tinisshouldbe spi checkedby

e anelysis.

In older formations,it is oftendifficult

vefi+y the establishedstandardsolelyby

ctionof drillang rate.

In these cases a

nationof drillm

g rate and sample analysis

y be

used There

is everyindicationthat

riationin torqueand rotarybounce can be

ed to definemore closelythe formation.

How-

er, it is easierand more accurateto use

mpleanalysiswhen using a mannedunit.

~afi~~g causes a major shtit in the pres-

re plot if it is not recognizedby a combi-

tion of sampleanalysisand an abruptoffset

the slope of the plot. Unfortunately,many

ultsoccur withinthe transitionzone where

th the lithologyand slopeof the plot are

=EQeA-A

~q~~&.~ s knwl due nf tb.~

u ...........---

ology of the area are some

this case.

The rate of penetration

llectedon a footagebasis

of the best guides

appearsto be best

(withfixed footage

d variabletime). Fixedtime and variable

otageincrementswere tried,but for some

ason,were not satisfactory. -m ~ener~, ~~

s been found that for any drillingrate up to

out 60 ft/hr a l-ft stsndti isquite satis-

At very low drillingrates, a standardof

ss than 1 ft appearsto rellectthe autc+

tic drillerratherthan the fomation. At

n? ~~ ft,lh-vf~ot.ag~

5Z2ingrates h excess..

andardof 10 ft appearsto be satisfactory.

e footageintervalmust be enoughto reflect

e formationratherthan the driller,but

ort enoughto showvariationsin the fomna-

Rot

ary sDe@

Rot~ speed is measuredby en impulse

vice, and rate is calculatedand reportedas ~

mericalvalue in rpm.

Eit WeiRht

Good snort-titenal averagesof bit weight

essentialto accuratesolutions.

The best

sults come as a

result

of the following. The

t weight is definedas the differencebet~eer

+l~+ngweight and stringweight when rotating

and pumping just off bottom and is automat-

ically calculatedand reportedin thousa??ds

f

pounds. A movitigaverage,

or

thifi-otier

electronicfilteris used betweenthe transduces

on the hook load diaphragmand the nook load

value end displayto dampen the bounce in the

drilling

assembly.

IW4JORCHANGESIN CONDITIONS

With presemtdrK1.i.ngtechnologythe casing

point is in the transitionzone. With the

settingof casingcomes a major change in the

values for the pressuredeterminationequation.

The bit sizeis changed,oftenthe mud weight

and mud characteristicsare changed,causinga

change in the differentialpressurerelation-

ship.

The changein bit size is correctedin the

ofig~~ lid ?

quation

where there is proVisioKI

for bit diameter. The changein bit type is

not

so

straightforward.On an empiricalbasis, it

was discoveredthat correctionin bit type or

correctionfrom mill tooth to carbidebits can

be made on a basis of bit tooth area in contact

w+.h ~h~ f~~_~~iQn,

..- ..

Then tM3 correctiontakes

the place of the bit diameter. So the bit

diameterencompassesbit type end is made.by a

proportionatecorrectionfor bit diameteras a

functionof bit tooth area in contactwith

formation. This, from a review of the etist~

literature,seemsto be a rationalcorrection

and may not be enttielyempirical.

The correctionto diammd bits is somewhat

3.

ma. -.-1 L 1 . . . a.-.

more axzx~cu~ and

to a AKSG u=6A=e As r.ct

been successful. When using diamondbits a

smell.sectionof hole must be dfled and the

correctionsput in by obsenation.

Changesin the drill stringcan cause some

difficulty,particularlywith additionof a

radicallydifferentstabilizer

assembly. This

may be aermlmt.~ f~~ s_@Q SS

change in the

--------

effect of bit weight,but it is difficultto

correct on any mathematicalbasis.

Again the

best solutionin this case is an additional100

ft of hole to establisha new trend pattern.

Changesin drillingmud propertiesalways

affectpressuredeterminationto some degree.

The changein mud properties,otherthen weight,

seem to affectthe equationin the same genersl

manner as was proposedby Eckel.7 me d~g

rate is affectedby tiscosityby a value

approachingthe 0.5 power of the changein the

Reynoldsnumber. For smd.i changesin tine

viscosity-relatedterms there is no apparent

effect on drillingrate.

Large changes,how-

ever,particularlythose increasesin tiscosity

causing significantchangein the Reynolds

number, can make the pressureequationinoper-

able. No attemptis made at this ttie to

make

these correctionsmathematically. Some


5/11

BILL REHM and RAY McC~tDON

prelimfia.ryork indicatesthat the Reynolds

n~mner cn~~~ct~o~ ~~obably could be made in such

.----

a manner as to cor;ecifor some of the tiscosity

Ck. ge.

With nigh viscositiesthere is no data

to indicatewhetherthe equationcould be made

valid or not.

Viscositiesmay introducesome

factorsin holecleaningthat we are unableto

handleat this time.

The effect of mud weight is more straight-

forward and the mud weight correctionallows for

these changes.

There is, however,a problem

hvolvedti.the mud weightcorrectionmuch akin

to that of viscosity. Wnen the mud weight is

more than 2 or 3 lb/gal.greaterthan the for-

mationpressure gradient,or the bottom-hole

presswe is ~reaterthan 1,000 to 1 500 lb more

than the fo~ation pressure,the solution

becomes erroneous. In general,the solution

indicatesa highermud weightthan is actually

needed. It appearsthat the drillingrate vs

differential-pressurecurve (Fig.I)-is on the

flat part of the slope and shows no effect of

increasedor decreaseddifferentialpressure.

The functionrelatingto increasedporosityis

not able to make the total correction.

RESULTS OF PRESSUREPLOTS

The field work done with the data collec-

tion units provideddrillingrate/pressure

plots of exceptionalaccuracy. The plots were

made utilizing only pure shsle or some other

agreedupon standard.

Tne potitspicked as

representativewere checkedagainstlagged

cutting samples.

Becauseof the accuracyof the

data co~ection equipment,it was possibleto

use representativedrillingvalues throughthe

standaxdsection.

The dcs

value was plotted

on the standardscale and the overlayapplied.

For the most part the solutionswere accuratetc

within 0.2 lb/gal of formationgradient.

While

it was possible in some cases to compareto

pressurevalues obtainedduring a well kick or

---a..+


6/11

MEZkSURINGORMATIONPFU3SSUR.EROM DRILLINGDATA

WE 3601

1

ecord can be used to supportthe log calcu-

ationsby means of Ecp. 4 and 5.

The effect

7

itnologyis unhewn; however,pressure

culationsder5Lvedb this mannerare ama-

accurate.

Thepressure tiWidS are

eciallygood, but with accuracylimitedto

out 1 lb/gal (Fig.7). Otherproblemsfith

t recordplots involve the difficultyin

ining any idea of correctionsmade for hole

ation. While dri2J_ingassemblychangesand

rJ light bit weights shouldbe indicatedon

record,more often tk,annot informationis

IERCCMFARISON

The exceptionalaccuracyexperiencedin

e field,raisedthe questionof using the

rlayand plot.

To controlthe titerpreta-

on by field personneland to maintainstrict

dards,a computersolutionw preparedby

ldingEqs. 4 and 5A together. Sinceitwas

annedto use an automaticplottingtechnique

s well

as derivingan answer,the equationwas

rthermodifiedto reduce the normal slope of

e decreaseh drillingrate with depthto

rticaiand to give the answerml a eomiinate

er than logarithmicaxis.

This term was resolvedas

[ ~2Lo~

f=c7.62Log Ha + C - ~LOg 60N

+16.52 , . . . . . . . . . . . . (6)

here P =

formationpressuregradient,lb/gsl

7.6 = slope constant

H = geologicaldepth, ft

a= slope of the

noxmal

penetrationrate

for the drill tools involveddcs

units/ft

= drillabilityconstantdc units

16.5:= interceptconstant,lb/gaf

The computergave essentifiy the same

olutionas did the hand plots (Fig.8). In

on-sitework, the variousparameters,wit-n

he exceptionof a and C, were enteredauto-

ALYSISOF THE NOMENCL4TUEE

Mud weight in poundsper gallonwas selec-

ed as a usable field texm. he use of a mud

texm is particularlyconvenientin the

eld for comparisonwith the mud weightin use

Slone Constant(7.62>

~i~ is the slope of the line of the plot

of lb/galVS dcs.

It is the slope of the

m.--v.vfrom Eq= 5A Or 0.398/0052.

G.&.aJ

,=..

g

This

term is genertiy used as T.V.D. in

feet.

However,the properdescriptionof the

texm is geologicaldepth. This shouldbe

correctedfor faulting,major foldingend

possibleu~lift.

The majorityof the work with

this equatzonhas been done in basin

areas.

Limited data indicatesthat the effectof up-

lift can be correctedby use of a reconstituted

depth.

g

This is the slope of the normal dcS. In

the most straightforwsmiversionof the equa-

tion, the term & actuallybecomesdcs for

the normal-pressuredzones. This is then ex-

tended to the overpressuredzonefor compara-

tive purposes. It is a vfid approachand is

~Acm,~Iydgp.evltb.had-plotted solutions. In

the case of an automaticplot, it is easierto

handle the circuitryor programwith a slope

term.

The slope term ~ is quiteconstantwith

geologicalage.

Tnere is, for exampie,very

little variationin the slopevalue a between

the Miocene of Louisianaand lndones~a.

:

The tilability constantis actualJ.ythe

drill tool constant. DifferentdriJJ.ingrigs,

formations,and differentcustomschangethe

absolutedcS.

In the basic d

equation the

value Q for any rig is correctedby inspection.

InterceptConstant(16.52)

The interceptconstantis the offsetvalue

fromEq. 4 (0.86/.052).

Mwl

-2 . & 4. +h. me- 1 nmmee??vm

L1lA=

U@LIU +- U..G ..w.m~ F. ---- -

gr=dfi~~~

for the area.

MW2

This term is the mud weightin use cor-

rected for the circulattigdensity. The equiv-

alent circulatingdensityis an importantcon-

siderationindeep slimholes.

~

This term is the drCMng rate in feet per


7/11


8/11

WAS TRTNG F XWATTON ? ESSUFE FROM DRILLINGDATA SPE 360

. ----- ------------- - -- --- .

(195 )~, 9-17.

Pet. Zn~. (Nov.,1969).

6. Dolpk, ;. R. and 3rown,K. E.:

Zffec?.of

IL

Jorden,J. P..and Shirley,O. J.: ..

~Aa~~

Rota.qySpeed and Bi~ tiight on Penetration

cationof DrillingPerformanceData to

Rate of a DiamondMicrobit,

J. pet. kch.

Overpressure

Detection,J. Pet. Tech.

(Sept.,1968) 915-916.

(Nov., 1966) 2387-1394.

7. Eckel, J. R.:

Tiicrobittudies of the

15.

Jorden,J. R. and Shirley,O. J.: Tfeth

Effect of Fluid Propertiesand Hydraulics

for Detem~ the Top of Abno~al Foma-

on DriilingRate,J. Pet. Tech. (April,

tion Pressures,U.S. Patent3368&O0,Feb.

1967) 5u-546.

13, 1968.

~a

**HowMud and ~yaratics

.rkel.J, R=: -----.

16. MaurerfW. C.:-..--, Bit-ToothPenetration

AffectDrill Rate,

Oil and Gas J. (June

Under SimulatedBoreholeConditions,~.

17, 1968).

Pet. Tech. (Dec.,1965) 1433-1U2.

9* Fcm? 7--A

Luyu ad Imt rein:

Wrm-. 4

ru4utau*O~i

~?e M,,W-F..W

.,WAW, ~= ~= @ ~l&n~~@~f R, A,:

Log ?ressu.reData Can ImproveDrilling,

? Effectof Mud COl~ pressureon Drillin

World CKL (Sept.,1966).

Rates, TYans.,AIME (1955)~, 196-20L.

10. GaX1.e,E. M. and Woods, H. B.:

Best

18.

Outmans,m.:

The Effect of Some

Constan;Bit Weight and Rotary Speed,

DrillingVariableson the Instantaneous

011 anc Gas J. (Oct.,1963).

Rate of Penetration,Trans.,

AIME (1960)

1. Gamier, A. J. and van Lfi.gen.N. H.:

219,~37_~49.

PhenorenaAffectingDrillingRates at

19*

~tison, L. H., Jr.:

Effectsof Pore an

Depth, Trans.,AME (1959)~, 232-239.

ConfiningPressures

on Fa ilw e

Character-

12.

Hottman,C. E. and Johnson,R..K.:

Esti-

isticsof SedimentaryRocks, Trans.,AIME

mation of FormationPressuresfrom Log-

(1959)~, 26-32.

Derived Shale Properties,J. Pet. Tech.

(June,1965)717-722.

20. Vidrine,D. J. and Benit, E. J.: Field

Verificationof the Effect of Differentia

Jones,F. T. and Barringer,S. H.: lm-

Pressureon DrillingRate, J. Pet. Tech.

proved Communicationswitinthe Drill Bit,

(Jtiy,1968)676482.


9/11


10/11

000

10000

12000

I II

d

C*

1.0

2.0

(

BULK DENSITY

IIo,ooa

ACOUSTICS

[2,000

14,000

16,000

1.0

\

10PPG.

\.

p \

~ \

x){m

~ ,>

L.

z

9

.

/

Pj

r

51?G.

.:

\

.\.

t

/

.

18f?f?G.

?

.)ACTUAL

, MUD WEIGH

/1

I

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-2,0

.

1.0

1.5

Fig t

. Jlmtlnrlty O

~lotn.

rig 5

Two curv~n,


11/11

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3601-measurements of formation pressure from drilling data

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