Drill-Stem Testing 2
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Drill-Stem Testing (DST)
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#
Drill-Stem Testing (DST)
Prepared by: Azad Adeeb Noori
Supervised by: Dr. Kosra! "azra#san
Petroleum $eology
%niversity o# Kurdistan- &e!ler
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Abstract
'ne o# te most important stages o# ompleting a !ell is disussed in tis report !i is
te Drill-Stem Testing (DST). Tis report disusses tree main aspets o# tis teniue* it
indiates te detailed #untion o# ea omponent o# te tool assembly. Ten it disusses te
reuired deisions to be made to per#orm a test. +ts main #ouses !ould be on te proedure o#
te test and igly empasizes on te best interpretation o# DST pressure arts.
Introduction
Drill-stem testing (DST) is one o# te most important ompletion teniues. +t is a type o#
temporary ompletion tat is used to evaluate te #ormation and inspet a reservoir,s properties.
Aording to (Ammann* /0)* te measurement o# te reservoir properties by te DST an be
delivered diretly or indiretly. Diret measurements means tat te data are reorded !en te
tool assembly !as do!n in te ole. Tose measurements inlude* te Stati 1eservoir Pressure*
#lo! rate measurement* reservoir depletion i# too2 plae during te test* and obtaining a reovery
sample o# te #ormation #luids. &o!ever* te indiret measurement or empirial measurements
are tose parameters tat yield #rom te use o# euations and it inludes* most importantly te
produtivity inde3 (P+)* e##etive permeability o# te #ormation to te #luid #lo!* #ormation
transmissibility* s2in #ator* drainage radius o# te investigation test* and detetion o# reservoir
anomalies (su as barriers* #luid ontats* permeability anges or layered zones). As ("la2*
4/) states tat speial ompletion euipment are reuired to per#orm te test* some o# tem are
ompulsory !ile oters are au3iliary depending on te !ell onditions and te test
reuirements. Te #ollo!ing setion disusses te tools tat ma2e up te DST tool assembly.
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Equipment of the Drill-Stem Test tool
Te drill-stem tool as #our basi or ompulsory omponents tat sould e3ist in every tool
assembly made by any servie ompany. Tese #our omponents are: te pressure reorders* te
test valves* te ydrauli by-pass or eualizing valves and te pa2ers. A general diagram o# te
DST tool is so!n belo! in #igure ():
5igure (): +llustrates te omponents o# te Drill-Stem Test tool inluding bot sur#ae
euipment and do!n-ole tool.
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. The Pressure recorders (the Brain of the DST tool assembl)!
Te DST tool is almost useless !itout te e3istene o# pressure reorders. Aording to
(Dolan* 46) te pressure reorders are built in a number o# pressure apaities as !ell as
lo2 speeds. Te pressure reorders used in te DST tool are usually sensitive #or lo! pressure gauges as mu as 7 psig and #or ig pressure gauges as mu as t!o tirds o#
te ma3imum pressure o# te !ell.
8. The Test "al"e!
Tis valve as a ma9or role in te drill-stem test. +t is plaed in te upper setion o# te
DST tool above te ydrauli by-pass valve. Aording to ("la2* 4/)* one o# its main
#untions is to provide a passage #or te #luids to #lo! into te drill pipe !en te pa2er is
set at te annulus. Seond* it prevents te drilling mud to enter te empty drill pipe !ile
running in te boreole. +t also assists in te prevention o# drilling mud entrane to te drill
pipe !ile pulling out te DST tool assembly and aids in te onservation o# te reovered
reservoir #luids to te sur#ae. 5igure (8) belo! so!s te test valve:
5igure (8): Test valve.
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. The hdraulic b-pass "al"e!
Te ydrauli by-pass valve as a role in relieving te pressure in te boreole. +t
provides an additional spae #or te drilling mud to pass around te pa2er !ile running in
or pulling out o# te boreole. +t allo!s te drilling mud under ydrostatis pressure to #lo!do!n!ard troug te pa2er mandrel at te end period o# te test into te oles belo! te
pa2er. Tis ertain #untion provides te eualization o# pressures around te pa2er
ausing it to be retrieved easily to te sur#ae.
;. The Pac#ers!
Te pa2ers used in te DST tool are temporary* !i means tat tey an be retrieved
to te sur#ae unli2e oter types o# permanent pa2ers !i stay in te !ell. Aording to
(Petro!i2i* 80;) pa2ers are o# di##erent sapes and are made o# rubber-li2e materials tat
an be ompressed to e3pand against te boreole !all. Teir main #untions are to seal te
annulus spae and prevent te do!n-ole movement o# te drilling stem. Tis sealing
meanism prevents te vertial #lo! o# te #luids in tat setion o# te !ell. Pa2ers very
o#ten improve te prodution rate o# te !ell by direting te #ormation #luids to one !ay
passage rater tan going into te annulus spae. Aording to ("la2* 4/)* pa2ers are
usually set above te assigned per#oration zone to prevent te #ormation #luids #rom #lo!ing
troug te annulus spae to te sur#ae. Te pa2ers are set in te ole by rotation o# tedrill pipe ontrolled by te driller at te sur#ae. 5igure () belo! so!s some types o#
pa2ers:
5igure (): So!s di##erent types o# pa2ers.
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+n addition to te basi omponent o# te DST tool tere are oter au3iliary omponents
tat most o# te modern DST assemblies are omposed o#* !i inlude te #ollo!ing:
. The Shut-in pressure "al"e!
Tis speialized valve is loated belo! te reverse irulating valve o# te DST tool
assembly. "redeoe#t (/4) states tat sut-in valves ave a role in te sut-in periods
!itin te test* meaning te initial sut-in and te #inal sut-in periods. 'ne o# its #untions
is to permit te test valve to be losed at te end o# te #lo! period !it redued prospet o#
unseating te pa2er or letting te pressure eualize around te pa2er troug te by-pass
valve. +t also elps in retaining te #ormation reovered liuids.
8. The Dis# "al"e!
Tis valve aids in te prevention o# te drilling mud entrane into te drilling pipe !ile
running in ole. +ts seond #untion is to allo! te pa2er to be set #irmly and te tester
valve to be opened* be#ore te tool is opened te dis2 valve rupture by te dropped go-devil
#rom te sur#ae. A sample o# te dis2 valve is so!n in te #igure (;) belo!:
5igure (;): Dis2 valve.
. The $e"erse %irculating "al"e!
Te importane o# tis valve is tat it allo!s te reovered #luid to be pumped out o# te
drill pipe by reverse irulation into sur#ae tan2s. +t also provides sa#e operation #or te test
by onditioning te mud in te annulus. A diagram o# te irulating valve is so!n belo!
in #igure (4):
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5igure (4): 1everse <irulating =alve.
;. The &ar!
Te type o# 9ar used in te DST tool is a ydrauli 9ar tat is designed to provide
impat blo!s to set #ree te stu2 pa2er or DST tool !enever possible. A sample o# teydrauli 9ar is so!n belo! in #igure (/):
5igure (/): &ydrauli >ar
4. The Safet 'oint!
Tis tool is used to unsre! and retrieve te DST tool !en eiter te anor or te
pa2er is stu2 in ole. +t allo!s sa#e reovery o# pressure data to te sur#ae as !ell as #luid
samples. A sample o# te sa#ety valve is so!n in te #igure (6) belo!:
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5igure (6): Sa#ety 9oint.
/. The Anchor shoe (Bullnose 'etting noles)!
Te anor soe is te ead o# te DST tool* plaed in te lo!er end o# te tool !i
enters te !ellbore #irst. +t is made o# ard material to absorb te damage aused by
restriting material in te !ell. Aording to (&yne* 808) anor soe ead ontains
nozzles or openings tat derease te buoyany o# te #luids in te !ell as !ell as brea2ing
te sur#ae tension o# te #luids. Anoter important #untion o# te anor soe is tat it
anors te DST tool in te bottom o# te !ell and olds it !eigt. Te bullnose #igure is
so!n belo!* in #igure (?):
5igure (?): Anor soe or "ullnose 9etting nozzles.
6. The Bottom ole %ho#e!
Te "ottom &ole <o2e is a sort sub tat an be loated belo! te pa2er and above te
per#orated pipe. +t aids in te restrition o# te #lo! do!n ole. +t olds some ba2pressure
under te pa2er and redues te ydrostati pressure on it.
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?. Perforated pipe!
Aording to (1aymond* 800/) te per#orated pipe is loated above te anor soe
and its #untion is to soot per#orating bullets into te #ormation* as te go-devil is sent
#rom te sur#ae to start te per#oration. A diagram o# te per#oration proess is so!n
belo!:
Diagram (): So!s per#oration o# te #ormation.
. The Surface %ontrol ead (%hristmas Tree)!
Tis sur#ae assembly ontrols te #luid #lo! #rom te drill pipe to te sur#ae troug a
set o# valves and o2es. A diagram o# te <ristmas tree is so!n in te #igure () belo!:
5igure (): <ristmas tree.
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#
Designing the DST plan
+n order to insure tat te desired in#ormation are delivered by te DST test detailed
onsiderations must be given to a number o# #ators. Ta2ing in onsideration te #ollo!ing
#ators inrease te probability o# suess o# te test:
. The amount of hole to test!
1aymond (800/) states tat it is needed to 2no! at !i dept or total dept (TD) te
test is going to be e3euted and !at type o# #ormation is inluded* !i o# ourse
most o# tese data ave been olleted !ile logging and oter geopysial teniues.
8. Pac#er sie selection and assigning the location of the pac#er seal!
Determining te suitable size o# te pa2er and its seal loation as a great e##et on te
suess o# te DST test. Aording to ("la2* 4/)* it sould be deided aurately
!i type o# pa2er is reuired tat totally mates te !ell onditions* !eter te
!ell is open-ole or ased ole* or !eter te #ormation #or inspetion is a sandstone or
limestone* et. Te loation o# te pa2er seals are assigned by te elp o# aliper logs
!i provide an appro3imate radius o# te boreole and te least learane bet!een te
!ell !all and te pa2er seal. As te pa2er size seletion depends on te type o#
#ormation* so te pa2er seal does.
. Selecting the suitable top and bottom hole cho#es!
Te seletion o# te top and bottom-ole o2es is made by onsidering te sa#ety point
#irst. Te rigt use o# te top and bottom o2es prevent o2e plugging or #luid #lo!
restrition. +n general* te bottom o2e is osen to be smaller in diameter tan tat o#
te top o2e to ontrol te amount o# #lo! to te sur#ae.
;. Estimation of the time required to perform the test!
Te pre-deision o# te lengt o# te test is a vital #ator in te proedure. $rant (4)
states tat troug tis step* te time reuired #or setting te pa2er* opening te test
valve* te initial #lo!* initial sut-in* #inal #lo! and #inal sut-in are all assigned teir
spei#i periods trougout te proess.
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#
4. Selection of pressure gauges and manner of displacement in the tool!
As it as been mentioned be#ore te pressure gauges are onsidered as te brain o# te
DST tool* tere#ore as <ristie (n.d) states tat to per#orm te test at least t!o
subsur#ae pressure gauges are needed to run te tool in te !ell as one o# tem is
plaed inside te anor soe #or it to reord te pressures belo! te bottom ole o2e*
!ile te oter is plaed outside te anor soe to reord te pressures e3erted by te
#ormation #luids or te drilling mud. Te pressure reorders sould be osen orretly
so tat tey are able to reord pressure iger tan te ma3imum pressure o# te !ell #or
obtaining more aurate results.
/. Assigning the location of circulating "al"e* 'ars and safet 'oints!
Te irulation valve is usually plaed above te test valve* tis oie is made #or it
!ill permit te retention o# unontaminated #ormation liuid samples. Te 9ars are
usually plaed above and as near as possible to te pa2er to set it #ree. Te sa#ety 9oints
are plaed in a loation belo! te pressure reorders so tat te data !on,t be lost in
ase o# stu2 anor or pa2er.
6. %onsidering the use of +ater or gas cushion!
Te use o# !ater or gas usion sould be onsidered in order to prevent te abrupt #lasrelease o# pressure #rom tousands (psia) o# drilling mud pressure to atmosperi
pressure. Aording to (Timmerman* 68) undesired #las release auses damage to te
#ormation o# te !ell in te #orm o# aving o# te !ellbore !all. +t may also ause te
plugging o# te anor per#orations or even te bottom-ole o2e. @ater usions are
usually plaed in te drill pipe to redue te pressure di##erentials tat our aross te
!all o# te boreole and te pa2er as te tool is opened.
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E,ecuting DST test and interpreting DST pressure chart
Te simplest !ay to desribe te proess o# Drill-Stem Testing is to present a typial DST
pressure art o# an open ole* see #igure (0) and desribe ea segment o# it. @en all te
#ators #or per#orming a DST are ta2en in onsideration as mentioned in te previous setion* te
plan #or te DST is ready to run. &o!ever* be#ore running te tool into te !ell* te tester inserts
te test art into te reorder and dra!s te baseline !i indiates (0 psig)* te blue line in
te #igure (0). Te !ell sould be onditioned and #illed !it drilling mud. Te driller pulls out
te !ole drilling string out to te sur#ae to replae te drilling bit !it te DST tool* ten e
enters te !ole string ba2 again into te !ell* stand by stand. Aording to "redeoe#t (/4)*
te DST test is per#ormed as #ollo!s:
igure (./)! DST pressure chart
• Te initial pase o# te test is observed in segment (A to ") as so!n in te art above.
As te tool runs do!n te ole te ydrauli by-pass valve is le#t open beause te
pa2er as limited learane bet!een te asing and te !ellbore. Te open by-pass
valve allo!s te drilling mud to go up te drilling pipe and up to te sur#ae* tis ation
is meant to lo!er te pressure surges reated as te tool runs do!n te ole. Te
pressure gauges start to reord an inrease in te pressure. Tis inrement is due to te
buildup in te ydrostati pressure o# te drilling mud olumn present inside te !ell. +t
an be observed tat te pressure urve is not smoot beause o# pressure surges !i
our even !en te by-pass valve is open. Te pressure surges are aused by te
addition o# onnetions
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to te drilling string. Anoter reason #or tat is te e3istene o# tigt spots enountered
in te ole as te !ell !all is not straigt do!n!ards. Sometimes pressure surges our
due to addition o# !ater usion or repair sur#ae euipment. All o# tese noises are
reorded by te pressure gauges as tey run do!n te ole.
• A#ter te per#orated setion pipe as reaed te test interval or total dept (TD)* te
sur#ae euipment is onneted to te drill pipe during tis time te pressure stabilizes
at point ("). Te pressure surges end and te initial ydrostati pressure is reorded
relatively at te point !ere tere is #lat pressure values. Te driller ten slags o## te
bra2es reating a !eigt on te DST tool ausing te pa2er to e3pand. Te pa2er seals
o## te area bet!een te interval o# interest as !ell as te gage #rom te olumn o# mud
above te pa2er. 'ne te pa2er is set te driller rotates te drilling stem ausing te
tester valve to open momentarily #or #e! minutes (#rom " to <). Te initial #lo! ta2es
plae #rom (< to D) tis period lasts #rom 4 to 0 minutes. Te initial #lo! pressure
reorded at point (<) is nearly atmosperi unless a !ater usion is plaed in te drill
pipe. Tis ation allo!s te pressurized #ormation #luid and drilling mud to #lo! into te
tool and up to te sur#ae.
• Te test valve is ten losed and te initial sut-in period ta2es plae !it a duration o#
0-/0 minutes #rom points (D to ). Sur#ae indiation o# te #lo! are observed and te
pressure builds up reaing te Stati 1eservoir Pressure at point ().
• Te test tool is opened again #rom ( to 5) and te #inal #lo! period ours #rom (5 to
$). Te sape o# te buildup !ill depend on te properties o# te #ormation and te
#luids. Te duration o# tis period ta2es #rom tree ours to maybe days depending on
te o!ner reuirement.
• At te end o# te #inal #lo! period te test valve is again sut-in at point ($) and te
#inal buildup period ta2es plae #rom ($ to &). To remove te DST tool te driller #irst
opens te reverse irulating valve. +t is opened ydraulially by pumping te drilling
mud do!n te annulus* !it te valve open te drilling mud irulates do!n te annulus
and te up te drilling pipe to te sur#ae. Te drilling #luid 2ills te !ell by 2eeping te
#ormation #luids under ontrol. Ten te pa2er is released at point (&) eiter by rotating
te drilling string or by te use o# ydrauli 9ar. Te ydrostati pressure o# te mud
olumn is #elt
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ba2 again by te pressure reorder at point (+)* ten te tool !ill retrieve #rom te ole
#rom points (+ to >).
%onclusion
Te integration bet!een tests results and data are ompulsory #or ompleting a !ell. $oing
blindly into ompletion o# a !ell !itout per#orming te drill-stem testing is a great loss. Tis
report as disussed te importane o# te DST. +t igligted te main omponents tat ma2es
up te DST tool ea !it teir o!n partiular #untion. +t also disussed te best design #or te
DST and o! it is e3euted. Te report ame up to onlude tat te ability o# a !ell to beompleted suess#ully is to orretly interpret te DST pressure art* !ere by te most
important parameter is obtained #rom it* te stati reservoir pressure* 2no!ing tis value and
oter parameters !ill aid in #urter development o# te !ell.
$eferences
) <. ". Ammann (/0). Case Histories of Analyses of Characteristics of Reservoir
Rock from Drill-Stem Tests. Soiety o# Petroleum ngineers. doi:0.8?B/-$8) .&. Timmerman C &.K. =an Poolen (68). Practical Use of Drill-Stem Tests. Te
>ournal o# <anadian Petroleum Tenology* ontreal* (pp. 8-;0).
) >.D. "redeoe#t* (/4). The Drill-Stem test: The Petroleum Industrys Dee!-"ell
Pum!in# Tests. Publised by te %.S. $eologial Survey.
;) >.P. Dolan C et.al (46). S!ecial A!!lication of Drill-Stem Test Pressure Data.
Petroleum Transations* A+* vol. 80* (pp. ?-8;).
4) . S. 1aymond C @.E. Ee##ler* (800/). $il and %as Production in &ontechnical
'an#ua#e( Penn @ell <orporation
/) N.>. &yne (808). &ontechnical %uide of Petroleum %eolo#y) *+!loration) Drillin# and
Production. Tird dition* Penn @ell <orporation.
6) 1. $rant C &. $ill (4). Ho" to Increase the Relia,ility of your $!en Hole Drill-
Stem Test Analyses( Te petroleum soiety o# <+.
?) 1.S. <ristie (n.d). Use of Recordin# Pressure %a#es in Drill-Stem Tests. Drilling
Pratie* (pp. ?-8).
) @. . "la2 (4/). A Revie" of Drill-Stem Testin# Techniues and Analysis. Soiety o#
Petroleum ngineers. doi:0.8?B4?-$
) ttp:BBpetro!i2i.orgBPa2ers
8) ttp:BBglossary.oil#ield.slb.om
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0nline sources?@ %nited States Department o# Eabor:
ttps:BB!!!.osa.govBSET<BetoolsBoilandgasB!ellFompletionB!ellFompletion.tml