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OilfieldTechnology
February
2014
excessrequired isminimised,or isascloseto0%aspossible, isthrough
properdrillingtechniques;however,thismaynotbepossible inall
formations.Thereforetheabilityto increasethepumprate isrequired in
somecases.
Thisrequired increasedpumpratehasbeenmanagedafewdi erent
wayswithinthe industry:
Increasethepumpingabilityofasingleunit.
Usemultipleunitsduringanoperation.
Reviewmethodsto increasedisplacementefficiencythrough
differenttechnologies.
It is importanttoconsiderhowthesetechnologieswillcontinueto
develop inthefutureasthewellboreconfigurationcontinuestochange
inane orttomaximiseproduction.E&Pcompaniesare investigating
di erentconfigurationsthatsuittheirspecificrequirements. Ifthe
wellboresizescontinuetogrow,thesechallengeswillbecomemore
prevalent.Anexampleofthis isshown inFigure3,whereeven larger
casingsizesthanwhatmightcommonlybeusedtodayareexamined.
Figure3showsthat inawellboreconfigurationwhere339.7mm
(13
⅜
in.)casinganda444.5mm(17
½
in.)openholeareused,apump
rateof5.16m
3
/min. (32.5bbl/min.) isrequiredtoachieve80m/min.
(262.5 /min.)when0%excess isassumed.When150%excess is
taken intoaccountforthesamewellboreconfiguration,thepumprate
increasesto12.91m
3
/min. (81.2bbl/min.).
Whenapproachingratesofthismagnitude,therearemanynew
challengesthatarisefortheservicecompany.These include,butarenot
limitedto,thefollowing:
Surfacetreating ironpipevelocityrestrictions (increasederosion).
Horsepowerrequirementstoachievepumprates.
Spaceavailabilityon location forrequiredequipment.
Otherchallenges
OtherchallengesariseforboththeservicecompanyandE&Pcompany.
Oneofthesechallenges isthe increasetotheECDthatthewellbore
experiencesduringtheoperation.Astherate increasesforagiven
wellboreconfiguration,theECDalso increases.Anexampleofhowthese
valuescanchange isshown inFigure4.
InFigure4,theholeandcasingsizesare311.2mm(12
¼
in.),and
244.5mm(9
⅝
in.)respectively.Thegraphshowsthatforeachofthe
threeexcessvaluesassumed,theECD increaseswithan increase inpump
rate. Italso illustratesthatthemostdramatic increaseoccurswhere0%
excess isassumed.Theothertwoexamplesshowamuchmoresubtle
increase inECD.
An increase intheECDcan increasethe likelihoodofbreaking
downtheformation,or inducing losses, iftherockcannotwithstand
theforcesexertedon it. Inmanyoperations,anallowableECD isknown
andtheservicecompanyplanstheoperation inordertomaintainan
agreed-uponvalue. InanattempttomaintaintheallowableECD,the
servicecompanymaybeforcedtoreducetherecommendedpumprates
and/ormodifythecementslurrytomake iteasiertopump.These
modifications includedi erentmethodstoreducetheviscosityofthe
cementslurry.
Increasingannularvelocityhasprovene ectivefor improving
cementbond logs inmanyoftheSAGDareaswhere ithasbeenutilised.
However,therearealsoexampleswhereahighpumpratehasnotbeen
ase ectiveasexpected,both inSAGDwellsandotherareas.Forexample,
higherrateswere introducedasapossiblesolution indealingwithsurface
casingventflows(SCVFs) intheLloydminsterareaofWesternCanada.
SCVFsaredefinedasgascomingtosurfacefromthegroundandbetween
thesurfacecasingandtheproductionstring.TheoccurrenceofanSCVF
indicatesthedesiredzonal isolationwasnotsuccessfullyachieved.
Sincehighratepumping is intendedto improvezonal isolation, itwas
consideredasapossiblesolution inthisareawhereSCVFsarecommon.
Table1. Comparisonof conventional andSAGDwell requiredpump rates
Conventionalwell
SAGDwell
Intermediatehole:
Intermediatehole:
Openhole 222.3mm (8
¾
in.)
Openhole 311.2mm (12
¼
in.)
Casing
117.8mm (7 in.)
Casing
244.5mm (9
⅝
in.)
Pump rate to
achieve80m/min.
(262.5 ft/min.)
1.1m
3
/min.
(6.9bbl/min.)
Pump rate to
achieve80m/min.
(262.5 ft/min.)
2.3m
3
/min.
(14.5bbl./
min.)
Table2. Pump ratesandexcess
Pump rate
Excess (%)
Annularvelocity
m
3
/min.
bbl/min.
m/min.
ft/min.
1
63
0
34.35
112.7
75
19.63
64.4
150
13.74
45.1
1.8
11.3
0
61.83
202.9
75
35.33
115.9
150
24.73
81.1
2
12.6
0
68.7
225.4
75
39.26
128.8
150
27.48
90.2
2.2
13.8
0
75.57
247.9
75
43.18
141.7
150
30.23
99.2
2.4
15.1
0
82.44
270.5
75
47.11
154.6
150
32.98
108.2
Figure2.
Gaugeholeandexcess.
Figure1.
Pumprateandzonal isolation.
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