38 |
OilfieldTechnology
February
2014
Thekeystatisticsof thewellsdrilledareshown inTable1.
Overall, thecampaigndemonstrated that thePOLARIS tool
is capableof directional andhorizontal drillingofwellswithhole
sizes ranging from6.25 in. to8.5 in., usingmudandanairmist as
adrilling fluid,whilst showcasing theabilityof itsAcrobat
gyro
system. This is the first time that a solid-stategyrohasbeenused
fordirectionalmeasurementwhiledrilling, providing reliabledata
at all inclinations (vertical, horizontal andduring thebuild section),
allowingorientation tobecarriedout accurately, evenwhile in the
casing.
Italsoprovidesevidenceofoperationalbenefits that
make itpossible foroperators todrillwells inshallow reserves
cost‑effectively,withminimal environmental impact.Precisewell
planscanbe followedandwellpathscanbeoptimisedbykicking
offearly (with thegyrostillwithin thecasing) reducingbuild rates,
making iteasier to runcasing.
Thesuccessof thiscampaigncamedown to threekey factors: It
wascarriedoutbyanexperiencedCTD teamwith thePOLARIS tool
andhybriddrilling rig. Thehybrid rig isacritical element.Hybrid
drilling rigsarehighlyadaptable, capableof runningCTand jointed
pipe, inaddition to runningandpullingcasing.Due to theiradaptable
nature,CTDoperationscanbecarriedoutwithasingle rig, greatly
reducing timeandcost. StudiesaboutCTD indicate thatdrilling times
are reducedby30% to60%, incomparisonwithoperationscarried
outwithstandard jointedpipedrilling rigs.
WhendirectionalCTDisbest
Coiled tubingdrilling iswidely recognisedas thebestway todrill
underbalancedwithina reservoir. Add to that theability todrill
directionallywith largerholesizesand thecapabilityenvelopestarts
toexpand.Hybrid rigscandrillwithbothcoil and jointedpipe, aswell
as runcasing, furtherenhancingefficiency levels. Fieldspreviously
deemed tobe tooexpensive toexploit cannowbeaccessedmore
economicallyandefficiently.
CTD isbestused indevelopmentand re-entryprogrammeswhere
thegeologyand reservoir conditionsarestraightforwardand familiar.
CTD isnotwell suited towildcatdrillingprojectsorone-offprojects
where thespeedandefficiencybenefitsdonothave time tocome
intoplay inasignificantway.
Phase1of theNiobrara campaign capitalisedon thePOLARIS
tool’s ability to target aprecise locationwithin the reservoir
without theneed toposition the rigdirectlyabove the target. In
Phase2, AnTechutiliseddirectional CTD toair-drill a reservoir
thatwas unable toeasily support a liquid column. This is an
ideal exampleof anapplicationwhereCTDhas anadvantage.
Alternativemethodswouldhave requiredagreat deal of drilling to
be carriedout.
Aswell as theapplications illustratedby theNiobraracampaign,
directionalCTD is recommended for the following:
Ì
Ì
Drilling in–or incloseproximity to–busy residential,
commercial or agricultural areas that necessitateaminimal
environmental footprint.
Ì
Ì
Drilling severalwells froma singlepadusing thegyrocapability
toavoidcollidingwithotherwells.
Ì
Ì
Drillingmultilateral branches from themainwellbore.
Ì
Ì
Drilling in sensitive reservoirs thatwould suffer excessive skin
damagedue tooverbalanceddrilling.
Thefuture
Whatdoes the futurehold fordirectionalCTD?Thesuccessof the
Niobraraprogrammedemonstrates that thePOLARIS tool –hybrid rig
drillingcombinationcanhelpmeetmarketdemands foraneconomic
andefficient solution. Thecurrent lownatural gaspriceshave
affectedactivity in thisarea,but therearestillmanydepletedoilfields
that couldbenefit from this typeof intervention.
CTDhasgained strongacceptanceover thepast 20years in
particular areasof theworld. Theopportunityhasnowcome to
broadenmarket acceptance; aprocess that canbe facilitatedby the
availabilityof newCTD technology.
Figure3.
TheAnTechteamputsthefinaltouchesonthecablehead
assembly.
Table1.Well data table
Well 1 Well 2 Well 3 Well 4 Well 5
Depthof casing shoe (ft)
500
325
350
365
336
Measureddepth (ft)
3030 1800 1467 2270 1884
Truevertical depth (ft)
2918 1520 1101 1090 1096
Maximumbuild rate (˚/100 ft)
13.5
19.6
15.3
15.8
15.9
Hole size (in.)
6.25
6.25
6.5
8.5 (intermediate);
6.25 (horizontal)
Horizontal offset (ft)
633
785
727
1452 1103
Dataproducedduring the five-wellNiobraradrillingprogramme indicates that awide
rangeofwells canbeefficientlydrilledwith thePOLARIS tool.
Figure4.
Well5drillingprofile.
VerticalSection(ft)
E-W(ft)
0
0
500
1000
500
1000
NS(ft)
-1000
-500
0
500
0
-500
-1000
-1500
WellPlan
SectionView-Planned
SectionView-AsDrilled
Asdrilled
PlanView
TVD(ft)
