kelessidis ergin drill blast nov 4-7-2010
TRANSCRIPT
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Drilling Fluid Advances forCore Drilling
Assoc. Prof. Vassilios C. Kelessidis,Technical University of Crete&
Prof. Hasan Ergin
Istanbul Technical University
Ankara, 4-6 November, 2010
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Summary of presentation
Issues for core drilling & drilling fluids
Coring and drilling fluids
Advances in coring drilling fluids
Drilling fluid problems while coring
Summary
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Geological controls during coring
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Rock mechanics - Stratigraphy
The higher hardness lower penetration rate BUT
better core recoveries
The lower hardness, higher penetration rate, BUT
poor core recovery in general
Startigraphy, bedding planes, foliations,
anisotropy,.. affect orientation of drill direction
Fractures, permeable formationsLOSS
CIRCULATION,borehole stability, core recovery
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Rock mass - Weathering
Rock characteristics, texture and grain size, jointcharacteristics, density and pattern of joints
Finer grains, dense texture, fewer joints High
core recovery lower penetration rates
Use polymer drilling fluids increase penetration
rates, decrease wear of bit
Weathering decomposes original composition of
rock, reduces compressive strength incompletecore recoveries
Use double-tube core barrels with bottom
discharge and polymers in drilling fluid in soft
weathered rocks to improve core recovery
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Minerals Ground water
Quartz minerals, lower penetration but
better recoveries
Soft minerals (gypsum, shale, dolomite),
not good core recoveries
Reason, the stress distribution around the
bit, with stress concentration in soft rocks
Ground water influx causes washing of
cores, poor recovery, potential blowout in
overpressured formations
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Information gathering job design
Prior historyGeological mapping outcrops
Geophysical investigation
Good penetration rate Core recoveryDefine optimum rotation rates
Minimum vibrationBest recovery
Proper design of drilling fluid program
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Design of coring drilling fluid
AIMHighest recovery, minimal cost, safely
DEPENDS
Ability of local crew
Local conditions & material availability
Purpose of coring no thinners, lubricants, corrosion
inhibitors IF special coring (e.g.permability, wettability, saturations
levels)
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Drilling fluid properties
DENSITYNecessary, if overpressured
formations
It occurs infrequently, but kicks mayoccur, one should be aware of this
Water, most of the time adequate
if higher density, add bentonite,which gives also rheology
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RHEOLOGY
Need adequate viscosity to transportcuttings to surface
Marsh funnel, one shear rate
water = 26 s Coring fluids ~ 35 50 s
Direct indicating viscometer, two shearrates
Bingham plastic, Plastic Viscosity & YieldPoint
Relate values to experience in the area
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Fluid loss control
AIMCreate filter cake across permeable
formations or core
Minimize fluid invasion
MEANS
Chemicals, clays, polymers (bentonite-polymer gels)
EFFECTS
Alteration geochemical characteristics ofcore
Pay assessment more difficult
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Fluid invasion areas
1. Ahead of the bit
2. Bit face and bitthroat
3. Inner barrel
IfR
OP low, may havesufficient time forinvasion safe drillingpractices
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Fluid invasion polymer additives
Xanthin biopolymer, gave Fannreading of 10, API fluid loss of 10-15ml/30min
Excellent core recovery, satisfactorypenetration rates
Non-ionic polymer (Polyethyleneoxide)
in small quantities, good results in phosphate rock
Trial and error procedure, dependingon the specificities of the area
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Advances in coring systems
Gel-Coring system
Preserves corewettability
Inner barrel containsnon-invading gel
Low fluid loss and high
viscosity~ 80 l of gel
Covers the core
keeps it intact
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Deep coring systems
Coring at 4000 m for goldExtreme care for drilling fluids, low solids,
minimal invasion
Add chemicals for pH control, caving, losscirculation
Volumes significant, cost is a big issue, maybe up to 5% of total coring services
These only if all goes well, IF problems(many times drilling fluid related, ~25%),big cost issue !
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Drilling fluid problems while coring
LACK OF QUALITY STANDARDS aim for very good core recovery
What does it mean?
If 100% recovery OKRQD Index
What about if 80% recovery?
How different from 70% recovery?NO QUANTITIVE INDICATOR EXISTSAFTERSO MANY YEARS!!
Industry should work towards defining
better standard
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Loss circulation
Significant drilling fluid related problemDetrimental to coring program
ISSUES
Detection, cause determination, cure If 100%, no returns, easily identifiable
If partial loss, how to detect it?
CAUS
ES
& CUR
EOverpressured formations density
Permeable and fracture formations losscirculation material
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Full flow monitoring
Use flow meters forIn & OUT flow
Electromagnetic
meters, handlesludges
Conductive fluids
Flow in suctionside, avoid highpressures
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Conclusions-1
Coring is expensive sound engineeringpractices design of sound drilling fluid
program
A sound core no drilling fluid invasion
In demanding applications, additives to
water, bentonite and polymers, minimize
invasion, add to cost, aim for cost
effective solutions
Prior experience in the area
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Conslusions-2
In critical situations, advanced andmore costly coring systems
Core-gel systems provide better
coresIf loss circulation is encountered be
prepared, monitoring flow in and flow
outMonitoring flow and pressure
parameters while drilling guarantee
safe drilling environment