Kelessidis Ergin Drill Blast Nov 4-7-2010

8/8/2019 Kelessidis Ergin Drill Blast Nov 4-7-2010

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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

Kelessidis Ergin Drill Blast Nov 4-7-2010

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