ROCK MAGNETISM AND RESERVOIR … - rock magnetism and... 1 FUGRO ROBERTSON LIMITED ROCK MAGNETISM...

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FUGRO ROBERTSON LIMITEDFUGRO ROBERTSON LIMITED

ROCK MAGNETISM ANDRESERVOIR CHARACTERISATION

AFES seminar,March 2007

Presented by: Ernie HailwoodManager, Core Magnetics UnitFugro Robertson Ltd,Sedbergh, UK

Outline of talk:

•Summary of applications.

•Background information on rock magnetism.

•Introduce the three techniques of particularrelevance and give examples of applications.

•Outline recent developments.

APPLICATIONS OF ROCK MAGNETISM INAPPLICATIONS OF ROCK MAGNETISM INRESERVOIR CHARACTERISATIONRESERVOIR CHARACTERISATION

•Interpreting aeromagnetic survey data

APPLICATIONS OF ROCK MAGNETISM INAPPLICATIONS OF ROCK MAGNETISM INRESERVOIR CHARACTERISATIONRESERVOIR CHARACTERISATION

APPLICATIONS OF ROCK MAGNETISMAPPLICATIONS OF ROCK MAGNETISMIN RESERVOIR CHARACTERISATIONIN RESERVOIR CHARACTERISATION

•Geological correlation and dating, using magneticstratigraphy.

•Paleomagnetic core re-orientation

•Interpreting aeromagnetic survey data.

•Paleomagnetic core re-orientation.

•Anisotropy of magnetic susceptibility (AMS):applications for determining reservoir sand sourcedirections and dispersal pathways.

•The Magpore technique for determining 3-Dpermeability anisotropy from pore fabricmeasurements.

•Using anisotropy of magnetic susceptibility (AMS)to determine source directions and dispersalpathways of reservoir sands.

•The Magpore technique for determining 3-Dpermeability anisotropy from pore fabricmeasurements.

•Microfracture characterisation from Magporemeasurements.

These two types of magnetism co-exist inrocks and are carried by differentpopulations of magnetic mineral grains.

Induced magnetism (Ji)

Remanent magnetism (Jr)

SOME BASIC PRINCIPLES: TYPES OFSOME BASIC PRINCIPLES: TYPES OFMAGNETISM IN ROCKSMAGNETISM IN ROCKS

Produced by applying a magnetic field, F, to a rock

•Exists only in the presence of that field.

INDUCED MAGNETISM (INDUCED MAGNETISM (JJii))

•Exists only in the presence of the applied field.

•Its intensity (Ji) is related to the applied fieldstrength (F), via the magnetic susceptibility, k, where:

Ji = kF

•Principal source of Ji is relatively coarse-grained(multi-domain) magnetite.

Ji = kF

•Principal source of Ji is relatively coarse-grained(multi-domain) magnetite.

•k varies with direction within the rock and thisproperty (anisotropy of magnetic susceptibility, AMS)can be used to determine the grain fabric of theformation.

REMANENT MAGNETISM (REMANENT MAGNETISM (JrJr))

•Acquired by rocks during their formation and/orat other specific times in their history.

•Carried by relatively fine-grained magneticparticles (principally magnetite).

•Carried by relatively fine-grained (SD or PSD)magnetic particles (principally magnetite).

•Stable remanent magnetism can remainunchanged in rocks indefinitely (for periods ofhundreds of millions of years or more)

•Acquired by rocks during their formation(Primary) and/or at other specific times in theirhistory (Secondary).

•Carried by relatively fine-grained magneticparticles, principally magnetite.

•Can remain unchanged in rocks indefinitely (forperiods of hundreds of millions of years).

•Used in paleomagnetic core re-orientation,magnetostratigraphy, paleomagnetic dating, andtectonic rotation studies.

PRINCIPAL CARRIERS OF REMANENTPRINCIPAL CARRIERS OF REMANENTMAGNETISM IN SEDIMENTSMAGNETISM IN SEDIMENTS

•Detrital iron oxides and sulphides, particularly magnetite

•Magnetosomes, secreted by magnetotactic bacteria

Photomicrographs of magnetosomes:

Components ofComponents of remanentremanent magnetismmagnetism

1. Primary magnetism - acquired when the rock isfirst formed. Points to paleo-North.

2. Viscous remanent magnetism (VRM) - acquiredin the Recent geomagnetic field at the drill site.Points to present geographic North.

3. Spurious components related to drilling,plugging, core storage etc.

These components are separated from each other in thelaboratory by incremental demagnetisation, using thethermal and/or alternating field techniques

ALIGNING FORCES ON MAGNETIC MINERALALIGNING FORCES ON MAGNETIC MINERALGRAINS DURING DEPOSITIONGRAINS DURING DEPOSITION

1. Gravitational couple.Rotates long axes of elongate grainstowards the horizontal. Preferentiallyaffects large grains (>50m), ie Ji andAMS, rather than Jr

2. Hydraulic shear.Rotates long axes of elongate grainsparallel to shear (bottom currents).Preferentially affects large grains,ie Ji and AMS, rather than Jr

3. Geomagnetic field.Rotates grains to align Jr withmagnetic North. Preferentially affectssmall SD grains with strong Jr.

PALEOMAGNETIC CORE REPALEOMAGNETIC CORE RE--ORIENTATIONORIENTATION

Uses the viscousremanent magnetism(VRM) of sets of plugsamples to define thedirection of present-day North in the core.

Directional propertiesof the core (such asthe fracture shown)can then be referredto North.

Graphic displayof fractureorientationsrelative to N

Direction of Ndefined fromVRM of plugsamples

Measuredorientation ofvisible fractureplane in core

PALEOMAGNETIC CORE REPALEOMAGNETIC CORE RE--ORIENTATION:ORIENTATION:EXAMPLE OF FRACTURE ORIENTATION STUDYEXAMPLE OF FRACTURE ORIENTATION STUDY

N = 30 N = 30

Beforere-orientation

Afterre-orientation

Fracture orientation study, Cretaceous limestones, Venezuela

PALEOMAGNETIC CORE REPALEOMAGNETIC CORE RE--ORIENTATIONORIENTATION

Features of paleomagnetic re-orientation:

–No requirement for deploying a scribingshoe and orientation tool during coring.

–Typical accuracy is ±3°.–Can be used for whole-core or slabbed

half-cores.–Can be applied to freshly cut core or core

that has been stored for decades.–Can be applied to all rock types.–Fast turn-around time.

DETERMINING SANDSOURCE DIRECTIONS

FROM THE ANISOTROPYOF MAGNETIC

SUSCEPTIBILITY (AMS) OFPLUG SAMPLES

SAND SOURCE DIRECTIONS FROM AMS

SEDIMENT SOURCE & DISPERSAL DIRECTIONSSEDIMENT SOURCE & DISPERSAL DIRECTIONSFROM AMS/GRAIN FABRIC DETERMINATIONSFROM AMS/GRAIN FABRIC DETERMINATIONS

Fluid shear duringdeposition, alignsgrain long axes parallelwith fluid flow.

The 3-D grain fabriccan be determined fromanisotropy of magneticsusceptibility (AMS)measurements onsets of plug samples.

GRAIN FABRIC DETERMINATIONSGRAIN FABRIC DETERMINATIONSFROM AMSFROM AMS

• The AMS of an assemblageof grains is controlled by theirshape alignments.

• The maximum susceptibility,axis, Kmax, corresponds withthe preferred orientation of grainlong dimensions and theminimum susceptibility axis,Kmin, with that of their shortdimensions.

GRAIN IMBRICATIONS AND SEDIMENTGRAIN IMBRICATIONS AND SEDIMENTTRANSPORT DIRECTIONSTRANSPORT DIRECTIONS

MAGNETIC FABRIC STYLESMAGNETIC FABRIC STYLES

Laboratory depositionexperiments confirmthat Kmax axesaccurately definetransport directionsand that grainimbrications definethe sense oftransport.

Fluid-flowdirection

Deposition from a

flowing fluid in aflume tank

Kmax axis

Kmin axis

Each point represents the grain fabric of a single 25mm plug sample

COMPARISON OF TRANSPORT DIRECTIONSCOMPARISON OF TRANSPORT DIRECTIONSDETERMINED BY AMS AND SOLE STRUCTURESDETERMINED BY AMS AND SOLE STRUCTURES

Sediment transportdirections determinedfrom Kmax axes(red squares) agree withthose defined fromsedimentary structuressuch as sole marks(blue arrow).

GRAIN FABRIC & TRANSPORT DIRECTIONSGRAIN FABRIC & TRANSPORT DIRECTIONSIN A CHANNEL SAND RESERVOIRIN A CHANNEL SAND RESERVOIR

Kmax axes are widelydispersed beforepaleomagnetic re-orientation, but well-grouped after.

In this examplethe mean sedimenttransport direction istowards the SE

SEDIMENT SOURCE DIRECTIONS IN A MULTISEDIMENT SOURCE DIRECTIONS IN A MULTI--WELLWELLSTUDY OF THE BRITANNIA FIELD, NORTH SEA, UKSTUDY OF THE BRITANNIA FIELD, NORTH SEA, UK

Transport directions in individual wells (red bars)confirm that the sand was derived from pointsources to the North.

CHANNEL SINUOSITY ANDCHANNEL SINUOSITY ANDRESERVOIR QUALITYRESERVOIR QUALITY

High sinuosity systems tend to producecomplex sand isopachs with poor connectivity,whereas low sinuosity systems produce morecontinuous sands.

DETERMINING DEGREE OF SINUOSITYDETERMINING DEGREE OF SINUOSITYFROM THE DISPERSION OFFROM THE DISPERSION OF KmaxKmax AXESAXES

Meanchannelorientation.

Mean channelorientation(from seismic).

PERMEABILITYANISOTROPY

DETERMINATION BYTHE MAGPORE

METHOD

PERMEABILITY ANISOTROPY DETERMINATIONSPERMEABILITY ANISOTROPY DETERMINATIONSBYBY ““TRADITIONALTRADITIONAL””METHODSMETHODS

Directional permeability in the Bradford Third Sand,Pennsylvania.

Depths Perm (md)Samplesets

Symbols

PERMEABILITY ANISOTROPYPERMEABILITY ANISOTROPY

1000 ft

Magnetic orientation

Drill pipe

Direction of maximum permeability in the Bradford Third Sand.From Johnson & Breston (1951)

Other methods fordetermining 3D permeability

anisotropy

Typical consistency ofpermeability anisotropy

directions

Dependence of flow-path length ongrain fabric in an anisotropic granularmedium

DETERMINING PERMEABILITY ANISOTROPYDETERMINING PERMEABILITY ANISOTROPYBY THE MAGPORE METHODBY THE MAGPORE METHOD

Dependence ofreservoir fluid flowproperties onpermeability anisotropy

PORE FABRIC DETERMINATIONSPORE FABRIC DETERMINATIONSFROM ANISOTROPY OF MAGNETICFROM ANISOTROPY OF MAGNETIC

SUSCEPTIBILITY (AMS)SUSCEPTIBILITY (AMS)

- The AMS of anassemblage of poresis controlled by theirshape alignments.

- The maximumsusceptibility, Kmax,correspondswith the preferredorientation of porelong dimensions.

TESTING THE MAGPORE METHOD AGAINST DIRECTTESTING THE MAGPORE METHOD AGAINST DIRECTPERMEABILITY ANISOTROPY MEASUREMENTSPERMEABILITY ANISOTROPY MEASUREMENTS

MICROFRACTUREFABRIC ANDPOROSITY

CHARACTERISATIONBY THE MAGPORE

METHOD

CHARACTERISING MICROFRACTURECHARACTERISING MICROFRACTUREORIENTATION & POROSITY BY MAGPOREORIENTATION & POROSITY BY MAGPORE

LABORATORY CONFIRMATION OF MICROLABORATORY CONFIRMATION OF MICRO--FRACTURE CHARACTERISATION BY MAGPOREFRACTURE CHARACTERISATION BY MAGPORE

OPENING OF MICROFRACTURE NETWORKS AT LOWOPENING OF MICROFRACTURE NETWORKS AT LOWAPPLIED STRESSES, MONITORED BY MAGPOREAPPLIED STRESSES, MONITORED BY MAGPORE

COMPARISON BETWEEN MACROCOMPARISON BETWEEN MACRO-- ANDANDMICROFRACTURE ORIENTATIONSMICROFRACTURE ORIENTATIONS

Microfractures

Macrofractures

Comparison betweenvisible (macro-) fracture

and microfractureorientations in a

carbonate fracturereservoir

CONTACTSCONTACTS

Dr Ernie Hailwood.Fugro Robertson Ltd., Core Magnetics UnitThe Green, Frostrow LaneSedbergh, LA10 5JS, UK

Fugro Robertson Limited

address

www.fugro-robertson.comand www.coremagnetics.com

internet

directline +44 (0)15396 21442telephone

ernie.hailwood@fugro-robertson.comand info@fugro-robertson.com

e-mail

ACQUISITION OF PRIMARY DETRITALACQUISITION OF PRIMARY DETRITALREMANENT MAGNETISM BY SEDIMENTSREMANENT MAGNETISM BY SEDIMENTS

CORE RUNS (CORE RUNS (““SETSSETS””))

Fitting core pieces into “Runs”(intervals within which

all pieces have a common orientation)

PALEOMAGNETIC PLUGGING PROCEDUREPALEOMAGNETIC PLUGGING PROCEDURE

Drilling paleomagnetic plug samples with a non-magnetic plugging bit

MAGPOREMAGPORE

Ferrofluid saturation procedure

ROCK MAGNETISM AND RESERVOIR … - rock magnetism and... 1 FUGRO ROBERTSON LIMITED ROCK MAGNETISM...

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