NONSEISMICEXPLORATIONMETHODS A O iMETHODS:AnOverview

DjediS.WidartoSr.Geoscientist,EPTechnologyCenter

UpstreamDirectoratePTPERTAMINA,JAKARTA,

GEOPHYSICS: GEOPHYSICS:Thestudyoftheearthbyquantitativephysicalmethods,especiallybyseismicreflectionandrefraction,gravity,magnetic,electrical,electromagnetic and radioactivity methods (Sheriff 1999)electromagnetic,andradioactivitymethods(Sheriff,1999).

EXPLORATIONGEOPHYSICS/GEOPHYSICALPROSPECTING//APPLIEDGEOPHYSICS:Makingandinterpretingmeasurementsofphysicalpropertiesoftheearthtodeterminesubsurfaceconditions,usuallywithaneconomicyobjective,e.g.,discoveryoffuelormineraldeposits.Propertiesmeasuredincludeseismic,gravity,magnetic,electric,andtemperature(Sheriff,1999).

PETROLEUMGEOPHYSICS:Making and interpreting measurements of physical properties of theMakingandinterpretingmeasurementsofphysicalpropertiesoftheearthtodeterminesubsurfaceconditionsrelatedtohydrocarbon.

Geophysical MethodsGeophysicalMethodsSurfaceMethods

Seismic Methods :BoreholeMethods

In Hole ProceduresSeismicMethods: Seismicreflectionmethods Surfacewave(refraction)methods

Potential Field Methods :

InHoleProcedures

CrossHoleProceduresPotentialFieldMethods:

Gravity&magneticElectricalMethods

Resistivitymethods

SurfacetoBoreholeProcedures: Velocitysurveys

Vertical seismic profiling Selfpotential Misealamassemethods Inducedpolarization

Electromagnetic Methods

Verticalseismicprofiling

LoggingTechniques: ElectricalmethodsElectromagneticMethods

Magnetotelluricmethods Timedomainelectromagneticmethods Groundpenetratingradar

Acousticlogging Nuclearlogging

FlowloggingOther methods of logging Verylowfrequencymethods

SeismoelectricmethodNuclearMethods

N l ti (NMR)

Othermethodsoflogging

Nuclearmagneticresonance(NMR)method

Geophysical Methods Techniquesapplyingphysicallaws(ortheory)tothestudyofthe

solidEarth,

GeophysicalMethods

, Estimationofsubsurfacephysicalpropertydistributionbymeasuring

relevantparameters:

Method Measured RockProperty

SEISMICS Travel time & amplitude Elastic moduli (density &SEISMICS Traveltime&amplitude Elasticmoduli(density&velocity)

GRAVITY Variationingravitationalfield Density

MAGNETICS Variationinmagneticfield Magneticsusceptibility

ELECTRICAL/ELECTROMAGNETICS

Specificresistivity ElectricalconductivityELECTROMAGNETICS

GPR Traveltime Dielectricconstant

NUCLEAR Variationinnaturalradioactivity Nucleardecay

Seismic Methods

Themethodprovidesusahighresolutionimage,comparedwithit d ti f th b f f th E th

SeismicMethods

gravityandmagnetic,ofthesubsurfaceoftheEarth,

The purpose of the method is to reduce risk In the search for Thepurposeofthemethodistoreducerisk.Inthesearchforpetroleum,seismicimagingreducesrisk ofmanykinds drillingdryholes,drillingmarginalwells,under andoverestimatingreserves.Seismicinformationisagoodinterpolatorbetweenwells.Ittransferthedetailedinformationobtainedatwelllocationstotheareabetween wellsbetweenwells,

Expensiveandcomplicatedoperation(3D/4D)p p p ( / )

Magnetic Method

ThemethodsensestheEarthsmagneticfield.Magneticanomalyisd b tit t t i ti

MagneticMethod

causedbymagnetitecontentvariations,

Themethod,inparticular,effectivelydelineatesbasementfaultblocksandlocatesintrusivebodiesthroughtheuseandinterpretationofmagneticresidualmapsandprofiles,

Basementlithologicchangesandtheresultingmagneticsusceptibilitychangesfromblocktoblockallowustomapthebasement fault block pattern and to use this information inbasementfaultblockpatternandtousethisinformationinimportantnewwaysforfindinghydrocarbon,

Fastandinexpensivetool

Gravity Method

ThemethodsensestheEarthslateraldensityvariation.Gravityt ff t d b h i k d it

GravityMethod

measurementsareaffectedbychangesinrockdensity,

The method surface and subsurface surveys are effective in Themethod,surfaceandsubsurfacesurveys,areeffectiveinlocatingfaultsandgeologicstructurewithdensitycontraststotheirsurrounding,

Theboreholegravitymeterhasbroadapplication,fromlocatingi i ild h h i i ld ll i i fl idporosityinwildcatsorthroughcasinginoldwellstomonitoringfluid

changesinproductionreservoirs,

Fastandinexpensivetool.

Electromagnetic Method (MT)

Themethodsensesnatural /controlledsource electromagneticfieldi ti i ti f d i

ElectromagneticMethod(MT)

variationintimeorfrequencydomain,

The method cant provide the resolution of seismic surveys it is less Themethodcan tprovidetheresolutionofseismicsurveys,itislessexpensiveandmoreimportantly,canbeusedinplaceswhereseismicisimpracticalorgivespoorresults.

Relativelyfastandinexpensivetomoderatecost.

GRAVITY METHODGRAVITYMETHOD

Gravity & its Units of Measurement 1Gravity&itsUnitsofMeasurement,1

Gravity the acceleration on a unit mass Gravity theaccelerationonaunitmass ObjectsfalltoEarthwithanaccelerationofabout980cm/s2

/ 2 Theunitcentimeterpersecondpersecond(cm/s2)=Gal

Ingravityexploration theaccelerationofgravityisfundamentalquantity measured w/ the basic unit is mGal (milli Gal)quantitymeasured,w/thebasicunitismGal(milliGal)

TheaccelerationofabodyneartheEarthssurfaceisabout980,000mGalmGal

Forboreholegravity amicrogalisusedasthebasicunit,w/1Gal=103 mGal

Gravity & its Units of Measurement 2

InSystemeInternationaldUnites(SI),theunitofgravity(acceleration)

Gravity&itsUnitsofMeasurement,2

InSystemeInternationald Unites(SI),theunitofgravity(acceleration)

isms2

1ms2 =106 ms2=109 nms2 AfterGalileo:1Gal=1cms2 =102 ms2 (SI)

Gravityanomaly:mGal (in exploration) 1 mGal = 103 GalmGal(inexploration) 1mGal=10 Gal Gal(4Dsurveyforreservoirmonitoring) 1Gal=103 mGal=106 Gal = 108 ms2 (SI) it is wellknown as microgravity survey10 Gal=10 ms (SI) itiswell knownasmicrogravitysurvey

1Galingravityisproportionalto1mmin1000km

A Historical PerspectiveAHistoricalPerspective

1590 Galileo Galilei free fall experiment 1590:GalileoGalilei freefallexperiment 1687:IsaacNewton NewtonLaw,establishmentoftheoretical

foundationfoundation

18th&19thcentury:

developmentofpendulumapparatus

firstglobalapplicationingeophysics

1928:

Vening Meinez shipborn / marine gravity survey VeningMeinez shipborn/marinegravitysurvey Firstoildiscovery(NastDome,Texas)usingEotvostorsionbalance

gravimeterg

A Historical PerspectiveA Historical Perspective

1932 : Pendulum gravimeter (Cleveland oil field Texas) 1932 : Pendulum gravimeter (Cleveland oil field, Texas) 1932-1935 : Gravimeter with 0.1 mGal accuracy 1940 : Gravimeter improvements by Worden and

LaCoste & Romberg

What is Gravity? Gravity gayaberat (istilah/padanandalamBahasaIndonesia)

WhatisGravity?y g y

Gravis heavy(berat) Gravimetrymeasurementofgravity

NewtonLaw,magnitudeofthegravitationalforceF betweentwopointmasses:

m1

rF

221

)(mm

GF rr

F

2)( rr

whereG=universalgravitationalconstant

m2=6.67x1011 Nm2/kg

m1,m2 =masses1and2,respectively

r = distance between center of massesr=distancebetweencenterofmasses

What is Gravity? Themagnitudeofgravityaccelerationorattractiona1 onm1 :

WhatisGravity?

22

221

1

GmmGmFa 2

12

11 rmrm

a

m1Note that a1 is independent of m1

rF

Notethata1 isindependentofm1.

Theaccelerationvector isr

F32

rGmrGma

m2

32 rrr

Theminus signindicatesthataccelerationdecreasesasrgincreases

What is Gravity? NewtonsUniversalGravitationalLaw:

WhatisGravity?

FirstNewtonsLaw force :

m1 221

)( rmm

GF r

rF

SecondNewtonsLawmotion :r

F2

E

RGM

gmgF m2

ER

EE VM

GravityVariationontheEarthsSurfacey

Th E th it l ti i ~983 000 000 G l TheEarthsgravityaccelerationis~983,000,000mGals Equatorradii>21kmthanthatofpolarradii,theirdifferentingravityis~5,000,000mGals Thegravitydifferentbetweenthehighestmountainanddeepestoceanis~3,000,000mGals Regionalgeologicalstructureis~100,000mGals Earthtideeffectis~300mGals

Microgravity contour map is 10 mGals Microgravitycontourmapis10mGals Gravitymeteraccuracyis1mGal

Geologic ApplicationGeologic Application

In gravity exploration density anomaly is a deviation from the corrected gravity values that would be produced by a uniform, layer-cake, subsurface geologic settinggeologic setting,

To produce a measurable gravity anomaly, there must be:

A lateral density contrast between the geologic body of interest and the surrounding rocks, and

A favorable relationship between the gravity station locations and the geometry (including the depth) of the geologic body of and the geometry (including the depth) of the geologic body of interest.

Gravity Instruments & Type ofGravityInstruments&TypeofMeasurement

LaCoste&Romberg Scintrex Worden Gravity meter WordenGravitymeter

Relativemeasurementb l Absolutegravitymeasurement

Gravity Acquisition ProcedureGravityAcquisitionProcedure InstrumentalCalibration,fromlow tohighelevationv.v.

bl h h d d b

Production Line

BaseStationEstablishment,tyingtotheneareststandardbasestation,i.e.DG0inBandung

AM PMProductionLineAM PM

B S i

AM PM

Measuredquantity: Observedgravityvalue(mGal)

BaseStation

Position(WGS84)&elevation,obtainedbydifferentialGPS/Totalstation