NON‐SEISMIC EXPLORATION METHODS A O i METHODS: An Overview Djedi S. Widarto Sr. Geoscientist, EP Technology Center Upstream Directorate PT PERTAMINA, JAKARTA
Oct 01, 2015
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&litude 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