09:29 *Course AimsThis course explains the major techniques for formation evaluation, covering the principles by which each works, the information obtained, and the reliability of that information.

Well logs are used to determine lithology, porosity, fluid content and type, enabling an assessment of hydrocarbons in place.

09:29 *Expected Outcomes 1Understand the fundamental rock properties that affect fluid storage and movement in the subsurface, and know how these are assessed to compute hydrocarbon volumes. Expected Outcomes 2Familiarisation with the procedures for downhole logging by wireline and by measurement-while-drilling; able to: Describe the practical steps involved and the procedures for gathering data; Discuss the limitations and uncertainties inherent to each approach; environment, and illustrate how these may impact logging reliability and resolution; Explain the causes, and significance to logging, of drilling-mud invasion; Use the caliper log to assess hole condition;

09:29 *Expected Outcomes 3For each of the standard downhole logging tools, able to describe the fundamental physical principles of operation, resolution, and uncertainties, and summarise potential applications: Electrical resistivity logs, in mud based on oil, brine or fresh water;Gamma Ray, Density and Neutron logsAcoustic or Sonic logs Borehole Imaging NMR loggingPressure Testing and Fluid Sampling

09:29 *Expected Outcomes 4Able to determine lithology by integrated analysis of a standard suite of logs. Able to identify hydrocarbon bearing zones, distinguish gas from oil, and calculate in-situ hydrocarbons by integrated analysis of a standard log suite, including: Assessment of fluid types and densities from pressure measurements; Assignment of fluid contacts from analysis of pressure data; Determination of porosity, with selection of optimum method; Calculation of shale volume (Vsh) and selection of pay intervals; Calculation of oil saturation from resistivity logs using standard Archie formulae and measurement of water resistivity; Estimate moveable oil fraction by analysis of the zone of mud invasion.

09:29 *SP The Simplest LogvSP (Spontaneous Potential)

Recording ofNatural VoltagevsDepth

09:29 *Todays Wireline CombinationTypical Diameter 3.5-4Slim tools 2 - 3Sensors depth delayed to output all on same depth

09:29 *LWD Hexacombo

09:29 *MWDMWD comprisesDownhole telemetry and sensor systemMud pulse transmission Surface receiver decoding/display/ archiveDepthDrill line encoderMeasurements in timeRegular TIME sampling5sec, 10sec, 20secBHA Diameters4 6 Bit6 8.5 Bit8 12.25 Bit9 Large

MWD crew required continuously while drilling

Basic Data DifferencesMWDRecorded Down

Time sampledResolution depends on ROP

while drilling

Memory - full dataset

Sensors fixed in drill collar

Recorded before full invasion

WirelineRecorded Up

Depth sampledSurface controlledHigh resolution possibleafter drilling

Future Memory options

Sensors positioned as required

Recorded after invasion

09:29 *

Environmental Effects Resistivity logs have large environmental effects due to their large volume of investigation

Invasion Shoulder Bed Effects Thin Bed (Resolution)

09:29 *Shoulder Beds Vertical EffectActual Measurement

INVASIONImpermeablePermeableSandDuring and after drilling fluid from the mud (mud filtrate) is forced into the formation.

This is called InvasionThis continues until the pore space on the borehole wall is sealed by a build up of particles (mud cake)

INVASIONImpermeableInvasion Profile:MUDMUD CAKEFLUSHED ZONETRANSITION/INVADED ZONEUNINVADED ZONE/ TRUE FORMATIONPermeableSand

09:29 * Basic Log Interpretation

ShalePorosity, Permeability, CoreX-plots, Minerals, Matrix ResponsesSaturations, Factors a/m/n Quicklook Shortcuts

09:29 *Environmental correctionsBefore doing any log interpretation ensure that all data is corrected for:Borehole effectsThin bedsTool artifactsAdditional effects due to Mineralogy and pore fluid content are part of the interpretation and are accounted for once minerals and fluid content is known

Gamma RayMeasures Natural radioactivity09:29 *Main radioactive elements:PotassiumThoriumUraniumK and TH mostly in shales U from other sources

Primary use a a basic lithology indicator (sand/shale)

09:29 *Gamma Ray-Because rock contain various amount of unstable elements.-Radioactive element tends to concentrate in shale (Chemically reactive).--

09:29 *Natural Occurring Radioactive Minerals Salts in solution that settle within sand or carbonate pore spacesSalts in solution that settle onto organic marine shaleMarine feldspar, micas, glauconite, etc. that result from radioactive salts dissolved in waterSmall percentages of clay dispersed in a sand can cause significant increases in radiation

High GR does not always indicatehigh clay/shale content

09:29 *Shale volume1) Pick a clean GR responseGR 90 -> Vsh = 55%2) Pick a shale GR response3) Scale between

09:29 *DensityUses gamma rays to measure bulk formation density in g/ccEach rock matrix (Lithology) has a characteristic density between 2-3 g/ccFluids generally have a lower density between 0.2 - 1.0 g/ccUsed to define porosity and lithology

Density1.952.95G/cc

09:29 *Density Porosity1.952.95G/ccShaleSandShaleShaleSandSand density = 2.65Water density = 1.0Density 2.15 -> Porosity = 30%

09:29 *NeutronUses Neutrons to measure apparent Hydrogen content of formationMost Hydrogen is in fluidsLog calibrated and scaled in Limestone porosity unitsOther rock types require small corrections to porositiesSand + 2-5%Dolomite 2-5%With Density -> gas indicatorDry clay may also have a high neutron response

09:29 *Neutron45-15Porosity

09:29 *Density and Neutron45-15Neutron1.952.95DensityGasLiquid

09:29 *Density and Neutron45-15Neutron1.952.95Density

09:29 *Density and Neutron Limestone scales45-15Neutron1.952.95DensityWater filled Limestone?Oil filled Dolomite?Shaly Sand?

09:29 *Density and Neutron Limestone scales45-15Neutron1.952.95DensityWater filled sand?Oil filled Limestone?Gas filled Dolomite?Gas filled shaly sand?

09:29 *Density and Neutron Limestone scales45-15Neutron1.952.95DensityShale?Water filled Dolomite?

09:29 *AcousticMeasures speed of sound in the formation in microseconds/ftEach rock type (lithology) has a characteristic DT 40-70 us/ft.Fluids have a much slower DT of 180-230 us/ft, gas even slower. Used to determine porosity and lithology.Links seismic depth in time to log depth in ft or m.

09:29 *Acoustic14040us/ft

09:29 *Acoustic Porosity Sand DT = 55Water DT = 189DT 80 -> Porosity = 18.5%

09:29 *ResistivityMeasures electrical conductivity due to:-Water in the pore spaceBound water in shalesInduction logs for oil or fresh water resistive mud systems.Laterologs for salty conductive mud systems.

Different depths show Invasion.Hydrocarbons are non-conducting

09:29 *Archie Clean Sand Equation

09:29 *ResistivitySw = water saturationRw = formation water resistivityRt = formation resistivity = porositya, m, n are constants(default a=1, m=2, n=2)Rw = .02 (at reservoir temp) Sw = 100%Sw = 3%Example porosity = .26 (26%)

09:29 *CrossplotsCrossplots are a simple method to combine sensor responses to extract additional information.PorosityLithologyShale volumeGas indicationsBad data

NOTE: 2 measurements in - 2 properties out.Fundamental part of computer programsEssential to understand what a computer is doing

09:29 *Density/Neutron crossplot

09:29 *SummaryLook at everything together!!

09:29 *Very Quick Log analysis WetAll curves move togetherTightShale opposite othersHydrocarbonResistivity opposite others

NB OR Fresh waterShalePorosityResistivity

09:29 * ImagesLow amplitudeHigh amplitudeLWD ResistivityWirelineLWD DensityLWD GRCoreAdvance Logging Method

09:29 *

END OF SESSION 09:29 *

***********************************