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Logs : how to use them for QUALITIATIVE reservoir evaluation

Logs : how to use them for QUALITIATIVE reservoir evaluation. how to use logs for qualitative reservoir evaluation. Program : - Introduction/Objective Drilling / Mudlogging – A brief overview Depth and Datum reference

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Logs : how to use them for QUALITIATIVE reservoir evaluation

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  1. Logs : how to use them for QUALITIATIVE reservoirevaluation

  2. how to use logs for qualitative reservoirevaluation Program : - Introduction/Objective Drilling/Mudlogging – A briefoverview • Depth and Datumreference • Drilling/Mudlogging. Mandatory data for logs interpretation Logging Tools/Data acquisition • Tools – Principles (Brief or Optional) • Data acquisition – QualityControl Quick-look Methodology – « Understand » the well • Main steps of the Quick Look approach • Example #1: Sand/Shale environment Correction with Quantitative results • Example#2 : Carbonates environment Correction with Quantitative results • Conclusion/Main points MGU – 20th Mar. 2014

  3. Different types of rigs… …always the samemeasurements

  4. Whylogging acquisition (LWD or WL) Geological aspect: • Sedimentology • Structural Links withGeophysic (seismic) • Time Depth conversion • Petro elastic Model Reservoir aspect  Main subject of this 1 day course • Net to Gross • Porosity • Saturation MGU – 20th Mar. 2014

  5. GEOLOGICAL ASPECT Large scaleinterpretation (decametric to hectometric) Logs = a continuousoutcrop of severalthousandmetersthickness Logs for Explorationists – Pau– 10 – 14 June 2013

  6. WELL vs seismicrelationship Well to seismicTie Petro Elastic Model • ReservoirCharacterization • Fluidcharacterization • Fluid Substitution • Monitoring (4D) Logs for Explorationists – Pau– 10 – 14 June 2013

  7. ReferencesDepth/Datum MD : MeasureDepth/RT TVD : True Vertical Depth / RT TVDSS : True Vertical Depth / MSL (MeanSeaLevel) For all of them (MD, TVD,…) « Driller » and « Logger » depth are available Wire Line depthis the reference MGU – 20th Mar. 2014

  8. Gas shows 2/2 MGU – 20th Mar. 2014

  9. DEPTH OF INVESTIGATION vs VERTICAL RESOLUTION FLUSHED ZONE Vertical resolution (cm) NMR Depth of investigation (cm) - MGU – 20th Mar. 2014

  10. INVASION PROFILE AND RESISTIVITY Unflushed Zone Flushed Zone Rt Rw Rxo Rmc Sw Rmf Mud cake Rm Rt Sxo Rs Resistivity Rxo Shoulders Rmc Rayon Rm DrillingMud Borehole axis - MGU – 20th Mar. 2014

  11. LOGS – QUICK-LOOK PRINCIPLES Raw data Logs QC andbadholedetection Non Reservoirlevels identification • Shalylevels • tightlevels Reservoirsintervals LithologyDetermination  Logs and Xplot Clean reservoir Shalyreservoir HydrocarbonBearingreservoir Gaseffect identification Waterbearingreservoir Porositydetermination Rw (SP, Archie…) Sw (Archie Formula) MGU – 20th Mar. 2014

  12. DEFINITION GROSS, NET RESERVOIR and NET PAY Net Reservoir and Net Paydefinitions SWT Gross reservoir Net Reservoir Net Pay Top Waste Zone Top réservoir HCWC Base réservoir MGU – 20th Mar. 2014

  13. LITHOLOGY DETERMINATION • Neutron/Density(limestone calibration) • Identification of lithology in the water zone Neut/Densseparationaround 6 p.u.value Pure Sandstone response Limestone compatible scale Water bearing zone + Shale PEF Quartz value : 1.8/2 B/E Sandstone Water bearing #6 pu Limestone Water bearing Dolomite Water bearing #14 pu Shale • PEF (Photo Electric Factor) Good consistencybetween all the ismandatory Neut/Densseparationaround 10/14 p.u. Pure Dolomite response PEF isindependant of the porosity. PEF Dolomite value : 3 B/E PEF Limestone value : 5 B/E Neut/Denssuperimposed Pure calciteresponse

  14. FLUIDS IDENTIFICATION – GAS EFFECT • ComparisonbetweenRhob and Nphi • Oil : extremelylimited impact (Rhob and Nphimainlyimpacted by lithology) • Gas : effectsuperimposed on lithologyeffect • Rhob value decrease Phi_Densoverestimated due to the verylowdensity of gas • Nphi value decrease Phi_Neutronunderestimated due to the verylow IH of gas • Neut/DensSeparationincreasewhenGas saturation ishigh close to the borehole. If this zone ispartially or completelyflushed by the mudfiltrate, the GasEffectisreduced or null • If the porosityisverylow (tightgas) Gaseffectcanbeverylow or null • Gas and Oilcan not bedifferentiatedwithresistivity Gaseffect in LimestoneReservoir Gaseffect in Sandstone Reservoir Gas Gas Water MGU – 20th Mar. 2014

  15. Porosity in the water or oil zone  Direct value on Neut/Dens Porosity of the reservoirwithgaseffect (knownlithology)  Direct value on Neut/Dens POROSITY Estimation / COMPUTATION From Quantitative interpretation From Quick Look Method Limestonecalibrated 0.00 Water Sst: Porosity15% Water Lst: Porosity15% Water Dolomite: Porosity15% Half of the Neut/DensitySeparation 0.00 GasSst: Porosity16.5% 2/3 1/3 1/3 – 2/3 of the Neut/DensitySeparation MGU – 20th Mar. 2014

  16. ComparisonRxo et Rt In the water leg: LowResistivities Rt // to Rxo over a significantthickness. Contact Water – HC  Rxotranslated on Rt Contacts determination From Quick Look Method From Quantitative interpretation Gas – Oil Contact Oil – Wat Contact HC – Wat Contact LowRes + curves// MGU – 20th Mar. 2014

  17. a R æ ö æ ö w n S = × è m è R ø F ø w t SATURATION ESTIMATION Archie Formula for clean reservoironly Rw= Fm x Rt • In a water bearingreservoir : Sw = 1  • - Common value for a :1 • Common value for m :2 • F determined by quick look • Rtmeasured by resistivitytools (Deep Investigation) a Rwcanbecalculated in the water zone Sw in thehydrocarbonbearing zone. Can becalculated on several points during a quick look approach Porosity estimation in the water zone  RwDetermination Sw = 100% Rt : Redcurve

  18. CONCLUSION/ MAIN POINTS Takeintoaccount all the mudlogging (gas, cuttings…) and drilling data (drilling phase, mudproperties…) Logs Quality Control is a mandatorystepbeforeany type of interpretation • Impact of a deepmudfiltrate invasion • Impact of boreholeshape (washout, mudcakes) • Detectanykind of acquisition problem Consistencybetweentoolanswersisvery important. If not questions have to beasked: • Problem of mineralogy • Problem of fluids • Problem of acquisition • … Be carefulwithresistivity variations: a lot of informations withinthesecurves but affected by manyparameters: • Fluid content (Water, mudfiltrate, HC) • Porosity • Water salinity • Cementation factor « m » • … Eachinterpretation – Quick Look or quantitative – has to begeologicalycoherent. It means volume of minerals and porosity have to be compatible with the regionalcontext MGU – 20th Mar. 2014

  19. NOTES/COMMENTS LOGGING TOOL RESPONSE IN SEDIMENTARY MINERALS • Be careful with resistivity variations: a lot of informations within these curves but affected by many parameters: • Fluid content (Water, mud filtrate, HC) • Water salinity • Cementation factor « m » linked to tortuosity of the porous network • 1.6/1.7 in unconsolidated reservoir (very high porosity and permeability) • Around 2 in “classical” clastic reservoir • Up to 2.3/2.5 in tight or very tight clastic reservoir • Extremely variable in carbonates reservoir • Porosity MGU – 20th Mar. 2014

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