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LOGS : HOW TO USE THEM FOR QUALITIATIVE RESERVOIR EVALUATION.

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Presentation on theme: "LOGS : HOW TO USE THEM FOR QUALITIATIVE RESERVOIR EVALUATION."— Presentation transcript:

1 LOGS : HOW TO USE THEM FOR QUALITIATIVE RESERVOIR EVALUATION

2 Program : - Introduction/Objective - Drilling/Mudlogging – A brief overview -Depth and Datum reference -Drilling/Mudlogging. Mandatory data for logs interpretation - Logging Tools/Data acquisition -Tools – Principles (Brief or Optional) -Data acquisition – Quality Control - 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 HOW TO USE LOGS FOR QUALITATIVE RESERVOIR EVALUATION

3 3 …always the same measurements Different types of rigs…

4 4 Geological aspect: Sedimentology Structural Links with Geophysic (seismic) Time Depth conversion Petro elastic Model Reservoir aspect  Main subject of this 1 day course Net to Gross Porosity Saturation MGU – 20th Mar WHY LOGGING ACQUISITION (LWD OR WL)

5 5 Logs = a continuous outcrop of several thousand meters thickness Large scale interpretation (decametric to hectometric) Logs for Explorationists – Pau– 10 – 14 June 2013 GEOLOGICAL ASPECT

6 6 Well to seismic Tie Petro Elastic Model -Reservoir Characterization -Fluid characterization -Fluid Substitution -Monitoring (4D) Logs for Explorationists – Pau– 10 – 14 June 2013 WELL VS SEISMIC RELATIONSHIP

7 MD : Measure Depth/RT TVD : True Vertical Depth / RT TVDSS : True Vertical Depth / MSL (Mean Sea Level) For all of them (MD, TVD,…) « Driller » and « Logger » depth are available Wire Line depth is the reference MGU – 20th Mar REFERENCES DEPTH/DATUM

8 MGU – 20th Mar GAS SHOWS 2/2

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

10 10 - Shoulders Borehole axis R mc R xo RtRt Resistivity R xo RtRt RwRw R mf SwSw S xo RsRs RmRm Unflushed Zone Flushed Zone Mud cake Drilling Mud Rayon R mc RmRm MGU – 20th Mar INVASION PROFILE AND RESISTIVITY

11 LOGS – QUICK-LOOK PRINCIPLES Raw data Non Reservoir levels identificatio Non Reservoir levels identification -Shaly levels - tight levels Reservoirs intervals Logs QC and badhole detection Lithology Determination  Logs and Xplot Hydrocarbon Bearing reservoir Gas effect identification Water bearing reservoir Clean reservoir Shaly reservoir Porosity determination Rw (SP, Archie…) Sw (Archie Formula) MGU – 20th Mar. 2014

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

13 LITHOLOGY DETERMINATION Neutron/Density (limestone calibration)  Identification of lithology in the water zone #14 pu #6 pu Limestone Water bearing Limestone compatible scale Water bearing zone + PEF (Photo Electric Factor) PEF Limestone value : 5 B/E PEF Dolomite value : 3 B/E Sandstone Water bearing Dolomite Water bearing Good consistency between all the is mandatory Shale PEF is independant of the porosity. Neut/Dens separation around 10/14 p.u.  Pure Dolomite response Neut/Dens superimposed  Pure calcite response Neut/Dens separation around 6 p.u.value  Pure Sandstone response PEF Quartz value : 1.8/2 B/E

14 FLUIDS IDENTIFICATION – GAS EFFECT Comparison between Rhob and Nphi  Oil : extremely limited impact (Rhob and Nphi mainly impacted by lithology)  Gas : effect superimposed on lithology effect  Rhob value decrease  Phi_Dens overestimated due to the very low density of gas  Nphi value decrease  Phi_Neutron underestimated due to the very low IH of gas  Neut/Dens Separation increase when Gas saturation is high close to the borehole. If this zone is partially or completely flushed by the mudfiltrate, the Gas Effect is reduced or null  If the porosity is very low (tight gas) Gas effect can be very low or null  Gas and Oil can not be differentiated with resistivity Gas effect in Limestone Reservoir Gas effect in Sandstone Reservoir Gas Water MGU – 20th Mar. 2014

15 Porosity in the water or oil zone  Direct value on Neut/Dens Porosity of the reservoir with gas effect (known lithology)  Direct value on Neut/Dens Water Sst: Porosity 15% Water Lst: Porosity 15% Water Dolomite: Porosity 15% Limestone calibrated /3 – 2/3 of the Neut/Density Separation 0.00 Gas Sst: Porosity 16.5% 1/3 2/3 Half of the Neut/Density Separation From Quick Look Method From Quantitative interpretation MGU – 20th Mar POROSITY ESTIMATION / COMPUTATION

16 Comparison Rxo et Rt In the water leg: –Low Resistivities –Rt // to Rxo over a significant thickness. Contact Water – HC  Rxo translated on Rt Low Res + curves // HC – Wat Contact From Quick Look MethodFrom Quantitative interpretation Gas – Oil Contact Oil – Wat Contact MGU – 20th Mar CONTACTS DETERMINATION

17 SATURATION ESTIMATION S aR R w m w t n            Archie Formula for clean reservoir only In a water bearing reservoir : Sw = 1  - Common value for a :1 - Common value for m :2 -  determined by quick look - Rt measured by resistivity tools (Deep Investigation) Rw =  m x Rt Rw =  m x Rt a Rw can be calculated in the water zone Porosity estimation in the water zone  Rw Determination Rt : Red curve Sw = 100% Sw in the hydrocarbon bearing zone. Can be calculated on several points during a quick look approach

18 - Take into account all the mudlogging (gas, cuttings…) and drilling data (drilling phase, mud properties…) - Logs Quality Control is a mandatory step before any type of interpretation -Impact of a deep mud filtrate invasion -Impact of borehole shape (washout, mudcakes) -Detect any kind of acquisition problem - Consistency between tool answers is very important. If not questions have to be asked: -Problem of mineralogy -Problem of fluids -Problem of acquisition -… - Be careful with resistivity variations: a lot of informations within these curves but affected by many parameters: -Fluid content (Water, mud filtrate, HC) -Porosity -Water salinity -Cementation factor « m » -… - Each interpretation – Quick Look or quantitative – has to be geologicaly coherent. It means volume of minerals and porosity have to be compatible with the regional context MGU – 20th Mar CONCLUSION/ MAIN POINTS

19 NOTES/COMMENTS RhobNphiDTPEFGR g/ccv/vus/ftB/eAPI Quartz Low Calcite Low Dolomite Low Anhydrite Low Salt Low Pyrite Low KFeldspar High Micas (muscovite) High Barite Low Lignite 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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