1. Logs : how to use them for QUALITIATIVE reservoir evaluation

2. Program : how to use logs for qualitative reservoir evaluation
- 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. 2014

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

4. Why logging acquisition (LWD or WL)
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. 2014

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

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

7. Wire Line depth is the reference
References Depth/Datum
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. 2014

8. Gas shows 2/2
MGU – 20th Mar. 2014

9. Vertical resolution (cm)
DEPTH OF INVESTIGATION vs VERTICAL RESOLUTION
FLUSHED
ZONE
Vertical resolution (cm)
L’amélioration de la résolution verticale des outils de résistivité profonde se fait en général au détriment de la profondeur d’investigation. Noter la bonne performance de la famille des «array inductions», qui provient d’un processing conbinant la bonne résolution des mesures proches et la lecture profonde de très mauvaise résolution verticale.
Les outils radio-actifs sont handicapés par le temps d’intégration (comptage des particules) et pour certains l’espacement entre les émetteurs/récepteurs.
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
Par la force des choses, les outils de mesure sont situés dans le trou de forage. Entre l’outil et la formation que l’on désire mesurer se trouvent la boue, le mud-cake et, pour les outils de résistivité profonde la zone envahie par le filtrat de boue. Ces effets indésirables se traduisent:
- dans le pire des cas, par la perte des données,
- sinon, par la nécessité de corriger d’effets d’environnement,
- ou bien de corriger d’invasion.
Il faudra également prendre en compte le fait que les zones d’investigation des différents outils peuvent être différentes.
Rxo
Shoulders
Rmc
Rayon Rm
Drilling Mud
Borehole axis -
MGU – 20th Mar. 2014

11. LOGS – QUICK-LOOK PRINCIPLES
Raw data
Logs QC and badhole detection
Non Reservoir levels identification
Shaly levels
tight levels
Reservoirs intervals
Lithology Determination
 Logs and Xplot
Shaly reservoir
Clean reservoir
Hydrocarbon Bearing reservoir
Gas effect identification
Water bearing reservoir
NEW 2009 – Anthony Price
Porosity determination
Rw (SP, Archie…)
Sw (Archie Formula)
MGU – 20th Mar. 2014

12. DEFINITION GROSS, NET RESERVOIR and NET PAY
Net Reservoir and Net Pay definitions
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/Dens separation around 6 p.u.value  Pure Sandstone response
Limestone compatible scale
Water bearing zone +
Shale
#6 pu
Sandstone Water bearing
PEF Quartz value : 1.8/2 B/E
Limestone Water bearing
Dolomite Water bearing
#14 pu
Shale
PEF (Photo Electric Factor)
Good consistency between all the is mandatory
Neut/Dens separation around 10/14 p.u.  Pure Dolomite response
NEW 2009 – Anthony Price
PEF is independant of the porosity.
PEF Dolomite value : 3 B/E
PEF Limestone value : 5 B/E
Neut/Dens superimposed  Pure calcite response

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
NEW 2009 – Anthony Price
Gas
Gas
Water
MGU – 20th Mar. 2014

15. POROSITY Estimation / COMPUTATION
From Quick Look Method
From Quantitative interpretation
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
Limestone calibrated
0.00
Water Sst: Porosity 15%
Water Lst: Porosity 15%
Water Dolomite: Porosity 15%
Half of the Neut/Density Separation
0.00
Gas Sst: Porosity 16.5%
1/3
2/3
1/3 – 2/3 of the Neut/Density Separation
MGU – 20th Mar. 2014

16. Contacts determination
From Quick Look Method
From Quantitative interpretation
Comparison Rxo et Rt
In the water leg:
Low Resistivities
Rt // to Rxo over a significant thickness.
Contact Water – HC
 Rxo translated on Rt
Gas – Oil Contact
Oil – Wat Contact
HC – Wat Contact
Low Res + curves //
MGU – 20th Mar. 2014

17. SATURATION ESTIMATION
Archie Formula for clean reservoir only S a R w m t n = æ è ö ø × F
In a water bearing reservoir : Sw = 1 
- Common value for a :1
Common value for m :2
F determined by quick look
Rt measured by resistivity tools (Deep Investigation)
Rw = Fm x Rt a
Rw can be calculated in the water zone
Sw in the hydrocarbon bearing zone.
Can be calculated on several points during a quick look approach
NEW 2009 – Anthony Price
Porosity estimation in the water zone
 Rw Determination
Sw = 100%
Rt : Red curve

18. CONCLUSION/ MAIN POINTS
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. 2014

19. NOTES/COMMENTS LOGGING TOOL RESPONSE IN SEDIMENTARY MINERALS
Rhob
Nphi DT
PEF GR
g/cc
v/v
us/ft
B/e
API
Quartz
2.65
-0.02 55
1.8
Low
Calcite
2.71 49 5
Dolomite
2.86
0.02 44 3
Anhydrite
2.96
-0.01 50
Salt
2.16 67
4.65
Pyrite 39 17
KFeldspar
2.52 69
High
Micas (muscovite)
2.82
0.2
2.4
Barite
4.48
267
Lignite
1.19
0.47
160
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
NEW 2009 – Anthony Price
MGU – 20th Mar. 2014