LOGS : HOW TO USE THEM FOR QUALITIATIVE RESERVOIR EVALUATION.

LOGS : HOW TO USE THEM FOR QUALITIATIVE RESERVOIR EVALUATION

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. 2014 2

HOW TO USE LOGS FOR QUALITATIVE RESERVOIR EVALUATION

3 …always the same measurements

Different types of rigs…

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. 2014

WHY LOGGING ACQUISITION (LWD OR WL)

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

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

MD : Measure Depth/RTTVD : True Vertical Depth / RTTVDSS : True Vertical Depth / MSL (Mean Sea Level)

For all of them (MD, TVD,…) « Driller » and « Logger » depth are available

Wire Line depth is the referenceMGU – 20th Mar. 2014

REFERENCES DEPTH/DATUM

MGU – 20th Mar. 2014

GAS SHOWS 2/2

9-

Relation résolution verticale-profondeur d'investigation

induction deep

array inductionlatérolog deepneutron

gamma-raydensité

micro-résistivité0

50

100

150

200

250

0 50 100 150 200 250

profondeur d'investigation (cm)

réso

luti

on

ver

tica

le (

cm)

Depth of investigation (cm)

Ver

tica

l re

solu

tio

n (

cm)

NMR

FLUSHED ZONE

MGU – 20th Mar. 2014

DEPTH OF INVESTIGATION vs VERTICAL RESOLUTION

10-

Shoulders

Borehole axis

Rmc

Rxo

Rt

Res

istiv

ity

Rxo

Rt

Rw

Rmf

Sw

Sxo

Rs

Rm

Unflushed Zone

Flushed Zone

Mud cake

Drilling Mud

Rayon

Rmc

Rm

MGU – 20th Mar. 2014

INVASION PROFILE AND RESISTIVITY

LOGS – QUICK-LOOK PRINCIPLES

Raw data

Non Reservoir levels identification-Shaly levels- tight levels

Reservoirs intervalsLogs QC and badhole detection

Lithology Determination Logs and Xplot

Hydrocarbon Bearing reservoirGas effect identification

Water bearing reservoir

Clean reservoir Shaly reservoir

Porosity determination

Rw (SP, Archie…) Sw (Archie Formula)

MGU – 20th Mar. 2014

Net Reservoir and Net Pay definitions

Top réservoirTop Waste Zone

Base réservoir

HCWC

Gross

rese

rvoir

Net R

eser

voir

Net P

ay

SWT

MGU – 20th Mar. 2014

DEFINITION GROSS, NET RESERVOIR and NET PAY

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

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

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 Gas

Water

MGU – 20th Mar. 2014

• 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

0.00

1/3 – 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. 2014

POROSITY ESTIMATION / COMPUTATION

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 Method From Quantitative interpretation

Gas – Oil Contact

Oil – Wat Contact

MGU – 20th Mar. 2014

CONTACTS DETERMINATION

SATURATION ESTIMATION

Sa R

Rwm

w

t

n= æè

öø×

æè

öøF

Archie Formula for clean reservoir only

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 Rta

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

- 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

CONCLUSION/ MAIN POINTS

NOTES/COMMENTS

  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 0 49 5 Low

Dolomite 2.86 0.02 44 3 Low

Anhydrite 2.96 -0.01 50 5 Low

Salt 2.16 -0.02 67 4.65 Low

Pyrite 5 -0.02 39 17 Low

KFeldspar 2.52 -0.02 69 2.86 High

Micas (muscovite) 2.82 0.2 49 2.4 High

Barite 4.48 -0.01   267 Low

Lignite 1.19 0.47 160 0.2  

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