How to Characterize Fractured Reservoirs

How to Characterize a Fractured Reservoir ?

Naturally fractured reservoirs

Part 2 - How to Character Characterize ize a Fractured Reservoir?

232, Avenue Napoléon Bonaparte P.O. BOX 213 92502 Rueil-Malmaison son France Phone: Phone : +33 1 47 08 80 00 Fax: Fax: +33 1 47 08 41 85 [email protected]

b a l n a r F p i c i e B @ @

How to characterize fractured fractured reservoirs ? MAIN OUTLINES 

METHODOLOGY



BOREHOLE SCALE DATA: - Core Core dat data a - BH BHII data data - Cores to to BHI calibratio calibration n - Statistical Statistical fracture fracture analysis analysis



2

INTERWELL SCALE DATA - Outcr Outcrop ops s - Seismic Seismic analys analysis is - Geomechanic Geomechanical al models models Part 2 - How to Characterize a Fractured Reservoir?

b a l n a r F p i c i e B @

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NATURALLY FRACTURED RESERVOIRS ADMA-O ADM A-OPCO PCO - from 06 to 07 of Januar January y 2008 2008 Copyright© 2008. Beicip-Franlab - All rights reserved

Part Part 2A - Page Page 1

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How to characterize a fractured reservoir?



 

Methodology to characterize fractured reservoirs Fracture analysis Data integration: conceptual model


Part 2 - How to Characterize a Fractured Reservoir?

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Data Integration for Fracture Network Modelling

Production Tests

Core data

L

0

75

150

225

3845

3846

3847

3848

3849

3850

Mud Losses

Image Logs

Geologic Models l b a Wireline Logs

Outcrops

Seismic At Attributes


n a r F p i c i e B @

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

 

Methodology to characterize fractured reservoirs Fracture analysis Data integration: conceptual model



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Data Integration for Fracture Network Modelling

Production Tests

Core data

L

0

75

150

225

3845

3846

3847

3848

3849

3850

Mud Losses

Image Logs

Geologic Models l b a Wireline Logs

Outcrops

Seismic At Attributes


n a r F p i c i e B @

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FRACA workflow WELL DAT DATA :

Core data, Logs

(GR, NPHI, …), BHI / DSI

Fracture analysis

OUTCROPS GEOLOGIC MODEL facies, porosity, matrix K

Fracture modeling Joints, fault related fractures, sub seismic faults

SEISMIC DATA – GEOMECHANICS Fault map, Seismic horizons, Seismic attribute maps, Stress/Strain maps

MULTI SCENARIO fracture length, fracture conductivity

DYNA DYNAMI MIC C DA DAT TA : PLT, PLT, well well test tests, s, PI, PI, Kh maps maps,, inte interf rfer eren ence ce test,productionhistory test,productionhistor y

Kf c a

b

K fx , K fy , K fz , a, b, c, φ φ f

Model validation Geological data Simulation of synthetic PLT and welltest

Kf Tensor & Matrix Block Size for Each Model Cell Part 2 - How to Characterize a Fractured Reservoir?


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A. BOREH BOREHOLE OLE SCA SCALE LE DAT DATA B. INTERWEL INTERWELL L SCALE DATA DATA



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How to characterize a fractured reservoir? BOREHOLE SCALE DATA 1. Cores 2. Borehole images - Microresistivity tools (FMS/FMI/STAR) - Acoustic Acoustic logs: UBI UBI / CBIL - OBM combined resistivity resistivity / acoustic logs (Earth) - Television elevision

3. Fluid flow logs - Flowmeter logs, Production Logging Tool Tool (PLT) (PLT) - Mud loggin logging, g,

4. Stress information - 4 arms calipers (breakout (breakout / washout), BHI BHI data (stress orientation) - DSI - DSI (shear wa ves anistropy) - Leak-off Leak-off tests, tests, Minifrac (stress magnitude)

5. Others - Weight on hook, ROP, …



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How to characterize a fractured reservoir? BOREHOLE SCALE DATA 1. FRACTURES FROM CORE OBSERV OBSERVA ATIONS Objective 1: identify the main types of fractures that may or not impact the reservoir performances

• Natural fractures • Induced fractures • Other features

Objective 2: provide fracture morphology (aspect ratio, etc. ), orientations, intensity, aperture b a l n a r F p i c i e B @


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Core Quality

1

2

3

4



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Tectonic fractures fractures – joints in quartzitic reservoir reservoir Joints form with a maximum stress oriented parallel to the joint surface

Open fractures

Oil staining staining « open fractures fractures » Part 2 - How to Characterize a Fractured Reservoir?


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Tectonic fractures – Partly open and cemented fractures in tight bed



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Tectonic fractures - Breccia

Sandstone Carbonate Part 2 - How to Characterize a Fractured Reservoir?


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NATURALLY FRACTURED RESERVOIRS ADMA-OPCO - from 06 to 07 of January 2008 Copyright© 2008. Beicip-Franlab - All rights reserved

Part 2A - Page 6


Faults - Evidences of faults in cores

The possible presence of a fault in the red inset is showed by: -The drastic contact between limestones (right) and shaly mudstones (left); -The core in the red inset is highly broken Fault damaged zone / fault core zone -Some pieces in the broken zone show striated surfaces, with slickensides



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Early diagenetic fractures

Compaction « hair-like » fractures



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Part 2A - Page 7


Early diagenetic fractures

The thin planar fractures only affect the central bed (early diagenesis criteria) Facies are shaly limestones Those fractures always exhibit a low aspect ratio (Length/width < 100 )



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Early diagenetic cemented fractures



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Part 2A - Page 8


Early diagenetic features

Cracks associated with dolomitic beds



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Diagenetic features: stylolites Stylolite related fractures observed on cores

Tectonic fractures

Tension gashes Paleo-minimum stress direction

Stylolite peaks Tight zone related to pressuresolution

Stylolite

Fracture

overburden b a l n a r F p i c i e B @


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Part 2A - Page 9


Diagenetic features: stylolites

1 cm thick Stratigraphic stylolite

Associated tension gashes b a l n a r F p i c i e B @


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Diagenetic features: stylolites

Associated fracture

20 cm thick Stratigraphic stylolite



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Diagenetic features: micro-stylolites



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Stylolite related fractures Tension gashes (indicated by the white arrows) associated to the micro-stilolites.



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Artefact related breaks Plug induced fracture



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Artefact related breaks

Disking 100% (1 cm)



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Artefact related breaks Examples of “not conventional” core disking

This photograph shows that disking is an obvious artifact: the core external surface is not affected by the slicing.



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Artefact related breaks Examples of “not conventional” core disking

comma-shaped disking

Artificial breaks >> core disking

post-slabbing desegregation. Part 2 - How to Characterize a Fractured Reservoir?


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Example of core description sheets

GENERAL

DISKING

C o r e N u m b e r

D e p t h d r i l . T O P

B o x e s

C o r e q u a l i t y

1

2

3

4

V i s u a l S a t .

5

A f f e c t e d t h i c k .

A v e r . d i s k t h i c k n .

%

cm

6a

6b

STYLOLITES S m a l l s t r a t i . S t y l .

C l a s s 5

D a m p e n e d S t y l .

M i c r o s t y l o l i t e s

General information, disking, Stylolite related fractures

A mp . N um . C um . A mp . A ff ect . % C um . A mp . 7

8

9

10

FRACTURE RELATED FEATURES

Fracture information

C E M E N T E D

P A R T . C E M E N T .

U N C E M E N T E D

u mb le ng th n um b l e ng th n um b l e ng th 11

12

D I P

d eg . to c or e axi s

13

14

W I D T H

T I P S

F R A C T U R E T Y P E

m m U /L /B S /X/ Y/ Z 15

16

17

S T A I N I N G

P 18



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How to characterize a fractured reservoir? BOREHOLE SCALE DATA

2. FRACTURES FROM BHI DATA • • • •

Basis of fracture picking Data QC Tool resolution Cores to BHI calibration • Statistical analysis of fractures • Fracture density log • The main types of fractures from BHI • Bed thickness record ? b a l n a r F p i c i e B @


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Principle of fracture picking on BHI images

Fractured zone on acoustic log

Sinusoide on BHI log

Fracture plane Bedding plane



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Tool resolution

Resistivity

Accoustic



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The different features on BHI Faults identification

Vertical displacement along the fracture plane

Fault breccia



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The different features on BHI Natural fractures identification

Conductive “open” fractures b a l n a r F p i c i e B @

Resistive “closed” fractures Part 2 - How to Characterize a Fractured Reservoir?

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The different features on BHI Induced fractures identification

Induced fractures

Breakouts Induced fractures



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BHI and Maximum horizontal stress

Breakouts

Induced fractures


SHmax


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Cores to BHI calibration Tectonic stylolite in core and in BHI image



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Cores to BHI calibration

Shaly intervalle



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Cores to BHI calibration

Low amplitude fractures

CLOSED FRACTURE Here the fracture is filled with soft material (gypse) Part 2 - How to Characterize a Fractured Reservoir?


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Cores to BHI calibration Broken zone in the core

The core broken zone correspo nd to a N030E oriented fracture swarm on borehole imagery Part 2 - How to Characterize a Fractured Reservoir?


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Cores to BHI calibration Correlation between facies (shaly limestones & tight limestones) and FMI images

Shaly limestones

Tight limestones



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Example of fracture analysis (1/5)

1

Polar projection of fractures

2

Density of points after bias correction

3 b a l n a r F p i c i e B @


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Example of fracture analysis (2/5) Upper fracture zones and FMI image

CLUSTER

1



41

Example of fracture analysis (3/5) Validation with cores Fault

CLUSTER

1

Fractures are partially open



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xamp e o racture ana ys s Example of sub-horizontal fractures

DIFFUSE

2 Projection polaire des fractures



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Example of fracture analysis (5/5) Validation with cores Fractures are partially open

BRECCIA

2



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Statistical fracture analysis (1/3) Statistical analysis of borehole imagery interpretation

 

Multi-well integrated analysis Fracture set identification / characterisation Part 2 - How to Characterize a Fractured Reservoir?


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Statistical fracture analysis (2/3) BOREHOLE SCALE DATA

Statistical analysis of borehole imagery interpretation Avg. Spacing

N70E

Avg. Strike

Fisher Strike Avg. Dip

Fisher Dip

0,5m

N70

5,2

85

6,6

N110E

0,49m

N105

3,3

85

4,6

N20E

0,46m

N23

2,6

88

3,7

 

Multi well integrated analysis Fracture sets identification / characterisation Part 2 - How to Characterize a Fractured Reservoir?


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Statistical fracture analysis (3/3) The fracture density log

4

 

Mean strike=N081

Well by well integrated analysis Fracture type identification / characterisation Part 2 - How to Characterize a Fractured Reservoir?


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The fracture density log

The bias correction



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Drivers on fracture density

FACIES VARIATION

DEVIATED WELL

BEDDING DIP VARIATION

BEDDING THICKNESS VARIATION

NO-DATA INTERVALS

FRACTURE SWARMS



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The main scales of fractures Cluster analysis: fracture swarm / fault 1

2

1 2 3 3 4



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The main scales of fractures Cluster analysis: diffuse fractures / joints

6



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The main scales of fractures Examples of diffuse fractures in outcrops Fractures extension from metric to decametric

Vertical variations of the diffuse fracture distribution are generally due to lithology and bed thickness.



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Influence of lithology Testing the relationship between lithology and fracture density

Main fractured intervals are found in tight sandstones

3 sets of fractures: Mean strike N071, mean dip = 82° Mean strike N107, mean dip = 83° Mean strike N032, mean dip = 62°



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Influence of lithology

Shalyness

has a large impact on fracture density Part 2 - How to Characterize a Fractured Reservoir?


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Influence of lithology

Shaly interval Fracture density b a l n a r F p i c i e B @


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Influence of bed thickness

Diffuse fractures are bed limited Part 2 - How to Characterize a Fractured Reservoir?


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Beds thickness / fracture density relationship 1/2



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Beds thickness / fracture density relationship 2/2 FD = Fracture density

Conceptual model of fracture distribution Part 2 - How to Characterize a Fractured Reservoir?


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Strain partitioning in a fold Fractures produced by extension are pure extensional and open fractures Fractures produced by compression are closed, stylolitic and/or partially open.

Present-day geo-structural setting around well A

Well A

Extension

Compression



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Fracture aperture from cores/BHI data Thin section analysis

BHI data

Fracture aperture 35

4000

30

3500 3000

25

3

Poiseuille law

2500

s e 20 l p m a S 15

2000 1500

10

1000

5

500

0

0

-6

C = e / (12*0,98*10 ) C = hydraulic conductivity in mD.m e = fracture aperture

Aperture (microns)

Limitations: questionable fracture aperture estimation that may have a very strong impact on fluid flow computation Part 2 - How to Characterize a Fractured Reservoir?


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How to characterize a fractured reservoir? INTERWELL SCALE DATA

Outcrops Seismic data Geomechanical models Others



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How to characterize a fractured reservoir? INTERWELL SCALE DATA 

A posteriori fault and fracture detection From outcrop analysis From seismic data • conventional picking • surface attributes • seismic facies analysis • seismic anisotropy



Geomechanical modelling geological times • curvature based approach • geomechanical based b a l n a r F p i c i e B @


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Outcrop analogs analysis

SWARMS JOINTS

Usefull observation to determine the type of fractures, the fracture chronology Limitations due to decompaction and weathering: • questionnable fracture densities and fracture length measurements • cannot be used for fracture aperture Part 2 - How to Characterize a Fractured Reservoir?


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Seismic data analysis

Objectives: • To identify fault AND sub-seismic faults in the reservoir

• To define the geometrical properties of the fault pattern (for extrapolation to lower scale)

• To assess their impact on the reservoir fluid flow behaviour b a l n a r F p i c i e B @


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Seismic data analysis CONVENTIONAL PICKING

Conventional seismic picking • faults and flexures location • fault throw measurement • fault geometry



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Seismic noise Spikes Top 1

Top 1

Seismic cross-section Part 2 - How to Characterize a Fractured Reservoir?


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Seismic data analysis Curvature methodology 1. The deformation (fault) induce a curvature (positive and negative)

2. Smoothing Horizon map

Fault plane

Positive curvature

+

Initial topography

Negative curvature

After n steps of smoothing

3. The second derivative of curvature highlights the deformation

4. The interpretation is computed between positive and negative lineaments



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Impact of smoothing on curvature signal

SM=200 10 Km b a l n a r F p i c i e B @


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Impact of smoothing step on curvature signal SM=200

SM=100

10 Km

SM=50

SM=10



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Seismic data analysis Large scale features interpretation : curvature analysis N Positive curvature

Negative curvature



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Seismic data analysis The main types of curvature:

• Principal curvature (maximum of curvature) • Oriented curvature • Minimum curvature

Maximum of curvature N70 oriented curvature N160 oriented curvature Part 2 - How to Characterize a Fractured Reservoir?


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Curvature analysis

NORTH Curv min = 0

Fold or flexure

EAST Curv min

Curv max

Low curvature

Fault zone Local or regional scale

High curvature



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Seismic data analysis

Top of the Reservoir Formation

Maximum curvature processed in Fraca®



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Integration of seismic data: curvature analysis •N130E is the main trend •seismic faults (blue) •sub-seismic lineaments (yellow) •E-W is a minor (only sub-seismic lineaments)

Validation with the other seismic attributes b a l n a r F p i c i e B @


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Seismic data analysis SEISMIC ATTRIBUTES ANALYSIS

Red

Amplitude map

Dip map illuminated from NW

Correlation map

= high amplitudes

Yellow = areas dipping toward NW

Red = areas of good correlation

Red = areas dipping away from NW Black = steep dips away from NW

Purple = poor correlation

White = medium Blue = low

“ “

A number of linear features occur on all 3 maps, many of which can be interpreted as faults; generally the shorter the lineament the less confident the interpretation Part 2 - How to Characterize a Fractured Reservoir?


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Seismic data analysis SEISMIC FACIES ANALYSIS 

Objective : Analyze the character of seismic traces and relate, if possible, its variations to geological variations of the reservoir.



Deliverables: Maps or cubes of « seismic facies with the associated interpretation.



Methodology: Statistical methodology based on principal component analysis that includes pattern recognition techniques.

Previous seismic interpretation not required Part 2 - How to Characterize a Fractured Reservoir?


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Seismic facies analysis (1/4) Selection of relevant seismic attributes 1250

1250

1250

N

1250

N

1000

1000

750

High

1250

1250

1250

N

1000

1000

1000

1000

750

750

750

750

500

500

500

500

250

250

250

250

High

1000

1000

750

750

750

500

500

500

500

250

250

250

250

High

Low cdp line

cdp line

150 250 350 450

150 250 350 450

Cur vature

Dissimilarity

1250

N

Low

cdp line

Low

150 250 350 450

cdp line

150 250 350 450

Dip

Edge b a l n a r F p i c i e B @


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Seismic facies analysis (2/4) Seismic facies definition Statistical segmentation

Seismic facies 3

dip ×

Edge

Dissimilarity

A3

×× ××× × × × ×

× ×× ×× ×× ×

Seismic facies 1

Ap

curvature

A2

×× ××

A1

Seismic facies 2

Attribute space



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Seismic facies analysis (3/4) Seismic facies definition facies 3

Attribute #3

×× ××× × × × ×

Attribute #p

Attribute #2

× ×× ×× ×× × facies 1

KS1

×× ××

KS3

KS2

Attribute #1

facies 2

Facies 1 Facies 1

Facies 2

Facies 3

Facies 2 Facies 3 Facies 4 Facies 5

Facies 5

Facies 6

Facies Facies 4



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Seismic facies analysis (4/4) Mapping of seismic facies that shows fracture occurrence Seismic facies

5 km Part 2 - How to Characterize a Fractured Reservoir?


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Fault geometry analysis Fault length analysis

T hin li nes sho w the portio ns of the curves which fit li nes wi th slop es of C . Because these data were collected f ro m t wo -d ime nsi on al s amp le s o f t hr ee -d ime nsi on al vo lu mes , e qua ti on ( 1) an d t he d at a i n f ig ur e d es cr ib e t wo dimensional fault populations. The actual (three-dimensional) power-law exponent for small faults is C + 1 (Marrett & Allmendinger 1991) . Also shown are the areas (A) in square kilometers of the maps from which the data were collected.



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Fault geometry analysis

Fault displacement analysis

Results of the combined analysis of nine data sets (lines), with the source data (symbols) b a l n a r F p i c i e B @


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Fault geometry analysis ILLUSTRATION OF THE FRACTAL DIMENSION ON THE FAULT PATTERN

Fractal dim. = 1.4 Fractal dim. = 1.6 Fractal dim. = 2 High values increase the lateral dispersion Part 2 - How to Characterize a Fractured Reservoir?


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Fault geometry analysis

2. Compartments analysis - From geometric criteria: comparison of reservoir thickness and fault throws (fault displacement contours ) - From fault surface properties: clay smearing related to throw magnitude and to shalyness of reservoir blocks - Compartmentalization also controlled by geomechanical criteria: (reverse faults are more likely seali ng; controlled by present-day stress)



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How to characterize a fractured reservoir? INTERWELL SCALE DATA



A posteriori faults and fractures detection From outcrop From seismic • conventional picking • surface attributes • seismic facies analysis • shear waves analysis



Geomechanical modelling geological times • curvature based approach • elastoplastic approach b a l n a r F p i c i e B @


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Geomechanical modelling

TIME

CURVATURE ANALYSIS

TOTAL DEFORMATION

T5

No deformation

T4

Max. of deformation

T3 T2

Deformation = Curv.(T1) – Curv.(T2)

T1

A coupled back-striping / curvature approach is required b a l n a r F p i c i e B @


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The conceptual fracture model

N

Fractures corridors

Fault

?

?

?

? ?

Diffuse fractures


10 m


91


Not fractured well (2) Not fractured well (1)

Fracture swarms

Faulted well



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The conceptual fracture model 1. The reservoir unit was fractured by means of large-scale fractures (faultrelated) (Northern Africa)

Fractures were clustered along the main faults and developed in spite of the lithological variations. Part 2 - How to Characterize a Fractured Reservoir?


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The conceptual fracture model 2. The reservoir unit was intensely fractured by means of diffuse and largescale fractures (Mexico)

Two proven main geological drivers on lateral and vertical distribution of diffuse fold-related fractures: lithology and the structure. Part 2 - How to Characterize a Fractured Reservoir?


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Locally connectedfractures

Regionaldiffusefractures



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How to characterize a fractured reservoir? FRACTURE MODELLING Objective:

To integrate fracture characterisation results for reservoir engineering purposes:

1. to predict the distribution of fracture sets properties w ithin the reservoir volume 2. to build 3D models of the fracture network for fluid flow computation: - to calibrate fracture hydraulic properties - to compute large-scale flow properties (input for field-scale flow simulation) b a l n a r F p i c i e B @


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How to model a fractured reservoir? Reservoir scale

Simulation cell scale

Well scale 1m 5 km

•Faults [Sub Seismic faults Swarms]

100 m

•Joints •Swarms •Faults b a l n a r F p i c i e B @


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How to model a fractured reservoir? The choice of the FRACTURE MODELLING APPROACH depends on fracture SCALE :

FAULTS (km ; throw: >10m) Large-scale fractures

sub-seismic faults (100 m-1 km ; throw: 0-20m) and

Global (reservoir-scale) discrete fracture model

fracture swarms (10 m -1 km; no throw) Small-scale fractures Matrix anisotropy

JOINTS (cm - 10 m)

Local discrete fracture model

microfractures (mm - cm) b a l n a r F p i c i e B @


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How to model a fractured reservoir? FRACTURE MODELLING OF LARGE SCALE FEATURES Procedure: 1. Integration of deterministic information - basic surfaces (geologic horizons, faults) are built from sets of points provided by the seismic - relationships between these surfaces are specified (according to faulting history, …)

2. Extrapolation at lower scales : sub-seismic fault (or fracture swarms) modelling - use of a statistical discrete modelling method based on the fault geometric properties . fault orientation map, . distribution law of fault lengths, . fractal dimension.



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How to model a fractured reservoir? Modelling of sub-seismic faults

3D SEISMIC

Major faults used as deterministic modelling constraints: •2 sets •1 orientation map for each set b a l n a r F p i c i e B @


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How to model a fractured reservoir? CONDITIONING the sub-seismic fault model From 3D seismic attributes picking

To the map of initiation probability for the stochastic modelling of sub-seismic faults



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How to model a fractured reservoir? MODELLING of sub-seismic faults Seismic-derived (sub-seismic) fault

Fault map

Constrained stochastic modelling

Simulated fault network



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How to model a fractured reservoir? SMALL-SCALE FRACTURES MODELLING Procedure: 1. Analysis and quantification of fractures from wellbore information: - distribution of fracture azimuths fracture sets

and

dips (Schmitt diagram,…)-->identification of

- fracture density (m2/m3) and fracture spacing (measurement depends on the relative orientation of fracture set and wellbore trajectory), in relation with lithology - identification of fracture swarms (versus systematic joints)]

2. Building a RESERVOIR DISTRIBUTION MODEL of f racture properties (orientation, density,..) : the global geocellular fracture model - by interpolation of property values between wells - by indexing fracture density: on lithology (global geocellular facies model) on proximity to faults indexing fracture density and orientation on local curvature. Part 2 - How to Characterize a Fractured Reservoir?


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How to model a fractured reservoir? Curvature analysis Geomechanics Interpolation between wells

Conventional Geo-cellular model

Maps of fracture properties

Spatial distribution of fractures Discrete model of faults

Local model at cell size

Modeling subseismic faults Part 2 - How to Characterize a Fractured Reservoir?


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How to model a fractured reservoir? Discrete fracture model Example of stylolite related fractures modelled at cell size

Top View b a l n a r F p i c i e B @

Side View Part 2 - How to Characterize a Fractured Reservoir?

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How to model a fractured reservoir? 3D view of the diffuse fractures generated by Fraca

N150

N140

N080

100x100 m cell Part 2 - How to Characterize a Fractured Reservoir?


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How to characterize a fractured reservoir? CONCLUSIONS (1) Fracture analysis and fracture modelling Identify the main type of fractures, Identify the geological drivers on fracture distribution Qualitatively asses the role of fractures on fluid flow Prepare upscaling phase through adapted modelling of objects with various scales  

All relevant data must be integrated in a rigourous package A transversal expertise to be shared by geologists, geophysicists and reservoir engineers b a l n a r F p i c i e B @


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How to characterize a fractured reservoir? CONCLUSIONS (2) 1. Borehole scale data • A carefull expertise of cores with BHI data is important to identify the main tectonic features that may have an impact on the reservoir

Discriminate between tectonic fractures, induced fractures, etc...

• BHI data provide essential informations on fractures orientation

- Statistical analysis of the main fracture sets, fracture orientations, fracture dips, fracture density and statistical dispersion - Identification of the fracture types Part 2 - How to Characterize a Fractured Reservoir?


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How to Characterize Fractured Reservoirs

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