Download - Introduction to reservoir-scale deformation and structural core description

Transcript
Page 1: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 1

Introduction toreservoir-scale deformation

and structural core description

Page 2: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 2

Reservoir scale deformation

• Small scale faults and fractures plus the internal structure of faults revealed by core and image logs

• Introduce basics of structural core description

• Aim to visit core store later in course

Page 3: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 3

Core basics

• Various diameters: 2” to 6”, 4” (10cm) commonest

• Runs of up to 120 feet per core (30’ to 60’ common)

• ‘Drillers’ depth not measured (log) depth

• Usually slabbed before logging

• Stored in 3ft, 4ft, 1m boxed lengths

• Half cut common

• Resinated ‘museum’ core also common

Page 4: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 4

Core orientationL R

Up

Core marked to show ‘way-up’

Page 5: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 5

Core to log shift

• Core taken whilst drilling

• Logs taken after drilling

• Stretch of log tool cable means that measured depth (log) and driller’s depth (core) do not correspond

• Apply a shift +’ve or –’ve to correlate core and logs

• Core gamma used to pick shifts

Page 6: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 6

What to record?

• Core width

• Continuous core sections

• Fault or fracture length - cuts centreline?

• Fault or fracture width

• Number of tips/terminations: upper or lower

• Layer boundaries?

• Displacement

• Slip sense/direction

Page 7: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 7

What to record 2

• Fracture spacing

• Cross-cutting relationships

• Intersection angle of sets

• Fault rock type: cataclasites/disaggregation, PFFR, clay-smear

• Shale/phyllosilicate smear – abrasion– shear zone– injection

• Cementation: whole or part

Page 8: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 8

What to record 3

• Clast sizes - cataclasite to breccia

• Distribution with respect to lithology

• Surface markings – fractography

• Rubble zones

• Natural vs. Induced

Page 9: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 9

Recognition of natural fractures

• Cementation

• No geometric relationship with core

• Shear offset

• Planar

• Propagation along bedding not down core

• Multiple sets

Page 10: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 10

Detailed Fault Rock Classification

Fisher & Knipe (1998)

Page 11: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 11

Faults in core

Page 12: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 12

Log of deformation features in core

0 4 8 12 16 20

D eform ation features

10000

10020

10040

10060

10080

10100

10120

10140

10160

10180

10200

10220

10240

10260

10280

10300

De

pth

Layer A

Layer B

Layer C

Layer D

W ell nam eFeature 1

Feature 2

Feature 3

Page 13: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 13

Naturalfractures

Fracture spacing and layer boundaries in Chalk core

Page 14: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 14

S p a cin g :th ickn e ss ra tioM axim um S /T = 0 .92

Average S /T = 0.42

M in im um S /T = 0.09

0 0.5 1 1.5Fra ctu re sp a cin g (m )

0

0.5

1

1.5

La

yer

thic

kne

ss (

m)

C ore d iam eter10cm

M axim um layerth ickness 1.22m

Average layerth ickness 0.49m

M inim um layerth ickness 0.16m

Fracture spacing vs. layer thickness: what is visible in core?

Closer than average

Wider than average

Page 15: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 15

Fracture spacing

• Recognition of mechanical layer boundaries

• Fracture spacing/layer thickness relationships

• Comparison with other data and methods– e.g. Average fracture spacing estimated using the technique

of Narr (1996)

Spacing = Core slab surface area Total fracture height in core

Page 16: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 16

Core orientation

• Scribed core

• Palaeomagnetic

• Dipmeter

• Image logs

Page 17: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 17

Orientation of deformation features relative to bedding

Page 18: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 18

Fracture spacing

Page 19: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 19

Coring induced fractures

• Can be mistaken for natural uncemented fractures and so influence identification of productive zones

• Types recognized using characteristic fracture surface morphology or fracture geometry:

– Centreline fractures

– Petal fractures

– Torsional fractures

– Scribe-knife related

– Core-plug related

– Unloading

Page 20: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 20

Fracture surface morphology

Page 21: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 21

Arrest lines indicating Propagation down core

Page 22: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 22

Petal-centreline fractures

Page 23: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 23

Petal-centreline fractures

Page 24: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 24

Scribe knife damage

Page 25: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 25

Scribe knife damage

Page 26: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 26

Core discs

Page 27: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 27

Core discs

Page 28: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 28

Torsional fracturesCore disc

Page 29: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 29

Core spin

From Paulsen et al. (2002)

Page 30: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 30

Rubble zones in core

• Induced

• Often at base of a core

• Can develop where lithologies change

• May correlate with ROP changes

Page 31: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 31

Image logs

• Sonic or resistivity tools

• FMI – Shows a resistivity image of the borehole wall

• UBI/CBIL – Show an acoustic image of the borehole wall

Page 32: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 32

UBI image of open fractures

• Fractures make a sinusoidal trace on the borehole wall

• Data on type and orientation

• Acoustic show open fractures

• Resistivity show open and cemented fractures/faults

Page 33: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 33

Faults on FMI log

• Offsets visible although throw is difficult to measure

• Dip changes may be visible

• Core to log – about 5 times number of features observable in core.

Page 34: Introduction to reservoir-scale deformation and structural core description

EARS5136 slide 34

High resolution image logs allow identification of minor, narrow-aperture fractures when calibrated against core