Confidential, not for distribution without prior written consent from Ikon Science Ltd

The regional informs the local

The role of regional rock physics knowledge in reducing uncertainty

Nick Huntbatch

27th September 2018

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Contents

1. The role of rock physics in prospect evaluation.

2. What do we need to include in the rock physics, how can regional knowledge help?

• Compaction state.

• Lithology.

• Pressure.

3. Case Studies.

1. Rock physics modelling in the Flemish Pass and Orphan Basin.

2. Taking this knowledge into the seismic inversion realm.

4. A robust rock physics framework.

5. Conclusions.

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• Overpressure?

• Igneous intrusion?

• High-porosity brine sand?

• Pay sand?

• Something else?

Prospect Analysis

• Overpressure?

• Igneous intrusion?

• High-porosity brine sand?

• Pay sand?

• Something else?

How to de-risk?

Geological information• Log data and basin modelling

• HC types

• Stratigraphy

• Lithology and facies

Prospect

?BasicsPolarity

Phase

etc.

+

Geophysical information

• Seismic + interpretation• DHI

• Structural conformance

4

Geological scenarios that explain

amplitudes

Geological information• Log data and basin modelling

• HC types

• Stratigraphy

• Facies• Lithology

• Compaction state and porosity

• Anisotropy

• Pressure and stress

Rock Physics Models

Prospect+

Geophysical information

• Seismic + interpretation• DHI

• Structural conformance

BasicsPolarity

Phase

etc.

Prospect Analysis including Rock Physics

Knowledge of (elastic) facies and stress

state are key.

5

Elastic Litho-Facies

Rock Physics Models

• The seismic responds to contrasts in elastic litho-facies.

• We need to understand the geological controls on the elastic properties of each facies, and include

them in the models.

• Most geological processes occur on a basin-wide scale – regional knowledge is key.

Lithology.

Compaction state and porosity.

Saturation.

Pressure and stress.

Anisotropy.

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What do we mean by regional knowledge?

Regional knowledge is any relevant information from a wider area that assists the interpreter in

understanding the geological signal behind the observed seismic responses.

1. Elastic log data

2. Direct pressure measurements

3. Core data, XRD, petrography

4. Reports, published data and publications

5. Etc.

https://www.ogauthority.co.uk/data-centre/interactive-maps-and-tools/

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Regional knowledge - compaction trends

Basin 1

Basin 2

Basin 3

Shale velocityfastslowhighlow

4km

4km

Sand porosity

Velocity and porosity data with depth for three basins in north-west Europe.

How do we understand these trends?

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Velocity

Porosity High

Low

Low

High

Mechanical

compaction dominates

Chemical

compaction

dominates

Shales

Sands

Qtz.

Mechanical compaction, sorting, grain packing, grain crushing

Chemical compaction, smectite – illite transformation,

quartz overgrowth

(after Avseth et al., 2008)

Regional knowledge - compaction trends

0 TVDml

~6km TVDml

70-100°C

~2.5km TVDml

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Up-lifted

cemented

sands

Up-lifted

unconsolidated

sands

Under-compacted

sands

Velocity

Porosity High

Low

Low

High

0 TVDml

Shales

Sands~6km TVDml

(after Avseth et al., 2008)

70-100°C

~2.5km TVDml

These effects change the relationship between

sands and shales at a particular depth, and

therefore the seismic response.

e.g. WoS under compaction results in false positive

class III AVO responses.

Uplift

Regional knowledge - compaction state

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Regional knowledge - compaction trends

Basin 1

Basin 2

Basin 3

Under-compacted

reservoirs

Smectite-Illite

transition?

Shale velocityfastslowhighlow

4km

4km

Early onset of

chemical compaction –

higher heatflow?

Sand porosity

We need to look at regional well data to capture and understand this

effect.

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Compaction and rock properties

Chemical and mechanical

compaction of sands

TV

Dm

l

Vp

PhIT

Chemical and mechanical

compaction of sands

TV

Dm

l

Vs

Vp

Regional data from 30 wells covering a range of depths and compaction states.

Compaction directly impacts elastic properties and seismic response.

Need regional knowledge to capture the effect.

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Regional knowledge - lithologyV

s

VpT

VD

ml

• Not all shales behave the same elastically.

• Organic rich shales can have elastic properties

that overlap with hydrocarbon bearing sands.

• Potential for false positives and false negatives.

• Different shale trends might not be obvious

without referring to a wider well dataset.

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Regional knowledge – lithology

• Campanian quartz claystone. A very-fine siliceous claystone encountered by numerous wells on both sides of the Atlantic Margin.

Identified as sandstone based on wireline response – needs core, XRD, microscopy data.

• Many published examples where Campanian sandstone fan systems were targeted – still a very real risk on either side of the Atlantic

Margin.

• Brown, A., Birkhead, S., Mclean, D., Towle, P., White, H., Wu, Y. 2017. The Campanian quartz ‘claystone’ conundrum of the Atlantic Transform Margin. Geol.

Soc. Special Publication no. 438. pp 27-18.

Work on the West African margin relevant to the South American Atlantic margin

c. 83 Ma – Late Cretaceous

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Fylla flat-spot – drilled, monotonous sequence of marine mudstones encountered. Post-drill studies indicate opal CT above the flat-

spot, and micro-quartz below the flat-spot (BSR).

Difficult to predict – need to understand basin-scale processes by referring to regional knowledge.

Simm and Bacon, 2014. Seismic Amplitude: an interpreter’s handbook. Cambridge.

Opal CT - density of 1.9 to 2.3 g/cc

Microcrystalline quartz - density of ~2.65

g/cc

Regional knowledge – lithology

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Case Study #1

Regional Study - Flemish Pass and Orphan Basin

Frontier basins with huge potential

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The challenge

The Flemish Pass and Orphan Basins are large

underexplored basins offshore Newfoundland and

Labrador.

There is little ‘hard’ data in terms of well control.

But there is huge potential in these basins, with oil proven by the

Mizzen well in 2009 (estimated 100-200 million barrels of oil

recoverable).

Ikon Science established a rock physics modelling framework based on

wells along the Newfoundland and Labrador continental shelf.

This framework was used to investigate amplitude anomalies of interest

in the two basins.

This report is publically available online:

exploration.nalcorenergy.com/exploration-reports/rock-physics/Rock Physics Report for East Coast Canada provided by Ikon Science for Nalcor Energy

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Basin porosity depth trend

Upper plot is up-scaled data from the study wells, lower plot is analogue data from mid-Norway – the other side of the

conjugate margin.

Under-compacted (higher porosity at depth) points from mid-Norway are over-pressured sandstones.

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Regional rock physics model

Ve

rtic

al d

ep

th b

elo

w m

ud

lin

e (

m)

De

ep

Sh

allo

w

Vp

(k

m/s)

PhiT (fract.)

Unconsolidated

The model provides a connection between

sandstone porosity, compaction state and

elastic properties.

For each prospect, a sandstone porosity

(high, mid and low case) and expected

compaction state is required.Slightly cemented

2km

0%

2%

4%6%

8%

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Friable2% grain contact cement4% grain contact cement6% grain contact cement8% grain contact cement

Predicted elastic properties of sandstone

TVDml (m)

Vp

(km

/s)

P-wave velocity against depth as predicted by the calibrated RPM and defined porosity-depth trend.

The spread of elastic properties per depth is captured via error bars in the porosity-depth trend, and changes in the

compaction state of the rock.

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Effective stress and elastic properties

The effect of pore pressure on the elastic response of the sands is difficult to separate from diagenetic effects.

Therefore elevated pore pressure in the sands was modelled as a preservation of porosity with depth.

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Shale elastic properties

Empirical Vp-TVD trends per shale facies.

• Mechanically compacted shales in grey.

• Chemically compacted shales in red.

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Prospect analysis

High porosity

Low porosity

Predicted elastic properties were used to populate a variety of different model geometries for prospect

evaluation.

OilOil

Brine

OilOil

Brine

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How to we get regional knowledge into seismic inversion?

Case Study #2

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The challenge

• Many weaknesses have been identified over the last few decades with the industry standard approach to seismic inversion.

These include:

• The difficulty associated with low frequency model construction.

• The lack of appropriate per-facies rock physics within the inversion.

• The fact that the discrete element of the problem (contrasts in facies) is not included in the inversion.

• The inability to include regional knowledge within the inversion scheme.

• Ikon Science, in collaboration with Tullow Oil and CSIRO, have developed an approach to inversion that addresses these

weaknesses.

• An example is provided here of how regional knowledge can be included within this type of inversion.

Gunning, J., Sams, M., 2018, Joint facies and rock properties Bayesian amplitude-versus-offset inversion using Markov random fields. Geophysical

Prospecting, 66, 904-919.

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Regional knowledge within seismic inversion

Seismic Angle Stack Data Wavelet Estimates Noise Estimates

Per Facies Depth Trends and Errors Geological Prior Information

+ +

+ +

Per Facies Rock Physics

=

Seismic Facies and Impedances

Regional knowledge

A method of including facies, and per facies rock physics in seismic inversion.

Allows the addition of regional knowledge to the inversion scheme.

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Regional knowledge within seismic inversion

Pink: wells available

Red: Forties field

Green: Brenda field

Modified from: Roknowledge CNS, Regional Rock Physics and Geopressure Study of the Central North Sea, UKCS presentation,

2014, Ikon Science. Slide 6, Study Database-Location

• Rock physics trends established per facies

and interval from a regional study of 30

wells in the CNS.

• Appropriate trends used to define a prior

model for use in the inversion.

• The inversion was run at two fields to the

north-west of the well database, away from

the wells used in the regional analysis.

• Somoza, A., Waters, K., and Kemper, M.,

2015, Improved Seismic Inversion and

Facies Using Regional Rock Physics Trends:

Case Study from the Central North Sea. Third

EAGE Workshop on Rock Physics.

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Regional knowledge within seismic inversion

Facies

Brenda field Forties field

Soft shale

Hard shale

Brine sand

Oil sand

Regional rock physics trends used within the inversion.

Wells from these fields were not used in the inversion scheme.

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A robust rock physics framework

• We need to use regional knowledge to define robust rock physics models.

• What are the rock types in the basin? – e.g. shale types.

• What is the porosity/compaction trend? Is up-lift or under-compaction at play?

• What is the pressure regime?

• What are the likely saturations?

• Etc.

Rock physics model(s)

Porosity and compaction Lithology

HC type and

saturationPore pressure

and stress

Rock Physics Framework

AVO models to compare to seismic response

Anisotropy

Predicted elastic properties

= regional knowledge

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Regional knowledge – how to tame it.

What we need:

1. To capture the regional rock property

information that we generate.

2. To ensure that work done is audited and

tracked.

3. To increase awareness of work done

across asset teams – has relevant work

previously been performed in an

neighbouring block?

4. To be able to interrogate this

knowledgebase as and when required.

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Conclusions

• Knowing what is happening across a regional scale is invaluable because it gives context to local

conditions.

• Elastic rock properties are controlled by basin-wide geological processes, which can often only be

identified using regional understanding.

• There is a degree of ‘global universality’ in rock physics, where geological processes have predictable

impacts on elastic properties.

• Regional knowledge, as well as integration between different disciplines, is key to developing and

deploying meaningful and robust predictive rock physics models and reducing the possibility of missing

something key.

• To push this further we need to incorporate this knowledge into our inversion schemes.

• Regional knowledge is the key to the successful use of rock physics in prospect evaluation.

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UKCS Regional Study

https://www.ogauthority.co.uk/news-publications/news/2018/new-contracts-awarded-to-help-stimulate-ukcs-exploration-activity/

Ikon Science are currently undertaking a regional analysis of wells in the UKCS for the OGA in order to further understand the

seismic amplitude responses in underexplored Jurassic and Triassic plays.

Thank you

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