seismic interpretation

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SEISMIC INTERPRETATION

&

RESERVOIR CHARACTERIZATION

UNIVERSITAS GAJAH MADA

20 OCT 2012

GERANICKY DELISATRA

PHE ONWJ

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Geranicky Delisatra, Geophysicist – PHE ONWJ

Presentation Outline

• Introduction

• Fundamental of Seismic

• Seismic Data Acquisition & Processing

• Seismic Interpretation

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Presentation Outline

• Introduction

• Fundamental of Seismic

• Seismic Data Acquisition & Processing

• Seismic Interpretation

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Introduction

• Seismic play an important role in every phase of oil &

gas industry

• Exploration phase  usually 2D seismic data;

exploration play concept, prospect identification,

exploration well drilling, appraisal well drilling

• Development phase  usually 3D seismic data;

reservoir characterization, geological modeling, infill well

drilling, field development

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Exploration

Source Rock ?

Structural Trap

Stratigraphic Trap

• Working with minimum data; wells, seismic, etc • Building exploration

concept

• Prospect identification • Prove petroleum system • If exploration well succeed,

drill appraisal well to estimate reserve accumulation Mass Transport Complex Basement high/ Thinned section

Figure 7: Idealized GDE

Highlighting Additional Features with Patterns

SLOPE MUDSTONES SHELF MUDSTONES BASIN FLOOR MUDSTONES Nonmarine Deep Water Sands

(Fans)

Deep Water Sands (Fans)

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Development

• Dealing with numbers of well data, 3D seismic, engineering data

• More detailed work; field scale to reservoir scale • Reservoir characterization; property prediction, fluid

identification

• Building geological model as an input for reservoir simulation

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EOR

• Using 4D seismic data

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Presentation Outline

• Introduction

• Fundamental of Seismic

• Seismic Data Acquisition & Processing

• Seismic Interpretation

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Basic Seismic Concepts

S = R * W S = Seismic R = Reflection Coeff. W = Wavelet RC IA1 IA2

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Polarity & Phase

Normal Polarity Reverse Polarity Minimum Phase Zero-Phase RC + RC +

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Knowing Polarity & Phase

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Exercise

Shale ρ = 2.4 g/cc V = 3000 m/s Tight Limestone ρ = 2.7 g/cc V = 6000 m/s Shale ρ = 2.4 g/cc V = 3000 m/s

RC = (IA2 – IA1)

(IA2+IA1)

IA = ρ x V Wet Sandstone ρ = 2.6 g/cc V = 4000 m/s RC1 RC2 RC3

*

=

RC S

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Vertical Resolution

Remember:

λ = V x f

Where λ = wave length (m) V = velocity (m/s) f = frequency (Hz)

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Presentation Outline

• Introduction

• Fundamental of Seismic

• Seismic Data Acquisition & Processing

• Seismic Interpretation

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Seismic Data Acquisition

• Type of survey:

– Land

– Transition

– Marine

• Type of data:

– 2D

– 3D

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Presentation Outline

• Introduction

• Fundamental of Seismic

• Seismic Data Acquisition & Processing

• Seismic Interpretation

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Seismic 2D/3D data

Subsurface Geological

Information

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Required Data for Seismic Interpretation

• Basemap

• Well Data

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Basemap

• Basemap is useful to know your map

view location while interpreting seismic

section

• Basemap will give us information about

coordinates, well location, 2D seismic

lines, 3D seismic area, scale bar, etc.

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Well Data

• Type of well data:

 Digital data (LAS or ASCII

format)

 Hardcopy (Final well report,

well completion, etc.)

• Well Data:

 Logs:

Gamma

Ray,

SP,

Resistivity, Density, Porosity,

Sonic

 Checkshot

• Well data will give us information

about geological condition, interest

zone, tested zone, top formation, etc.

CS KORINCI-1A y = 0.0003x2_{+ 0.6078x + 9.5} R2 = 0.9992 0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1200 TIME (ms) D E P T H ( m )

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General Steps in Seismic Interpretation

WELL-SEISMIC-TIE

FRAMEWORK MAPPING

- HORIZON PICKING - FAULT MAPPING

TIME-STRUCTURE

MAP

DEPTH-STRUCTURE

MAP

TIME-DEPTH

CONVERSION

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Well-to-Seismic Tie

• A process of tying well data

with seismic data by

correlating synthetic

seismogram with seismic

data

• Matching between well

marker (formation top,

top/bottom reservoir, etc.)

with certain reflector event in

seismic data

• Decide which reflector event

will be picked as horizon

Top B2a

Top B2b

Top B3a

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Horizon Picking

• This step is done after defining

which recletor event will be

picked as horizon

• Most of seismic interpretation

work is horizon picking

• Purpose : framework mapping,

amplitude mapping

What event to be picked? Well-to-seismic

tie will give you the answer

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Horizon Picking

Amplitude Extraction

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Fault Interpretation

• Fault interpretation must be

confirmed with regional geology

(strike/dip), tectonic regime

(extensional/compressional), etc.

• Know your fault better; is it normal

fault? Thrust fault? Wrong fault

interpretation will lead into wrong

framework

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Time-Structure Map

• Picked horizon and fault will be grid to

generate structure map. Since horizon

value is in time domain, the structure map

is called time-structure map

• To have a real subsurface information,

time-structure map should be converted

into depth-structure map

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Time-Depth Conversion

• Required data to convert

time-structure map to depth-time-structure

map is velocity

• Remember; D = V x t

• Velocity data can be obtained

from:

– Checkshot – Stacking data – VSP

• Depth-structure map is a product

of multiplying time-structure map

with velocity function. Velocity is

varied with depth and geological

condition

CS KORINCI-1A y = 0.0003x2 + 0.6078x + 9.5 R2_{= 0.9992} 0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1200 TIME (ms) D E P T H ( m )

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Depth-Structure Map

Time-structure Map Depth-structure Map

• Depth-structure map represent subsurface structural condition

• Due to velocity variation, depth-structure map can be different with time-structure map

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Direct Hydrocarbon Indicator (DHI)

• A quick look for hydrocarbon indicator

• Common DHI:

– Bright spot

– Dim spot

– Polarity reversal

– Flat spot

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Some Technique to Guide Seismic Interpretation

• There are some technique to guide seismic interpretation

• Using seismic attributes (phase, frequency, amplitude)

• Good for quick interpretation

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Coherency

Coherence

Reflectivity (amplitude)

• Coherency attribute

detects discontinuity

in seismic reflector

• Good in detecting

fault or stratigraphic

features

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Instantaneous Phase

Reflectivity (Amplitude)

Instantaneous Phase

• Instantaneous Phase

attribute balance the

weak

and

strong

reflector

• Good

in

tracing

reflector continuity

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Instantaneous Frequency

Reflectivity (Amplitude)

Instantaneous Frequency

• Instantaneous Frequency gives an information

regarding frequency at certain time

• Gas column will absorp frequency content,

therefore, frequency below gas column will be

decreased

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Some Problems & Pitfall

• False Bright Spot

• Pull-up effect

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False Bright Spot

• Gas sand and coal have a low impedance contrast with overlying shale

• Both gas sand and coal will give strong negative amplitude

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Mis-tie

• Mis-tie is a time gap between

intersecting seismic lines due

to different vintage or different

processing parameter ataupun

parameter processing yang

berbeda

• Mis-tie only occur in 2D

seismic data

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Presentation Outline

• Introduction

• Fundamental of Seismic

• Seismic Data Acquisition & Processing

• Seismic Interpretation

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Reservoir Characterization Method

• Seismic reservoir characterization is necessary

to predict reservoir property (porosity, Sw, etc.)

and its fluid contents (oil, gas, water)

• More quantitative analysis

• Require Rock Physics

• Basically, there are 2 main methods:

– Seismic AI Inversion

– Amplitude Variation with Offset (AVO)

– Multi-attribute

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Basic Theory

Seismic

Acquisition

Earth * Wavelet = Seismic

Seismic / Wavelet = AI

Seismic

Inversion

AI Earth

Reservoir

Characterization

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Workflow

Wavelet

Estimation

Feasibilty

Study

Buidling

Initial Model

Invert

Seismic

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Workflow

Wavelet

Estimation

Feasibilty

Study

Buidling

Initial Model

Invert

Seismic

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Workflow

Wavelet

Estimation

Feasibilty

Study

Buidling

Initial Model

Invert

Seismic

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Workflow

Wavelet

Estimation

Feasibilty

Study

Buidling

Initial Model

Invert

Seismic

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AVO

AVO stands for Amplitude Variations with Offset, or

Amplitude Versus Offset

The AVO technique uses the amplitude variations of

pre-stack seismic reflections to predict reservoir fluid effects

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Basic Concept

Velocity

NMO

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Basic Theory

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Offset

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AVO Classification

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The Rutherford and Williams classification scheme as

modified by Ross and Kinman (1995).

Class 1 AI Sand > AI Shale Class 2 AI Sand ≈ AI Shale Class 3 AI Sand < AI Shale

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Background

• Shallow biogenic gas in Lower Petani

Fm. → main exploration target

• Appear as

‘bright spot’ on Post-stack

seismic section

• Coal in Upper Petani Fm. also appear

as ‘bright spot’

• Bright spot can be a DHI, but also a

pitfall as well

• Several dry-holes by the same pitfall

Coal

Gas Sand

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Geranicky Delisatra, Geophysicist – PHE ONWJ Decrease Impedance Decrease Impedance Top Gas Sand Top Coal

What Makes it Happen?

Decrease in Impedance cause a negative Reflective Coefficient, and therefore appear as strong negative amplitude in seismic section

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Relationship Between AI & AVO Class

• Shallow biogenic gas

are above 1200 m

• AI value of gas sands

< shale  Low

impedance sand

• The crossplot between

AI and depth suggest

that those shallow gas

is classified into class

3 gas sand

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AVO Modeling of Gas Sand and Coal

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AVO Classification

Gas Sand Coal Intercept (-) Gradient (-) AVO Class 3 Intercept (-) Gradient (+/-) AVO Class ???