Geophysics Part 2

EXPLORATION PHASE

Sedimentary Sedimentary Basin in Indonesia

PSC Blocks in Indonesia

Common Practices • In Exploration New Ventures; company is looking for new oil & gas fields Subsurface team commonly need to design • Subsurface seismic acquisition – e.g. 2D regional  – Seismic data to validate structure from potential methods  – Seismic in denser grid than initial 2D set

Geophysicist should have familiarity familiarity with seismic • Geophysicist operations  – Acquisition  – Processing

Acquisition - Considerations • Depth of target horizon  – 2,000 m? 3,000 m?

• Objectives of the data  – Structure  – Stratigraphy

• Resolution? Fold? • Think of structure size we want to image  – 10x10 km? 20x20km? Other?

• Cost will be trade-off 

Seismic Acquisition – Case Kalimantan

Denser grid around the exploration well

20km

Goal of Seismic Processing • In Exploration New Ventures phase, processing usually focus on getting good seismic image for structural interpretation • Due to very far distance between seismic line, the objective of using amplitude is rare • Hints to stratigraphy / deposition of environment generated using geological concepts (tectonics, sequence stratigraphy, and depositional model)

Pre Seismic Interpretation •

Data Loading; QC of seismic navigation

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Seismic Balancing

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Amplitude balance?  – Only if there is working AVO case Davin et al, IPA 2003

Seismic Section of Data Used for Structural Interpretation

Before

Seabed Increase impedance

After

Shift for better match

Regional Seismic Interpretation - Example •

Regional Structural Cross-section

Barber et al, IPA 2005

Focus on package of sedimentation (formation/group) Thinking on sedimentation and deformation timing

FIELD APPRAISAL GEOPHYSICAL VIEWS

Appraisal • So we have a discovery. What’s next? Map View Consideration

Area 1  – small size Area 2 – medium size

Exploration Discovery

Area 3 – large size

• The one million dollar question: how much is the true recoverable hydrocarbon?

Appraisal Objective • We need to know the real ‘prize’  – Better understand key elements • Structure • Reservoir distribution • Fluids  – HC phase  – SW

• Well performance

 Appraisal Example  – ABC Field ABC field:

Uncertainties : •

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Discovered in 1998.

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Large closure but low pressure gas

Mapping Interpretation Gridding Depth modeling Reservoir Properties Reservoir distribution unknown Water Saturation issue High SW despite evidence gas content No flow test •

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•

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Wide range of potential EUR

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Dedicated field to a gas contract

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Limited study to date

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Preliminary map cases:   

Sand A Sand B Sand C

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•

•

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ABC Field Appraisal Objective • Appraisal well would be required to

determine : 1. Water Saturation 2.Flow-rate 3.Permeability 4.Gas Composition 5.Optimum viable development with right amount of wells tied to cost –

3D Seismic in Field Appraisal • It is common practice to acquire 3D seismic after well discovery  – Whenever condition allows • Oil price • Access to the area (onshore)

 – When VOI (Value of Information) is positive • e.g if 2D seismic alone is not sufficient • e.g if reservoir is complex laterally

3D Seismic Simple Workflow

Seismic for Better Image • 3D seismic acquisition justification  – To reveal faults/compartments  – To reveal reservoir facies  – AVO for fluid effects • AVO Amplitude Variation with Offset

3D Seismic Acquisition – General Workflow

3D Seismic Advantage • Improved Structural Correlation between wells Well 1

Well 2

Well 3

3D Seismic Reveals Reservoir Geometry Seismic Horizon Slice

IPA, 2008

Seismic Section

3D Seismic in Very Thick Carbonate Reservoir

Detailed intra-carbonate reflections stand out on the final PreSTM volume

Seismic Identified HC Pay Structure Overlain by

M well

Arang Z-2 Amplitude map MFS 900

Top Arang Z-0

Far Stack Seismic Amplitude Top Arang Z-1

1 Top Arang Z-2

Top Arang Z-3

Top Arang Z-4

Base Arang Z-4

Bright spot conforms to structure

2

Another bright spot conform to structure

PetroZuata Case – Why Seismic is Needed

Geologic Background Reservoirs Characterized by: • • • •

Mixture of fluvial, distributary, and tidal estuarine deposits Mean sand thickness is 22ft Seismic resolution ~20-30 ft Can’t resolve top/base for most sands.

PetroZuata Background - Seismic

East Area Main Area 3D Seismic Acquired 1996

South Area

10 km

How do seismic data impact well planning? HI22-1S

IJ21-1S

? 4400 ft.

How far does the thick sand in IJ21extend?

How do seismic data impact well planning? IJ21-1S

HI22-1S

4400 ft.

3D seismic are critical data needed to interpret between the wells. Identifying Targets, Placing Laterals

How do seismic data impact well planning? IJ21-1S

HI22-1S

4400 ft.

Seismic stratigraphy fundamentals correctly predicted the edge of the channel system.

How do seismic data impact well planning? IJ21-1S

HI22-1S HI22-1C

HI22-1C

Identifying Targets, Placing Laterals

How do seismic data impact well planning? Mapping depositional trends with seismic attributes.

Shale

Sand

Better Prediction of ‘Economic Value’ • Since we know better the key elements  – Structure • Know better shape of the trap

 – Reservoir distribution • Know better shape of the reservoir (e.g sand distribution)

• Improvement of HCIP and EUR  – RF is based on analogue

• Better predict the ‘economic value’

Quiz Define the terminology in the picture

Quiz • What is migration apron? • Mention at least three critical parameters we want to know/improve during field appraisal.

FIELD DEVELOPMENT GEOPHYSICAL VIEWS

Development – The Workflow 

Seismic interpretation 

Horizon picks 

consistency with reg. framework 

Depth conversion   Amplitude extraction 

 Aim

for stratigraphic features  Fluid detections 

Geology Sequence stratigraphic frameworks  Reservoir characterization   Volumetric - GeoX  Geomodel 

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Reservoir Engineering 

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Reservoir model

Well Planning

Critical Risks and Uncertainties: • Hydrocarbon Saturation • Seal Capacity • Reservoir Quality

3D Seismic Interpretation in Ideal Development Case (Fluids & Stratigraphy)

Seismic data drives interpretation of stratigraphy and depositional environment

geoseismic-asia.blogspot.com

Seismic data indicates presence of fluid contact

Case – HC Well Defined Structure Overlain by

Arang Z-2 Amplitude map

Far Stack Seismic Amplitude 1

2

Within this example; There is little HC uncertainty due to seismic data is very good and correlated very well with Pay

Rock Physics Importance for Reservoir Characterization

Forward Modeling

• Modeling approach – sensitivity of reservoir to different seismic frequency • The reservoir is ideally to resolved by 55 Hz • Low frequency case still work for 30 Hz

Forward Modeling

• Modeling approach – does impedance alone differentiate reservoir vs non-reservoir? • The reservoir could not be differentiated using seismic impedance • Another seismic attributes is required

Seismic Reflection: Well-Planning • 3D View of Integrated Subsurface System • Define detailed subsurface targets

Seismic Time Lapse • Rock physics models are required to interpret time lapse changes in elastic properties • Whether it is due to reservoir pressure or fluid saturations

Time Lapse Responses

Time Lapse Case