Introduction to Seismic Interpretation

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EPT-LD

C. Höcker, SIEP, EPT-S 1

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3D seismic

-an overview

• an acoustic image of the subsurface

• a volume made up by a series of ‘seismic lines’ • reflection time contains

information on depth of subsurface interface

• reflected energy contains information on properties

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Aspects of Seismic Interpretation



Bridge between Geophysics and Geology

(can we see a seismic section as a geological profile?)



Tries to overcome the ‘non-uniqueness problem’



Balance between ‘Science’ and ‘Art’

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History of Seismic Exploration





1900

theory of reflected and refracted waves



1914-1918 (WW1) locating heavy guns by recording arrival

times



1919

Mintrop: patent on the refraction method

(salt dome discovery, Texas)



1920’s

reflection method (Oklahoma)



1953

magnetic tape: analog recording



1956

patent on CDP method



1975

first 3D surveys

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The Old Way

A refraction shot in West Texas. 2,000 pounds of dynamite shot by Humble Oil & Refining Company (now Exxon), 1930.

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Salt dome exploration (Texas, 1930)

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The seismic reflection technique

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Advantages of 3D over 2D Seismic



Spatial continuity

(less correlation problems)



Correct positioning

due to 3D migration

(no ‘side-swipes’)

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2D vs. 3D Migration

Dipping

events are not

focussed with

2D migration

but are with

3D

Events with out-of-plane dip are not focused with 2D migration but are with 3D

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Maps from 2D and 3D Seismic Interpretation

2D

3D

• 3D likely increases the number of faults in a subsurface description • but it also likely will increase the geological feasibility of a fault pattern

closure shape updip of 15-B-4X

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Reacquisition and/or Reprocessing:

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1983 1994

Reacquisition and/or Reprocessing:

Improving Resolution

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Time Migration 1993 Cluster PreSDM 1998 Enhanced PreSDM 1999/2000 Post Migration

Structurally Oriented Filtering 1999/2000

Improvements in Migration and Noise-Suppression

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Influence of Workstation Technology on Interpretation

Started new era by:



high accuracy of time picking



autotracking of seismic horizons



immediate extraction of amplitudes in grids, next to time grids



application to 3D seismic opens up new manipulations like:

 creation of random lines

 interpretation of timeslices

 reservoir characterisation from continuous attributes

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3D data cube in visualisation environment

Detailed faults can

be seen on the 3D

cube. Hydrocarbons

(gas) show as green.

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The Interpreter at work

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Virtual Reality

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Seismic Interpretation – Positioning the Skill



An inter-disciplinary skill

 between geology, geophysics, petrophysics & reservoir engineering -often ‘homeless’ between geology and geophysics skill pools

 strong presence in E&A and early development –

straddling prominent boundaries in Global Processes



Boundary towards quantitative interpretation (QI) not well

defined



Traditionally more involved in early modelling steps in the asset

life cycle

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Skill Position of Seismic Interpretation

depth conversion

velocity model

quantitative interpretation

property model

sequence-stratigraphic interpretation

stratigraphic / facies architecture model

structural interpretation

structural model

Seismic

Interpretation

Geologist:

marker depths from logs facies from logs and cores,

depositional history

Reservoir Engineer:

volumetrics, simulations, development options, field development plan,

well plans Petrophysicist: physical properties from logs Geophysicist: seismic (Re-) Processing Bio-Stratigrapher:

Markers and bio-facies from cores & cuttings

Structural Geologist:

faults & fracture prediction, tectonic history

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Subsurface Modelling Stages

as applied in the Oil&Gas Industry

Field Development Planning Development Plan Facilities Planning Facility Design Dynamic Reservoir Modelling

Fluid Movement Model

Static Property Modelling Property Model Reservoir Architecture Modelling Layer/Object Model Velocity Modelling/ Seismic Processing Velocity Model Structural Framework Modelling Struct.&Stratigr. Model

 = impact of seismic data

    

Seismic Processing

 Velocity Model

Structural Framework Modelling

 Framework of Structural &

Large-Scale Stratigraphic Surfaces

Reservoir Architecture Modelling

 Detailed Layer/Object Model of Reservoir

Static Property Modelling

 3D Model of Properties

Dynamic Reservoir Modelling

 4D Model of Fluid Movements

Field Development Planning

 HC Development Scenarios

Facilities Planning

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Velocities

from Seismic Data

Velocities from Well Data

Velocity Model Building Stacking & Migration Pre-Stack Processing Well Data Preproc/Interpr

Velocity Modelling and Seismic Processing

• Exploration / Appraisal / Production • 2D and 3D Seismic

Processing Geophysicist Seismic Interpreter

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Structural Framework Modelling

Filtering & Interpret. Proc.

Structural&Stratigraphic Segmentation

Tops & Faults from Well Data

Closure-Catchment Analysis Structural&Stratigraphic Model Building Volumetric Analysis Compartmentalisation Analysis Well Data Preproc/Interpr Palinsp. Reconstruction Basin Modelling Depth Conversion Velocity Model

• Exploration / Appraisal / Production • 2D and 3D Seismic

Seismic Interpreter

Quantitative Interpreter (GP) Petrophysicist

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Segmentation into Layers/Objects

Genetic/Property Units from Well Data

Layer/Object Model Building Deposition Modelling Interpretive Processing Volumetric Analysis Well Data Preproc/Interpr

Stratigraphic / Reservoir Architecture Modelling

• Appraisal / Production • 3D Seismic

Seismic Interpreter Petrophysicist Geologist

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Static Property Modelling

Seismic Modelling/ Seismic Inversion Rock/Fluid Properties & Fractures from Well Data

Property Model Building Seismic Preprocessing Volumetric Analysis Compartmentalisation Analysis Well Data Preproc/Interpr Reservoir Simulation • Appraisal / Production • 2D and 3D Seismic Quantitative Interpreter (GP) Petrophysicist Geologist Reservoir Engineer

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4D Seismic Analysis / Seismic Modelling

Fluid Properties / Pressure / Production

from Well Data

Property Model Update Seismic Preprocessing Well Data Preproc/Interpr Volumetric Analysis Compartmentalisation Analysis Reservoir Simulation / History Matching Quantitative Interpreter (GP) Geologist Reservoir Engineer Production Technologist

Dynamic Reservoir Modelling

• Production

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0 200 400 600 800 1000 1200 1991 1992 1993 1994 1995 1996 (MM BOE) $0.00 $1.00 $2.00 $3.00 $4.00 $5.00 $6.00 $7.00 $8.00 ($/BO E) cost of finding resources found from Brown 1999

Amoco’s exploration balance,

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Seismic Interpretation in Integrated Reservoir Modelling



Who are the customers of seismic interpretation results?



What do they want?



When do they want it?



Software portfolio – recent movements

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Reservoir

Properties

Optimised

Field

Development

Reservoir

Structure

Production

History

Integrated Field Model

Reservoir

Architecture

Integrated Field Study Methodology (1)

 Global Process #5: IRM

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Raw Data Rock Model Property Model Upscaled Simulation Model Rule Sets

Multiple Realisations Constructed Using Different Assumptions

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Integrated Field Study Methodology (3)

STUDY

COMMENCES

STUDY CONCLUDES

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Model Complexity STUDY CONCLUDES STUDY COMMENCES Data Analysis

DATA

Field

Development

Plan

Economics

Forecasting

0 2 4 6 8 10 12 14 16 18 20 No Prod.&Inj .Constr

Sm.Comp+Opt W orkovers W .Inj ection H.well3 Lg.Comp+Opt Optim. Void

Scenario U R ( M M m 3 ) Low Case Median Case High Case Simple/ Conceptual Models Simple Full Field Model Regional Seismic Logs Core SCAL PVT Well Data Production Data Detailed Full Field Model

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Iterative Cycles in Subsurface Interpretation



Execution in iterative cycles:

 parallel rather than sequential work in integrated teams

 cycles of improving the model and assessing its behaviour in dynamic and economic modelling

 additional cycles increase detail and confidence of single instances or generate new instances / scenarios

 intermediate products should be complete at current level of maturity and detail  interruption or abandonment of work due to changed priorities does