Introduction

1

Fundamentals of Seismic Acquisition and Processing

Overall Learning Objectives

1. Understand seismic fundamentals as they affect the interpretation of seismic data.

2. Understand the concepts involved in imaging geologic structures and properties through seismic data acquisition and processing.

3. Comprehend the parameters that can seriously affect seismic data quality and costs.

4. Determine if seismic data has been recorded and processed in a technically correct manner for subsurface objectives.

5. Apply quality assurance steps in acquisition and processing.

6. Communicate effectively with seismic specialists.

Introduction

2

Jeff Johnson

3 years Schlumberger NExT Director of Training: Geoscience/Petrophysics - Tulsa

22 years Experience with Amoco/BP Applied Seismic Technology – New Orleans Manager, Geophysical Technology, Amoco International General Manager, Geoscience Research and Technology –

Tulsa/Houston

Academics Stanford Geophysics Degrees Boston College Prof. Geophysics University of Oklahoma Adjunct Research Associate

Introduction

3

Fundamentals of Seismic Acquisition and Processing

Course Overview

• Seismic Wave Propagation and Reflection Principles• Signal Analysis Methods• Acquisition

– Principles– Design– Operations– Quality Control

• Data Processing– Objectives – Signal Corrections– Velocity– Statics– Imaging– Quality Assurance

• Acquisition/Processing for:– Attributes, Inversion, and AVO– Multicomponent

Introduction

4

Learning Methodologies

• Modular • Why modules are important• Powerpoints, short problems, “workshops”,

flip chart• Interactive

– Discussion questions– Share experiences/problems– Learn from each other

• Ask Questions• Daily feedback

Introduction

5

Texas A&M UniversityPetroleum Engineering Center of

Excellence

The University of OklahomaWell Engineering, Geoscience /

Petrophysics Centers of Excellence.

• Commercial Joint-Venture: E&P Training• 150 Short Courses/Programs• University and SLB Instructors• Computer-Based Training• Global Presence• Global Presence

Heriot-Watt University Distance Learning in Petroleum Engineering Center of Excellence

NExTNetwork of Excellence in Training

www.nexttraining.ie

Introduction

6

Module 1

Introduction

Learning objectives

Awareness Level:• Various geophysical methods• Seismic trace, record, section, cube• History of seismic method• Seismic reflection basics• Role of seismic in reservoir life cycle

Introduction

7

Geophysical Surveying MethodsMost geophysical surveying methods can be used either on land or offshore. Each of these methods measures a parameter that relates to a physical property of the subsurface. List of different methods, the parameters they measure, and the related rock properties are indicated in the table 1

Table 1 Geophysical Surveying Methods

METHOD MEASURED PARAMETERPHYSICAL PROPERTY MEASURED OR

DERIVED

SEISMIC TRAVEL TIME AND AMPLITUDE OR REFLECTED/REFRACTED SEISMIC WAVES

ELASTIC MODULI, PROPAGATION VELOCITY, DENSITY?

GRAVITY SPATIAL VARIATIONS IN THE STRENGTH OF THE EARTH’S GRAVITATIONAL FIELD

DENSITY

MAGNETIC SPATIAL VARIATIONS IN THE STRENGTH OF THE GEOMAGNETIC FIELD

MAGNETIC SUSCEPTIBILITY

ELECTRICAL RESISTIVITY

EARTH RESISTANCE ELECTRICAL CONDUCTIVITY

INDUCED POLARIZATION

FREQUENCY-DEPENDENT GROUND RESISTANCE

ELECTRICAL CAPACITANCE

SELF-POTENTIAL ELECTRICAL POTENTIAL ELECTRICAL CONDUCTIVITY

ELECTRO-MAGNETIC

RESPONSE TO ELECTROMAGNETIC RADIATION

ELECTRICAL CONDUCTIVITY AND INDUCTANCE

Introduction

8

Types of Seismic Applications

• 2D land• 3D land• 2D marine• 3D marine• Long offset• Transition zone• Borehole• Multicomponent land• Ocean bottom multicomponent• Time lapse/4D

Introduction

9

Seismic Interpretation

• Objective of seismic acquisition and processing is the accurate interpretation of seismic data

– Travel times– Amplitudes– Attributes– Tied to subsurface control

Introduction

10

Seismic Interpretation

3D Seismic Cube3D Seismic Cube

Introduction

11

S R

• Structure• Lithology• Pore fluid• Fractures• Pressure

What Do We Desire?

Introduction

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Predict and Characterize Subsurface Reservoirs

Introduction

13

Seismic Interpretation

• Basic Seismic Data Concerns– Travel time distortions– Amplitude fidelity– Noise and artifacts– Resolution– Spatial positioning– Cost

Introduction

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Today’s Major Problems

• Backscattered noise• Complex near-surface• Multiples• Anisotropy• Parameters for model driven processing

– Velocity– Q– Anisotropy

Introduction

15

SS RR

Measure:Measure:• Travel timeTravel time• AmplitudeAmplitude• Particle motionParticle motion

Infer:Infer:• VelocityVelocity

The Seismic Experiment

Introduction

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Basic Seismic Measurements

ParticleVelocity

ParticleDisplacementPressure

Tim

e

Introduction

17

The Seismic TraceThe basic unit of seismic data

Amplitude0 +-

Tra

vel T

ime

Introduction

18

Recording Seismic Data

Introduction

19

Typical Scales of Reservoir Investigation

Simulation 100 - 500 feet

Seismic 10’s – 100’s of feet

Logs Inches - feet

Lab Fractions of inch

Introduction

20

Scales of Geological Reservoir Heterogeneity

Fie

ld W

ide

Inte

rwel

lW

ell-B

ore

(modified from Weber, 1986)

Hand Lens orBinocular Microscope

Unaided Eye

Petrographic orScanning Electron

Microscope

DeterminedFrom Well Logs,Seismic Lines,

StatisticalModeling,

etc.

10-100'smm

10-100'smm

1-10'sm

100'sm

10'sm

1-10 km

100's m

Well WellInterwell

Area

ReservoirSandstone

Introduction

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Subsurface Reservoirs• Can seismic predict some key characteristics and properties?

- Depth

- Geologic Setting - Origin of Rocks/Fluids

- Geologic Structure

- Geometry – thickness, areal extent, volume, seals

- Rock Type

- Heterogeneity – Layering, Faults/Fractures, Compartments

- Porosity

- Fluid Content/Distribution

- Pressure Distribution

- Mechanical Strength

- Permeability

- Drive Mechanisms

- Temperature

Introduction

22

Earth Propertiesas seen by seismic waves

• Inhomogeneous• Attenuative• Anisotropic• Porous• Fluid filled

Introduction

23

Characteristics of Seismic Data

• Band Limited– Low End 5-10 Hz– High End 50-100 Hz

• Spatial Coverage Redundant yet Incomplete• Large Data Volumes (up to 10’s of terabytes)

– 2000-4000 time samples per trace– Record length 6-12 sec– 100,000 - 1,000,000 spatial locations– 12-1000 fold redundancy

Introduction

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Exploration Seismic

• Most seismic reflection techniques uses only compressional waves– Easier to acquire– Resolution, data quality generally better– More sensitive to fluid properties

• Use of shear and converted wave data is increasing– May give a good image where compressional data

cannot– Sensitive to porosity; insensitive to pore fluid– Combined with compressional data, tells more

about rock and fluid properties -- Poisson’s Ratio

Introduction

25

Seismic Trace, Record and Section

• A seismic trace, or "wiggle trace" is the response of a seismic detector to the earth's movement due to seismic energy.

– Direct arrival– Refraction– Reflection– Noise

• Excursions of the trace from the central line appear as peaks and troughs; the peaks represent "positive" signal voltages, and the troughs represent "negative" signal voltages.

• A seismic record, or common‑shot record, is a side‑by‑side display of all the wiggle traces that were recorded simultaneously from a number of detectors for a single shot point. The "peaks" are toward the right side of the display and are filled in with black to make patterns more visible.

• Zero time is at the top of the record, with time increasing downward . This display is a raw image of the subsurface over a limited area, and it contains noise and other signal distortions.

Seismic Trace and Record

Distance

Introduction

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Stacking A CMP (Common Midpoint) Gather

S1S2S3S4S5 R1 R2 R3 R4 R5

Collect all data with the same source-receiver midpoint

C M P

Introduction

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Some Terms

CMP - Common MidpointCDP - Common Depth PointCRP - Common Reflection Point

• These terms are sometimes used interchangeably (and erroneously).

• Individual traces are summed (stacked) to form a single trace trace at each CMP surface location

• Much in seismic acquisition and processing is based on assumptions of horizontal beds and homogeneous media.

Introduction

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• Moving the “spread” (source plus receivers) one-half spread length between shots produced continuous subsurface coverage

Seismic Reflection Exploration Overview

Shot 1 Shot 2 Shot 3

First Receiver

Last Receiver

First Receiver

Last Receiver

First Receiver

Last Receiver

Surface

Subsurface Reflector

Subsurface Coverage

Continuous or Single-Fold Subsurface Coverage

Introduction

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• Later, a method called multi-fold or common mid-point (CMP) shooting was developed

• In this method, the spread is moved less than one-half spread length resulting in more over-lap in coverage

• Moving 1/4 spread length means that the same reflections are recorded by two different shots at two different receivers at two different shot-to-receiver distances but the midpoint between shots and receivers is the same! This is called 2-fold shooting

• Increasing the overlap, increases the fold– Move-up of 1/6 spread gives 3-fold– Move-up of 1/8 spread gives 4-fold– Move-up of 1/12 spread gives 6-fold, etc

Seismic Reflection Exploration Overview

S1 S2 M R2 R1 Surface

Reflector

S1 = 1st Source S2 = 2nd Source M = Midpoint R1 = 1st Receiver

R2 = 2nd Receiver

CMP Shooting.

Introduction

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Seismic Reflection Exploration OverviewMulti-fold Coverage

Introduction

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Stacked Trace AfterGeometry Correction

CMP0

Tw

o-W

ay T

rave

l Tim

e

Introduction

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Seismic Trace, Record and Section

• A seismic survey generates a large number of shot records to cover the area under study. Many steps of processing are applied to the data to enhance the signal, to minimize noise, and to increase resolution. All the traces corresponding to a surface midpoint are combined into a single trace, called a common‑mid‑point stack.

• Seismic section

When processing is complete, all the common‑depth‑point stacks are displayed side by side to make a seismic section, which is the final output of a 2D seismic survey.

A Seismic Section

Introduction

33

3-D Seismic3-D Seismic

Introduction

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3-D Prospect Layout Example

Introduction

35

Major Steps in Seismic Reflection Exploration

• Pre-planning

• Data Acquisition

• Data Processing

• Interpretation

Introduction

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Pre-Planning

• Primary & secondary targets• Survey main objectives• Document objectives and priorities• Allocate acquisition & processing budgets• Set data quality specifications• Establish reasonable schedules and deadlinesEstablish reasonable schedules and deadlines• Locate & modify lines of survey• Specify methods & equipment types• Determine acquisition parameters

Introduction

37

Geologic Objective

• Trap type - structural, stratigraphic or combination

• Depth, thickness and areal extent

• Maximum dip expected

• Regional dip

• Modeling

Introduction

38

Acquisition Parameters

• Receiver group spacing• Receiver group arrays• Number of receiver groups• Line spacing/bin size• Number of lines/bins• Maximum and minimum source-to-receiver

distances (offsets)• Source spacing• Source type/arrays• Recording geometry

Introduction

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Processing Parameters• Amplitude scaling parameters to compensate

for signal variation in time and space

• Filter frequencies to suppress noise

• Deconvolution parameters to expand signal bandwidth and shape the wavelet

• Surface wave and refraction velocities for noise suppression

• Near-surface velocities to correct for static shifts

• Velocity fields for stacking CMP data and migrating reflections to their proper position

Introduction

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Reservoir Life Cycle and

Business ValueExploration Appraisal Development Maturity

-

+

Minimize Capex

Minimize Opex

Defer Abandonment

Maximize Production

Maximize Recovery

Accelerate Production

Time

Optimized Development Traditional Development

Cas

h F

low

Introduction

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Seismic in the Reservoir Cycle

• Exploration –increasing 3D but sometimes still 2D

• Appraisal – 3-D

• Development – High Resolution 3D, Borehole

• Management – 4D/Time-lapse

Introduction

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Discussion

Is 2-D seismic ever done today?

If so, what is its role?

How does your company perceive the value of seismic methods?

Introduction

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Business Success Depends on Technology Integration Focused on the Reservoir

Geophysics

Petrophysics Geology

Engineering

Drilling Computing

Reservoir

Prediction Description

PerformanceOptimization

Characterization

Introduction

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Seismic Today

Quantitative seismic images have become critical for business success in all subsurface reservoir projects.

Introduction

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Critical Capabilities forSeismic Reservoir Prediction

Rock Physics

Imaging

Attributes

Introduction

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A Technical Vision

• Seismic data will be routinely transformed to depth images

• Volume image processing and multi-volume picking will provide accurate reservoir / trap frameworks

• Attribute analysis, multi-component inversion, and petrophysical calibration will provide reliable estimates of 3D subsurface rock and fluid properties throughout the reservoir exploration / production cycle.

• Every geophysical prediction will be qualified by its uncertainty / risk.

Introduction

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Seismic to Reservoir Transformation

Detection

Visualization

Classification

Detection

Visualization

Classification

ReservoirModels

ReservoirModels

FrequencyFrequency

CoherencyCoherency

AngleAngle

PP SS

VectorSeismic

Data

VectorSeismic

Data

MultidimensionalDepth

Images

MultidimensionalDepth

Images

MultipleAttributeVolumes

MultipleAttributeVolumes

AIGeostatisticalInterpretations

AIGeostatisticalInterpretations

Geological / Rock PhysicsConstraints

Geological / Rock PhysicsConstraints

Rock / Fluid Physics Modeling

Calibration

Rock / Fluid Physics Modeling

Calibration

SimulationIterations

SimulationIterations

RatesVolumes

Uncertainty

RatesVolumes

Uncertainty

AVOAVO

QQ

Rock / Fluid Physics Modeling

Calibration

Rock / Fluid Physics Modeling

Calibration

Amoco, RIP - 1997Idealized Multidimensional Process

Introduction

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Summary

What have we learned?

• Objectives of seismic and overall role in reservoir cycle

• Basics of CMP seismic

• Steps in seismic projects

• Role of seismic in E&P business