Seismic Inversion

Pre and Post Stack

Carlos CobosSeptember 2010

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

What is Seismic Inversion?

Seismic inversion is the process ofconverting seismic reflection datainto seismic impedance (volumetricrock properties).

Seismic Inversion Classification

Seismic

Inversion

Deterministic

Stochastic

Band Limited Inversion

Generalized Linear Inversion

Sparse Spike

Parametric (Gaussian)

Non-Parametric

Post-Stack

(Single)

Pre-Stack or

Elastic

(Simultaneous)

Post-Stack

(Single)

General Seismic Inversion Work Flow

Low Frequency

Model

Seismic

Data

Wavelet

ExtractionInversion

QC Impedance

Data

Seismic Inversion Limitations

Vertical Resolution: The vertical resolutionof the seismic impedance is limited by thebandwidth of the input seismic data.

Low Frequency Model: The accuracy ofthe calculated impedance volume isaffected by artifacts in the low frequencymodel.

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

Vertical Resolution

A typical deterministic inversion exhibits

a vertical resolution of approximately

/4. At a frequency of 30 Hz andassuming a P-wave velocity of 9000 ft/s,

the tuning wavelength (/4) is 75 ft.

Vertical Resolution

1 20 Hz Ricker Wavelet

2 30 Hz Ricker Wavelet

3 40 Hz Ricker Wavelet

4 60 Hz Ricker Wavelet

5 80 Hz Ricker Wavelet

Inverted with Generalized

Linear Inversion

1 20 Hz Ricker Wavelet

2 30 Hz Ricker Wavelet

3 40 Hz Ricker Wavelet

4 60 Hz Ricker Wavelet

5 80 Hz Ricker Wavelet

Original Seismic Data

Central Frequency: 30 Hz

Average Velocity: 12500 ft/sec

Vertical Resolution: 104 ft

High Resolution Spectral Inversion

Central Frequency: 310 Hz

Average Velocity: 12500 ft/sec

Vertical Resolution: 10 ft

Original Seismic Data

Central Frequency: 30 Hz

Average Velocity: 12500 ft/sec

Vertical Resolution: 104 ft

High Resolution Spectral Inversion

Central Frequency: 310 Hz

Average Velocity: 12500 ft/sec

Vertical Resolution: 10 ft

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

Low Frequency Model

Due to the band limited nature of the

seismic data, seismic inversion cannot find

a unique solution. Therefore, two types of

data are needed for the inversion process:

the seismic data and a low impedance

model that constrains the possible

solutions.

Low Frequency Model

Low frequency models are derived from well log

data, NMO or pre-stack time migrated velocities.

Low frequency models generated from well log data

are influenced by the amount of wells and the

interpolation algorithm used for the model creation.

On the other hand, seismic velocities models are, in

many cases, too smooth for a high resolution

inversion process.

Raw Dense Interval Velocities

Interval Velocities

After Spatial Smoothing

Interval Velocities After REVEL

Interval Velocities After REVELwith Seismic Overlay

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

General Inversion Process

Relative

Impedance Trace

Absolute

Impedance Trace

Wavelet

Reflectivity Trace

Seismic Trace

Synthetic Trace

Low Frequency

Model

High Resolution Velocity Model

Post Stack Inversion Generalized

Linear Inversion[m*g]/[cc*sec]

High Resolution Post Stack Inversion

Generalized Linear Inversion[m*g]/[cc*sec]

Post Stack Inversion Generalized

Linear Inversion[m*g]/[cc*sec]

High Resolution Post Stack Inversion

Generalized Linear Inversion[m*g]/[cc*sec]

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

Why Pre-Stack Inversion?

1. The seismic inversion process is better

constrained if S-wave information is

included into the minimization process.

2. Information carried by a pair of seismic

attributes is typically more robust than

the information obtained by a single

seismic attributes.

Why Pre-Stack Inversion?

0.2 0 0.2 0.4 0.6 0.28000

8500

9000

9500

10000

10500

11000

Probability Density

Vp [

ft/s

ec]

0.2 0 0.2 0.4 0.6 0.23500

4000

4500

5000

5500

6000

Probability Density

Vs [

ft/s

ec]

0.4 0.2 0 0.2 0.42.2

2.3

2.4

2.5

2.6

2.7

Probability Density

Bulk

Density [

gr/

cc]

0.2 0.1 0 0.1 0.21.9

2

2.1

2.2

2.3

2.4

2.5x 10

4

Probability Density

Acoustic I

mpedance

Sands-Shales Elastic Properties

AVO Intercept-Gradient Statistic

Success

Rate

Brine

Success

Rate

Gas

Success

Rate

Shale

Success

Rate

Total

Information

Entropy

Intercept 0.52 0.84 0.54 0.61 0.33

Gradient 0.47 0.63 0.62 0.59 0.30

Inter-Grad 1 1 1 1 1.09

Why Pre-Stack Inversion?

1 2 3 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Ro G Rp Rs AI EI Ip Is

Information Carried By single

Attribute

0.9

0.95

1

1.05

1.1

1.15

Info

rmat

ion

R0-G Rp-Rs

AI-EI

Ip-Is

Information Carried By Pair of

Attributes

Fusions Flow for High Resolution Simultaneous Absolute Impedance Inversion

BRAVOTM

REVELTM

Low Frequency Models

P-Impedance S-Impedance

Reflectivity Sections

P-Reflectivity S-Reflectivity

High Resolution

Reflectivity Sections

P-Reflectivity S-Reflectivity

High Resolution

Impedance Sections

P-Impedance S-Impedance

Rock Properties Analysis

Rock Properties Analysis

Outline

What is Seismic Inversion?

Vertical Resolution

Low Frequency Model Estimation

Post Stack Seismic Inversion

Pre Stack Seismic Inversion

Observations

Observations

1. The combination of high resolution velocityresidual analysis and high resolution spectralinversion coupled with seismic inversionengines improve the accuracy and verticalresolution of the final absolute impedancevolume.

2. Simultaneous elastic inversion is the mostrobust deterministic inversion method becauseit is better constrained by the inclusion of S-wave information into the minimizationprocess.