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Phase and Polarity Issues in Modern Seismic Interpretation*

Alistair Brown1

Search and Discovery Article #40397 (2009)Posted March 26, 2009

*Adapted from oral presentation at AAPG International Conference and Exhibition, Cape Town, South Africa, October 26-29, 2008

1Consulting Reservoir Geophysicist, Allen, TX (alistair@airmail.net)

Abstract

Zero phase is the objective of almost all seismic data processing today and its interpretive benefits are well knowdifficult to achieve. No more than 50% of seismic data achieves zero phase sufficiently closely for its benefits an

properly enjoyed. Furthermore, 90 degree phase is a remarkably common accident and, if not identified, can caus

interpretation.

All interpreters should know how to visually assess the phase and polarity of their data. I regularly meet those wh

interpretation that the data has a different phase or opposite polarity to what was first thought. In this paper recom

phase and polarity assessment will be made, and several phase circles will be presented. For zero phase data timeco-located, and many interpretive procedures on modern workstations are based on this fact. For other phases com

because time and amplitude are in different locations. Suggestions will be offered for handling the all-too-comm

data.

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PHASE AND POLARITY

ISSUES

INMODERN

SEISMIC INTERPRETATION

AAPG CONVENTION CAPE TOWN, SOUTH AFRICA

26-29 October 2008 by Alistair Brown2008 Alistair Brown

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NATURAL PAIRING2008 Alistair Brown

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ZERO PHASE

GULF OF MEXICO

GAS SAND

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BASEMENT

ZERO PHASE

OFFSHORE EASTERN CANADA

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TOP AND BASE

GAS SAND

TOP OF

BASEMENT

INCREASE IN IMPEDANCE

IS

RED

INCREASE IN IMPEDANCE

IS

BLUE

EUROPEAN

POLARITY

AMERICAN

POLARITY2008 Alistair Brown

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900

600

300

00

P

H

A

S

E

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ZERO PHASE 900 PHASE

AND THERE ARE TWO POLARITIES OF EACHCc 2008 Alistair Brown

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P

H

A

S

E

A

N

D

P

O

LA

R

I

T

Y

A

S

S

ES

S

M

E

NT

O

P

P

OR

T

U

N

IT

I

E

S

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INTERPRETIVE ASSESSMENT OF

PHASE AND POLARITY

EXAMINE CHARACTER OF HIGH AMPLITUDE REFLECTIONS

RELATE TO GEOLOGIC UNDERSTANDINGONE OR TWO INTERFACES?

PAY PARTICULAR ATTENTION TO TERMINATIONS

AND TO UNCONFORMABLE REFLECTIONS

SEEK CONCENSUS AMONG SEVERAL OBSERVATIONS

ITS NOT EASY BUT ITS IMPORTANT2008 Alistair Brown

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GULF OF MEXICO

ZERO PHASE EUROPEAN POLARITY2008 Alistair Brown

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SHALLOW GAS GULF OF MEXICO

ZERO PHASE

EUROPEAN POLARITY

SALT2008 Alistair Brown

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SHALLOW GAS GULF OF MEXICO

PHASE = +900

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MIOCENE GAS GULF OF MEXICO

PHASE = +9002008 Alistair Brown

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ITALIAN PLIOCENE FLUID CONTACT

PHASE = -900

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IGNEOUS INTRUSIVE ROCK

ZERO PHASE

AMERICAN POLARITY2008 Alistair Brown

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MALAYSIAN CARBONATE BUILDUP

PHASE +90

0

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Dont assume thephase and polarity

of your data.

Confirm them with

interpretive observation.

2008 Alistair Brown