AVOAmplitude Variation with Offset

PSTM STACKStandard Wiggle Trace

COMMON MID-POINT RECORDINGUsing multiple source to receiver combinations at varying offset distances.

CMP

SOURCE POINTS RECEIVERS

First offset trace 220 feet

Last offset14,245 feet

COMMON MID-POINT RECORDINGUsing multiple source to receiver combinations at varying offset distances.

CMP

SOURCE POINTS RECEIVERS

First offset trace 220 feet

Last offset14,245 feet

AVO – The amplitude does vary with offset, but its not necessarily an AVO “anomaly” if it looks this way throughout the volume, say due to a

general lithology contact! If its localized, then its anomalous.

COMMON MID-POINT RECORDINGUsing multiple source to receiver combinations at varying offset distances.

CMP

SOURCE POINTS RECEIVERS

First angle4°

Last angle36°

Offset amplitudes converted to angles (AVA). This is the most proper way to investigate such features as the physics of the phenomenon is

related directly to angle of incidence and indirectly to offset.

REFLECTION AT ANGLE OF INCIDENCE

(Vp1)ρ1

(Vp2)ρ2

REFLECTION AT NORMAL INCIDENCE

THE KEY TO AN AVO “ANOMALY” The Bulk Modulus (Incompressibility)

A function of incompressibility only; no shear

Gamma

P-Wave

S-Wave

P-wave and S-wave are proportional to each other except in the pay zone where the P-wave magnitude decreases as a function of gas in high porosity sand.

Vertical case:K = Bulk Modulus only

(Vp1)ρ1

(Vp2)ρ2

(Vp1)/(Vs1)ρ1

(Vp2)/(Vs2)ρ2

COMPRESSION

COMPRESSION&

SHEAR

GENERAL AVO CLASSIFICATION“Intercept”

Zero offset amplitude“Gradient” (slope)

The rate at which the “intercept” amplitude

will change with increasing angle of

incidence

Think of P-Impedance as determining the amplitude of the first trace, and Vp/Vs (Poisson’s Ratio) as determining how that amplitude will change with increasing angle of incidence.

ONSHORE DATA The CDP below is very typical of onshore pre-stack data. It

requires significant pre-stack processing efforts to convert the data into a condition suitable for pre-stack interpretation.

PAY

MISLEADING ATTRIBUTE VOLUMES

STRONG MULTIPLES CAUSE ATTRIBUTE SOFTWARE TO CALCULATE A STRONG NEGATIVE GRADIENT

FALSE AVO INDICATION ON GRADIENT VOLUME CAUSED BY MULTIPLES

False positives on AVO volumes can be very

enticing to drill especially if they

occur on structure. Drilling this feature

based on the attribute volume alone without direct examination of

the gathers would have been a certain

dry hole.

ATTENUATION OF MULTIPLES REVEALS THE TRUE GRADIENT TO BE IN THE POSITIVE DIRECTION

MULTIPLE ATTENUATION YIELDS A MORE ACCURATE AVO ATTRIBUTE VOLUME

The false positive AVO indication observed

on the previous gradient volume has

been removed due to the proper

attenuation of the strong multiples in the

pre-stack data.

FAST ROCK AVO

• SAND – OIL & GAS• LIMESTONE – Gas with liquids• CRYSTALLINE DOLOMITE - GAS• BASEMENT – OIL

UPPER MORROW – AVO

PENNSYLVANIAN QUARTS SAND

ANADARKO BASIN

PENNSYLVANIAN SAND - OKLAHOMAFULL OFFSET MODEL RESPONSE

PAYCLASS I

AVO

STACKED RESPONSE OF PAY SAND VS NO SAND AT ALL?

GEOLOGIC SECTION – FOR SEISMIC SECTIONDICKENSON #1 – P S REYNOLDS #2

108,635 BO10 Foot sand

No sand?

PSTM (Wiggles) - Over AVO Gradient (Color)

AVO Gradient Analysis On Upper Morrow

Peak to trough phase change at

Morrow producer. Negative gradient.

Positive to no gradient at

Morrow interval.

WYLIE #1 - 14 Feet of “Tight” Sand Within 3D

GR - DENSITY GR-ILD

Note the strong reflection across full

range of angles; no AVO

PENNSYLVANIAN SAND - OKLAHOMARAW PSTM OUTPUT VS. FINAL ANGLE GATHER

PAY PAY

FINAL ANGLE GATHERRAW PSTM GATHER250,000 BO 108,000 BO

WELL 1 WELL 2 WELL 1 WELL 2

250,000 BO 108,000 BO

PAYPAY

RED FORK – AVOPENNSYLVANIAN QUARTZ SAND

(Desmoinesian)

ANADARKO BASIN

RED FORK – PSTM STACK

TOP RED FORKPAY

RED FORK – AVO GRADIENT

TOP RED FORK

PAY

RED FORK ANGLE GATHERS

Typical AVO response of a reflector encompassing roughly 100 feet of section, and consisting mostly shale mixed with several small productive sand stringers.

RED FORKALL TROUGH CLASS II AVO

RED FORKPEAK TO TROUGH CLASS II AVO

Typical AVO response of a reflector encompassing roughly 100 feet of section, and containing a 40 foot blocky channel sand .

MARMATON LIMESTONE- AVO

ANADARKO BASIN

MARMATON – LIMESTONEDRY HOLE VS. PRODUCER.

COURTESY OF RYAN PETROLEUM OKC, OKLAHOMA

MARMATON LIMESTONE

ANGLE ANGLE

180,000 BO

COURTESY OF RYAN PETROLEUM OKC, OKLAHOMA

MARMATON LIMESTONE

ANGLE ANGLE ANGLE ANGLE

COURTESY OF RYAN PETROLEUM OKC, OKLAHOMA

OSWEGO – AVOPENNSYLVANIAN LIME

(Desmoinesian) ANADARKO BASIN

“Reservoir quality within phylloid algal mounds is controlled by variations in the abundance of moldic, vuggy, andfracture pore types”

(average porosity = 2%, median permeability = 0.2 md)

James R. Geary 2008

OSWEGO LIMESTONE – AVO ANOMALY

OSWEGO Perfs on

AVO

1 2

COURTESY OF RYAN PETROLEUM OKC, OKLAHOMA

OSWEGO LIMESTONE PRODUCERS1 2

COURTESY OF RYAN PETROLEUM OKC, OKLAHOMA

OSWEGO PRODUCERS PRE-STACK AVO RESPONSE

1 2

OSWEGOUNDRILLED ANOMALY

WIGGLE TRACE OVER AVO ATTRIBUTE

HUNTON – AVO

CRYSTALLINE DOLOMITE (Silurian – Devonian)

ANADARKO BASIN

HUNTON CRYSTALLINE DOLOMITE

COURTESY OF RYAN PETROLEUM OKC, OKLAHOMA

TOP HUNTON LIME

POROUS DOLOMITE

The porous crystalline dolomite is ~1,000 ft/sec slower then the limestone overburden. It therefore has the reflectivity of a trough. Without hydrocarbons, the trough essentially stays the same amplitude across all angles. However, with the introduction of “gas” Poisson’s ratio changes such that the amplitude of the trough dies out with increasing angle, forming a positive gradient.

POROUS WET DOLOMITETROUGH

TOP HUNTON LIME

CLASS IV AVO

UNTESTEDLOCATION

WET DOLOMITE VS GAS DOLOMITE Full Offset Model Response

Wet Porous Dolomite

Gas Porous Dolomite

WET MODEL

GAS MODEL

HUNTON CRYSTALLINE DOLOMITE

TOP HUNTON LIME

CLASS IV AVO IN DOLOMITE

WET DOLOMITENO AVO

RESPONSE

WOODFORD SHALE

SHALE – AVO FREQUENCY ENHANCEMENT

ANADARKO BASIN

WOODFORD SHALE AVOAnomaly weakens down-dip; Possible transition from gas to liquids

Woodford AVO

Woodford

STANDARD PSTMVERTICAL 60 INCHES/SEC

Woodford

FREQUENCY ENHANCED PSTMVERTICAL 60 INCHES/SEC

Woodford

Frequency enhancement significantly improves resolution of the target horizon and better identifies lithology changes and faults. Drilling horizontal wells without it creates unnecessary risk.

THANKS FORYOUR ATTENTION

&CCF RESOURCESOklahoma City