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
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