--> Delineation of a Diagenetic Trap Using P-Wave and Converted-Wave Seismic Data in the Miocene McLure Shale, San Joaquin Basin, California, by Robert Kidney, John Arestad, Anne Grau, Robert Sterling, #20012 (2003).
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Delineation of a Diagenetic Trap Using P-Wave and Converted-Wave Previous HitSeismicNext Hit Data in the Miocene McLure Shale, San Joaquin Basin, California*

By

Robert Kidney1, John Arestad2, Anne Grau1, and Robert Sterling1

 Search and Discovery Article #20012 (2003)

 

*Adapted from an oral presentation at the AAPG’s annual convention, 2003, Salt Lake City, Utah, May, 2003. A companion article, entitled “Success! Using Previous HitSeismicNext Hit Attributes and Horizontal Drilling to Delineate and Exploit a Diagenetic Trap, Monterey Shale, San Joaquin Valley, California,” is Search and Discovery Article #20011 (2003).

1EOG Resources, Inc, Denver, CO ([email protected])

2ExplorTech, Littleton, CO

Abstract

North Shafter and Rose oil fields, located in California’s San Joaquin Basin, produce hydrocarbons from a subtle stratigraphic trap within the Miocene Monterey Formation. The trap-reservoir system was created during the burial process of a thick diatomaceous shale sequence that forms various diagenetic facies. Integration of well and 2-D p-wave Previous HitseismicNext Hit data shows that a significant amplitude anomaly is present over both the reservoir (quartz) and seal (Opal-CT) facies, making delineation of the updip edge problematic. The porosity of the Opal-CT and reservoir quartz facies ranges from 50% to 24%.

From petrophysical analysis and Previous HitseismicNext Hit Previous HitmodelingNext Hit the following conclusions can be drawn. The Opal-CT and hydrocarbon-saturated quartz have nearly the same acoustic impedance. The Opal-CT is low density while the hydrocarbon-saturated quartz is low velocity. The presence of gas-saturated oil in the quartz reduces the interval velocity in a manner similar to the Gassmann effect in high porosity sandstones. The down-dip wet quartz interval is not associated with a Previous HitseismicNext Hit amplitude anomaly since its impedance is similar to the bounding shales. Finally, converted-wave data, which primarily images lithology rather than fluids, can be used to delineate the low density Opal-CT from the higher density quartz.

Based on the above conclusions, 2-D converted-wave data were acquired to complement the p-wave data. From these data sets the regional Opal-CT to quartz phase transformation boundary was mapped and a matrix of amplitude signatures versus facies was constructed. This work then formed the basis for mapping the hydrocarbon saturated quartz facies.

 

 

uAbstract

uFigures captions

uRock properties & Previous HitseismicNext Hit attributes

uDiscrimination of lithology & fluid type

uPrevious HitSeismicNext Hit anomaly

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures captions

uRock properties & Previous HitseismicNext Hit attributes

uDiscrimination of lithology & fluid type

uPrevious HitSeismicNext Hit anomaly

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures captions

uRock properties & Previous HitseismicNext Hit attributes

uDiscrimination of lithology & fluid type

uPrevious HitSeismicNext Hit anomaly

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures captions

uRock properties & Previous HitseismicNext Hit attributes

uDiscrimination of lithology & fluid type

uPrevious HitSeismicNext Hit anomaly

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure Captions

Figure 1. Regional P-wave Previous HitseismicNext Hit amplitude anomaly with discovery well. Early drilling that targeted the P-wave Previous HitseismicNext Hit amplitude anomaly resulted in McLure penetrations of both the trap and reservoir facies.

 

Figure 2. Cross plotting density vs. sonic identifies pay on wells logs--but not on Previous HitseismicNext Hit. Typical values in oil reservoir  are 150 msec/ft (sonic) and 2.00 gm/cc (density).

 

Figure 3. Tie of Previous HitseismicNext Hit attributes to rock properties. Previous HitSeismicNext Hit anomaly reflects change in fluid content and change in mineralogy.

 

 

Figure 4. Gassmann effect (reduction of interval velocity in quartz section with gas-saturated oil), shown by P-wave/S-wave plot.

 

 

Figure 5. P- and S- wave Previous HitseismicNext Hit Previous HitmodelingNext Hit, with Gassman effect in the P-wave model, which shows both mineralogical and fluid effects, while only the mineralogical changes are shown in the S-wave model.

 

Figure 6. P- and C- wave Previous HitseismicNext Hit program developed for Rose / North Shafter development.

 

 

Figure 7. Previous HitSeismicNext Hit lithology discrimination: Lower interval, North Shafter Field, with P-wave Previous HitseismicNext Hit showing Gassman effect and C-wave Previous HitseismicNext Hit showing the change in mineralogy.

 

Figure 8. Previous HitSeismicNext Hit lithology discrimination: Lower interval, North Shafter Field. Both P-wave and C-wave show only the change in mineralogy.

 

 

Figure 9. Regional conversion in lower interval of opal CT to quartz on P-wave and C-wave Previous HitseismicNext Hit profiles. The two lines are from North Shafter Field and the northern boundary of North Shafter Field.

 

Figure 10. Regional conversion in upper interval of opal CT to quartz on P-wave Previous HitseismicNext Hit profiles. One profile is from the northern boundary of North Shafter Field, and the other is from the north boundary of Rose Field.

 

Figure 11. Previous HitSeismicNext Hit profile, illustrating that an amplitude map necessarily is a composite of both upper and lower intervals.

 

 

Figure 12. Previous HitSeismicNext Hit profiles (top profile from Rose Field and lower profile from North Shafter Field), demonstrating that amplitudes downdip from the regional are the anomalies.

 

 

 

Rock Properties and Previous HitSeismicNext Hit Attributes

(Figures 1, 2, 3, 4 and 5)

An integrated study of the Miocene Monterey Formation in the San Joaquin Basin resulted in discovery of oil in its McLure Member and in the subsequent development of North Shafter and Rose oil fields (Figure 1). Integration of density vs. sonic data from well logs with 2-D (P-wave) Previous HitseismicNext Hit data does not delineate the reservoir from the updip seal. The two corresponding reservoir and trap facies (hydrocarbon-bearing quartz and Opal-CT, respectively) have essentially the same impedance (velocity x density). On the other hand, the impedance of the downdip, water-bearing quartz stratigraphic section is similar to that of the bounding shales.

 

Discrimination of Lithology and Fluid Type by Previous HitSeismicNext Hit

(Figures 5, 6, 7, 8, 9 and 10)

Planning of a Previous HitseismicNext Hit program (Figure 6) subsequent to Previous HitseismicNext Hit Previous HitmodelingNext Hit (Figure 5) of P- and S- wave data focused on discriminating lithology and fluid type, given the following:

Opal-CT stratigraphic section is low-density.

Hydrocarbon-saturated, quartz section has low velocity.

C(converted)-wave data images lithology rather than fluids.

Data from the Previous HitseismicNext Hit program shows that the gas-saturated oil in the quartz section in both an upper and a lower interval reduces the interval velocity in a similar fashion to the Gassmann effect in sandstones with high porosity (Figures 4 and 5). There is no Previous HitseismicNext Hit anomaly associated with the water-bearing quartz section in both intervals. Converted-wave data delineates the Opal-CT section (with low density) from the quartz section (with higher density).

In effect, the P-wave data define the downdip water-bearing interval, and the converted-wave data defines the updip diagenetic seal formed by the Opal-CT interval (Figures 7, 8, 9, and 10). The region in between these two areas is the hydrocarbon-bearing reservoir interval.

 

Previous HitSeismicNext Hit Anomaly

(Figures 1, 11, and 12) 

Amplitude anomalies of the upper interval and the lower interval are downdip from the regional (Figures 11 and 12). The Previous HitseismicTop-anomaly map (Figure 1) presents a composite of both intervals (Figure 12).

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