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PSSuccess! Using Seismic Attributes and Horizontal Drilling to Delineate and Exploit a Diagenetic Trap, Monterey Shale, San Joaquin Valley, California*
By
Anne Grau1, Robert Sterling1, and Robert Kidney1
Search and Discovery Article #20011 (2003)
*Adapted for online presentation from poster presented at AAPG’s annual convention, 2003, Salt Lake City, May, 2003. A companion article, entitled “Delineation of a Diagenetic Trap Using P-Wave and Converted-Wave Seismic Data in the Miocene McLure Shale, San Joaquin Basin, California,” is Search and Discovery Article #20012 (2003).
1EOG Resources, Denver Colorado (anne [email protected])
The Miocene Monterey Formation of California’s San Joaquin valley has long been recognized as a prolific source rock and underdeveloped resource. In this case study, the thick sequence of diatomaceous shales and hydrocarbon-rich sediments of the Miocene form a subtle diagenetic trap. As these sediments are buried to increasing depths, these siliceous shales convert from opal A to opal CT and finally to quartz-phase “chert”, undergoing a significant change in porosity and other rock properties during this transition. Seismic data and modeling have been successfully utilized in the identification and mapping of these diagenetic facies.
North Shafter and Rose Oil Fields produce from a porous, hydrocarbon-charged
reservoir
that formed as a result of silica diagenesis and favorable timing of
kerogen maturation in these sediments. The
reservoir
consists of fractured,
porosity-enhanced, oil-saturated quartz-phase rocks. A trap is formed by the
updip, opal CT - phase rocks that have no hydrocarbon saturation and poor
porosity characteristics.
The juxtaposition of these drastically different rock types is reflected by seismic amplitude anomalies that were used to determine the extent and shape of the fields. Horizontal drilling technology and strategic placement of wells have been key in the viability of this program. Close to 60 horizontal wells have been drilled in North Shafter and Rose oil fields since 1998, when the first horizontal well was drilled.
uStratigraphy,
t uStructural & stratigraphic control
uSeismic
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uStratigraphy,
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uStratigraphy,
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uSeismic
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uSeismic
imaging of
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Location,
Stratigraphy, Figure Captions (1-7)
Right: Higher-magnification view of silty mudstone texture illustrates an abundance of discontinuous, horizontal microfractures and patches of microporosity (magenta). Close examination reveals that these microporous lenses (m) are not as clayey and are presumably composed of micro- or cryptocrystalline silica. Microfractures at the top of view are likely induced by dehydration. Also note abundance of pyrite and carbonaceous debris. Scale bar = 0.2 mm. Plane-polarized light. (100×).
North
Shafter and Rose oil fields are in the San Joaquin Basin (Figure 1). The
Miocene Monterey Formation, composed primarily of diatomaceous siliceous shales (Figures 2,
3, and 4), is the source and the
The heterogeneous
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