Criteria for
Differentiating Channel and Sheet Reservoirs: A Deep-Water Field Example
Stelting, Charles E.1,
Jennifer Beall2, Lisa Goggin1, William H. Crane3,
William J. Schweller4, Janet Murphy5, Michael Richey6
(1) Chevron Energy Technology Company, Houston, TX (2) Chevron, Houston, TX (3)
Chevron Energy Technology Company, San Ramon, CA (4) Chevron Energy Technology
Company, San Ramon, (5) Chevron International Exploration & Production,
Houston, TX (6) Chevron Interntional Exploration & Production, Houston, TX
Channelized and unconfined (sheet)
reservoirs are characterized by thick, clean, sand-rich deposits. These
elements compromise the bulk of reservoir bodies in deepwater depositional
systems and may be distinguished from one another by their geometries, facies
associations and hierarchical stratigraphy. Seismic data reveal that the bulk
of the reservoir sands in this field example are confined to a broad,
low-relief depositional fairway which trends roughly normal to a structural
monocline. Because low seismic resolution precludes delineation of geometric
planforms within the fairway, reservoir characterization and prediction are
accomplished by integrating borehole data (well logs, cores, OBMI) with the
broader seismic framework.
Individual sand bodies are dominated by
blocky gamma ray log signatures. Calibration to core demonstrates this log
signature is associated with massive, amalgamated sands. Conversely, irregular
or serrated gamma ray log signatures are indicative of lithologic variability consisting
of intermixed turbidite sands and muddy-sandy mass transport deposits;
interbedded sand and shale less common. Stratigraphic correlation and degrees
of heterogeneity are the key to classification of the
reservoir sands into channel or sheet elements within this ‘mixed channel/sheet
depositional system.' Sheets consist of laterally continuous, massive sands
with rare internal heterogeneities and exhibit minor facies gradation along the
fairway edges. The channel bodies are also dominated by massive sands but are
more heterogeneous reflecting facies trends from an axis to margin setting and
common slump or debrite deposits. In addition to the integrated field
correlations, outcrop analogs proved invaluable in establishing the
depositional interpretation.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California