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Dipmeter-Enhanced Interpretation of Proximal Turbidites, Hasley Canyon Field, Los Angeles County, California

Jim Vohs, Mike Mulhern

Turbidite sands of the Val Verde zone of the late Miocene Monterey Formation (Modelo) were characterized in several wells by dipmeter patterns, synthetic dipmeter curves, and lithofacies associations. Complex structural and stratigraphic features, in part a result of proximity to the San Gabriel fault system, control oil traps.

Modified Schmidt diagrams of dips for each sedimentary unit were computer-generated to select accurate structural dips for removal. Stratigraphic analysis was then performed on arrow plots computed using a short correlation interval and step distance. Modified Schmidt diagrams then rapidly summarized paleocurrent and channel directions and highlighted many unconformities. A DUALDIP display included pattern recognition correlation of the dip curves to highlight laminated sequences. A SYNDIP computation illustrated and quantified degree of lamination, nonplanar features, dip dispersion (related to depositional energy) and fining- and coarsening-upward sequences where present. GEOCOLUMN assignment of lithofacies from a database aided selection of sedimentary units.

Blue dipmeter arrow patterns indicate a dominant sediment transport direction of south-southeast, reflecting paleoslope direction. Several shifts in transport direction to the north-northwest occur, especially in the upper section of the Val Verde as the depocenter filled. These shifts reflect change in sedimentary source, corroborated by subtle compositional changes, decreased dispersion, and poorer reservoir character. Red patterns reveal many channels, with axes predominantly north-south.

The poorly sorted (fine to pebbly), mineralogically immature sands suggest nearby uplifted source. The predominance of sand and pebbles, varying bed thickness, uncommon graded beds, and the dipmeter patterns are typical of a channeled suprafan complex or midfan facies association.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.