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Distribution of Conglomerates in a Submarine Canyon System, Upper Miocene Potter Sandstone, Midway-Sunset Field, Kern County, California

Sean O'Connor
Aera Energy LLC, 10000 Ming Avenue, Bakersfield, CA 93311

A study of the western edge of the super-giant Midway-Sunset field, Kern County, California, was undertaken to assess the distribution of conglomerates in the Upper Miocene Potter sands. The Potter was deposited as a submarine fan complex with sediments fed from both the granitic Salinian Block and earlier, reworked Miocene sands that were uplifted and eroded in response to compression along the “big bend” in the San Andreas fault. Individual depositional events across the western edge of the field are laterally discontinuous, typical of very high-energy depositional environments, related to the area's positioning within a major Upper Miocene submarine canyon system. Isochore maps of gross Potter thickness, outcrop maps, and the lack of preservation of any significant shales across the area support this interpretation. Reservoir quality in the Potter sands improves both stratigraphically up-section, and in the distal direction as a function of sorting. The Potter reservoir in the study area is characterized by extremely poor sorting, exhibited in both core and thin-section, relating to its proximal position at the head of the submarine fan system. Core-to-log correlations performed for three cores taken in the study area reveal that high-density, matrix-supported conglomerates composed of granitic cobbles shed from the Salinian Block fall at or below a density-porosity cutoff of 18 percent. Construction of a three-dimensional geologic model and accompanying density-porosity property model enabled mapping of the spatial distribution of these conglomerates. The depositional patterns that emerged from mapping reflect channel-forms that terminate in thick conglomerate deposits at the base of paleo-slope with fan-lobe geometries at the toe of the basal sand unit.


AAPG Search and Discovery Article #90076©2008 AAPG Pacific Section, Bakersfield, California