WILLIAMS, BRIAN P. J., and S. E. LOVE, Univ. of Aberdeen, Department of Geology and Petroleum Geology, Aberdeen, Scotland; and D. K. DAVIES, D. K. Davies and Associates, Kingwood, TX

ABSTRACT: Fluvial Channel Reservoirs: Prediction and Location Using Floodbasin Paleosols

Prediction of the location and geometry of reservoir sandstones in low net to gross fluvial systems can be achieved through detailed analysis of flood-basin mudrocks (ed. note: shales). Some well documented predictive phenomena include crevasse sandstones, abandonment fills, volcanic air-falls and lacustrine intervals. Paleosols are an important, overlooked, predictive element in fluvial reservoir exploration and development in that they possess distinctive mineralogical characteristics that allow for ready recognition using wireline logs.

This study focuses on paleosols as predictive components in mudrock-dominated fluvial sequences. Four such sequences in a diversity of tectonic settings have been analysed in detail: (1) the Upper Triassic Chinle Formation of NE Arizona, (outcrop), (2) the Lower Devonian (ORS) S Wales, UK (outcrop), (3) the Lower Cretaceous Travis Peak Formation of East Texas, (subsurface), and (4) the Upper Triassic Snorre field, Norwegian Sector North Sea, (subsurface).

Outcrop studies demonstrate that variations, in Vertisol maturity and morphology appear to be controlled by topography and channel proximity. Variations in topography reflect proximal-distal floodbasin paleosol relationships. Such topographic variations result in significant mineralogical differences (particularly quartz: carbonate: clay ratios). Subsurface evaluation of conventional cores and wireline logs show that these mineralogical variations can be determined from logs alone. Thus wireline logs can be used to reconstruct flood-basin paleotopography and architecture, significantly improving the prediction of sandbody morphology and proximity to potential fluvial channel reservoirs.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.