--> Locating Reservoir Rock in Powder River Basin Using Sediment Mass Conservation

AAPG ACE 2018

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Locating Reservoir Rock in Powder River Basin Using Sediment Mass Conservation

Abstract

Currently, petroleum production in the paleodeltaic portion of the Parkman Sandstone Member of the Cretaceous Mesaverde Formation is concentrated in clusters of subsurface sand bar deposits that trend northwest throughout the southern Powder River Basin (PRB), WY, USA. Because the morphology and progradational behavior of deltas are highly reactive to variations in sediment flux, the location of facies shifts within these deltas depends heavily upon the basin sediment budget. This study couples sediment mass conservation (SMC), stratigraphic observation, and sediment distribution patterns in order to spatially model productive facies within the Parkman Sandstone. Though SMC has been long utilized, the framework of spatially modeling the distribution of facies relative to the amount of total sediment deposited has rarely been applied in a field setting.

Lithological data was collected from 10 outcrops, 73 cores, and hundreds of well logs from the southern PRB. During the outcrop studies, the orientation and dimensions of cross-stratification generated by bedforms, barforms, and channel forms were examined to constrain the paleohydraulic system. Grain size distribution and sequence thicknesses were also evaluated to estimate transport conditions during deposition. To further model facies and sediment distributions, the fraction of total sand deposited was calculated for outcrop, core, and well locations across the study area. Contour lines were generated and mapped based on the spatial spread of these sand fractions as well as model predicted sand fractions from areas without collected data. Based on the study area’s streamwise sand distribution, sediment flux was constrained and used to estimate the quantity and extent of Parkman reservoir that resides throughout the southern PRB.

This SMC model was applied to determine the spatial structure of the sand fraction deposited from which the fluvial portion of the Parkman Sandstone currently produces oil. By using the contours for that range, we hypothesize that the distribution of other potential reservoir rock can be predicted. At a grander scale, this model can be used to estimate the total volume of sediment transported through the Parkman paleodeltaic complex and the spatial distribution of where that sediment was deposited. Though preliminary, this framework and application of SMC may provide a valuable explorative tool for the petroleum and natural resource management industries.