--> ABSTRACT: Identification of Point-Bar Reservoirs Within Units of Fall River Formation Through Comprehensive Electric-Log Interpretation, Powder River Basin, Wyoming, by Alvin L. Schultz and Walter Coppinger; #91033 (2010)

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Identification of Point-Bar Reservoirs Within Units of Fall River Formation Through Comprehensive Electric-Log Interpretation, Powder River Basin, Wyoming

Alvin L. Schultz, Walter Coppinger

Quantitative and qualitative electric-log interpretation, using multiple log responses, can be used as a tool to identify Fall River point-bar reservoirs. Many authors have shown how SP curve shapes can be used to identify point bar and fluvial deposits. However, few have attempted to characterize and identify point-bar deposits through quantitative and qualitative interpretation using several electric-log responses in combination.

Multiple log responses are used to identify the sharp basal contact, high permeability, and larger grain size typical in the lower portion of Fall River point-bar deposits, and the gradation into finer grain size and lower permeabilities typical in upper portions. The technique works best in producing wells that are at irreducible water saturation. In these, porosity can be plotted vs. water saturation, and relative estimates of vertical grain size changes can be determined. Gamma-ray and density logs are unitized to aid in identifying the narrow, channel filling "clay plugs" associated with point bars. Reservoirs from two fields in the Powder River basin demonstrate the technique. One field includes reservoir rocks interpreted in several ways by previous authors. The second is a more recent Dakota Third Bench reservoir in the Lonetree Creek field, where many of the techniques applied in this study were developed.

Observation of porosity and resistivity development in vertical sequence, and the position on porosity and water saturation crossplots are used to aid in distinguishing between regional depositional environments, point-bar deposits, and channel fill.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988