ABSTRACT: Coarse-Grained Meander-Belt Reservoirs, Rocky Ridge Field, North Dakota
John O. Hastings, Jr.
The Rocky Ridge field study presents an integrated evaluation of the depositional controls and reservoir characteristics of a coarse-grained meander-belt system from a macroscale to a microscale. The field produces oil in two pools from Pennsylvania fluvial channel sandstones of the Tyler Formation in the Williston basin. Ultimate production will be 5 MMBO.
Seismic data show higher amplitudes in the Tyler section where channel sandstones are present and attenuation of the basal Tyler event. The four major channel sandstones developed at Rocky Ridge field show a dip-oriented linear morphology. Individual channels show mapped sinuosity and are 10-40 ft thick. Sandstone deposition was focused in underlying paleotopographic lows.
The structure at the field is characterized by a dome with 30 ft of closure at the main pool and a northwest-plunging nose at the southeast pool. Trapping is due primarily to differential compaction over amalgamated channel sandstones. The structure is filled to closure.
Chute-bar modification of Tyler point bars has resulted in a relatively homogeneous lithofacies assemblage. The three major lithofacies are (1) channel fill, (2) channel margin, and (3) interchannel flood basin. The channel-fill facies contain the best reservoir quality. Tyler sandstones are quartzarenites, medium grained, well sorted, and rounded. Chlorite grain coatings in reservoir sandstones prevented later reservoir deterioration caused by quartz overgrowths and authigenic cements. Porosity is primarily intergranular.
This integrated geological/geophysical model permits the explorationist to prioritize specific lead areas where fluvial channel development is likely.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990