Abstract

Although ancient estuarine deposits are generally characterized by complex facies distributions, their associated sandstones commonly constitute prolific hydrocarbon reservoirs. Ebb-tidal delta, barrier-bar, tidal-inlet, flood-tidal delta, tidal-channel, tidal-flat and bayhead delta sub-environments can all be associated with sandstones that may potentially have excellent reservoir properties. Distinguishing between depositionally distinctive sandstones is crucial to the accurate reserve and deliverability assessment of reservoirs within estuarine systems. This knowledge can help plan an optimum development strategy for a hydrocarbon play.

In this study, the quality and distribution of sandstones from wave-dominated estuaries is compared using subsurface data from the Lower Cretaceous Bluesky Formation of the Peace River area in Alberta. Modern sediments from Willapa Bay, Washington, are used to support observations made in the Bluesky Formation, and fill in information gaps inherent with subsurface datasets. The modem and fossil estuarine systems studied show that tidal-inlet and barrier-bar sandstones are characterized by the best reservoir qualities, followed by tidal delta, bayhead delta, tidal-channel, and lastly tidal-flat sandstones. Variability in preservation potential amongst ancient estuarine complexes can be significant, however, and is an important factor with respect to recognizing, evaluating, and ranking the economic importance of individual units from any given estuarine deposit.

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