--> ABSTRACT: Heterogeneities in Clastic Reservoirs: Lessons from Outcrop Studies of Facies Architecture, by Andrew D. Miall; #91022 (1989)

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Heterogeneities in Clastic Reservoirs: Lessons from Outcrop Studies of Facies Architecture

Andrew D. Miall

Heterogeneities in clastic reservoirs are a major concern during the design of enhanced recovery projects. Quantitative information about heterogeneities is sparse, and most projects assume the existence of tabular flow units with properties described by arbitrary statistical distributions.

Of particular concern are channelized deposits (fluvial, deltaic, tidal, canyon, submarine fan), which are characterized by complex three-dimensional heterogeneities of at least eight scales. Studies of Jurassic-Cretaceous fluvial deposits in the Colorado Plateau area indicate six types of heterogeneity on the scale of the core to the total field: (1) individual lithofacies units, (2) lithofacies cosets, (3) growth increments of compound bars (e.g., point bars and sand flats), (4) the complete compound bar (macroforms), (5) channels, and (6) channel belts and paleovalleys (stratigraphically mappable members or submembers). Each scale may be identified in the field by bounding surfaces enclosing individual depositional units and is characterized by a distinctive control on direction pe meability. At scales 3-5, lithofacies assemblages and the nature and geometry of bounding surfaces permit the three-dimensional classification of heterogeneous beds into suites of characteristic architectural elements. Eight distinctive fluvial elements have been defined.

A similar approach may be adopted for analysis of other types of deposits. For example, shelf and estuarine sand banks have the geometry of macroforms, with convex-up fourth-order bounding surfaces and internal third-order erosion surfaces. Some fan-channel deposits show macroform geometries and bounding surfaces virtually identical to those of fluvial origin.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.