Depositional remnants, part 1: Common components of the stratigraphic record with important implications for hydrocarbon exploration and production

Abstract

The preservation of sedimentary strata below erosion surfaces can be highly variable laterally, and commonly only small remnants of originally more extensive deposits remain. The concept of remnants is not new, but their abundance and the fact that they commonly develop below low-relief erosion surfaces, as well as below those that incise deeply, may not be fully appreciated. Spatial variations in accommodation because of paleotopography, synsedimentary and penecontemporaneous tectonics, and differential compaction occur on a variety of scales in all settings. In low-accommodation and shallow-shelf settings, spatial variations in accommodation commonly result in the formation of remnants ranging in size from small (few to tens of square kilometers) to basin scale (hundreds of square kilometers). Remnants of porous and permeable facies encased in low-permeability facies are an important and relatively common type of stratigraphic trap. Conceptual models for three scales of remnants are used to illustrate their significance to petroleum exploration and production.The recognition of these deposits, herein referred to as depositional remnants, is commonly critical to systems analysis because stratigraphic terminations caused by erosional truncation must be interpreted differently from those caused by lithofacies change. In addition, the preserved geometry of remnants can be quite different from the geometry of the original deposit, and because geometry is heavily relied upon in interpretations of ancient systems, interpreting a preserved geometry as a geometry can result in significant misunderstandings. Depositional remnants are common in the stratigraphic record and represent an important concept to open up new hydrocarbon plays in mature basins.