Facies Analysis and Sequence Stratigraphy

Abstract

The three-dimensional distribution of bodies of rock and sediments with different sedimentological properties and associated hydraulic properties is controlled to varying degrees by the depositional history of the strata of interest. Primary (depositional) variations in sediment textures and fabrics are modified by diagenetic processes, such as compaction, dissolution, and cement precipitation. A facies is a body of sedimentary rock with specified characteristics, which may include lithology (lithofacies), fossils (biofacies), and hydraulic properties (hydrofacies). Sedimentary facies analysis is based on the concept that facies transitions occur more commonly than would be expected if sedimentation processes were random. A facies model (or type model) is an idealized sequence of facies defined as a general summary of a specific sedimentary environment. Sequence stratigraphy is based on the concept that the sedimentary rock record can be divided into unconformity-bounded sequences, which reflect the sedimentological response to sea level changes, subsidence, and sediment supply. The value of facies analysis and sequence stratigraphy is that they can provide some predictability to the facies distribution between data points (i.e., wells). Where there is an underlying sedimentological control on the distribution of the hydraulic properties in aquifer systems, facies analysis can be used to better incorporate the underlying sedimentological fabric into groundwater models.