AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
The Evolution of Dryland Fluvial Systems: An Architectural Analysis of Heterogeneity
(1) School of Earth and Environment, The University of Leeds, Leeds, United Kingdom.
Understanding heterogeneity within fluvial successions is important for well correlation, facies prediction and for forecasting the locations of marginal pay hydrocarbon reservoirs.
The Permian Cutler Group, Paradox Basin Utah, comprises a progradational dryland fluvial succession that was subject to penecontemporanous eolian activity and salt diapirism. Detailed sedimentological data (logs and architectural panels) collected from a setting proximal to the thrust-bound basin margin have enabled characterisation of the nature and occurrence of a variety of types of heterogeneity due to the juxtasposition of primary facies and architectural elements arising from fluvial system evolution and its interaction with competing depositional systems and with evolving salt structures that had surface expression.
Interactions between the fluvial system and competing eolian dune fields occurred on a range of scales. Macro-scale interactions involved the re-working of sediments and complete fluvial destruction of eolian dunes. Micro-scale interactions include inter-digitations of eolian and fluvial facies in a manner indicative of contemporaneous activity and the occurrence of facies that are a product of both eolian and fluvial systems (wet sand-sheets). In the area studied, these effects are more pronounced i) at the margins of large dune field successions, ii) with increasing distance from the fluvial source, and iii) during times of low rates of accumulation.
The syn-sedimentary movement of underlying salt in the proximal part of the basin formed barriers to active fluvial systems, resulting in channel diversion and changes in fluvial channel-belt orientation. Additionally, syn-sedimentary salt growth induced widespread deformation of facies and the development of sheltered marginal areas within evolving salt mini-basins characterised by overbank and sheet flood facies and abundant bioturbation. Eolian systems developed during times of growth of salt topographic highs, whereby dunes were established in zones protected from fluvial reworking by salt highs. The resultant distribution of sand bodies and low-permeability, fine-grained units significantly affected the resultant heterogeneity and related reservoir properties of the succession. Facies occurrences and associations are presented as depositional models to illustrate the three-dimensional occurrence and lateral extent of architectural elements.