Investigation of permeability patterns and diagenetic heterogeneity along the J-2 unconformity (UT, CO, AZ)

Abstract

It is important to understand the variation in permeability along eolian bounding surfaces in subsurface eolian reservoirs for hydrocarbon recovery, CO 2 sequestration, aquifer management, and groundwater contaminant transport. The objectives of this investigation are to identify features associated with the J-2 unconformity and measure the range of permeability for each of these features. These features include dune lithofacies contacts, lag and reworked deposits, polygonal fracture networks, interdunes and paleowater tables. Petrographic image analysis, cathodoluminescence, x-ray diffraction and energy dispersive x-ray elemental analysis are used to characterize possible depositional and diagenetic influences on the range of permeability for each feature. J-2 dune facies are the most common and have a similar range in permeability to that shown by wind ripple laminations. Polygonal fracture networks can be weak or well developed and can be poorly to well cemented. Permeability variation in polygonal fracture networks is based on the intensity of cementation and would only significantly affect horizontal communication in a reservoir. Paleowater tables are generally well cemented, much like wet interdune deposits, and act as permeability barriers to fluid flow. Lag and reworked deposits are likely the result of sediment gravity flows generated either by topographic relief or from dunes bypassing on the incipient J-2 surface. Depending on the thickness and cementation of the lag and reworked deposits, these could act as significant permeability barriers and even generate stratigraphic traps. While permeability is reduced in many of these deposits by their depositional character, samples with ~5% cement generally have permeabilities that are 150mD or less and samples with more than 10% cement generally have permeabilities less than 10mD. Samples with this intensity of cementation are intensely concretionary, interdunes, paleowater tables, polygonal fractures, or reworked deposits.