Modelling of dipping clinoform barriers within deltaic outcrop analogues from the Cretaceous Western Interior Basin, USA

Deltaic reservoirs typically contain seaward-dipping surfaces termed clinoforms. Shale and carbonate cements covering clinoforms can frequently form a barrier or baffle to horizontal flow within reservoirs, However, clinoforms are not typically included in static or flow simulation models because they are often not identified in well data and little is known about their 3D geometry. High quality outcrops such as Cretaceous deposits of the US Western Interior Seaway provide an ideal opportunity to study clinoform geometry and shape, and to model their effects on flow. Within this study, two deltaic systems have been studied. The first is the Ferron Delta which crops out in the Wasatch Plateau, central Utah and is a highstand complex comprised of a number of small, overlapping lobes. Clinoforms are common and their 3D geometry is controlled by the position of the lobes. Large growth fault structures within the lobes add to the potential reservoir complexity. The forced regressive Panther Tongue Delta crops out in the Book Cliffs of Utah and is comprised of downstepping lobes with internal clinoforms. Data for modelling included traditional sedimentary logs, photomontages and calibrated photo logs. Models were built in IRAP RMS using a variety of modelling techniques from simple Truncated Gaussian Simulations on a regular grid to object modelling of shale barriers within a dipping grid designed to follow the clinoforms. The models were flow simulated as a means of comparing the different techniques for representing the heterogeneity results show that not modelling clinoforms explicitly in a dipping grid can lead to significant overestimates in the forecasted production; water injection in a down depositional dip position is optimum, and that there are only limited production differences between highstand and lowstand deltas.