Sedimentology, Ichnology, Sequence Stratigraphy, and Petrography of the Falher F Unit, Wapiti Area, Northwestern Alberta

Abstract

The lower Albian (Cretaceous) Falher F submember of the Spirit River Formation in the Wapiti area consists of four stacked coarsening-upward successions of northward prograding strandplain to wave-dominated delta deposits. Routine core analyses revealed that four facies associations can be identified within the study interval, which reflect a shoaling-upward trend from storm-dominated shoreface, wave-dominated shoreface, brackish embayment, to coastal plain settings deposited adjacent to wave-dominated delta. Integration with geophysical well logs enabled the construction of the local paleogeographic evolution of various depositional environments within each parasequence in the study area, which can be explained using a sequence stratigraphic model.The complexity of the microscale reservoir characteristics within the tight sandstone intervals is largely due to the abundance of chert clasts and grains as well as interstitial allogenic and authigenic components, which contribute to the challenges related to the sandstone drillability and hydrocarbon storability, respectively. In this study, a petrographic approach was primarily employed to understand the relative distribution of the chert content and the diagenetic events within the tight sandstone units. The resulting reservoir characteristics can then be explained in reference to the palaeogeographic framework.This study shows that changes in the chert-controlled drillability of the Falher F tight sandstone correspond to variations in depositional energy and settings. In terms of hydrocarbon storability, secondary porosities such as dissolution, microfractures, and other micropores that followed the pore-occluding diagenetic events are primarily responsible for retaining the porosity of the unit.