Petrophysical Characterization of the Upper Cretaceous Second White Specks Alloformation, Willesden Green Area, Alberta: An Updated Workflow for Anisotropic Fine-Grained Reservoirs

Abstract

The Upper Cretaceous Second White Specks Formation, a thin-bedded heterogeneous mudrock succession, is a prolific self-sourcing tight oil reservoir within the Western Canada Foreland Basin in Alberta. Despite significant production from some wells, the Second White Specks Formation has been treated as a “bail-out zone” due to unpredictable inflow performance. Formation damage, extreme heterogeneity and dependency on natural fracture permeability have been implicated as factors that govern initial rate and decline behaviour of Second White Specks reservoirs. This formation presents an intriguing petrophysical problem due to its anisotropy and fracture dependency. This study, focused in the Willesden Green area of west-central Alberta, will test the predictive capacity of mappable petrophysical attributes for locating areas with enhanced oil production potential in the Second White Specks tight oil play. Zonal petrophysical analyses are constrained to coeval depositional units within a high-resolution allostratigraphic framework. The workflow could have broad application in analogous heterogeneous self-sourcing reservoirs. This study represents work in progress, and will demonstrate how proper data conditioning can increase the reliability of petrophysical modeling. The Second White Specks presents two challenges for petrophysical analysis: washouts and thin bed effects. Both of these problems are addressed in this work. Severe wellbore instability is often encountered during drilling of the Second White Specks Formation, causing environmental effects that degrade measured parameters, like density and neutron porosity. This study uses a multi-parameter inversion method to eliminate borehole contributions to raw measurements, notably improving the quality of acquired data. Resistivity measurements can vary significantly between individual thin beds in heterogeneous reservoirs like the Second White Specks. Due to their resolution limits, conventional resistivity tools are incapable of capturing this heterogeneity. This study applies 2D inversion to enhance resolution, improve accuracy, and evaluate the contribution of laminations to measured parameters. As open natural fractures can improve flow capacity, developing a fracture prediction method for the Second White Specks is essential for sweet spotting. Mineralogy and brittleness, which are key contributors to fracturing, are characterized using a multi-mineral model for the carbonate-rich Second White Specks.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016