Core-Scale Modelling of Permeability on Highly Bioturbated Tight-Oil Samples, Burrow Pathways and Connectivity in the Cardium Formation, Pembina Field

Abstract

In this study, core-scale simulation of highly bioturbated rock samples from the tight-oil reservoir halo of the Pembina Field is performed. The rocks are bioturbated siliciclastic, litharenitic wackes that accumulated in the lower shoreface to offshore transition. The core was first analyzed using a combination of XRCT, profile permeability, SEM and optical petrography. The datasets were processed using image analysis algorithms and cross-correlations were developed to obtain a three-dimensional representation of the physical sample along with its key petrophysical parameters. These parameters were then used as input in the core simulation. A non-destructive sample analysis procedure to investigate the intricate internal architecture of bioturbated samples has been developed in this study. Notably the geometry, composition and flow/storage capacity of individual sedimentary fossil traces, diagenetic fronts, and relic bedding structures are characterized. These analyses provide the data required to evaluate the combined effect of these features on core permeability using numerical simulation. In addition, calculations are performed on virtual sub-samples using different geometries to evaluate rock heterogeneity, anisotropy, and sample-size effects. The methodology offers a direct comparison to results obtained from laboratory measurements. Three dominant lithologies or microlithofacies (μLFs) are present in the samples evaluated: a) μLF SS1 – clay-poor, fine-grained sandstone; b) μLF SS2 – argillaceous, fine-grained sandstone and siltstone; and c) μLF SH – mudstone. These three elementary μLFs exhibit contrasting permeability within the microdarcy (μLFs SS2+SH), and millidarcy ranges (μLF SS1). Discrete volumes of μLF SS1 are usually elongated and run parallel to sub-parallel to former bedding planes. Most of the longer, well preserved sand-filled traces have elliptical cross-sections, are unbranched, and exhibit some sinuosity resembling the morphology of Planolites isp. Sand-filled traces provide higher permeability conduits across the core samples; this is particularly true in the absence of preserved current bedding structures which otherwise would outperform the flow capacity of sand-filled burrows. This study illustrates the detailed characterization of petrophysical properties of geologically complex rock volumes. It provides an important advance for efficient and effective estimation of resource in place, and production from hydrocarbon reservoirs.

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