October Luncheon Meeting

Abstract

Exploration of the Cretaceous Nanushuk and Torok formations on the North Slope of Alaska is a hot topic these days. These formations are progradational clastic deposits in the Colville basin of Alaska. The Nanushuk Formation is a clastic fluvial-deltaic-shelf succession, whereas the Torok Formation is its basinward equivalent. These formations offer new opportunities to the oil and gas community because of their shallow depth, vast spatial extent, publicly available data, and scope of development. In this study, we integrate the results from eight large 3-D seismic surveys, well logs, and core (poro-perm and special core scan) data. The study area covers ~2,389.21 square miles.

Seismic sections show the presence of low-angle clinothems all over the study area, where the Nanushuk Formation is expressed as topset, and the Torok Formation is expressed as foreset and bottomset. Seismic-attribute-assisted mapping reveals the presence of prograding shelf edges, channels, and basin-floor fans, all with significant amplitude anomalies, which could be potential reservoirs. Apart from these deposits, abundant mass-transport deposits and sediment wave deposits are observed. Co-rendering of seismic attributes, such as coherent energy, Sobel-filter similarity (coherence), and spectral decomposition reveals these geomorphological features in more detail.

Both Nanushuk and Torok formations are internally heterogeneous, as revealed by petrophysical data. These formations are composed of laminated sand-shale sequences and contain thin-bedded, low-resistivity pay intervals. Only a few zones in the parasequences are oil saturated. Based on the core data, the porosity and permeability in these formations range from 5% to 35% and approximately 0.001 to 1,000 millidarcies, respectively. The ratio of P-wave and S-wave velocity (VP/VS) is a good indicator of hydrocarbon-bearing sandstones in these formations, which can be used in seismic inversion to identify and predict the sweetspots for further exploration.

Bio

Dr. Bhattacharya is a researcher at the Bureau of Economic Geology, UT Austin. He is an applied geophysicist/petrophysicist by background. Dr. Bhattacharya is primarily interested in extracting and integrating fundamental rock and fluid properties across multiple scales of resolution (core, well log, and seismic). Prior to joining BEG, he worked with the University of Alaska Anchorage, Battelle, and other organizations in different roles, such as an assistant professor and petroleum geoscientist. He completed multiple projects for energy resources exploration and carbon sequestration in the US, Australia, South Africa, and India. He has published over 50 technical articles in different journals and conferences.