Dolomitization and its impact on porosity evolution in the Middle Bakken,  Elm Coulee Field, Williston Basin

Current state of the art on the characterization of sub-micron sized pores in tight carbonate rocks are mostly limited to limestones and chalks. But sub-micron sized pores are also common and are of significance in dolostones since they affect hydrocarbon saturation and production performance. In this paper, we present a case study on the characterization of the sub-micron sized pores in the Middle Bakken(MB) silty dolomites of the Elm Coulee field, Williston Basin. This paper also develops an understanding of the various stages of dolomitization, which affects the evolution of porosity in the MB silty dolomites. 

The shallow marine mixed-siliciclastic-carbonate deposits of the middle Bakken (MB) Formation in Elm Coulee field are dolomitized to varying degrees and the dolomite content ranges from 5 to70%. Petrographic work, XRD, and stable isotope (C and O) analysis from 10 wells across the field were used to define the dolomitization process. Routine core analysis, Mercury Intrusion Porosimetry, and FESEM studies were performed to determine total porosity, pore-size distribution, and pore types.

Speaker: Dipanwita Nandy, Colorado School of Mines

Biography
Dipanwita Nandy is a PhD candidate at Department of Geology and Geological Engineering, Colorado School of Mines (CSM). Her research is focused on sedimentology and diagenesis of unconventional and carbonates reservoirs. Prior to joining CSM, she worked as a Development Geologist for ONGC Ltd in India for 4 years.

Hydraulic Tortuosity: From Artificial Packs to Natural Rocks

Hydraulic tortuosity is an important parameter in characterizing fluid flow heterogeneity in porous media. The most basic definition of tortuosity is an average flow path length divided by the length of a sample.  Although this definition seems straightforward, the lack of understanding and proper way to measure tortuosity make it one of the most abused parameters describing transport properties. Hydraulic tortuosity is often treated merely as a fitting factor or, worse, is neglected by combining tortuosity with a geometrical factor in the Kozeny-Carman equation. In this paper, we focus on hydraulic tortuosity in various porous media ranging from artificial packs to natural rocks to improve our understanding of this parameter. Conventionally, the tortuosity is obtained through laboratory measurements of porosity, permeability, and specific surface area using the Kozeny-Carman equation. In contrast, this study was conducted on 3-D binary segmented images to obtain the tortuosity through streamlines extracted from a local flux, the output from a Lattice Boltzmann flow simulation (LBM). This approach allows us to calculate the flux-weighted tortuosity, and also to study the tortuosity on a larger number of samples. Numerical simulations were performed on 8 simple cubic packs, 8 face-centered cubic packs, 32 variations of Finney packs, 125 subsamples of Berea sandstones, and 125 subsamples of Grosmont carbonate.

Speaker: Natt Srisutthiyakorn, Stanford University

Biography
Natt is currently working with Professor Gary Mavko at Stanford University on understanding the relationship between pore space geometry in digital rocks and transport properties. In order to gain insights into the pore space geometry, she employs various methods such as image processing, numerical simulations (i.e. Lattice Boltzmann simulation and Finite Element Method), and machine learning. She graduated from the University of Michigan, Ann Arbor in 2010 with a triple major in Geological Sciences (Highest Honors), Economics, and Mathematics. She worked as a geophysicist at Petroleum of Thailand, Exploration and Production (PTTEP) from 2010 to 2013. Before pursuing a Ph.D. degree in geophysics, she worked on various research topics such as the slip-rate on low-angle normal fault, spatial distribution of volcanoes on the moon, and AVO analysis.