SEMINAR: MGG Student Seminar: Jan Norbisrath 4/29 @ 12PM

[Kelly Jackson <kjackson@rsmas.miami.edu>]

MGG STUDENT SEMINAR 

presents

JAN H. NORBISRATH

Sub-micron Digital Image Analysis (BIBSEM-DIA), Pore Geometries and Electrical Resistivity in Carbonate Rocks

Tuesday, April 30, 2013

12:00 PM 

CIMAS Conference Room

Abstract:  Assessment of electrical flow properties in heterogeneous carbonate rocks with pore sizes spanning several orders of magnitude requires a multiscale investigation. A new technique using Digital Image Analysis (DIA), ranging from millimeter to nanometer scale, allows for imaging and quantification of the sub-micron pore space in unprecedented detail. Nanometer-scale pores are captured with a new method of Broad-Ion-Beam (BIB) milling, which produces true 2D cross-sections for SEM image mosaic acquisition (BIB-SEM).

Four samples were chosen from different depositional and diagenetic environments to compare their distinct microstructures. All samples have similar porosity (16%) for the sake of comparability. Electrical resistivity was measured on all samples; pore throat size distribution was analyzed with MICP, and macropore structure was analyzed with DIA from Optical Light Microscopy (OLM) on epoxy impregnated thin sections. For imaging micropores, the sample surfaces were milled down to nanometer-precision flatness with a JEOL SM-09010 BIB cross-section polisher. The large BIB surfaces (up to 2 square mm) are investigated at 5000x and 15000x magnification (resolution: 58.6 nm/pixel and 18.5 nm/pixel, respectively). Resulting mosaics are composed of up to 570 images each. Integrating DIA results from BIB-SEM and OLM yields a multiscale analysis.

The ultra-high-resolution BIB-SEM image mosaics reveal the diverse micro-architectures of the different rock types, allowing for qualitative estimation of flow properties. The most interesting finding from quantitative DIA is that pore size distribution follows a power law. This implies that pore densities outside the scale of investigation can be predicted. Connectivity was estimated by combining conventional image analysis with spatial analysis using GIS software. The hypothesis is that the closer the next pore, the more likely a connection exists. Pore body and throat sizes have dominant control on electrical resistivity. The smaller the pores and, counter-intuitively, also the pore throats, the better the flow. Pore-body to pore-throat ratios (BTR) similarly behave opposed to what has been speculated, as larger BTR values result in better flow.