Comparing and Contrasting Analytically Quantified Porosity and Pore Size Distributions in the Wolfcamp Formation From SEM Imaging, Nuclear Magnetic Resonance (NMR), and Crushed Rock Core Analysis

Abstract

Total porosity has been measured using crushed rock shale analysis, ion-milled scanning electron microscope (SEM) imagery, and fresh-state, nuclear magnetic resonance (NMR) in a Delaware Basin case study. One objective of this analysis was to compare results from different methodologies and determine if SEM quantified pore size distributions can be used to interpret or calibrate fresh-state NMR results with parameters explicit to mimicking open-hole wireline physics. Another objective was to understand how organic vs non-organic pores are or are not detected and quantified by standard analytical methods The main application of this work is to quantify organic- vs. non-organic hosted porosity from SEM images and to relate it to fresh-state NMR data. SEM total porosity was compared to crushed rock data from the same samples. The difference between SEM and crushed rock total porosity was directly correlated to clay content with the apparent clay bound water being ~20% of the dry clay bulk volume. Then comparing the discrepancies between fresh-state NMR and SEM-based total porosity, we have quantified the clay-bound water ‘correction’. There is a relationship observed between fresh-state NMR T2 and SEM-derived pore size distributions. However, fresh-state NMR response is dominated by non-organic rather than organic hosted pores (physical limitations of techniques). Understanding the relationships between these different analytical techniques and resulting quantification is key to integrating various pore-scale systems in horizontally-stimulated source rock reservoirs. Defining the link through correlation between fresh-state NMR data, SEM imaging and crushed rock analysis for shale evaluation could help resolve the challenging ‘up-scaling’ limitations the industry encounters. To conclude; 1) SEM analysis can be used to quantify organic and non-organic porosity, 2) Crushed rock total porosity for these samples included a substantial clay-bound water component that was directly correlated to XRF clay volume, 3) SEM-based pore size distributions may provide a simple and fast way to calibrate fresh-state NMR-computed pore size distributions and lead to storage and flow characterization, 4) Fresh-state NMR total porosity best matched the SEM non-organic porosity plus computed clay-bound water porosity bridging the gap between independent techniques exploiting various analytical methodology to arrive at a consistent and precise porosity quantification.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017