Variation in Particle Size on the Determination of Permeability in Crushed Shale Samples

Abstract

In recent years, precision directional drilling coupled with multi-stage hydraulic fracturing has transformed the low permeability shale rock into world class petroleum reservoirs necessitating the understanding of its petrophysical properties in the laboratory and subsurface. Standard methods for determining permeability exist for conventional reservoirs, ensuring that, accurate, precise, and repeatable measurements are obtained from different laboratories. The Gas Research Institute (GRI) standard method and particle size (0.7 mm) suggested for shale matrix permeability measurement does not yield precise and repeatable results. Variations of more than an order of magnitude exist among laboratories and the 0.7 mm particle size has been shown to have microfractures and pressure decay curves are not representative for matrix permeability measurements. This project seeks to determine the influence of crushed rock particle size on matrix permeability and use noninvasive scanning electron microscopy (SEM) techniques to investigate the presence of microfractures in particle sizes ranging from 0.6 mm to 2.0 mm. Routine core analysis (petrology, porosity and fluid saturation) was carried out on the shale samples after which the sample was crushed and sieve analysis used for particle size distribution. Matrix permeability was measure using the shale matrix permeameter (SMP) which functions based on the pressure decay method. Preliminary results suggest all particle sizes 0.6 mm to 2.0 mm have microfractures. Also, an optimal particle size range of 0.85 to 1.4 mm is been proposed to be most representative of pressure decay curves.

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