Pore Network Investigation in Marcellus Shale Rock Matrix

Abstract

AbstractThe ever-growing energy demand and recent discoveries of vast unconventional oil and gas reservoirs have brought significant attention to shale oil and gas resources as potential game-changers for the petroleum industry and energy markets worldwide. The complex structural features and mineralogy of shale has broad implications on the development of the unconventional oil and gas industry. Although shale reservoirs are large in scale and offer the potential for long-lived production, extremely low matrix porosity and permeability, as well as complex heterogeneity, pose major challenges in obtaining economically viable oil or gas. A lack of predictive understanding of microstructure-based heterogeneity in shale limits the effectiveness of currently used production technologies. Hence, addressing the challenges of shale oil and gas production requires an in-depth understanding of microstructural features that control the oil and gas storage, release, and transport mechanisms.Because anisotropy of shale exists across multiple scales, determining changes in pore distribution has proven to be difficult. Recent studies have indicated that shale pores significantly vary in number, size (from nano- to micropores), and classification (organic and nonorganic pores). Thus far, the role of pore network and, more specifically, what pores contribute the most to the gas and/or oil storage or to the production process, is not well understood and remains largely unknown. Hence, it is vital to determine how well different pores are connected and how they create possible flow pathways for hydrocarbon migration.Here we present a comprehensive digital rock physics (DRP) framework for pore network investigation in a Marcellus Shale rock matrix using nano X-ray microscopy (nano-XRM) and focused ion beam scanning electron microscopy (FIB-SEM) data. Pore networks within both organic and nonorganic matter are reconstructed from FIB-SEM images of the shale specimen. Through this process, porosity, pore size distribution, pore connectivity, and mineralogy – organic-matter-hosted and nonorganic-matter-hosted pores – of the sample are obtained. The impact of obtained parameters on fluid flow in shale is analyzed.