Investigation of petrophysical properties and fluid migration in unconventional oil/gas reservoirs

Abstract

Petrophysics deals with the physical and chemical properties of petroleum-bearing rocks and their interactions with associated fluids. The investigation of petrophysical properties of interest, such as porosity, specific pore surface area, pore size distribution, permeability, fluid saturation, and wettability, is of great importance to understand hydrocarbon storage and transport in unconventional oil/gas reservoirs, especially shale reservoirs. Characterized as low-porosity and ultra-low permeability, unconventional reservoir rocks have complicated pore structure which is significantly affected by their dominant compositions (minerals and organic matters) and vary along with the depositional environment, burial depth, diagenesis, and thermal maturity. Therefore, to better understand the shale properties and their controlling factors, a combination of various laboratory-based petrophysical measurements was designed to study core samples from major U.S. and China shale plays. The techniques involved are mercury injection capillary pressure (MICP) analysis, low-pressure gas (N2/CO2) physisorption, scanning electron microscopy (SEM) imaging, and as a major focus of this dissertation, the small- and ultra-small-angle neutron scattering (SANS and USANS) techniques. Assisted with geochemical analyses of X-ray diffraction, pyrolysis, and total organic carbon content, the combined petrophysical studies depict a more comprehensive picture of the multiscale pore structure across the nm-m spectrum. In addition, the application of a contrast matching technique in SANS/USANS measurement allows the differentiation of wettability to various fluids and quantification of their volume at multiple scales, which has guiding importance to the recoverable volume of oil and gas. In general, this study shows a comprehensive petrophysical study of several shale samples and provides valuable insight for predicting and optimizing oil and gas production.