Water-Oil Displacement in Shale: New Insights from a Comparative Study Integrating Imbibition Tests and Multiscale Imaging

Summary Water-oil displacement is an important process that occurs in a shale matrix after hydraulic fracturing and in water-based enhanced oil recovery. Current understanding of this displacement process is limited because of the complicated pore structure and surface properties in shale. In this work, this process and its controlling factors are investigated through a comparative study of three shale samples that have different types of pore systems and wettability. An integrated method of imbibition and multiscale imaging was applied, and a modified oleic tracer that can better represent oil flow was used in imbibition testing and micro-computed tomography (CT) imaging. Scanning electron microscope (SEM) pore characterization was then performed under high magnification with guidance from the micro-CT images showing the changes caused by oil or water imbibition. New insights were obtained on the importance of both wettability and pore size effect on oil recovery and the distribution of residual oil after water-oil displacement. Connectivity of pores with different wettability is also discussed based on 3D analysis and SEM pore characterization. Collectively, these new findings improve the understanding of the complicated process of water-oil displacement and the role of influencing factors. Important implications for improved oil recovery strategy in shale are discussed for different types of reservoir rocks. The integrated imaging and imbibition technique provides a new path for further investigation of improved oil recovery in shale.

Pore Characterization of the Marcellus Shale by Nitrogen Adsorption and Prediction of Its Gas Storage Capacity

In a shale gas reservoir, pore characterization is an important factor to determine gas storage capacity. However, the nanometer (nm) scale pore system in shale is difficult to explore by traditional optical, scanning electron microscopy (SEM) or even nuclear magnetic resonance (NMR) well logging. We investigated the pore structure and storage capacity of the Marcellus Shale through integration of petrophysical analysis from lab and well logging data, and nitrogen adsorption. The isotherm of Marcellus Shale is a composite isotherm, which has features of Type I, Type II and Type IV isotherms with Type H4 of hysteresis loop, suggesting slit-like pores developed in the Marcellus Shale. Quantitative analysis of pore volumes from the nitrogen adsorption indicates that density porosity may be more proper to approximate shale porosity and estimating the shale gas volume. In addition, the specific surface area, micropore and mesopore volumes have positive relationship with kerogen volume and total organic content (TOC). By employing Langmuir and Brunauer-Emmet-Teller (BET) models, simulated result indicates that higher adsorbed quantity of the Marcellus Shale could be the result of increase of micropore volume contributed, by increase of kerogen or TOC content. The proposed equations rapidly compute TOC, a key parameter to predict gas storage capacity in over-matured shale such as the Marcellus Shale.

Characterization of Steel Slag Filler and Its Effect on Aging Resistance of Asphalt Mastic with Various Aging Methods

Steel slag is the by-product of the steelmaking industry, the negative influences of which prompt more investigation into the recycling methods of steel slag. The purpose of this study is to characterize steel slag filler and study its feasibility of replacing limestone filler in asphalt concrete by evaluating the resistance of asphalt mastic under various aging methods. Firstly, steel slag filler, limestone filler, virgin asphalt, steel slag filler asphalt mastic and limestone filler asphalt mastic were prepared. Subsequently, particle size distribution, surface characterization and pore characterization of the fillers were evaluated. Finally, rheological property, self-healing property and chemical functional groups of the asphalt mastics with various aging methods were tested via dynamic shear rheometer and Fourier transform infrared spectrometer. The results show that there are similar particle size distributions, however, different surface characterization and pore characterization in the fillers. The analysis to asphalt mastics demonstrates how the addition of steel slag filler contributes to the resistance of asphalt mastic under the environment of acid and alkaline but is harmful under UV radiation especially. In addition, the pore structure in steel slag filler should be a potential explanation for the changing resistance of the asphalt mastics. In conclusion, steel slag filler is suggested to replace limestone filler under the environment of acid and alkaline, and environmental factor should be taken into consideration when steel slag filler is applied to replace natural fillers in asphalt mastic.

Multi-technique structural characterization of glass foams with complex pore structures obtained through phase separation

Typical pore characterization techniques combined with computed tomography provided a complete description of the multimodal porous architecture of novel glass foams synthesised via foaming process followed by phase-separation and selective leaching.