46670-G8
High Resolution Characterization of Crude Oil Distribution at the Pore Scale: Effects on Enhanced Petroleum Recovery
Introduction
Crude oil mobility in porous reservoirs is controlled by several physical parameters such as capillary force and surface tension existing between the oil and solid media, and the geometry of the pore spaces. As a result, petroleum mobilization is controlled by the heterogeneity of the porous medium and the related distribution of oil. The outcomes of this research are beneficial to understanding the pore-scale interfacial processes controlling tertiary oil recovery from existing reservoirs. The purpose of this research is to quantify the oil distribution as a function of crude oil fraction and quantify relative changes in blob morphology and distribution as a function of the heterogeneity of the porous medium. Experiments have been conducted and are on-going characterizing the changes in blob morphology for varying crude oil fractions and porous media heterogeneities.
Pore scale studies were conducted in a controlled environment to quantify the distribution and the morphology of various fractions of crude oil in different types of porous media. Multiple columns were packed with three different types of sediments with increasing heterogeneity. The columns were saturated with water, and injected with three different fractions (light, medium and heavy) of crude oil. The columns were flushed with anionic surfactants in two episodes. Utilizing the Advanced Photon Source Facility at Argonne National Laboratory, synchrotron X-ray microtomography was used to capture high resolution (9.9-µm) images of the oil and water distributions within the prepared columns before and after each flooding event. Three fractions of crude oils (Chevron) were chosen as model oil-phase liquids with high (14.0°), medium (29.6°) and light (41.4°) API gravity. A 0.1 vol% alkylpropoxy sulfate solution was used as the anionic surfactant of choice for the flooding experiments. This surfactant was chosen for its ability to develop low interfacial tension at very low concentration and because it is not sensitive to insensitive to salinity.
Results and Discussions
An observation of the oil distribution reveals that all three fractions of oil within the homogeneously packed columns show drastic differences in oil morphology and distribution. The distribution of chains of blobs along the column walls, attributed to the development of preferential flow paths, are more prevalent in the heavy and medium oil fractions compared to the light crude oil fraction. The heavy oil fraction distribution has numerous interconnected blobs, exhibiting large high-surface area ganglia structures. In comparison, the distribution of the other light and medium oil fractions are dominantly characterized by individual oil particles called “blobs” or “singlets”. The aqueous phase exists in continuous complex network structure with light and medium oil fractions. It is expected that these differences will control the recovery efficiency of the different oil fractions. Ongoing analyses are being conducted to evaluate these effects on oil recovery.
Medium gravity crude oil shows a significantly greater number of smaller volume blobs than light and heavy crude oils. All of the medium fraction crude oil blobs are less than 0.008 cu mm. Heavy oils are also dominated by small blobs except along the column walls where preferential flow and distribution are likely occurring. The light crude oil fraction has a median blob diameter approximately 16 times greater than that of the medium crude oil fraction and 4 times greater than the heavy oil fraction. Cumulative distribution of the three fractions with respect to blob volume shows log-normal distribution. Medium fraction crude oil shows relatively homogeneous distribution (CU =1.29) unlike the other two fractions, where uniformity coefficient is 2.29 and 3.04 for light and heavy fractions, respectively. The median blob diameter of the light crude oil is approximately equal to the particle length (0.35 mm) of the porous medium, whereas the median blob length of the medium crude oil is significantly smaller than that of the sand grains. It is expected that these differences will control the recovery efficiency of the different oil fractions. Ongoing analyses are being conducted to evaluate these effects on oil recovery.
Further research will continue to investigate oil distribution within increasingly heterogeneous porous media. In the last three trips to Argonne National laboratory, almost 80% of the columns have been imaged and stored for continued processing. Additional travel to Argonne National Labs is necessary to complete imaging the entire series of nine columns. Over the next year, three more research trips are planned and the continuation of image processing will take place. A full synthesis of the results will be completed into a final report and it is expected that this research will produce three separate articles for publication in highly-reputable peer-reviewed journals. In addition, the results of this research will be developed into the teaching curriculum of classes taught at the University of
Acknowledgements
Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for support (or partial support) of this research.
