Investigation of Unresolved Interface "Rag Layer" in Athabasca Oil Sand Bitumen In Situ Recovery

Steam-assisted gravity drainage (SAGD), the leading commercial in situ bitumen recovery process, involves the underground injection of steam and produces at the well head a hot fluid containing water, hydrocarbons, and sand. This fluid is subjected to separation by diluent addition and gravity in several parallel treaters. Occasionally, the separation may be disrupted in one or few treaters by the occurrence of an unresolved interface or "rag layer" while continuing without disruption in the rest of the treaters. In the current study, we investigate "rag layer" occurrence based on the quantification of laboratory-scale and SAGD field tests and imaging of the "rag layer" morphology. The quantification results show that the formation and volume of the "rag layer" are affected by solids, mixing speed, and solvent addition. The microscopic images demonstrate the presence of both water-in-oil or oil-in water emulsions with a distinct transition between the continuous phases. The visual detection boundaries of the "rag layer" are defined as the threshold between the agglomerated and individual droplet layers. The extent of agglomeration increases in the proximity to the oil-water interface. The contribution of hydrophobic fine inorganic solids (less than 10 μm) to forming a "rag layer" is supported by their accumulation observed at the treaters' oil-water interface, compared to the feed. In well-controlled field operations, the perceived randomness of "rag layer" occurrence could be associated with the fluctuation of fine solid contents in the feed.

Forecasting the Problem of Excessive Oil Entrainment in a Desalter Using Spinning Drop Method

Frequent desalter upsets in the refineries processing opportunity crude oils are often triggered by a rapid and uncontrollable buildup of the rag layer, a thick water-in-oil emulsion, at the oil-brine interface. This is caused by spontaneous emulsification of brine in oil. This study investigates a unique observation from a spinning drop (SD) tensiometer, revealing the low apparent interfacial tension and rigidity of SD caused by spontaneous emulsification. Fine droplets of brine generated through spontaneous emulsification decorate the SD surface and form a stable, low-energy bilayer. Simulated rag layers using the brines from upset incidences exhibit similar behavior, indicating that spontaneous emulsification is driven by chemical species in brine, which promote osmotic water transport. The rate of rag layer buildup correlates with the rate of spontaneous emulsification, with the temperature coefficient of interfacial tension reduction serving as a sensitive indicator. An imminent upset in the operation can be forecasted by measuring this temperature coefficient, enabling preventive measures.

Emulsions in external electric fields

Water is co-produced with crude oils, generally in the form of water-in-crude oil emulsions. The oil and water phases need to be separated before export. Separation is performed in gravity separators with the addition of chemical demulsifiers and, sometimes, with the application of an electric field by using an electrocoalescer. The present article reviews several aspects of electrocoalescence by considering the effect of the electric field from the molecular to a macroscopic scale: the oil-water interface, single drop effects, two drop interactions, and finally emulsions at laboratory scales. Experimental results together with Dissipative Particle Dynamics (DPD) simulation results are presented. The review begins with water-oil interface under an electric field and followed by single drop electrohydrodynamics. The electric field is shown to influence the adsorption of crude oil indigenous surface-active components (asphaltenes) due to the electrohydrodynamic (EHD) flows. The interactions between two droplets in the presence of electric field and the factors governing the drop-drop coalescence are discussed in detail. DPD simulations help to elucidate thin film breakup during (electro)-coalescence of two water droplets, where the oil film has drained out to nanometer thickness. The film is comprised of surfactant and demulsifier molecules, and the simulations capture the pores formation in the film when a DC field is applied. The results demonstrate influence of the molecular structure of the surfactant and demulsifier, and their interactions. The subsequent section describes experimental techniques to assess the resolution of crude oil emulsions at the laboratory scale. The focus is on low-field Nuclear Magnetic Resonance (LF-NMR) which allows a determination of various emulsion features such as the droplet size distribution (DSD) and the brine profile (variation of the concentration of water with the height of the emulsion sample) and their evolution with time. Application of the technique in emulsion treatment involving chemical demulsifiers and electric field is presented. The review concludes with description of commercial industrial electrocoalecers such as the Vessel Internal Electrostatic Coalescer (VIEC) and the Compact Electrostatic Coalescer (CEC).

Interfacial sciences in unconventional petroleum production: from fundamentals to applications

With the ever increasing demand for energy to meet the needs of growth in population and improvement in the living standards, in particular in developing countries, the abundant unconventional oil reserves (about 70% of total world oil), such as heavy oil, oil/tar sands and shale oil, are playing an increasingly important role in securing global energy supply.