Asphaltenes yield curve measurements on a microfluidic platform

Physicochemical Characterization of Asphaltenes Using Microfluidic Analysis

Crude oils are complex mixtures of organic molecules, of which asphaltenes are the heaviest component. Asphaltene precipitation and deposition have been recognized to be a significant problem in oil production, transmission, and processing facilities. These macromolecular aromatics are challenging to characterize due to their heterogeneity and complex molecular structure. Microfluidic devices are able to capture key characteristics of reservoir rocks and provide new insights into the transport, reactions, and chemical interactions governing fluids used in the oil and gas industry. Understanding the microscale phenomena has led to better design of macroscale processes used by the industry. One area that has seen significant growth is in the area of chemical analysis under flowing conditions. Microfluidics and microscale analysis have advanced the understanding of complex mixtures by providing in situ imaging that can be combined with other chemical characterization methods to give details of how oil, water, and added chemicals interface with pore-scale detail. This review article aims to showcase how microfluidic devices offer new physical, chemical, and dynamic information on the behavior of asphaltenes. Specifically, asphaltene deposition and related flow assurance problems, interfacial properties and rheology, and evaluation of remediation strategies studied in microchannels and microfluidic porous media are presented. Examples of successful applications that address key asphaltene-related problems highlight the advances of microscale systems as a tool for advancing the physicochemical characterization of complex fluids for the oil and gas industry.

An automated microfluidic system for the investigation of asphaltene deposition and dissolution in porous media

Asphaltenes, among the most complex components of crude oil, vary in their molecular structure, composition, and self-assembly in porous media. This complexity makes them challenging in laboratory characterization methods. In the present work, a novel microfluidic device was designed to access in situ transient, high-fidelity information on asphaltene deposition and dissolution within porous media. The automated microfluidic device features three independent 4.5 μL packed-bed microreactors on the same chip. The deposition of asphaltenes was investigated at five different temperatures (ranging from 25-65 °C) in addition to dissociation with xylenes. Our findings demonstrate a decrease in the dispersity of asphaltene nanoaggregates in the porous media when the deposition temperature is increased. Furthermore, the direct quantification of the dissociation solvent was made possible by in situ Raman spectroscopy. The average occupancy of xylenes and xylene-free porous media (or unrecognized sites) was estimated to be 0.41 and 0.66, respectively. It was observed that asphaltenes deposited at higher deposition temperatures are more difficult to dissociate by xylenes than those deposited at lower temperatures. In order to develop efficient remediation treatments in energy production operations, the convoluted behaviours of asphaltenes in porous media must be understood on a molecular level. Automated microfluidic systems have the potential to streamline treatment designs, improve their efficiency, and enable the design of green chemistry in conventional energy production operations.

Microfluidic and nanofluidic phase behaviour characterization for industrial CO2, oil and gas

Microfluidic systems that leverage unique micro-scale phenomena have been developed to provide rapid, accurate and robust analysis, predominantly for biomedical applications. These attributes, in addition to the ability to access high temperatures and pressures, have motivated recent expanded applications in phase measurements relevant to industrial CO₂, oil and gas applications. We here present a comprehensive review of this exciting new field, separating microfluidic and nanofluidic approaches. Microfluidics is practical, and provides similar phase properties analysis to established bulk methods with advantages in speed, control and sample size. Nanofluidic phase behaviour can deviate from bulk measurements, which is of particular relevance to emerging unconventional oil and gas production from nanoporous shale. In short, microfluidics offers a practical, compelling replacement of current bulk phase measurement systems, whereas nanofluidics is not practical, but uniquely provides insight into phase change phenomena at nanoscales. Challenges, trends and opportunities for phase measurements at both scales are highlighted.

Microfluidic technique for measuring wax appearance temperature of reservoir fluids

A microfluidic technique for measuring wax appearance temperature (WAT) of reservoir fluids is presented. The technique is based on continuous monitoring of pressure across a microchannel as wax particles are deposited and gradually clog the channel. A rapid pressure increase was observed as the temperature was systematically decreased to wax appearance temperature. The relationship between pressure change rate and sample temperature is explored as the working principle in the proposed WAT measurement technique. This technique yields results which are comparable to measurements obtained from a cross-polar microscopy technique (CPM); the current industry-standard for WAT measurement. The method is validated by systematically investigating phase transition of pure hydrocarbons, binary mixtures, and real crude oils. The new technique has two distinct advantages over the existing industry standard methods in that its experimental setup is much simpler and it can be adapted to field applications. The microchannel can be easily cleaned and reused to test different samples.

Examining Asphaltene Solubility on Deposition in Model Porous Media

Asphaltenes are known to cause severe flow assurance problems in the near-wellbore region of oil reservoirs. Understanding the mechanism of asphaltene deposition in porous media is of great significance for the development of accurate numerical simulators and effective chemical remediation treatments. Here, we present a study of the dynamics of asphaltene deposition in porous media using microfluidic devices. A model oil containing 5 wt % dissolved asphaltenes was mixed with n-heptane, a known asphaltene precipitant, and flowed through a representative porous media microfluidic chip. Asphaltene deposition was recorded and analyzed as a function of solubility, which was directly correlated to particle size and Péclet number. In particular, pore-scale visualization and velocity profiles, as well as three stages of deposition, were identified and examined to determine the important convection-diffusion effects on deposition.

A microfluidic flow focusing platform to screen the evolution of crude oil-brine interfacial elasticity

Multiphase fluid flow dynamics dominate processes used to recover the majority of hydrocarbon resources produced by global energy industries. Micromodels have long been used to recapitulate geometric features of these processes, allowing for the phenomenological validation of multiphase porous media transport models. Notably, these platform surrogates typically preserve the complexity of reservoir conditions, preventing the elucidation of underlying physical mechanisms that govern bulk phenomena. Here, we introduce a microfluidic flow focusing platform that allows crude oil to be aged against brines of distinct composition in order to evaluate the pore-level effects of chemically-mediated interfacial properties upon snap-off. Snap-off is a fundamental multiphase flow process that has been shown to be a function of aqueous phase chemistry, which in turn establishes the limits of crude oil recovery during enhanced oil recovery operations. Specifically, this platform was used to evaluate the hypothesis that low salinity brines suppress crude oil snap-off, thus enhancing recovery. This hypothesis was validated and conditions that promote the effect were shown to, unexpectedly, develop over a matter of minutes on the pore scale. Microfluidic snap-off experiments were complemented by finite element fluid dynamics modeling, and further validated against a classical instability framework.