Numerous enhanced oil recovery (EOR) techniques entail injecting chemical treatments such as surfactants at a predetermined concentration to achieve targeted results. Typically, these formulations are prepared on-site prior to injection into the reservoir using large mixing tanks. The current quality assurance practice for proper concentration of treatment materials uses indirect methods such as interfacial tension (IFT) and/or viscosity measurements. These measurements can be lengthy or only suitable for a specific range of dispersed phase volumes. We examined the prospect of using acoustic measurements as a method to determine surfactant concentration for quality assessment of chemical injections on-site. The advantage of ultrasound is that it can characterize both concentrated systems and low dispersed phase volumes. In this study, we acquired the sound attenuation of an amphoteric surfactant, Cocamidopropyl Hydroxysultaine (CBS), and in-house petroleum sulfonate surfactant nano-capsules (NanoSurfactant), within a frequency range of 3-99.5 MHz. We conducted a set of experiments to establish the relationship between acoustic attenuation and surfactant concentration, and assess the measurements’ dependence on variable factors including applied frequency, suspending fluid, and temperature. The data showed a nearly perfect linear fit in the higher frequency range (65-99.5 MHz) where the coefficient of determination was between 0.979-0.998. Consistent with theoretical predictions, this method showed sensitivity to water salinity where the surfactant, at a constant concentration, displayed higher attenuation values in response to the increase in water salinity, allowing the contribution of surfactants to the acoustic attenuation to be isolated. Our method accurately determined surfactant concentrations using acoustic attenuation regardless of the surfactant used. Adopting such a robust protocol that can determine surfactant concentration and has the potential to improve field quality assurance methods would be beneficial for EOR research and industry applications whether as a standalone system or in conjunction with other commonly available methods.
Improving long-term stability and reducing retention are active areas of research for nanoparticle-based technologies for the oil and gas industry. A common strategy to improve nanoparticle stability and reduce retention is the use of polymer and/or surfactant coatings. This manuscript describes a method to improve the transport properties of FITC-dextran through carbonate media. The proposed method is based on the observation that during Alkaline-Polymer-Surfactant flooding, polymer retention reduces as pH increases, likely as a consequence of transitioning through the point of zero (PZO) charge for the porous media. Multiple alkali agents have been identified in the past, but most of them are incompatible with brines containing a high concentration of divalent cations, such as Ca2+ and Mg2+, and are therefore incompatible with carbonate reservoirs. Sodium metaborate, however, has been reported as being compatible with hard brines and carbonate reservoirs. This study evaluates the effectiveness of sodium metaborate as an alkali agent to reduce FITC-dextran retention through carbonate matrices as a proxy for dextran-coated nanoparticles. A series of transport experiments were conducted using chromatography columns packed with fine marble powder to evaluate the impact of pH on FITC-dextran retention. The columns were initially saturated with treated saline water and let rest for three weeks followed by the injection of three pore volumes (PVs) of treated saline water for washing purposes. Next, five PVs of a solution of FITC-dextran dissolved in treated saline water (with or without sodium metaborate tetrahydrate) was injected through the columns. Finally, 5 PVs or treated saline water (with or without sodium metaborate tetrahydrate) were used to displace the injectant. Effluent samples were collected during each phase of the experiment and analyzed using a fluorescent spectrometer. Fluorescence intensity data was converted to concentration and plotted as a function of injected volume to create a breakthrough curve and to estimate FITC-dextran recovery. The results show a slight decrease in retention when using sodium metaborate to increase the solution pH. FITC-dextran recovery was estimated to be 47% for the injectant without sodium metaborate tetrahydrate, and 49% for the injectant with it. This trend is in agreement with previous studies looking at polymer retention and FITC-dextran retention. The experiments suggest that pH plays a significant role during the flushing phase. The ability to transport nanoparticles through oil reservoirs can lead to a whole new range of applications including smart tracers, contrast agents and improved EOR agents and other technologies for reservoir characterization.
Mesoporous silica nanoparticles (MSNs) have a great potential as carriers for controlled release of surfactants for enhanced oil recovery (EOR) applications. Herein, MSNs containing a cationic surfactant were surface functionalized with amino groups and their surfactant release behavior was studied and compared with that of non-functionalized MSNs. The responsive release of surfactant molecules from the mesoporous particles was studied under high salinity conditions normally encountered in subsurface environments. Fourier-Transform Infrared Spectroscopy (FTIR) analysis was carried out to characterize the functionalized particles spectroscopically. Zeta potential measurements were made to study the alteration in surface charge of the capsules. Thermal Gravimetric Analysis (TGA) was conducted to investigate the amount of encapsulated cationic surfactant in the silica capsules. Dynamic Light Scattering (DLS) and Scanning electron microscopy (SEM) analyses were performed to confirm the morphology and size of these surfactant incorporated particles in saline water containing 56,000 mg/L salts. FTIR and zeta potential data confirmed the presence of amino groups on the MSN surfaces, and the results from the TGA demonstrated that the cationic surfactant concentration is directly affected by the functionalization and amino groups bound to the MSNs. DLS and SEM analyses showed that the amino functionalized MSNs are 100 nm in size and maintain their chemical stability when present in high salinity water (HSW). IFT measurements showed that interfacial tension is reduced when the amino functionalized MSNs are suspended in HSW compared to when suspended in DI water. The oil-brine interfacial tension was reduced up to 3×10-4 mN/m when the amino functionalized MSNs are suspended in HSW. The functionalized MSNs higher IFT values when suspended in DI water indicate that the surfactant release only happens in ion rich environments which is representative of subsurface conditions. The release data indicate that the presence of the amine functional groups in MSNs results in a regulated-release mechanism where the functionalized particles in HSW released 30% of the cationic surfactant in one day. The release data indicated that the presence of the amino functional groups in MSNs improved the release properties of the encapsulated cationic surfactant. Therefore, the slow release of surfactant from these amino functionalized nanocapsules around the wellbore will result in a farther reach and deeper penetration in the reservoir.
Tracers are practical tools to gather information about the subsurface fluid flow in hydrocarbon reservoirs. Typical interwell tracer tests involve injecting and producing tracers from multiple wells to evaluate important parameters such as connectivity, flow paths, fluid-fluid and fluid-rock interactions, and reservoir heterogeneity, among others. The upcoming of nanotechnology enables the development of novel nanoparticle-based tracers to overcome many of the challenges faced by conventional tracers. Among the advantages of nanoparticle-based tracers is the capability to functionalize their surface to yield stability and transportability through the subsurface. In addition, nanoparticles can be engineered to respond to a wide variety of stimuli, including light. The photoacoustic effect is the formation of sound waves following light absorption in a material sample. The medical community has successfully employed photoacoustic nanotracers as contrast agents for photoacoustic tomography imaging. We propose that properly engineered photoacoustic nanoparticles can be used as tracers in oil reservoirs. Our analysis begins by investigating the parameters controlling the conversion of light to acoustic waves, and strategies to optimize such parameters. Next, we analyze different kind of nanoparticles that we deem potential candidates for our subsurface operations. Then, we briefly discuss the excitation sources and make a comparison between continuous wave and pulsed sources. We finish by discussing the research gaps and challenges that must be addressed to incorporate these agents into our operations. At the time of this writing, no other study investigating the feasibility of using photoacoustic nanoparticles for tracer applications was found. Our work paves the way for a new class of passive tracers for oil reservoirs. Photoacoustic nanotracers are easy to detect and quantify and are therefore suitable for continuous in-line monitoring, contributing to the ongoing real-time data efforts in the oil and gas industry.
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