The controllability of mining is a key factor affecting the commercial application of methane hydrates, and the addition of chemical additives can significantly accelerate the mining process. However, the effect of additive concentration on hydrate decomposition is not yet well understood. In this study, we systematically investigate the effect of ethanol concentration on the decomposition of methane hydrate under varying thermodynamic conditions using molecular dynamics (MD) simulations. To quantitatively characterize the decomposition process and mechanism of methane hydrates, the combination of angular order parameter (AOP), radial distribution function (RDF), mean square displacement (MSD), diffusion coefficients and system energy was for the first time used. The results showed that the addition of ethanol contributed to the formation of methane bubbles and accelerated the decomposition of hydrates. The mass transfer effect of ethanol molecules and the reconstruction of the hydrogen bond network of water molecules determined the stability of hydrates. From 0 to 40 mol% ethanol concentration, the hydrate decomposition increased with increasing the concentration of ethanol. Both increasing the temperature and decreasing the pressure are beneficial to the decomposition of the hydrate system. These results provide the selection of optimal ethanol concentration for the decomposition of methane hydrate and reveal its decomposition mechanism, and shed important light for the controllable production of gas hydrates.@en

Calcium carbonate (CaCO3) deposition plays a significant role in processes such as scale formation in power plants and in oil or gas production wells. The development of appropriate methods based on well suitable in situ sensors is important to evaluate and predict the deposition process. In this study, a combination of electrochemical techniques and quartz crystal microbalance with dissipation monitoring (QCM-D) in one analysis setup (EQCM-D) was used for the first time to monitor the CaCO3 deposition in real time and provide kinetic details of the CaCO3 deposition process. Through recording the frequency change of quartz crystal sensors, it allows us to perform a quantitative analysis of the morphology, coverage, deposition rate, and mass changes with nanogram sensitivity. By varying the applied voltage, it was found that a lower applied voltage resulted in more deposition of CaCO3 mass and increase of the thickness of the deposited layer. Under the absence of flow, the CaCO3 growth rate switched from accelerating to decelerating and this point is characterized by an inflection point (IP). A lower applied voltage resulted in a lower IP. Increasing Ca2+ and HCO3− concentrations, both the deposited amount of CaCO3 mass and coating thickness increased correspondingly. With the addition of 50 mM Mg2+, a reduction in the deposition rate of CaCO3 as high as 73% was achieved. The higher the Mg2+ concentration, the larger the deposition rate reduction, which was attributed to the incorporation of Mg2+ into the growing CaCO3 mineral, resulting in the reduction of growth sites (inhibiting effect). The obtained results contribute to a better understanding of electrochemically induced CaCO3 deposition and provide valuable insights into the determination of optimal precipitation parameters, with the aim to optimize industry scaling and anti-scaling processes.@en

Chemical loss such as surfactants and alkalis by adsorption to reservoir rock surface is an important issue in enhanced oil recovery (EOR). Here, we investigated the adsorption behaviors of anionic surfactants and alkalis on silica for the first time as a function of temperature using quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that the temperature dependent critical micelle concentration of alcohol alkoxy sulfate (AAS) surfactant can be quantitatively described by the thermodynamics parameters of micellization, showing a mainly entropy-driven process. AAS adsorption was mediated under varying temperature conditions, by divalent cations for bridging effect, monovalent cations competitive for adsorption sites but not giving cation bridging, pH regulation of deprotonated sites of silica, presence of alkoxy groups in the surfactants, and synergistic effect of surfactant co-injection. The addition of organic alkalis can enhance the overall adsorption of the species with AAS, whereas inorganic alkali of Na2CO3 had capability of the sequestration of the divalent ions, whose addition would reduce AAS adsorption. The typical AAS adsorption indicated a non-rigid multilayer, estimated to have between 2 and 5 layers, with a likely compact bilayer followed by disorganized and unstable further layering. The new fundamental understanding about temperature effect on surfactants and alkalis adsorption contributes to optimizing the flooding conditions of chemicals and developing more efficient mitigation strategies.@en

In view of enhanced oil recovery, the adsorption behavior of surfactants is usually monitored on smooth model rock surfaces using quartz crystal microbalance with dissipation (QCM-D). However, this is an impractical situation as the effect of the surface roughness of reservoir rocks and its role in surfactant adsorption processes are not yet completely understood. The coupling of electrochemical techniques and QCM-D in one analysis setup (EQCM-D) provides a new methodology to explore complex surfactant adsorption processes. In this work, a uniform, rough, and well-covered model CaCO3 surface was obtained on gold and platinum sensors to model carbonate rocks. This was achieved by the electrochemically formed hydroxide ions in the presence of bicarbonate and calcium ions, by which the controlled deposition of CaCO3 resulted in sensor surface coverages in the range 35-40%. Before using the deposited CaCO3 surfaces, the adsorption of anionic surfactant alcohol alkoxy sulfate (AAS) on a smooth commercially available CaCO3 surface was studied with varying CaCl2 concentrations. For the first time, the structure and characteristics of the formed AAS layer were quantitatively described, indicating the formation of an incomplete bilayer. Compared to the smooth CaCO3 surface, an increase in the frequency shift from 5 to 15 times was observed in sensors covered with rough CaCO3 deposit. This observation was primarily attributed to the rougher surfaces that possess more adsorption sites for AAS binding and also to the effect of liquid trapping, inducing additional frequency shifts. The obtained results show that surfactant adsorption on rough surfaces was vastly different from that on smooth surfaces, and they provide a better understanding of the adsorption behavior of surfactants to mineral surfaces. @en

In view of enhanced oil recovery, the adsorption behavior of surfactants is usually monitored on smooth model rock surfaces using quartz crystal microbalance with dissipation (QCM-D). However, this is an impractical situation as the effect of the surface roughness of reservoir rocks and its role in surfactant adsorption processes are not yet completely understood. The coupling of electrochemical techniques and QCM-D in one analysis setup (EQCM-D) provides a new methodology to explore complex surfactant adsorption processes. In this work, a uniform, rough, and well-covered model CaCO3 surface was obtained on gold and platinum sensors to model carbonate rocks. This was achieved by the electrochemically formed hydroxide ions in the presence of bicarbonate and calcium ions, by which the controlled deposition of CaCO3 resulted in sensor surface coverages in the range 35-40%. Before using the deposited CaCO3 surfaces, the adsorption of anionic surfactant alcohol alkoxy sulfate (AAS) on a smooth commercially available CaCO3 surface was studied with varying CaCl2 concentrations. For the first time, the structure and characteristics of the formed AAS layer were quantitatively described, indicating the formation of an incomplete bilayer. Compared to the smooth CaCO3 surface, an increase in the frequency shift from 5 to 15 times was observed in sensors covered with rough CaCO3 deposit. This observation was primarily attributed to the rougher surfaces that possess more adsorption sites for AAS binding and also to the effect of liquid trapping, inducing additional frequency shifts. The obtained results show that surfactant adsorption on rough surfaces was vastly different from that on smooth surfaces, and they provide a better understanding of the adsorption behavior of surfactants to mineral surfaces. @en