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Oil leakage, which is inevitable in the process of extraction, processing, transportation and storage, seriously undermines the soil and groundwater environment. Surfactants can facilitate the migration and solution of oil contaminants from nonaqueous phase liquid (NAPL) or solid phase to water by reducing the (air/water) surface tension, (oil/water) interfacial tension and micellar solubilization. They can effectively enhance the hydrodynamic driven remediation technologies by improving the contact efficiency of contaminants and liquid remediation agents or microorganism, and have been widely used to enhance the remediation of oil-contaminated sites. This paper summarizes the characteristics of different types of surfactants such as nonionic, anionic, biological and mixed surfactants, their enhancements to the remediation of oil-contaminated soil and groundwater, and examines the factors influencing surfactant performance. The causes of tailing and rebound effects and the role of surfactants in suppressing them are also discussed. Laboratory researches and actual site remediation practices have shown that various types of surfactants offer diverse options. Biosurfactants and mixed surfactants are superior and worth attention among the surfactants. Using surfactant foams, adding shear-thinning polymers, and combining surfactants with in-situ chemical oxidation are effective ways to resolve tailing and rebound effects. The adsorption of surfactants on soils and aquifer sediments decreases remediation efficiency and may cause secondary pollution, Therefore the adsorption loss should be noticed and minimized. Unlabelled Image • Surfactant enhanced remediation through mobilization and solubilization effects. • Biosurfactants and mixed surfactants show great application potential. • Co-injection of foams or xanthan improves uniform distribution of surfactants. • Surfactant-enhanced in-situ chemical oxidation eliminates tailing and rebound. [ABSTRACT FROM AUTHOR]

We present the first example of electrocatalytic three‐component annulation–iodosulfonylation of indole‐tethered 1,6‐enynes with arylsulfonyl hydrazides and KI for accessing various iodosulfonated pyrrolo[1,2‐a]indoles in moderate to excellent yields with high stereospecificity. This electrosynthesis opens new avenues for the construction of pyrrolo[1,2‐a]indoles skeleton with good functional group compatibility under environmentally benign condition. Based on the control experiments and cyclic voltammetry data, we suggested the plausible reaction mechanism which included anodic oxidation, homolysis of arylsulfonyl iodide, arylsulfonyl radical addition, 5‐exo‐dig cyclization, radical coupling or nucleophilic attack of iodide ions cascade. [ABSTRACT FROM AUTHOR]

Background: This study aimed to investigate the efficacy and safety of retroperitoneal laparoscopic tuberculous nephrectomy (RLTN) and open tuberculous nephrectomy (OTN). Materials and Methods: One hundred fifty-eight patients treated with RLTN were enrolled in the RLTN group. One hundred patients treated with OTN were enrolled in the control group. Surgical parameters and postoperative conditions were recorded to assess the effect of the operation, and complications were recorded throughout the follow-up time. The follow-up time was 2-72 months. Results: Eight cases in the RLTN group were moved to the OTN group due to intraoperative bleeding. There were significant differences in the diameter of the incision between the 2 groups (P < .01). The resumed time and length of hospitalization in the RLTN group were significantly shorter than those in the OTN group (P < .05). During surgery, 6 cases (3.79%) in the RLTN group presented pus overflow due to a rupture of the empyema space. The same happened to 3 cases (3.00%) in the OTN group. After surgery, there was 1 case of abdominal tuberculosis (TB) in the RLTN group. There was no tuberculous sinus or systemic disseminated TB during the follow-up period. Conclusions: Both treatment approaches were safe and effective, but RLTN presented more advantages. Therefore, RLTN can be used as a first-line method for tuberculous nephrectomy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Secondary hydrate formation (SHF) are studied both experimentally and numerically. • A new kinetic model integrates hydrate pore-scale morphology and the SHF characteristics. • Heterogeneous manner of hydrate formation are quantified in Cubic Hydrate Simulator. • The SHF significantly exacerbates the hydrate formation heterogeneity. The challenge of secondary hydrate formation (SHF) is frequently encountered in hydrate formation and dissociation experiments. However, there is currently a lack of modeling theory of SHF kinetics in the field and laboratory tests. In this work, the hydrate formation experiments concerning the SHF are carried out in a cubic hydrate simulator (CHS), where the pressure profiles and temperature spatial distributions are measured. A new kinetic model of hydrate formation integrating hydrate pore-scale morphology and SHF characteristics is developed. The newly developed model with unified kinetic parameters is employed in the Tough + hydrate (T + H) simulator to duplicate the experiment processes numerically, which achieves excellent agreement with the experimental data. The results show that the evolutions of the spatial distributions of the temperature and hydrate saturation behave in heterogeneous manners in the hydrate formation processes. This also reveals that the SHF can significantly exacerbate the hydrate heterogeneity in the CHS. Two additional experiments and comparisons with currently available models have validated the feasibility and accuracy of the new model. This work provides a reliable and adaptable model for describing the entire lifecycle of the hydrate formation kinetics in the porous media. [ABSTRACT FROM AUTHOR]

Natural gas hydrate is a promising strategic energy resource in marine and permafrost sediments. To precisely characterize the coupled Thermal-Hydraulic-Chemical (THC) process in hydrate reservoirs, a bona fide mathematical model with improved key parameters is needed. We developed a Full Implicit Simulator of Hydrate (FISH), a three-phase, four-component mathematical model, to simulate gas recovery from hydrate reservoirs. The experiment of methane hydrate formation and dissociation under depressurization via a single vertical well was executed in the Cubic Hydrate Simulator (CHS). FISH was employed to reproduce the experiment of hydrate dissociation in quartz sands. This study successfully obtains unified parameters that are suitable for the entire hydrate dissociation process. Simulation results of gas and aqueous production profiles and the temperature distribution agreed well with that in the experiment. The Mean Absolute Percentage Error (MAPE) of the simulated volume of gas produced was 2.845%. The mass conservation in the pressure vessel was confirmed by both experimental data and numerical simulation results. This numerical simulator can be applied to predict the behavior of hydrate-bearing-sediments in the laboratory or to evaluate the gas production potential from the marine or permafrost hydrate reservoirs. [Display omitted] • We develop Full Implicit Simulator of Hydrate to simulate gas hydrate reservoirs. • Experiment of methane hydrate reaction is executed in Cubic Hydrate Simulator. • We use FISH to reproduce the hydrate dissociation experiment in quartz sands. • We obtain first group of unified parameters suitable for hydrate dissociation. • This study provides a novel numerical simulator to evaluate hydrate reservoirs. [ABSTRACT FROM AUTHOR]

• Heterogeneous decomposition of gas hydrate was studied in pilot-scale gas-saturated and water-saturated hydrate reservoirs. • Hydrate decomposition heterogeneity was classified into planar heterogeneity and interlayer heterogeneity. • The dimensionless factor D H was proposed to quantify the intensity of the heterogeneity. • The heterogeneity of hydrate decomposition was used to evaluate the hydrate distribution in the hydrate simulator. • Related the hydrate decomposition heterogeneity to the 2D geometric model for hydrate distribution in the pore space. The heterogeneity of hydrate distribution and decomposition in sandy reservoirs is an important issue. Because large hydrate simulators are scarce and visualization difficult, heterogeneity in large-scale hydrate reservoirs has been consistently underestimated. In this study, a pilot-scale hydrate simulator with an effective volume of 117.8 L was used to simulate the horizontal well depressurization decomposition of two different types of hydrate reservoirs: gas-saturated and water-saturated. The production performance and heterogeneity of these two hydrate reservoirs were analyzed during the hydrate decomposition process. For the first time, hydrate decomposition heterogeneity was classified into planar heterogeneity and interlayer heterogeneity based on the heterogeneous characteristics in the horizontal and vertical directions. Based on the pressure difference and duration, a dimensionless factor was proposed to quantify the intensity of the heterogeneity at a specific location. Furthermore, this study related the hydrate decomposition heterogeneity intensity variation process to the variations in the two-dimensional geometric model for hydrate distribution in the pore space. The experimental results showed that horizontal well extraction using the depressurization method was highly efficient. During the hydrate decomposition process, planar heterogeneity was stronger in the water-saturated hydrate reservoir than in the gas-saturated hydrate reservoir. In gas-saturated hydrate reservoir, hydrate saturation and heterogeneity increased from top to bottom. In water-saturated hydrate reservoir, hydrate saturation and interlayer heterogeneity increased first and then decreased from top to bottom. The study of heterogeneity was critical for optimizing the hydrate extraction scheme, and emphasis should be placed on the placement of production enhancement facilities in regions with significant heterogeneity. [ABSTRACT FROM AUTHOR]

Heterogenous distribution of gas hydrate in pores is the common characteristic of hydrate formation at various experimental scales. In this work, in order to fill the gap of defining the hydrate phase heterogeneity degree of hydrate-bearing sediments, we conduct a series of pore-scale experiments and simulations on hydrate formation behaviors and two-phase flow properties in hydrate-bearing samples by micro X-ray CT. The enhanced heterogeneous distribution of gas hydrate in small pores has been observed from experimental results, suggesting that the degree of hydrate heterogeneity in sandy or silty sediments may be underestimated. Therefore, the definition of hydrate heterogeneity degree is firstly proposed to characterize the hydrate phase heterogeneity of hydrate-bearing sediments. Additionally, we further investigate the effects of hydrate heterogeneity on fluid flow properties by introducing three types of hydrate distribution in porous media, which are homogeneous, clogging, and clumpy distribution. The clogging type of hydrate distribution could result in the sharply increased rate of permeability reduction, while the clumpy type of hydrate distribution might result in the declined rate of permeability reduction. Meanwhile, the heterogenous hydrate distribution leads to the rapid decrease in gas relative permeability. These findings are significant for laboratory studies and gas recovery in field tests. [Display omitted] • First definition of hydrate heterogeneity degree has been made. • Effect of hydrate heterogeneity degree on fluid flow properties has been addressed. • Three types of hydrate distribution in pores have been firstly proposed. • Hydrate heterogeneity leads to the rapid decrease in gas relative permeability. [ABSTRACT FROM AUTHOR]

Natural gas hydrates have attracted much attention in recent years. It is important to investigate the effects of gas occurrence pattern on hydrate growth habits since distribution and morphology characteristics of gas hydrates have significant effects on physical properties of hydrate-bearing reservoirs. In this work, the differences in distribution and morphology properties of gas hydrates under two gas occurrence patterns have been analyzed via the X-ray computed tomography for the first time. Experimental results reveal direct correlations between the hydrate growth habit and the gas occurrence pattern. In the presence of free gas, grain-attaching hydrates are formed at the arc-shaped contact surface of gas and water, and mass transfer at the gas-water interface is the key controlling factor in hydrate formation process. In the presence of dissolved gas, dispersed and dendritic hydrates are formed in liquid phase as the result of gas solubility change, and gas diffusion is the crucial factor that influences the growth habit and morphology of gas hydrates during hydrate formation from dissolved gas. Besides, the maximum saturation of dendritic hydrates formed from dissolved gas is limited by the gas solubility. These conclusions are valuable in the improvement of prediction accuracy of gas production from hydrate-bearing sediments. • 3D structures of hydrate-bearing samples are studied by X-ray CT. • Morphologies of gas hydrates under two gas occurrence patterns are firstly addressed. • Evidences of correlations between mass transfer and hydrate growth habit are found. • Growth habit of gas hydrates depends on gas diffusion and water migration processes. [ABSTRACT FROM AUTHOR]

Gas hydrate is considered as a new promising energy resource, and it is extensively distributed in offshore sediments and permafrost region. Two important factors affecting the gas hydrate dissociation are the water saturation in the sediments and the particle size of the sediments. In this study, the influences of the water saturation on the hydrate dissociation by depressurization in the sediments with different particle sizes were analyzed. It was found that there could be an optimum water saturation (S w,op), at which the hydrate dissociation rate reached to the maximum value. When the water saturation (S w) was smaller than S w,op , the hydrate dissociation was mainly limited by the heat transfer rate of the sediments, and the hydrate dissociation rate increased with the increase of the water saturation. When the water saturation (S w) was larger than S w,op , the hydrate dissociation rate was limited by the mass transport rate of the gas released from the hydrate dissociation, and the hydrate dissociation rate decreased with the increase of the water saturation. The experimental results showed that for the sediments with the particle size of 40–60 mesh, the optimum water saturation is smaller than 0.042. For the sediments with the particle size of 325–400 mesh, the optimum water saturation is larger than 0.415. For the sediments with the particle size of 105–125 mesh, the optimum water saturation is closed to 0.413. Therefore, the optimum water saturation for hydrate dissociation increased with the decrease of the particle size of the sediments, and it was inferred that the optimum water saturation was related to the irreducible water saturation of the sediments. It was a new knowledge about the influence of the water saturation on the hydrate dissociation in the sediments with different particle sizes, and it could provide some guidance for the production method of gas hydrate in different types of hydrate reservoirs. • There was an optimum water saturation (S w,op) to make the hydrate dissociation rate be largest. • The hydrate dissociation rate was limited by the heat transfer when S w < S w,op. • The hydrate dissociation rate was controlled by the mass transport rate of gas when S w > S w,op. • It's inferred that the S w,op was related to the irreducible water saturation of the sediments. [ABSTRACT FROM AUTHOR]

In nature, gas hydrate is mainly distributed in permafrost region and deep ocean sediments. For these two types of hydrate reservoirs, water contents in the sediments were different. The water content has a large influence on the characteristics of heat transfer and fluid flow in the sediments, thereby affecting the hydrate dissociation behavior. In this paper, the experiments of hydrate dissociation by depressurization in sediments with different water saturations were conducted. The influences of water saturation on the pressure, the temperature, the gas production, the water production, and the hydrate dissociation rate were analyzed. The experimental results showed that, in the depressurization stage (DS), the rate of pressure dropping and the amount of hydrate reformation increased with the raise of the water saturation in the sediments. In the constant pressure stage (CPS), although the heat conduction rate of the sediments increased with the increase of the water saturation, the mass transport rate of the gas released from hydrate dissociation was limited due to the increase of water saturation. As a result, the hydrate dissociation rate decreased with the increase of the water saturation in the sediments. According to these experimental results, during the hydrate dissociation in the sediments with different water saturations, the hydrate dissociation rate is determined by the mass transport rate of the gas released from the hydrate dissociation. For the hydrate reservoirs with the high-water saturation, the hydrate dissociation rate is largely limited by the diffusion rate of gas released from hydrate dissociation. Hence, the key factor to improve the hydrate dissociation rate in the sediments with high water saturation is to increase the diffusion rate of gas in the sediments. • Hydrate dissociation rate decreased with the increase of water saturation in the sediments. • Water surrounding the hydrate particle limited the diffusion of gas released from hydrate. • The mass transport rate of gas released from hydrate determined the hydrate dissociation rate. [ABSTRACT FROM AUTHOR]