This article conducts three-dimensional simulations for transcritical flow and heat transfer of methane in a rectangular channel under asymmetric heating conditions and compares the accuracy of three different Nusselt number correlations. A correction method for the Nusselt number correlation based on the secondary correction of the radial velocity distribution is proposed. The results show that by correcting the three correlations using the proposed method, the error of the average Nusselt number under the condition of heat transfer deterioration between the calculated values and the ones obtained from numerical simulations are reduced from 88.26%, 11.41%, 19.29% to 13.71%, 0.47%, and 6.02%, respectively. Compared with the correlation obtained by directly modifying based on the heat transfer deterioration condition data, the Nusselt number correlations modified by the proposed method achieve higher accuracy, and the calculation error are limited to within 15%. Overall, the modified Bishop correlation has the highest calculation accuracy among the three correlations, and the errors between the calculated values and those obtained from numerical simulations are limited within 6% under different mass flow rates.

A straightforward microfluidic approach has been developed to fabricate the monodisperse thermo-responsive self-bursting poly(N-isopropylacrylamide) (PNIPAM) microcapsules for the rapid on-demand release of liposoluble drugs. The PNIPAM microcapsules possess excellent structural integrity with a dense shell and spacious cavity, providing ample space for encapsulating liposoluble matters. The swollen hydrogel shells effectively prevent drugs leakage and contamination below the volume phase transition temperature (VPTT), while the shrunken hydrogel shells enable drugs to release from microcapsules above the VPTT. The microcapsules demonstrate rapid thermo-responsiveness, with drug release occurring within 4-6 minutes and subsequent swelling taking place within 2-3 minutes. The PNIPAM microcapsules exhibit a reversible and repetitive swelling/shrinking response to temperature changes. The thermo-responsive self-bursting PNIPAM microcapsules exhibit great potential as microcarriers for encapsulating, storing, and rapidly releasing liposoluble substances such as drugs, fluorescent dyes, corrosion inhibitors, and other chemical ingredients. The simple, controllable and reproducible microfluidic approach presented here provides valuable guidance for the design and fabrication of monodisperse PNIPAM microcapsules.

The lacustrine shale in the Da’anzhai member of Jurassic in the central Sichuan Basin is a key exploration target for shale oil and gas resources in China in the future. This paper presents a detailed study of shale rock types and component characteristics, shale pore types and structural characteristics, and shale pore evolution characteristics under thermal simulation conditions through experimental analyses such as rock thin section and field emission scanning electron microscopy (FE-SEM) observation, conventional physical property test, X-ray diffraction (XRD) analysis, TOC test, liquid nitrogen adsorption (LNA) test, and thermal simulation (pore) experiment. The results show that minerals in the Da’anzhai shale are mainly clay minerals, quartz, and calcite, with a small amount of feldspar, dolomite, and pyrite. In the shale oil reservoirs, there are dominantly inorganic pores (e.g. clay intergranular pores), and relatively few organic pores. The specific surface area ranges from 1.064 m 2 /g to 9.227 m 2 /g, with an average of 4.949 m 2 /g. The pore volume is 0.003–0.016 cm 3 /g, with an average of 0.010 cm 3 /g. Mesopores contribute the most to the total pore volume and total specific surface area. With the increase of thermal simulation temperature, the degree of shale thermal evolution increases, and the shale porosity increases, predominantly, owing to the contribution of organic pores. It is concluded that inorganic pores, especially clay intergranular pores, are the dominant pore type in the Da’anzhai shale oil reservoirs, and the evolution degree, burial time and depth of organic matter can obviously improve the organic pores.

Occurrence and transport are two important nanoscale behaviors in the exploitation of shale gas. Nanopores in a realistic shale organic matrix are composed of kerogen molecules, which will have a great impact on surface-gas interactions and gas nanoconfined behavior. Although there are previous studies, the physics of gas transport through shale systems remains ambiguous. In this work, cylindrical nanopore models representing different pore sizes and organic-rich shale were constructed. By applying the molecular dynamics simulation method, the occurrence characteristics and transport characteristics of CH4 in the nanopores of organic-rich shale were studied. At last, the process of the adsorbed CH4 displaced by CO2 and N2 in shale nanopores at the subsurface condition was explored. This work can provide a better understanding of gas nanoscale behavior in shale systems and assist the future design of the CO2 sequestration and enhanced gas recovery technique.

CO2 enhanced coalbed methane (CO2-ECBM) technology has been recognized as one of the most important technologies to enhance the recovery of CBM. However, due to the complex pore structure and strong heterogeneity of coal rocks, the industry still lacks a unified understanding of the adsorption mechanism of CH4 and CO2. In this study, three models of different coal rank were established based on realistic coal macromolecules. The grand canonical Monte Carlo (GCMC) method and equilibrium molecular dynamics (EMD) method were used to study the adsorption mechanism of CH4 and CO2 gas molecules. Then the occurrence characteristics of the two gas molecules in coal nanopores were analyzed. By analyzing the two-dimensional (2D) cloud maps of the density distribution of a total of 96 sets of CH4 and CO2 schemes, the non-uniformity of the gas adsorption behavior in the nanopores of coal can be observed. The results show that CH4 is mainly adsorbed as a mono-layer in coal nanopores; occurrence of gas within the nanopores, there are high-density adsorption layer region and bulk region; density ratios are negatively correlated with both pressure and pore size; the reduction of the pore size will help to improve the gas storage capacity in the nanopores. Cylindrical nanopore models representing different coal ranks and pore sizes were constructed that embody the complex amorphous structure and strong heterogeneity surface properties within the coal nanopores. The research in this paper can enrich the theory of CBM accumulation and provide theoretical guidance for highly efficient development of CBM.

传统水基压裂液易对储层造成水敏伤害,二氧化碳压裂液技术成为非常规油气开发研究的新方向.但是由于纯二氧化碳压裂液黏度较低,严重影响了其压裂效果,因此寻找合适的增稠剂来提高二氧化碳压裂液的黏度势在必行.通过文献调研,综述了表面活性剂、碳氢聚合物、含氟聚合物及硅氧烷聚合物4类二氧化碳增稠剂的结构特征和性能特点,并从增稠机理和增稠性能两方面概述了目前二氧化碳压裂液增稠剂的研究现状.最后总结了各类增稠剂的特点并对以后的研究方向提出了建议.

Supercritical CO2 has been widely concerned because of its clean environmental protection and excellent performance. However, the low viscosity limits its wide application. To this issue, researchers usually use thickeners to improve its viscosity. The siloxane-type polymer is regarded as clean and cheap thickener. In this work, we screened potential supercritical CO2 thickeners by comparing the thickening properties of vinyl polysiloxane, hydroxyl polysiloxane and polydimethylsiloxane. The results show that vinyl polysiloxane has the best thickening performance. The dissolution and thickening behavior of vinyl polysiloxane are further studied. The results indicate that the dissolution pressure and thickening capacity of vinyl polysiloxane in supercritical CO2 increase with the increase of kinematic viscosity and concentration. At the experimental conditions, the maximum viscosity of supercritical CO2 can be increased to 14.87 mPa.s. In addition, the dissolution pressure of vinyl polysiloxane in supercritical CO2 decreases with the increase of cosolvent concentration, while the viscosity slightly decreases. Finally, the thickening mechanism of these thickeners was studied by molecular dynamics simulation. Based on the molecular simulation results, the roles of functional groups of thickeners in the dissolution and thickening process are discussed. It can provide theoretical support for the synthesis and screening of CO2 thickeners in the future.

The conventional water-based fracturing fluids have such defects as large water consumption, serious environmental pollution and water-sensitive damage to reservoirs in the development of tight oil. In this study, a novel anhydrous CO2 fracturing fluid system was constructed with the compositions of 7 wt% polydimethylsiloxane (100 cs), 5 wt% ethanol and 88 wt% liquid CO2. The viscosity of the system could reach 6.52 mPa s, which was 37 times higher than that of pure liquid CO2 at -15 degrees C and 30 MPa. The pressure resistance, temperature resistance, anti-swelling property, filtration loss property, core damage property, corrosion property and wetting inversion property of anhydrous CO2 fracturing fluid were systematically evaluated by physical simulation experiments. The environmental scanning electron microscopy (ESEM) and mercury injection experiment were conducted. The viscosity retention rate of anhydrous CO2 fracturing fluid reaches 47.92% when the temperature increases by 50 degrees C. When the pressure increases by 25 MPa, the viscosity increases by 2.6 times. It ensures that the viscosity of anhydrous CO2 fracturing fluid is well retained after injection into the formation. In addition, the anti-swelling rate of anhydrous CO2 fracturing fluid reaches 90.91%. The filtration coefficient is reduced by 69.20%. For low permeability sandstone cores, the permeability damage rate is 18.80% and the porosity damage rate is 12.58%. After aging for 30 h, the permeability and porosity of core increased 39.23% and 5.52%, respectively. Meanwhile, the wettability of the core could be changed from hydrophilic to neutral, which reduced the flow resistance of the oil phase and improved tight oil recovery. Through this study, we hope to broaden the application of anhydrous CO2 fracturing fluids in tight oil development.

Chemical demulsification is the most effective, common and the cheapest method to break crude oil emulsion during oil extraction. The chemical demulsification process is related with the natural emulsifier displacement by demulsifier. In this article, a single droplet in situ displacement method was employed to evaluate demulsifier displace capacity and the experimental device was built. This device determines the displacement capacity of demulsifier by measuring the oil-water interfacial tension, demulsifier concentration and saturated adsorption amount of demulsifier. Displacement capacities of four commercially available polyether demulsifiers and the relationship between demulsifier displacement capacity and demulsification performance were investigated. The results showed that the demulsifier displacement capacity was not affected by natural emulsifier type (asphaltene, resin, or mixture of asphaltene) and was related to the demulsifier type, concentration, and temperature. Demulsifier displacement capacity increased with demulsifier concentration and temperature. However, only when the asphaltene concentration of was over 6.78 wt%, the demulsification increased with demulsifier displacement capacity.

Compared with conventional water-based fracturing fluid, supercritical CO2 fracturing fluid has the characteristics of inhibiting water sensitive damage and improving flowback efficiency. In view of the problems of low viscosity, poor sand-carrying performance and large filtration loss capacity of pure supercritical CO2, a supercritical CO2 fracturing fluid system had been prepared: 5% polydimethylsiloxane +5% kerosene +90% supercritical CO2. The rheological property, sand-carrying property, filtration loss property, core damage property and wetting inversion property of the system were systematically studied through performance evaluation experiments. At 325 K, the viscosity of the system can reach 4.67 mPa s, which was 54.26 times higher than that of pure supercritical CO2. The performance evaluation showed that the system had a good rheological property. The sand-carrying capacity was improved by 38.17%, and the filtration loss coefficient was decreased by 71.71% at most. The interaction results between CO2 and reservoir showed that the system could effectively increase the porosity and permeability of the core. For ultra-low permeability sandstone core, the porosity was increased by 7.71%, the permeability was increased by 115.20%. While for shale core, the porosity was increased by 6.99%, permeability was increased by 102.44%. At the same time, the system can change the core wetted by water phase into a neutral wetted one which was favorable for oil and gas flow. This system is expected to be further studied in oilfield applications.

The bedding plane of shale is related to anisotropic mechanical property, which apparently affects the shale fracturing. To investigate the influence of shale bedding on the fracture morphology and perforation damage under Supercritical Carbon Dioxide (SC-CO2) jet fracturing, the experiments were comprehensively studied via the macro fracture analysis, strain monitoring, Scanning Electron Microscope (SEM) test and Energy Dispersive Spectroscopy (EDS) test. The results demonstrated that the average Young's Modulus (YM) and Uniaxial Compressive Strength (UCS) of shale specimen with the bedding plane angle of 0 degrees is 9.37 times and 2.89 times of the shale specimen with bedding plane angle of 90 degrees, respectively. During jet fracturing, both the jet pressure and existing bedding are beneficial for fracture initiating and propagating naturally along the weak bedding planes, and shear fracture can enhance the fracture complexity. When the perforation distributes in the direction perpendicular to the bedding plane, the less strain can be obtained, and the mass loss and CO2 absorption of shale specimen significantly increase by 350% and 300%, respectively, as the jet pressure increases from 25 MPa to 50 MPa, which is larger than the shale specimen with bedding plane angle of 0 degrees. The perforation damage is explored after jet fracturing via SEM and EDS, and it is found the direction of perforation perpendicular to the bedding plane is beneficial for micro-cracks generation, and leads to 10% decline of carbon (C) and oxygen (O) elements in the samples. These studies clearly show the influence of the bedding plane angle on the fracture morphology and perforation damage, which are crucial for SC-CO2 fracturing and CO2 storage in shale reservoir.

The effects of surfactant structures on the supercritical carbon dioxide (scCO(2)) solubility are investigated to shed some light on the application of scCO(2) in chemical procedures. The dissolution pressure of three nonionic surfactants (TX45, TX100 and OP-10) in scCO(2) was measured. Solubility results reveal that surfactant with branched alkyl chains shows better solubility than surfactant with linear alkyl chains. This may be due to the volumes occupied by the hydrophobic tails of these nonionic surfactants. TX45 with the largest tail volume and lowest molecular weight performs the largest solubility in scCO(2). In addition, the solubility results of three nonionic surfactants in scCO(2) at the temperature range of 305 K to 325 K show that solubility is proportional to the pressure and density of scCO(2), and inversely proportional to the experimental temperature. Finally, two density-based models (Chrastil model and Bartle model) are applied to correlate the experimental solubility data, and the results show good agreements for the experimental data of investigated nonionic surfactants. Similar agreements with experimental solubility data of surfactants are obtained by both models and the average absolute relative deviation (AARD) values lower than 2% were obtained. (C) 2020 Elsevier B.V. All rights reserved.

Maleic anhydride (MAH) and β-cyclodextrin (β-CD) were chosen to synthetize vinyl β-cyclodextrins monomer (MAH-β-CD) by alcoholysis reaction. A kind of thickener (PAADM) was synthesized with MAH-β-CD, AM, AMPS, and DMDAAC via free radical aqueous polymerization by adjusting the polymerization conditions through orthogonal method. The structure of the obtained quadripolymer was characterized by IR spectroscopy, 1H NMR, and UV spectrum. Subsequently, its acid-soluble time was 100 min, not 120 min, and the apparent viscosity can be over 36 mPa s at the concentration of 0.8 wt %, which could meet the needs of on-site construction. Besides, the zirconium acetylacetonate was compounded with glutaraldehyde to be crosslinking agent for PAADM acid. When the concentration of hydrochloric acid was 20 wt %, the amount of thickening agent was 0.8 wt %, the crosslinking agent was 0.12 wt % (zirconium acetylacetonate and glutaraldehyde mass ratio of 1: 1), and when the crosslinking temperature was 70°C, the system could even reach 750 mPa s. Further, a series of performance evaluations were made on this crosslinked acid. The results showed crosslinked acid with good temperature resistance, retarding performance and compatibility. The core corrosion method showed that retardation rate could be enhanced to 60%, indicating the retarder performance of the crosslinked acid solution was significantly better than that of the thickening acid and the blank acid. The residual acid after breaking the gel kept a relatively low concentration of 2% at 60°C for 1 h, which could achieve the purpose of effective return of residual acid while the damage to the formation was smaller consequently, indicating great potential applications in petroleum and natural gas industry for unconventional reservoir recovery.

As a high-efficiency clean energy and chemical raw material, coal-bed methane (CBM) has received wide attention in recent decades. At the present stage, new strategy to achieve a breakthrough in the CBM exploration and development is regarded as the primary goal for China's lignite region. Usually, lignite contains a high moisture content in our country. Therefore, it is of great practical significance to understand the effect of moisture content on methane adsorption in lignite. Herein, molecular simulations of Monte Carlo and molecular dynamics methods are employed to elucidate this effect on methane adsorption with three moisture contents of 0%, 1.6% and 3.2%, and three temperatures of 298 K, 313 K and 373 K and the pressure range of 0-10 MPa are considered in the work. The lignite substrate model is composed of an aromatic skeleton amorphous structure with 88 atoms, including carbon, hydrogen, oxygen, nitrogen and sulfur. The adsorption amount, adsorption heat, and atomic radial distribution function along N, O, and S atoms are investigated in turns. The results show that the adsorption amount of methane decreases with the increase of moisture content in lignite, because the water molecules would be superior to methane to occupy the adsorption sites in lignite at the initial stage. The adsorption amount of methane decreases with the increase of temperature due to the molecules thermaldynamic property. The adsorption heat of methane decreases with the increase of moisture content in lignite. In addition, the N and S atoms exhibit the stronger interactions with methane than the O atom in lignite. This molecular simulation results are not only helpful to understand the adsorption mechanism of methane in lignite, but also provide theoretical prediction and scientific evidence for the exploration of CBM.

A new scale inhibitor MA/AA/MA-β-CD/SHP was prepared from maleic anhydride, acrylic acid, sodium hypophosphite, and MA-β-CD via the method of free radical polymerization in aqueous solution. The MA-β-CD was obtained through the modification of β-cyclodextrin (β-CD) with maleic anhydride (MA). Results of performance evaluation showed that the synthesized copolymer has excellent scale inhibition effect for the calcium scale, and the resistance rate of silicon scale up to 79.81%. The structure, thermal property, and morphology of the copolymer were characterized by FTIR, TGA, and SEM. From crystallization data and morphology of the scale crystals it was found that the copolymer scale inhibitor can make the crystal lattice distortion, and has a good dispersing ability after addition of the scale inhibitor.

An acrylic emulsion-type inverse demulsifier (named as PMEMA latex) was prepared by using methyl methacrylate (MMA), ethyl acrylate (EA), methacrylic acid (MAA), and acrylamide (AM) as monomers. The effects of reaction conditions toward the copolymerization results were investigated by evaluating various evaluation parameters, including conversion, molecular weight, and diameter. In addition, the interfacial properties of PMEMA latex were investigated to study its demulsification mechanism about treating the O/W emulsion. [GRAPHICS] .

Coacervate behavior of polyelectrolyte complexes has been studied by many papers. Few studies have focused on the coacervate behavior of amphoteric polymer. In this study, amphoteric copolymer of diallyldimethylammonium chloride (DM) and sodium styrenesulfonate (SS) (the copolymer was noted as DMS) was synthesized with the mole content of SS to DM ranged from 0 to 10%. Firstly, DMS was characterized by static light scattering, FTIR, H-1-NMR, TGA and DSC. Then, its phase and coacervate behaviors were studied. Turbidity was utilized as an indicator for the coacervate formation. It was found that when the SS content was more than 4 mol%, DMS coacervate would be formed in deionized water at a certain concentration. Temperature and pH have no effect on the formation of DMS coacervate. Meanwhile, salts has a great influence on the DMS coacervation. Unlike the results of the other polyelectrolyte complexes, Na2SO4, Na2HPO4, NaCOOCH3, sodium citrate and NaI cannot prevent the DMS coacervate formation. However, the addition of NaCl, NaNO3, NaBr and NaSCN can prevent the coacervate formation. The influence cannot be described by Hofmeister-like behavior. Results of surface tension and fluorescence spectrum presented that the driving forces to formation of DMS coacervate are the electrostatic interaction and the intermolecular hydrophobic interaction.

The purpose of this paper is to study the difference of tectonic coal with different degrees of damage (DoD) in terms of gas adsorption, desorption and emission. To this end, by taking the 3# coal seam coal sample in Gaohe Coalfield as an example, the isothermal adsorption-desorption test was carried out in this paper to study the gas adsorption-desorption and emission law of tectonic coal with different DoD. The results show that with the DoD deepening of tectonic coal, the adsorption capacity of coal seam gas (CSG) in the geological structure area is better, and the CSG adsorption limit (adsorption constant a) increases; the coal seam gas desorption capacity is also better in the geological structure area, and the gas adsorption constant b decreases. Besides, the gas emission curve of fitting results indicate that Sun Chongxu Formula can accurately describe the gas emission process of tectonic coal. By comparing the numerical analysis results with the experimental results, it is found that the variation trend of the two is in good agreement.