Most coalbed methane (CBM) reservoirs contain moisture that can have an impact on adsorption and diffusion of CBM, so moisture content is an important factor that affects CBM production. CO2 can be used to improve CBM production on site. Combined with these two points, regulations of CH4 adsorption and diffusion are sought under different conditions when CO2 is injected into coal seams with moisture. Slit pores with different moisture contents (1%, 2%, 4%, and 6%) and random models are established. Molecular simulations are carried out, respectively, from 0 MPa to 10 MPa at 293.15, 303.15, and 313.15 K. Relative to CO2, the interaction of CH4 and −C–C– is weaker, indicating that CO2 can adsorb more steadily on the surface of coal. Water molecules preferentially adsorb on the oxygen functional groups, and then water molecules adsorb each other with hydrogen bonding to form clusters that can interfere with the adsorption and diffusion of CO2 and CH4. Because of the influence of functional groups, hydrogen bonding, and micropore filling, the adsorption capacity of H2O can increase steeply at very low pressure. The phenomenon is not beneficial to the CBM exploitation.

Nanofluid of graphene-based amphiphilic Janus nanosheets produced high-efficiency tertiary oil recovery at a very low concentration (0.01 wt %). The more attractive way is to use nanofluid during the secondary oil recovery stage, which can eliminate the tertiary stage and save huge amounts of water, especially at times when the price of oil is low. Here, we continue to report our findings on the application of the same nanosheets in secondary oil recovery, which increased oil recovery efficiency by ≤7.5% at an ultralow concentration (0.005 wt %). Compared with nanofluids of homogeneous nanoparticles, our nanofluid achieved a higher efficiency at a much lower concentration. The nanosize dimension of this two-dimensional carbon material improves transport in rock pores. After single-side surface hydrophobization of oxidized graphene with alkylamine, the partial restoration of the graphitic sp2 network was detected by Raman, ultraviolet–visible, etc. The amphiphilic Janus nature of nanosheets led to their unique behavior at toluene–brine interface. Oil immersion testing clearly showed the change in the shape of the droplet. The three-phase contact angle decreased from 150° to 79°, indicating the change in the wettability of the solid surface from oleophilic to oleophobic. On the basis of the measured three-phase contact angles, the interfacial tension in the presence of the nanosheets was further calculated and was lower than the interfacial tension without the nanosheets. These interfacial phenomena can help residual oil detach from the solid surface, which contributes to the improved oil recovery performance.

Traditional methods of exploiting oil shale such as mining or in situ electric heating cause environmental pollution, and they have huge energy losses and high costs. These problems can be solved by combining microwave heating with hydraulic fracturing for the in situ exploitation of oil shale. In this study, an experimental microwave apparatus was manufactured for laboratory experiments. Different weight proportions of iron oxide nanoparticles (0.1, 0.5, and 1 wt %), microwave output power (600, 800, and 1000 W), and ultimate reaction temperatures (550, 750, and 950 °C) were taken into account in the design of an orthogonal experiment. Temperature distributions were influenced by microwave power, as well as by the concentration of iron oxide nanoparticles. The iron oxide nanoparticles facilitated a noticeable rise in the temperature of the oil shale in a short time. The experimental results confirmed the advantages of microwave heating, compared to conventional heating, in terms of temperature increases and improved yields of higher quality oil. Specifically, the oil collected under microwave irradiation contained more saturation and aromatics, and less sulfur and nitrogen, than that obtained by conventional heating. The highest oil yield and the best oil quality were obtained with the parameters of output power of 800 W, ultimate reaction temperature of 950 °C, and iron oxide nanoparticles at 0.1 wt %. Our findings contribute to the application of microwave technology to unconventional resources, and field tests at small scale should be supported.

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The CO 2 -enhanced coalbed methane recovery (CO 2 -ECBM) technique is based on competitive adsorption. In this study, three models of different coal ranks were established using the molecular dynamics (MD) method. A combination of MD and grand canonical Monte Carlo (GCMC) simulations was used to investigate the competitive adsorption of CO 2 /CH 4 on dry and moist coal. The effects of coal rank and moisture content on pore structure, chemical structure, mixed gas adsorption capacity, and adsorption selectivity are discussed in detail. Simulation results show that from low-to high-rank coals, the total pore volume, porosity, and proportion of effective pores increase, which leads to an increase in their adsorption capacity. In addition, the oxygen-containing functional groups on the pore surface of coal enhance the displacement effect of CO 2 on CH 4 , and with an increase in coal rank the adsorption selectivity of CO 2 /CH 4 decreases. Moreover, the adsorption capacity of CO 2 and CH 4 will decrease owing to moisture. Water molecules will preferentially occupy the high-energy adsorption sites on the pore surface of coal, and then hydrogen bonding and capillary condensation will form water clusters. Therefore, in the case of moist coal, the adsorption selectivity of CO 2 to CH 4 fluctuates and shows different patterns of variation according to the different effective pore volumes of different coal ranks. From the perspective of CO 2 -ECBM, achieving a certain moisture content can have a beneficial effect, and the optimal moisture content of medium-and high-rank coal should be higher than that of low-rank coal. Under low-pressure conditions, the adsorption selectivity of CO 2 /CH 4 of dry and moist coal is larger than that of high-pressure conditions. In our work, we advance the understanding of the microscopic mechanism of competitive adsorption of CO 2 /CH 4 , which provides a theoretical basis for improving CO 2 -ECBM technology.

A new flow model in triple media carbonate reservoir is established. There exists a triple total system including the matrix, fracture and vug subsystem, and the three subsystems are relatively independent in physical properties; in the process of oil flow, the inter-porosity flow of the vug subsystem to fracture subsystem would occur and the interporosity flow of the matrix subsystem to fracture subsystem would also occur and ignore the inter-porosity flow between the matrix subsystem and vug subsystem. Compared with the traditional model (the inter-porosity flow of vug to fracture is pseudo-steady), the new model considers the unsteady inter-porosity flow, based on the hypothesis that the shape of vug is spherical. The new model is illustrated and solved, and the standard type curves are drawn up, so the process and characteristics of flow are analysed thoroughly, and it is found that the new-style type curves in shape and characteristics are evidently different from the type curves of traditional model. The research would not only deepen the understanding of flow law but also enrich the theoretical models for carbonate reservoir. The research results on this new model could be applied to a real case study.

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