The characteristics of in situ coal tar reforming with char were investigated. Subbituminous coal was continuously fed and pyrolyzed at 1173 K in a drop-tube reactor in the presence of additional ...char. The ratio of the additional char to coal was varied to clarify the effect of the amount of the additional char on tar reforming. The effect of the operation pressure was also evaluated. The experimental results showed that the heavier tar having more than four ring aromatics decreased with the increase in the amount of char. The reforming reaction of the heavy tar with additional char was somewhat restricted with the increase in the operation pressure (<0.9 MPa). The pore structure analysis of the char indicated that the micro-, meso-, and macropores were plugged after the tar-reforming reaction. A reaction model was proposed considering the pore plugging of the additional char to explain the experimental results. The results of the model fitting indicated that the amount of pore available for tar reforming decreased with the increase in the operation pressure. The model also suggested that the kinetic constant and residence time are more effective in increasing the conversion of tar than the amount of the available pore.
The research on the differential enrichment mechanism of shale gas under the complex tectonic background is a key problem to be solved currently. The southern Sichuan Basin is taken as the research ...object, and the geochemical experiment, overburden porosity and permeability experiments, direction test of a ground stress experiment, and seismic interpretation method are used to clarify the structural deformation characteristics and fault characteristics under different structural styles and structural parts and summarize the differences of shale gas preservation critical conditions in different structural units. The results show that (1) the fracture level controls the boundary and scale of shale gas reservoirs. The primary/secondary faults within 3 km greatly influence shale gas reservoirs, and the complex combination of fault systems will cause obvious indigenous damage to shale gas reservoirs. (2) The angle between the fault strike and the direction of the maximum principal stress determines the sealing of the fault, and the angle greater than 45° can effectively inhibit the loss of shale gas. (3) The coupling effect of burial depth and dip angle controls the migration of shale gas along the strata. The greater the burial depth and the smaller the dip angle, the better the page sealing and preservation conditions. Based on the enrichment factors of shale gas in different tectonic units, three enrichment models of syncline, anticline, and slope are established, and the enrichment favorable areas are optimized, which has important guiding significance for shale gas exploration and development in Sichuan Basin.
Natural gas hydrates are considered as a high-potential source of unconventional hydrocarbons. Economically viable and environmentally safe production of gas sequestered in hydrates requires ...estimating the amount of liquid pore water that resides in hydrate-bearing sediments, including one in permafrost. In this work, we present results of estimating the content of residual pore water in gas hydrate reservoirs using nuclear magnetic resonance relaxometry on a low-field NMR rock analyzer with a designed high-pressure core holder at pressures up to 8.0 MPa. The measurements are conducted on artificial samples of fine sand with inclusions of kaolinite and montmorillonite clay. The NMR results reveal the presence of liquid pore water in all hydrate-bearing samples, with its content decreasing under increasing gas pressure and cooling. The content of residual pore water approaches the calculated amount of nonclathrated water, the minimum for hydrate-bearing media, in samples exposed to repeated heating–cooling cycles. Results confirm that samples with higher percentages of clay (especially montmorillonite) contain more residual pore water, which varies from <0.2 wt % in pure sand to 5.0 or 6.8 wt % (at −5.5 and +2.5 °C, respectively) in a mixture of sand with 25 wt % of montmorillonite clay. It is also noted that the content of residual water is sensitive to initial moisture content and residual ice content in permafrost hydrate-bearing reservoirs.
The presence of asphaltenes in crude oil is a key factor in stabilizing water-in-oil emulsions. Changes in asphaltene aggregation have a definite effect on the formation of an elastic and highly ...resistant film that stabilizes such emulsions. Herein, we report asphaltene aggregation changes using two different methods. First, with a quartz crystal resonator sensor, clear changes in the resonant parameters (Δf n and ΔΓ n ) of the quartz sensor fully immersed in a heavy crude oil + cyclohexane solution were observed when the asphaltene concentration in the solution reached approximately 1000 ppm. Second, using an oscillating spinning drop interfacial rheometer, a distinct discontinuity of the trend of the optimum formulation is found when the asphaltene content C A attains this threshold value. The formulation variation was obtained by two kinds of scans, which were shown to be equivalent: an increase in water salinity for an anionic surfactant-containing system and an ethylene oxide number (EON) decrease of a non-ionic surfactant. In both cases, the hydrophilic surfactant was used as a demulsifier in a fixed concentration C D. It is seen that the variation of the asphaltene concentration C A generates an unexpected sudden change at the interface, according to Winsor’s affinity ratio R and hydrophilic–lipophilic deviation (HLD) premises about the compensation of the effect of asphaltenes by a formulation variable change. These newly reported results happening around C A = 1000 ppm could help to further understand how the asphaltene aggregation models and the HLD equation can be tools for the formulator to find fast and efficient answers to crude oil dewatering.
The emulsification of heavy oil is universal in various stages of heavy oil extraction, processing, and transportation. In this study, molecular dynamics simulations were employed to reveal the ...emulsification of heavy oil from different regions. When the water mass fraction is low, metal ions in the Karamay emulsion exist at the oil–water interface and interact with naphthenic acid (NA), which results in strong emulsion stability. The dominant interactions between resin and water molecules cause weak emulsion stability for Liaohe and Canada heavy oils. On the basis of the thermodynamic analysis, we found that the interaction between the metal ion and NA in the Karamay emulsion is much stronger than the interaction between the asphaltene/resin molecules and water molecules in Liaohe and Canada emulsions, which is the main reason for stronger emulsion stability in the Karamay region. As the water concentration increases, the emulsion stability of Karamay heavy oil will have a significant change as a result of the lower metal ion concentration. The water-phase structures and emulsion viscosity were investigated, and the water aggregations present spherical, worm-like, stick, net, and honeycomb structures with the increase of the water concentration. The breakup of the emulsion structure leads to a sudden decrease in the viscosity of the Karamay heavy oil.
Affected by the global low-carbon strategy, high-maturity shale, as one of the major sources of shale gas resources, exhibits important energy value and economic benefits. However, the microstructure ...evolution of high-maturity shales under thermal metamorphism and microscopic deformation remains unclear. In this study, we selected 20 high-maturity coal-bearing shales from the western Guizhou to reveal the evolution of shale microstructure during thermal maturation and the effects of microscopic deformation on pore distribution. The maximum pyrolysis temperature (T max) and vitrinite reflectance index (R o) values (averaging 578 °C and 3.08%, respectively) suggest that the Upper Permian Leping shale reaches the dry gas generation stage, and the average hydrogen index (HI) and carbon isotope of kerogen (δ13C) values indicate that all samples have already undergone intense hydrocarbon generation. Brittle minerals represented by quartz have negative relationships with the pore volume (PV) and surface area (SA), and ductile clay minerals significantly improve the PV and average pore size (AP). Layered clay minerals, especially illite/smectite (I/S), are more conducive to the development of nanopores in a shale matrix. Both H/C and O/C ratios are positively correlated with δ13Corg values, suggesting that the variation in organic elements in kerogen is closely related to carbon isotope fractionation. With the enhancement of thermal evolution, the correlation between AP and T max is negative at the first stage and then positive at the second stage. At the high maturation stage, the accumulation of gas leads to the expansion of the organic matter surface and the formation of gas pores, resulting in a rapid increase in AP. The distribution of the pore–fracture system is closely related to the microscopic deformation. Compared with the contact zone of ductile deformation, more microfractures can be observed in the contact zone between brittle deformation and ductile deformation.
Rh-based catalysts are widely used in CO hydrogenation to ethanol. In this work, Rh/TiO2 catalysts were prepared by glow discharge plasma. Rhodium salt was reduced by electrons in an electric field ...at room temperature. Oxygen vacancies and Ti3+ were produced on the surface of Rh/TiO2 by plasma. The defects promoted the synergistic effect of Rh and TiO2 through the enhanced interaction between active metal and supporter. Ti3+ is beneficial for the adsorption of intermediate formyl group. In situ IR revealed that the bridged and linear adsorption mechanisms of CO can promote the formation of ethanol intermediates. Rh/TiO2 catalysts by plasma exhibited a superior space-time yield of 0.106 gMeOH·gcat –1 h–1, at 260 °C and 3 MPa, which was approximately 1.8 times that by traditional hydrogen reduction.
Fracture initiation expansion and external fluid sensitivity evaluation have become the main focus of the coal reservoir fracturing effect. Therefore, a study on fracture propagation of hydraulic ...fracturing and the coupling mechanism between the fracturing fluid and pore structure of coal reservoirs need to be studied. In this paper, fracture conductivity and external fluid sensitivity evaluation were carried out. First, an automatic reservoir fracturing simulation tester and a large-scale computed tomography scanner are used to compare the fracture distribution and calcite content and evaluate the fracturing effects of different fracturing fluids and construction parameters. Second, the variation of porosity and permeability of coal before and after the injection of different external fluids are measured by an overlying pressure porosimeter, high-pressure mercury injection, and two-dimensional nuclear magnetic resonance. The results are as follows. (1) The T 1–T 2 spectra of dried and saturated water samples indicate adsorbed water and mobile water in the adsorption pore, while mobile water mainly exists in the seepage pore and fracture. Different occurrence states of water have different T 1 ∼ T 2 spectrum ranges. (2) The experiments of external fluid injection show that different external fluids have different effects on the porosity of the adsorption pore, seepage pore, and fracture. High-viscosity slick water and the acidizing fluid harm the seepage pore porosity, while low-viscosity tricky water and active water improve it. Fracture porosity is not sensitive to the guanidine gel-breaking fluid. (3) Experiments of fracturing initiation show that acid fracturing can reduce the fracture pressure and cumulative injection by 6.9 and 33.9%, respectively. The reaction of the acidizing fluid with carbonate mineral components can significantly increase the acid dissolution ratio and porosity of calcite, which forms the complex fractures and contributes to the increase of fracturing reconstruction volume.
Chemical looping oxidative coupling of methane (CLOCM) is a promising method for the direct conversion of methane to produce C2+ hydrocarbons. However, high reaction temperatures (800–900 °C) are ...required to ensure high redox activity, leading to the server sintering of oxygen carriers. Here, we report plasma-assisted chemical looping oxidative coupling of methane and investigate its performance under mild conditions (100–400 °C). The results demonstrate that the plasma-assisted CLOCM reaction can be initiated at temperatures as low as 100 °C. Particularly, LaMnO3 shows a high CH4 conversion of 35.33% and a C2+ yield of 12.26% at 400 °C. The performance merely decreased after 20 redox cycles. A mechanistic study implies that the high-performance results from plasma generate high-energy electrons (1–20 eV) to activate methane (4.3 eV) at low temperatures and to increase the electron vacancies on the surface of the oxygen carrier for binding oxygen species, inhibiting methane overoxidation. We hope that the promotion effect of plasma can be extended to enable more fuel conversion processes under mild conditions.
