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This study presents a low-field hydrogen-1 nuclear magnetic resonance (1H NMR) method to accurately determine water and oil in oil-contaminated coastal sand. Rapid, efficient separation of water and oil signals in the overlapping transverse relaxation (T2) spectra was achieved using a novel approach combining physical (paramagnetic ions Mn2+) and mathematical separation (deconvolution algorithm). High correlation coefficients of 0.998 and 0.982 were obtained between the prepared and NMR determined contents for water and oil together with the maximum errors of 0.84% and 0.54% for the water and oil content separately, which suggests NMR measurement of water and oil contents in oil-contaminated coastal sand is fairly accurate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A method to enhance geological storage of CO 2 by applying electric field is proposed. • The vertical static electric fields are more pronounced in enhancing carbon dioxide geological storage with an extra 15.58 %. • The effects of both oscillating electric fields and static electric fields on CO 2 geological storage are explored. • The mechanisms of electric fields enhancing CO 2 geological storage are explained. The microscopic understanding of adsorption and storage of CO 2 in minerals is of great significance for large-scale geological storage of CO 2. The behaviors of the H 2 O − CO 2 system absorbed on the kaolinite surfaces with oscillating and static electric fields were investigated by the non-equilibrium molecular dynamics simulation. The results show that the H 2 O molecules will adsorb onto clay surfaces and reduce the adsorption of CO 2 , which results in lower amounts of geological storage of CO 2. However, the applied external static electric fields can break hydrogen bonds which formed between H 2 O molecules and clay surface, and thus promote the desorption of H 2 O and geological storage of CO 2. The static electric fields are more pronounced in enhancing CO 2 geological storage with an extra 15.58 % when the surface is vertical to the electric field direction. Meanwhile, the initial dipole orientation of H 2 O in the adsorption phase, which is parallel to the surface, decides that electric fields are more efficient on the surface vertical to the electric field direction. This research will be helpful to understand how electric fields promote CO 2 geological storage on the molecular level. [ABSTRACT FROM AUTHOR]

In recent years, the backward trajectory model has been widely used in the research of meteorological and atmospheric environmental quality. This paper presents a comprehensive study on a stepwise clustering analysis algorithm in the clustering process of backward trajectory model and an application of the clustering analysis of single-particle backward trajectory in 2016 in Changchun City. This study starts with an analysis of the original stepwise clustering algorithm and its application to a clustering process of 8784 backward trajectories during 48 h in Changchun City as a benchmark test case. Then, two improvements are made in the algorithm: First, in the process of finding the optimal classification, the algorithm complexity is improved from original O(n3) to O(log(n)*n2) through algorithm improvement. The algorithm performance is enhanced by log(n) times. Second, in the process of re-establishing the classification, the algorithm complexity is improved from the original O(m*n2) to O(m*log(n)*n), that is another algorithm performance improvement by a factor of log(n). Therefore, the accumulative execution efficiency improvement through the algorithm optimization is 2*log(n) times, which has been further verified in the practical application in Changchun City. [ABSTRACT FROM AUTHOR]

• We study the adsorption behaviors of hydrocarbon mixtures in kerogen pores including slit pore and matrix pores. • The evolutions of CO 2 flooding are detail descibed by density and quantity distribution of C 8 H 18 /CO 2 along the z-direction. • The interaction energy between kerogen, CO 2 and oil are calculated respectively to explain the mechanism of CO 2 flooding. • It is a challenge to recover oil from kerogen matrix pores due to the lower D of C 8 H 18 and strong E kerogen-oil. • The storage capacity of CO 2 is computed to clearly show that there is great potential for CO 2 storage in kerogen. The strong interactions between kerogen and CO 2 give an opportunity to enhance shale oil recovery (EOR) by CO 2 injection, and also reduce greenhouse gas emissions through CO 2 capture and geological storage. Understanding the mechanism of CO 2 enhanced shale oil recovery is important significance for achieving optimum shale oil exploration and development. In this work, the oil storage behavior and mechanism of CO 2 enhanced shale oil recovery in kerogen pores are studied by using molecular dynamics (MD) simulations. For oil storage, the density curves are calculated and the results show that it can be found that there are two adsorption layers near the wall, and the slight fluctuations density near the two opposite wall presents different trends due to the roughness of the walls surface. For flooding behavior, CO 2 molecules are easily dissolved into the oil phase and drive out most of the oil within the kerogen slit pores after 3 ns with differential pressure of 10 MPa for our model. The higher differential pressure corresponds to earlier CO 2 breakthrough and smaller value of oil recovery. Oil molecules located in smaller pores require a longer flooding time to be displaced. The displacement is the main mechanism of oil recovery in nanoscale kerogen pores for CO 2 flooding. The diffusion coefficients of CO 2 /oil and interaction energy are calculated and analyzed. Further, the CO 2 storage capacity in shale formations are computed and its value is 466 kg/m3. This work reveals oil storage behavior and the mechanism of CO 2 flooding in shale reservoirs, and the results are significant for the CO 2 enhancement of oil recovery, and for CO 2 capture and storage in kerogen pores. [ABSTRACT FROM AUTHOR]

Highlights • An electrical heating method to enhance shale gas production is proposed. • A mathematical model of shale gas production by electrical heating is developed. • The effects of parameters on gas production are investigated by numerical simulation. • Numerical simulation suggests that electrical heating method has a good performance to enhance shale gas recovery. Abstract Gas production from shale gas reservoirs can be enhanced by increasing the temperature of the reservoirs due to the increased desorption of the adsorbed gas. However, limited techniques are currently available for practically introducing heat into such low permeability reservoirs. This paper investigates the feasibility of an electrical resistance heating method to promote shale gas production by increasing the temperature of the reservoirs. To achieve our research goal, a mechanistic numerical model is developed to describe electrical field, temperature field, and pressure field. To capture gas flow in a shale gas reservoir, non-linear flow, diffusion and adsorption/desorption which are all dependent on temperature are incorporated into a dual continuum media model. In our study, the gas production enhancement by electrical heating with two parallel horizontal electrode wells is evaluated using this model. We then assess impacts of the thermal properties of the formation, electrode length, electrical power, Langmuir volume and starting time of heating on gas production. The results indicate that the electrical heating method using two parallel horizontal electrodes can be an efficient method to enhance shale gas production. The heat capacity and conductivity of the formation have significant impacts on gas production. Reservoirs with low conductivity and low heat capacity tend to produce more gas due to heating. Meanwhile, shale gas reservoirs with high Langmuir volume also tend to yield more gas due to heating for. To maximize gas production, electrical power should be optimized based on the properties of shale gas reservoir and heating equipment. Longer electrodes heat more formations of the reservoir and thus lead to higher gas production by using the electrical heating method. In order to efficiently enhance shale gas production, electrical heating should start later in gas production, instead of earlier. [ABSTRACT FROM AUTHOR]

There has been a lot of research on flight delays. But it is more useful and difficult to estimate the departure delay time especially three hours before the scheduled time of departure, from which passengers can reasonably plan their travel time and the airline and airport staff can schedule flights more reasonably. In this paper, we develop a Spatio-temporal Graph Dual-Attention Neural Network (SGDAN) to learn the departure delay time for each flight with real-time conditions at three hours before the scheduled time of departure. Specifically, it first models the air traffic network as graph sequences, what is, using a heterogeneous graph to model a flight and its adjacent flights with the same departure or arrival airport in a special time interval, and using a sequence to model the flight and its previous flights that share the same aircraft. The main contributions of this paper are using heterogeneous graph-level attention to learn the influence between the flight and its adjacent flight together with sequence-level attention to learn the influence between the flight and its previous flight in the flight sequence. With aggregating features from the learned influence from both graph-level and sequence-level attention, SGDAN can generate node embedding to estimate the departure delay time. Experiments on a real-world large-scale data set show that SGDAN produces better results than state-of-the-art models in the accurate flight delay time estimation task. [ABSTRACT FROM AUTHOR]

Oil production from shale has grown dramatically in North America, and has the potential to do so globally. Understanding the adsorption and transport of liquid hydrocarbon through nanopores of inorganic minerals is crucial not only to develop liquid-rich shale reservoirs, but also to grasp oil migration from deeply buried extremely low permeability source rocks. In this work, the adsorption and transport behavior of n-octane (pentane, dodecane) confined in nanoscale dolomite slit pores have been investigated by grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The adsorbed phase density, molecular-scale structures at the interface, self-diffusion are then calculated and analyzed by equilibrium molecular dynamics (EMD). The number of adsorption layers is related to the size of pore. Increasing temperature will decrease the amount adsorbed, while pressures have little effect on amount adsorbed. Near the dolomite surface, the n-octane molecules adopt a preferential alignment parallel to the substrate, better packed and diffuse more slowly. Consider three alkanes, the long alkanes (octane, dodecane) are more easily to be adsorbed on dolomite surface. Lastly, the nonequilibrium molecular dynamics (NEMD) have been used to study the pressure-driven flow of n-octane in dolomite slits, flow characterization, viscosity, and slip length are analyzed. A larger driving force will increase slip length, while having only a negligible impact on the effective viscosity of the n-octane. • The GCMC and MD simulations were conducted to study the n-octane (pentane, dodecane) adsorption and diffusion behavior. • The dolomite was introduced as clay to study the liquid hydrocarbon adsorption and transport behavior. • The depressurization may not be the best way to extract oil in nanopores, especially for oil in the adsorbed layer. • The flow characterization, viscosity and slip length of n-octane are analyzed by nonequilibrium molecular dynamics [ABSTRACT FROM AUTHOR]