Abstract

Imbibition is an important mechanism for resource development in tight reservoirs. Scaling models describe the mathematical relationship between imbibition cumulative production and time, which is important when associating experiments with reservoir behavior. For tight reservoirs, diffusion and water sensitivity have a great influence on imbibition, and the scaling effect of the classical model is poor and needs to be modified. In this study, nuclear magnetic resonance (NMR) method was used to test the imbibition process of eight samples, and a new model considering diffusion and water sensitivity was proposed, and the scaling effect of the new model was verified by the experimental results. The results show that diffusion and water sensitivity have an important influence on the imbibition of tight reservoirs. A new parameter of imbibition diffusion radius is proposed. It has two characteristics. One is that it increases with the increase of imbibition recovery rate, which can reflect the diffusion capacity, and the other is that it decreases with the increase of small holes, which can reflect the influence of water sensitivity. Compared with the average radius used by the classic model, it can better describe the process of tight reservoir imbibition. The scaling effect of the new model modified with new parameters is better than that of the classic model, and the dispersion of imbibition curve is well eliminated, which can make laboratory imbibition data more conveniently used to guide reservoir production. The research results provide a new model and experimental reference for the development of unconventional oil and gas resources.

Abstract

As a low-cost grid-scale electrical storage, Carnot battery has attracted increasing interest due to the rapid growth of renewable energy. However, the low-grade efficiency and technological maturity are the problems in the development of the Carnot batteries. This paper proposes a technical approach to transform the thermal power stations into high-efficiency storage plants, combining existing equipment with new technologies. For this, a case study using a typical 1000MW supercritical coal-fired plant is investigated in this paper. The dynamic cycle and the high-temperature reservoir are comprehensively re-designed to enhance the round-trip efficiency of the Carnot battery. The results show that the optimization of the Rankine cycle increases the cycle efficiency by ~2% through rising the feedwater temperature. In the design of the high-temperature reservoir, volcanic rocks are used as the storage medium to be heated at 750~800 °C, combined with the cascade utilization of thermal energy, which makes a great contribution to the round-trip efficiency of 49.5%. Based on the obtained results, it is concluded that the high-temperature Rankine Carnot battery has the potential to become a promising grid-scale electrical storage in the coming future.

Abstract

Gas hydrate formation on gas bubble prefers to exist in the deep-sea pipelines during the oil-gas transportation, resulting into the clogging of pipelines. The hydrate inhibitors are generally added to deal with the huge threat and challenge. This study provided the growth kinetics behaviors of hydrate film on gas (CH4 – C3H8) bubble suspending in the water with the inhibitors (ethylene glycol: thermodynamic inhibitor of small molecular weight and LuviCap EG: kinetic inhibitor of big molecular weight, respectively) at extreme high undercooling degree (10 – 15 K), including the growth modes, the lateral growth rate, and the evolution of the morphology and mass transfer channels. The optical microscope was used to observe the kinetics growth phenomenon. Study showed the growth mode of pasty hydrate in the liquid phase instead of hydrated bubble when the inhibitor concentration increased to the critical 8000 ppm. For both inhibitors, the difference is that the craters embodied in the hydrate film were formed for LuviCap EG concentration from 500 to 4000 ppm. These craters were considered as the aggregative LuviCap EG molecules, which attached to the hydrate lattice in the lateral growth of hydrate film. Hence, the craters were a type of new mass transfer channels, accelerating the initial thickening growth of hydrate film. The craters quickly enlarged in the initial thickening and finally formed the uniform and coarse texture. The initial size and the enlarged rate of craters were determined by the concentration of LuviCap EG. In conclusion, the critical concentration indicated that the inhibitors should be added to more than 8000 ppm, which helps keep the good fluidity of oil-gas in the pipeline transportation. The morphology and kinetics behaviors of craters of new mass transfer channels on hydrate film on bubble shed light on the mechanism of hydrate formation in water with hydrate kinetics inhibitor, providing the theoretical basis of the hydrate anti-blockage mechanism for the oil gas transportation in the deep-sea pipelines.

Abstract

Marine hydrate reservoir has great resource potential, but its accumulation mode is not clear yet. At present, the study of hydrate accumulation mode is mainly carried out by in-situ exploration results and the analysis of hydrate formation conditions. In this study, methane hydrate is generated in the sediments of South China Sea on four modes, and the influence of the initial state and generation mode on the reservoir temperature and pressure change trend and the final temperature and pressure state is obtained, which provides guidance for the exploration of hydrate accumulation mode in South China Sea.

Abstract

A building or a group of buildings may be considered as a set of thermal zones which exchange energy with the environment through the envelopes and systems: walls, thermal bridges, glazing, HVAC. A thermal model of a building (or group of buildings) may thus be represented by a graph where the vertices stand the capacitive nodes (thermal zones and wall meshes) and the edges carry the heat flows. Therefore, it is possible to convert a BIM representation of a building such as a gbXML file into a graph holding the physical laws of the heat flows and heat balances involved.
The aim of this paper is to introduce a novel methodology to generate building energy models (BEM) from BIM digital mock-ups. This new approach consists in creating a graph model using the Python NetworkX library from the available geometric and physical data extracted in the BIM representation. The graph model is used to generate a set of linear invariant systems for numerical simulation assuming linear or linearizable heat fluxes (such as radiative exchanges). In this contribution, the approach is applied to a test case building and validated by comparison with a reference model generated with an already tested tool chain.

Abstract

The increase in refrigerated food demand, due to increase on urban population is involving the replacement of conventional diesel-powered transport refrigeration units (TRUs) by electrical-based auxiliary power units APUs, in an imperious. This paper presents a turnkey solution of a hydrogen-based APU for a refrigeration unit integrated in short haul trucks, for its use in the food industry.

Abstract

The importance of renewable energy sources like solar energy in reducing carbon emissions and other greenhouse gases has contributed to an increase in grid integration. However, the intermittent nature of solar power causes reliability issues and a loss of energy balance in the system, which are barriers to solar energy penetration. This study proposes a unique three-step approach that identifies weather parameters with moderate to strong correlation to solar radiation and uses them to predict solar energy generation. The combination of an on-site weather station and a reliable local weather station produces relevant data that increases the accuracy of the forecasting model irrespective of the machine learning algorithm used. This data source combination is tested, along with two other scenarios, using the exponential Gaussian Process Regression machine learning algorithm in MATLAB. It was found to be the most effective algorithm with a Normalized Root Mean Square Error of 1.1922, and an R2 value of 0.66.

Abstract

Hydrogen fuel cell vehicles (HFCVs) replacing internal combustion engine vehicles are a viable option to achieve net-zero carbon emission in transportation. Higher hydrogen storage pressure is necessary for increased recharge mileage, necessitating a hydrogen decompression mechanism. A unique pressure-lowering construction (Tesla-type orifice structure) is proposed in this study, in which Tesla-type channels are paralleled and incorporated into a standard orifice plate structure. A complete parametric analysis is used to optimize the Tesla-type orifice construction further. Compared to a standard orifice plate, at low inlet mass flow rates, the Tesla-type secondary orifice construction gives higher pressure drop performance. The presented study may provide a feasible technical structure for achieving high-efficiency hydrogen decompression in HFCVs.

Abstract

Both effective utilization of renewable energy and multi-generation system are promising ways to reduce greenhouse gas emissions. This paper proposed a combined cooling, heating and power (CCHP) system, which is based on a basic system and consists of a transcritical CO2 cycle, an ejector refrigeration cycle, a domestic water heater and a thermoelectric generator. The parametric and comparative analyses are performed to show the system performance enhancement of the modification system. The multi-objective optimization is also conducted for the involved CCHP systems. Results show that compared to basic system, the novel system owns a higher exergy efficiency (30.75 VS 27.42%) and a lower total product unit cost (27.39 VS 32.28 $/GJ), confirming the obvious performance improvement.

Abstract

The catalytic mechanism of Cu(111) surface on the pyrolysis of HFO-1234yf has been investigated by Density Functional Theory (DFT). Firstly, search for the most stable adsorption structure of HFO-1234yf and its pyrolysis products on the Cu(1 1 1) surface. Secondly, The most stable co-adsorption structure of the products of Path1-4 on Cu(1 1 1) surfaces was calculated. Finally, the transition state structure of Path1-4 were investigated. The results prove that the copper surface reduces the energy needed for the pyrolysis of HFO-1234yf.