The abundant nanopores in shale make it an unconventional reservoir for oil and gas. Matrix compressibility and heterogeneity are crucial for fluid accumulation and migration, yet these two ...properties remain unclear in shale reservoirs. Herein, we investigated the matrix compressibility, multifractal properties, and their geological governing factors for nanoporous Yanchang shale from the Ordos Basin, China, utilizing petrophysical experiments, mercury injection capillary pressure (MICP), and low-pressure gas adsorption. Furthermore, a valid method was proposed to correct MICP data point by point. The results show that matrix compression in shale becomes apparent at onset pressures of 12.4–42.1 MPa during mercury injection, which can be assessed by compressibility coefficients varying within (3.85–18.77) × 10–5 MPa–1. Notably, the original MICP results overestimate the actual pore volumes due to the compression-induced error, within 16.19–102.95%, leading to potential misinterpretation of the pore size distributions, particularly for pores below 100 nm. Well-developed nanopores significantly contribute to the matrix compressibility. Among the shale compositions, organic matter (OM) is the primary controlling factor for matrix compressibility, with a positive effect. Ductile clay minerals promote matrix compressibility, whereas rigid brittle minerals resist matrix compression. Our findings also reveal the multifractal nature of pore structures in shale, with an upward-convex parabolic shape for multifractal singular spectra α–f(α) and an inverted “S” shape for the generalized dimension spectra q–D(q). Singularity spectrum width and Hurst exponent offer effective solutions to quantify the pore heterogeneity and connectivity. Pores over 100 nm tend to be relatively homogeneous and well-connected, while pores smaller than 100 nm increase heterogeneity and limit connectivity. OM, quartz, and easy-dissolve minerals positively impact pore heterogeneity but negatively affect connectivity. Nevertheless, clay minerals display no obvious correlation with pore heterogeneity and connectivity. This study provides valuable insights for predicting dynamic permeability and evaluation of unconventional reservoirs.
Pore characteristics are crucial in the occurrence, aggregation, migration, and potential for CO2 sequestration in shale gas reservoirs. We employed N2 adsorption/desorption, CO2 adsorption, mercury ...intrusion porosimetry (MIP), focused ion beam-scanning electron microscopy (FIB-SEM), and three-dimensional reconstruction of FIB-SEM images to characterize the pore characteristics in the Longmaxi Formation of the Sichuan Basin, southwestern China. These methods allowed for the detailed study of microstructure, porosity, and permeability down to the micropore scale (<2 nm). Meanwhile, N2 and CO2 isotherm analyses revealed a range of pore sizes, including micropores, mesopores (2–50 nm), and macropores (>50 nm). Micropores significantly contribute to the specific surface area, while mesopores and macropores predominantly contribute to pore volume. MIP results indicated extremely high pore tortuosity and connected porosity less than 1.43%. FIB-SEM and its three-dimensional reconstructions showed significant pore distribution within organic matter. At the FIB-SEM resolution (5 and 10 nm), pore connectivity is notably poor, with many large pores several hundred nanometers in diameter, undetected by the N2 isotherm method. Permeabilities estimated by FIB-SEM are 1–2 orders of magnitude lower than those measured by MIP, exhibiting anisotropy. Assessments of gas in place and CO2 storage capacity suggest that porosity evaluations via MIP may underestimate the quantifiable gas content in shale formations. The combined use of N2 adsorption/desorption, CO2 adsorption, MIP, and FIB-SEM techniques for integrating pore size characteristics offers a holistic perspective of the pore size spectrum in shale gas reservoirs, effectively addressing the limitations inherent in each individual method.
Methane hydrate is considered as a new environmentally friendly energy to meet future society development. To achieve safe and efficient hydrate production, it is critical to understand the hydrate ...accumulation characteristics in different deposits, considering the geological feature differences. In this study, the hydrate distribution characteristics in the gas-excess and water-excess deposits were visually investigated by using magnetic resonance imaging technology. Moreover, the effect of the initial gas pressure on hydrate formation behaviors and stability was analyzed. The results showed that methane hydrate first formed in the water–gas interface for the water-excess deposit, and then, the hydrate formation front gradually expanded into the water phase accumulation area. Moreover, the methane hydrate distribution was mainly determined by the initial distribution of water and gas in the porous media. For the water-excess deposit, the spatial distribution of methane hydrate showed an obvious heterogeneity, and the mass hydrate accumulated at the bottom of the deposit. However, a uniform distribution of methane hydrate in the gas-excess deposit was observed. Furthermore, methane hydrate that formed in the higher initial gas pressure and the water-excess environment had good stability during the water flow process, which prolonged the duration of the hydrate decomposition process. The findings attempt to provide valuable information and guidelines for understanding the gas hydrate system.
This research work presents a novel unsupported NiCo aerogel with high electrocatalytic activity, which was synthesized by an ultrafast method combining microwave heating and lyophilization. The ...novel aerogel was used as an electrocatalyst for the oxidation reactions of two different nitrogen compounds: urea and ammonium, with the aim of reducing the pollutant content in water and generating clean energy from the reduced hydrogen of oxidizing species. The NiCo aerogel was incorporated/evaluated in a microfluidic device in two ways: as an ammonium fuel cell and an alkaline urea electrolyzer, producing clean hydrogen in both systems. The unique physicochemical properties, particle size smaller than 0.1 nm, surface area of 52 m2 g–1, and the presence of NiCo metal alloys with the addition of species Ni–O, Ni–OH, and a higher percentage of Ni2+ enable the effective oxidation of species in the alkaline medium. Hydrogen production and power densities of up 3 × 10–4 μg s–1 and 0.74 mW cm–2, respectively, are observed. This work demonstrates for the first time an aerogel structure of non-noble metal (NiCo) used in two different microfluidic devices that oxidize nitrogenous compounds such as urea and ammonium and produce clean fuel as hydrogen.
In this study a mixed integer linear programming (MILP) model is created for the design (i.e. technology selection, unit sizing, unit location, and distribution network structure) of a distributed ...energy system that meets the electricity and heating demands of a cluster of commercial and residential buildings while minimising annual investment and operating cost. The model is used to analyse the economic and environmental impacts of distributed energy systems at the neighbourhood scale in comparison to conventional centralised energy generation systems. Additionally, the influence of energy subsidies, such as the UK's Renewable Heat Incentives and Feed in Tariffs, is analysed to determine if they have the desired effect of increasing the economic competitiveness of renewable energy systems.
•A MILP model was created to design a distributed energy resource system for a cluster of buildings.•The optimal DER system was found to decrease annual costs by 40% and CO2 emissions by 50%.•Small wind turbines and biomass boilers were found to be the optimal technologies.•Energy subsidies are vital because they increase the affordability of low carbon technologies.
The increasing integration of distributed energy resources (DERs) has provided the opportunity to deliver clean, and low-cost power for energy consumers. However, without appropriate coordination, ...injected power by DERs can violate the operational limits of the electricity distribution networks and cause issues such as over-voltage and lines congestion. Recently, the promising concept of Operating Envelopes (OEs) has been introduced to support the efficient integration of DERs without directly controlling their output. Within this context, this paper presents a novel framework in which prosumers are routinely provided with dynamic active and reactive OEs and can manage their assets accordingly. The network operator in each time step, collects customers’ expected export, and considering nodes voltage and lines current limits, calculates the dynamic OEs for each prosumer. Then, an energy management algorithm for prosumers is presented, which enables them to control their PV and battery energy storage system according to their defined PQ region. The performance of the proposed framework is evaluated using various simulation studies to demonstrate its significant effectiveness in solving the over-voltage and over-current problems associated with DERs. Furthermore, the comparison of the proposed framework with the state of the art exhibits its superiority in decreasing DERs power curtailment.
•A novel dynamic PQ operating region to prevent the unnecessarily curtailment of DERs.•Indirect control of DERs to preserve their privacy.•Fully exploiting the reactive power capability of smart inverters
In a multienergy system, there are different types of dependencies among the energy carriers. Internal dependencies refer to possible changes in the energy source in the presence of energy converters ...and storage, and are managed by the system operator through the control strategies applied to the equipment. External dependencies (EDs) are due to the choice of the energy supply according to customer preferences when alternative solutions are available. This paper introduces a new model of EDs within a multigeneration representation based on energy hubs. EDs are addressed through a stochastic model in order to take into account the possible uncertainty in the customers' decisions. This model is then used to introduce carrier-based demand response (DR) in which the user participates in DR programs aimed at promoting the shifting among different energy sources by preserving the service provided to the end users. The results obtained from the new model in deterministic and stochastic cases indicate the appropriateness and usefulness of the proposed approach.
Due to the surge in load demand, the scarcity of fossil fuels, and increased concerns about global climate change, researchers have found distributed energy resources (DERs) to be alternatives to ...large conventional power generation. However, a drastic increase in the installation of distributed generation (DGs) increases the variability, volatility, and poor power quality issues in the microgrid (MG). To avoid prolonged outages in the distribution system, the implementation of energy management strategies (EMS) is necessary within the MG environment. The loads are allowed to participate in the energy management (EM) so as to reduce or shift their demands to non-peak hours such that the maximum peak in the system gets reduced. Therefore, this article addresses the complication of solutions, merits, and demerits that may be encountered in today’s power system and encompassed with demand response (DR) and its impacts in reducing the installation cost, the capital cost of DGs, and total electricity tariff. Moreover, the paper focuses on various communication technologies, load clustering techniques, and sizing methodologies presented.
The study of fractal percolation in shale pores is beneficial to the exploration and development of shale oil and gas, and the application of the fractal dimension to the characterization of ...percolation capacity can help to clarify the mechanism of gas percolation in shale. In this study, gas adsorption (CO2 and N2) and high-pressure mercury injection porosimetry (MICP) and gray correlation method are mainly used to investigate the shales of the Lower Silurian Longmaxi Formation in the Luzhou–Changning area in the southern Sichuan basin. In this study, we establish a new template to evaluate the degree of matching between the template and actual geological data considering the effects of shale fractal dimension, tortuosity, the Knudsen number (Kn), and porosity on permeability. The results reveal three observations. First, the deep organic shale pores of the Longmaxi Formation in the area have obvious multiscale fractal characteristics, and the fractal dimension (D) values reflect the complexity of shale pores at different scales. There are significant differences in the fractal dimensions among the three shale lithofacies types. Siliceous shale of D1 with the highest micropore fractal dimension, D2 with mesoporous, and D3 with macroporous indicate more complex pore structures, which provide plenty of gas adsorption and enrichment spaces. These structures are conducive to gas accumulation. Second, there are complex correlations between the total organics content (TOC), the mineral composition, and the inhomogeneity parameters of shale. The TOC, siliceous mineral content, and inhomogeneity parameters of porosity, tortuosity, Kn, and D are positively correlated. The carbonate mineral content and clay mineral content are negatively correlated with the inhomogeneity parameters porosity, tortuosity, Kn, and D. Third and finally, based on correlation analysis, the three main parameters of D, porosity, and tortuosity were ultimately determined, and corresponding templates were established. It reflects that permeability, which is a parameter of seepage capacity, has a high correlation with fractal dimension, tortuosity, and porosity.
•Proposing a novel resiliency-oriented DER planning model for distribution grids.•Considering both normal and event situations in the model as objectives.•Developing a procedure for obtaining ...components outage scenarios against earthquakes.•The proposed model leads to a plan with an acceptable resiliency and planning costs.
Distribution systems are one of the most important infrastructures of each country which are exposed to numerous damages through unexpected events. The development of distributed energy resources (DERs) is one of the solutions which can bring several benefits to the operation and planning of distribution systems in both normal and event situations. This paper proposes a new multi-objective planning model for optimal siting and sizing of DERs in distribution systems to minimize the total planning costs including operation and active power loss costs, as the normal operation objective, and to minimize the expected prioritized load shedding exposed to an earthquake incident, as the resilience improvement goal. Also, a novel incident-based outage scenario determination procedure is proposed using the fragility curves of distribution components to model the impact of earthquake events in resiliency evaluation stage. Since the proposed model is a non-linear and non-convex optimization problem with two contradictory objectives, the non-dominated sorting genetic algorithm II (NSGAII) followed by fuzzy decision making are utilized to find the Pareto solutions and the final optimal plan. Finally, the numerical results based on the IEEE 33-bus and IEEE 69-bus distribution systems are reported to evaluate the effectiveness of the proposed model.
PDF
