Abstract

With the international energy demand and the development of exploration and development technology, the development of shale reservoirs has gradually become a hot topic all over the world, and the existing theories of fluid flow can no longer accurately characterize and describe the flow characteristics of shale oil reservoirs. The formation pressure performances in shale reservoirs are quite different with that of conventional reservoirs due to the strong low-velocity nonlinear flow and starting pressure gradients, which will result in dynamic boundary. Few research mentioned the effects of dynamic boundary caused by the flow mechanism in shale oil reservoirs. In this paper, the nonlinear equation of shale oil reservoirs, segmented linearization, division of the flow space into matrix and SRV regions, application of the source function and Newman product method, and creation of finite-length strip source functions are employed to analyze the effects of dynamic boundary. A novel model of unsteady flow in horizontal wells with multi-fractured section volume fracturing taking the development of natural fractures into consideration was established, and the method of solving the pressure of this model by applying the iterative method of immovable point was put forth using the principles of pressure superposition and unsteady flow superposition. The characteristics of the dynamic boundary of pressure propagation in volume fractured horizontal wells were determined, as well as the effects of various reservoir physical parameters on the movement of the dynamic boundary, with the aid of the proposed mathematical model of unsteady flow in volume fractured horizontal wells taking the development of natural fractures into consideration. The analysis demonstrates that, under the nonlinear flow condition, the formation pressure propagation manifests as a dynamic boundary problem. The pressure propagation dynamic boundary expands more quickly in the early period due to the natural fractures in the reservoir, but tends to stabilize in the later period, indicating the existence of a limiting distance for pressure mobilization in the reservoir. The major determinants of formation pressure wave and mobilization are the physical characteristics of the reservoir (permeability, natural fractures). The stronger the flow nonlinearity and the more developed the natural fractures, the greater the degree of effects on pressure propagation.

Abstract

The extraction of geothermal energy from hot dry rock resources has gradually received widespread attention. How to efficiently extract geothermal energy has become a key technology to be developed. In this study, based on 5 existing vertical geothermal wells with a depth of about 4000 meters in a basin in northwest China, numerical simulation of the well structure optimization has been carried out to improve the heat extraction performance. Research has found that, compared with a single vertical well, the outlet temperature of the heat-extraction fluid from a 3-branch L-shape horizontal well has increased by 74.65°C, with the corresponding heat extraction rate being increased by 2.2MW. The outlet temperature of the connecting well cluster (4 L-shape wells connected to a common vertical production well) is 8.66°C higher than that of the vertical well, with the total heat extraction rate being 0.11MW higher than that of the five vertical wells. One important finding in this case is that, the outlet pressure of this connecting well cluster is about 4 bars higher than its inlet pressure, indicating that there is an obvious thermal siphon effect. This implies that using the proposed connecting well cluster can greatly reduce the pump power required for system operation and hence greatly reduce the operating costs. The results obtained from this study is of theoretical-guiding significance for hot-dry-rock geothermal energy exploitation.

Abstract

Lithium battery energy storage system (ESS) needs high-power refrigeration equipment to maintain a comfortable operating temperature to ensure the operating performance and long-life of the batteries. But this dramatically increases the size and cost of the system. Here, we proposed a battery cooling system coupled with phase-change thermal energy storage (PHTES) unit. The PHTES unit pre-cools the cooling fluid, greatly reducing the refrigerating capacity of the chiller, thus reducing the volume and cost of the refrigeration system. In addition, we have established the lumped heat model of PHTES unit and battery liquid cooling system. Based on this model, we can optimize the storage capacity of PHTES unit and cooling capacity of chiller, thus minimizing the energy consumption and cost of the system. This work proposes a low energy consumption and low-cost thermal management method for battery ESS, and provides a simple and accurate model for the optimization of thermal management system.

Abstract

The fracture-caved gas carbonate reservoirs raise serious concerns in China. However, there are numerous large-scale caves in the fractured-caved gas reservoirs due to the structural fracture and dissolution. To solve the problems of fracture-caved gas reservoirs, like strong heterogeneity, obvious differences in fracture-caved connection characteristics, and great difficulty in well testing. In this paper, a novel pressure transient analysis model under a complex fracture-caved connection mode is established to estimate fracture region and cave parameters. First, governing equations considering the coupling of fracture linear flow and cave storage flow are derived. Furthermore, the dimensionless fracture pressure solution in Laplace space is solved after dimensionless treatment, and the dimensionless bottom-hole pressure solution in real space is produced using the Stehfest numerical inversion method. Finally, the flow phases are divided, and a multi-parameter sensitivity analysis is performed after identifying the type curves of the complex fracture-caved connection mode. The results indicate that the conductivity and length of the fracture region have the greatest influence on the start time and duration of linear flow, whereas the volume of the cave has the greatest influence on the storage flow. Matching with the recorded pressure and flowrate data, the established pressure transient analysis model can effectively invert the fracture length, conductivity, and cave volume of fracture-caved reservoirs, which provides a basis for evaluating the geological characteristics and underground reserves of fracture-caved gas reservoirs and has significant guiding significance for the development of carbonate reservoirs.

Abstract

Solar-aided coal-fired power plant (SACFPP) is cost-effective to ensure energy security with less CO2 emission than coal-fired power plant. Its efficient and low-carbon operation is important but difficult because of the time-varying solar energy. This paper evaluates the thermodynamic performance and CO2 emission characteristics of SACFPP under off-design conditions. Three SACFPP configurations (marked as HP123, HP23 and HP3) were analyzed and the optimized operation strategy is proposed to achieve highest solar-to-power efficiency and lowest CO2 emission rate through adjusting feedwater ratio to trough collector system. The best achievable solar-to-power efficiency and CO2 emission rate depend on the power load, DNI, system safety limitation and system configuration. The annual CO2 emission reductions of the 600 MW SACFPP are about 61352.2, 54009.9 and 51769.8 tonnes under configurations of HP123, HP23 and HP3, respectively. The results can guide the SACFPP operation optimization.

Abstract

Stratified flames have gained prominence in recent years due to the improved flame stability with reduced NOx and CO emissions and resilience to high turbulence. In the present study, the thermoacoustic instability in a stratified swirl dual annular burner was investigated for swirling flames varying the equivalence ratio at constant Reynolds number. The stratification ratio was varied from premixed condition (SR=1) to rich inner stream (SR=3) to study the effect of stratification on the suppression of thermoacoustic instabilities. The premixed swirling flames indicated the onset, coupling and amplification of thermoacoustic instability in the range of equivalence ratios from 0.8 to stoichiometry (1.0). This was followed by the subsequent decoupling of the oscillations at rich equivalence ratio conditions (Φg = 1.1). Under stratified conditions (SR=2 and SR=3), thermoacoustic instability was triggered across the same range of equivalence ratio as well. However, stratification helped to reduce the peak amplitudes in the sound pressure by 72% at SR=2 and 64% at SR=3. The heat release amplitude was also damped by approximately 70% in both cases. This shows that stratification can be deployed, within certain range, to suppress and control the thermoacoustic instabilities. The absence of thermoacoustic instability under very lean conditions near blowoff also allows the stratified burner for lean operation thus reducing the CO emissions.

Abstract

The feasibility of a solar-driven chemical looping dry reforming of methane (DRM) process, which converts solar energy and methane into syngas via a looping material oxygen carrier is investigated experimentally. Thermogravimetric analysis (TGA) experiments were firstly carried out to verify the effect of the Rh-doped LaCeO3.5 which were synthesized via modified Pechini method and incipient wetness method and the result shows that Rh greatly improved the reaction kinetics. Photo-TGA experiments were conducted to evaluate the light effect in chemical looping DRM. Under the light condition, the Rh-doped LaCeO3.5 shows higher methane conversion, oxygen extraction rate and CO selectivity compared with the undoped one, decreasing the apparent activation energy of the reaction at the same time. Insights obtained from the UV-Vis spectroscopy verified that the surface Rh under the light could promote the activation of surface methane species and increase the light absorbance. Through the integration of solar energy, a high methane to solar fuel conversion efficiency could be achieved. The proposed process has the potential to produce solar fuels at high efficiency with reduced carbon footprint.

Abstract

With the proposal of China’s “dual carbon” strategy, zero-carbon transformation has become an important direction for the development of various industries, and the education field has also issued documents. The scale of construction, the number of students and energy consumption of colleges and universities continue to increase, and the carbon emission remains high. Taking Balitai Campus of Nankai University as an example, this paper starts with the analysis of the energy consumption of the school in recent years, carries out correlation analysis, excavates the main influencing factors of energy consumption, and proposes corresponding zero-carbonization transformation strategies. It adopts the scenario simulation method to analyze the benefits of energy conservation and emission reduction, and marks the relevant requirements of carbon emission indicators of university campuses in cold areas. This achievement is expected to provide a useful reference for existing universities in China to achieve carbon neutrality and provide a reference for the construction of zero-carbon campuses.

Abstract

The construction of energy system digital twin relies on accurate models. This paper proposes a new modeling method for natural gas station hydraulic systems by integrating physical models and data-driven models to improve the accuracy of models. Taking a natural gas station of long-distance gas pipeline as an example, this paper builds the physical model of a station, including compressors and regulating valves. Then a hydraulic calculation algorithm of the station is developed. A data-driven model Back Propagation Neural Network (BPNN) is introduced for physical model error compensation. Finally, the calculation results show that the hybrid model has better accuracy than the physical model and the energy consumption of key equipment, such as compressors, air coolers in the station is monitored. Moreover, the hybrid model better integrates the advantages of the two types of models, it can serve as a soft sensor to enrich the status monitoring data of station equipment and lay the foundation for further optimization of station energy consumption.