Semi-Analytical Modeling of Fractured Horizontal Wells in Heterogeneous Formations Considering the Interference between Hydraulic Fractures

In this study, a semi-analytical model is developed for the pressure and rate transient analysis of multi-stage fractured horizontal wells. This model simulates the fluid flow towards a fractured horizontal well centered in an unconventional formation with considering the interferences between hydraulic fractures under various heterogeneity conditions. In this proposed model, the formation is divided into sub-systems, and each sub-system is further composed of linear flow regions. Boundaries of the linear flow regions are being updated in real-time response to the interferences between hydraulic fractures. Applicability of the proposed model in heterogeneous reservoirs is demonstrated by the comparison with the five-region model published in literature. The proposed model is applicable to the heterogeneity conditions including a fractured horizontal well having heterogeneous completions and/or the formation being heterogeneous in reservoir properties. Furthermore, the proposed model is utilized to analyze field data from fractured horizontal wells in heterogeneous conditions

Simulation Study of the Transport Characteristics of the Ice Core in Ice Drilling with Air Reverse Circulation

Ice core drilling with air reverse circulation is a promising technology that uses high-speed airflow to transport the ice core from the bottom of the hole along the central passage of the drill pipe to the surface. Understanding how the ice core moves through the pipe is crucial for this technology in order to calculate the pneumatic parameters. In this paper, experimental study and the CFD dynamic mesh technique are used to analyze the ice core transport process and flow field characteristics. In order to prove the correctness of the dynamic mesh technique, the simulation results were verified with the experimental results, and it was found that all the simulation data were in agreement with the experimental data trend, and the maximum error was less than 10%. According to the study, once the ice core’s velocity reaches its maximum throughout the transport process, it does not change. The ice core’s maximum velocity increases with the diameter ratio and decreases with the length-to-diameter ratio, while eccentricity has no impact on the maximum velocity. When the air velocity reaches 21 m/s, the diameter ratio for the ice core with a length-to-diameter ratio of 2 increases from 0.80 to 0.92, and the maximum velocity increases from 8.92 m/s to 17.45 m/s. Data fitting demonstrates that the equation Vmax=−1.04V0 + 1.04Va describes the relationship between the ice core’s maximum velocity, Vmax, and air velocity, Va. Finally, we obtain the ice core’s suspension velocity model using CFD simulation to calculate the suspension velocity, V0

Simulation Study of the Transport Characteristics of the Ice Core in Ice Drilling with Air Reverse Circulation

Ice core drilling with air reverse circulation is a promising technology that uses high-speed airflow to transport the ice core from the bottom of the hole along the central passage of the drill pipe to the surface. Understanding how the ice core moves through the pipe is crucial for this technology in order to calculate the pneumatic parameters. In this paper, experimental study and the CFD dynamic mesh technique are used to analyze the ice core transport process and flow field characteristics. In order to prove the correctness of the dynamic mesh technique, the simulation results were verified with the experimental results, and it was found that all the simulation data were in agreement with the experimental data trend, and the maximum error was less than 10%. According to the study, once the ice core’s velocity reaches its maximum throughout the transport process, it does not change. The ice core’s maximum velocity increases with the diameter ratio and decreases with the length-to-diameter ratio, while eccentricity has no impact on the maximum velocity. When the air velocity reaches 21 m/s, the diameter ratio for the ice core with a length-to-diameter ratio of 2 increases from 0.80 to 0.92, and the maximum velocity increases from 8.92 m/s to 17.45 m/s. Data fitting demonstrates that the equation Vmax=−1.04V0 + 1.04Va describes the relationship between the ice core’s maximum velocity, Vmax, and air velocity, Va. Finally, we obtain the ice core’s suspension velocity model using CFD simulation to calculate the suspension velocity, V0

A critical review of windcatcher ventilation: Micro-environment, techno-economics, and commercialisation

Windcatcher natural ventilation is a low-energy approach that can provide effective ventilation during favourable weather conditions. When combined with different cooling, heating, and dehumidification technologies, windcatchers can provide enhanced indoor environment quality. This work provides a critical review of windcatchers' performance. It covers aspects such as ventilation, thermal comfort, overheating risk, indoor air quality (IAQ), energy performance, economic cost, and life cycle assessment (LCA). Although many studies have investigated windcatchers' performance in terms of thermal comfort, little attention has been paid to the potential overheating risk. This oversight is particularly important in the context of global warming trends and the increasing likelihood of extreme weather conditions. Moreover, previous studies on windcatchers’ IAQ performance have primarily focused on indoor CO2 concentrations, while the influences of pollutants such as volatile organic compounds (VOCs) have not been reported. The quantification of energy performance for windcatchers remains an underexplored area, and very few studies have conducted economic analyses or LCAs of windcatcher systems. There is a clear need for more field experiments to investigate these aspects comprehensively. This review also provides insights into the current trends and future perspectives in the commercial windcatcher market, including available options, opportunities, and threats. The findings highlight the importance of several factors that must be considered before the large-scale commercial rollout of windcatcher technology. These include the lack of awareness and regulatory incentives, cost considerations, aesthetic preferences, and misconceptions or concerns regarding the effectiveness of windcatchers

Experimental and Numerical Analysis of Flow Behavior for Reverse Circulation Drill Bit with Inserted Swirl Vanes

A swirling drill bit designed with an integrated vane swirler was developed to improve reverse circulation in down-the-hole hammer drilling. Its entrainment effect and influential factors were investigated by CFD simulation and experimental tests. The numerical results exhibit reasonable agreement with the experimental data, with a maximum error of 13.68%. In addition, the structural parameters of the swirler were shown to have an important effect on the reverse circulation performance of the drill bit, including the helical angle and number of spiral blades, swirler outlet area, and the flushing nozzles. The optimal parameters for the swirling drill bit without flushing nozzles include a helical angle of 60°, four spiral blades, and the area ratio of 2, while it is about 30°, 3, and 3 for the drill bit with flushing nozzles. Moreover, the entrainment ratio of the drill bit without flushing nozzles can be improved by nearly two times compared with one with flushing nozzles under the same conditions