Reverse Circulation Research Articles

Mathematical model of velocity and distribution law in gas lift reverse circulation well washing flow field for drilling shaft sinking

To reveal the velocity distribution law of a gas lift reverse circulation well washing flow field in drilling shaft sinking, a velocity mathematical model of well washing flow field is established. The theoretical analytical solutions and velocity distribution laws in the drill pipe and bottom hole were provided and validated through numerical simulations and similar model tests. Furthermore, this study explores the impacts of mud circulation, wind pressure, rock debris, and mud properties on the flow field distribution, presenting the sensitivity order of the factors. This study indicated the following findings. (1) The velocity theoretical model of well washing flow field was validated through numerical simulation and similar model tests, and the relative error ranged from 4.2 to 18.5%, demonstrating the high consistency. (2) The rock debris and mud experienced slight and consistent deceleration within the drill pipe. Upon reaching the gas input end, the axial upward return of the multiphase flow resulted in a “jumping” sharp increase. (3) The mud circulation, wind pressure, and void fraction positively correlated with the multiphase fluid velocity in the drill pipe, but negatively correlated with the mud density and slag content. The axial upward velocity of the rock debris decreased with increasing particle size and density. (4) The sensitivity of each factor to the discharge speed of rock debris was summarized as follows: air content > mud circulation > wind pressure > mud density > rock debris density > rock debris particle size > slag content. These findings could offer a theoretical basis for selecting well washing parameters and enhancing drilling and washing efficiency.

Optimization of hydraulic structure and well flushing parameters of a truncated cone drill bit for drilling shaft sinking

ABSTRACT Based on a research method combining numerical simulations and model testing, a numerical model and test platform for gas lift reverse circulation multiphase coupling in well washing were developed. The hydraulic structure and well washing parameters of a φ5 m truncated cone bit used in the Beifeng well at Taohutu Coal Mine were optimized, and the distribution law of the well washing flow field was determined. The findings revealed that: (1) with a bit taper of 40 and a length-diameter ratio of 0.32 for the truncated cone, the hydraulic structure was optimal. Compared with the original bit structure, the axial speed of mud at the slag suction port increased by 15.9%, and the average sliding speed of mud at the inclined rock surface increased by 63.2%. (2) The multiphase fluid in the slag discharge pipe flowed successively in the form of “low-speed stable two-phase flow” and “high-speed disordered three-phase flow,” while the multiphase fluid in the horizontal and inclined bottom holes flowed predominantly in radial and tangential patterns, respectively. (3) The optimal parameter combination for efficient well washing with the truncated cone bit included a bit rotation speed of 8 r/min, a gas injection rate of 5600 m3/h, an air duct sinking ratio of 0.79, and a mud viscosity of 176 mPa·s, with bit rotation speed being the most significant factor affecting effective washing efficiency. These results could provide a valuable reference for improving the efficiency of drilling and well flushing in Jurassic strata of western China.

Human interventions alter meandering channels evolution: Insights from the inner bank scouring and outer bank deposition in the Jingjiang Reach after the operation of the Three Gorges Dam

Geomorphic abnormal responses of consecutive river bends to human activities, such as reservoir constructions and bank protection projects, have not been understood sufficiently. Based on the measured hydrological and topographic data, and remote sensing data, we investigated the morphological adjustments of 17 typical consecutive bends with different curvatures (the ratio of bend width B and bend radius R at the bend apex ranging from 0.22 to 1.96) in the Jingjiang Reach after the Three Gorges Dam (TGD) (2004–2021). The results show that these bends generally experienced inner bank scouring (IBS) and outer bank deposition (OBD). The distance to the dam affects the mechanism of IBS, from being primarily controlled by the water scouring intensity near the dam to the bend curvature and the regime adjustment of the upstream bend. Our results also show that the locations of IBS and OBD in the bends are related to the bend curvature. In sharp bends (B/R > 0.5), IBS occurs in the upper half of the bend, accompanied by OBD near the bend apex. In moderate bends (B/R ≤ 0.5), IBS occurs throughout the whole bend, with OBD near the bend entrance. A higher curvature bend tends to experience greater scouring of the inner bank near the bend apex. Moreover, the effect of upstream bends on downstream bends is revealed. In response to IBS and OBD in the upstream bend, the thalweg at the entrance shifts towards the inner bank, further promoting IBS in the downstream bend. OBD in the downstream bend is intensified by the residual reverse circulation of upstream bend. The results of this study can enhance the understanding of the evolution of meandering rivers in response to human activities, and may serve as a rational reference for managing the meandering rivers downstream of cascade reservoirs.

Performance study of the rapid heating drying system based on the reverse Brayton air cycle for agricultural application

Air temperature and humidity control are important for crop storage. Current drying methods in agriculture include solar heating and air source heat pumps, whereas solar heating may lead to poor quality of the dried product and air source heat pumps may not reach the desired temperature when the environment is harsh. In this paper, a rapid heating and drying system based on reverse Brayton air circulation is proposed to obtain high temperature and low humidity air quickly by adjusting the pressure ratio to achieve an adjustable crop drying process. An improved rapid heating and drying system with a water cooler is also proposed to increase the drying efficiency of the system. The results show that the total dehumidification rate of the improved system can reach 11.51 g/s, which is 1.48 g/s higher than that of the rapid heating and drying system without a water cooler, and the dehumidification energy efficiency of the improved system can reach 1.26 kg/(kW.h), which is 0.11 kg/(kW.h) higher than that of the rapid heating and drying system without a water-cooling device.

Parametrical design and optimization of a reverse circulation drill bit for dust control

The reverse circulation down-the-hole air hammer drilling (RC-DTH) method is renowned for its efficiency in hard rock formations and exceptional dust control performance. It presents opportunities for cost-saving, efficiency improvement, energy conservation, and environmental protection. Reverse circulation drill bits are critical components of this method. This study focused on the air reverse circulation regime, investigating various geometric parameters of the RC drill bits through computational and experimental methods to enhance its dust control performance. Results indicate that increasing the layers of suction nozzles, enlarging the diameters of the suction and mixing nozzles, and optimizing the input airflow rate can effectively channel airflow toward the central passage of the drill tool. Consequently, this optimization significantly improves the dust control performance of the RC drill bits. Conversely, increases in the flushing nozzle diameter and alterations in the suction nozzle location have detrimental effects on the dust control capability of the RC drill bits. Field tests were conducted at the Yuan Jiacun iron mine, affiliated with Taiyuan Iron and Steel (Group) CO., LTD. The field tests demonstrate that the optimized RC drill bit exhibits excellent dust performance.

CFD–DEM method is used to study the multi-phase coupling slag discharge flow field of gas-lift reverse circulation in drilling shaft sinking

To elucidate the distribution law of the multiphase coupling slag discharge flow field in gas-lift reverse circulation during drilling shaft sinking, a numerical analysis model of gas–liquid–solid multiphase coupling slag discharge was established by CFD–DEM (Coupling of computational fluid dynamics and discrete element method) method, taking the drilling of North Wind well in Taohutu Coal Mine as an example. This model presented the distribution of the multiphase flow field in the slag discharge pipe and at the bottom hole, and was validated through experimentation and theoretical analysis. Finally, the impact of factors, including bit rotation speed, gas injection rate, air duct submergence ratio, and mud viscosity on the slag discharge flow field was clarified. The results indicated that the migration of rock slag at the bottom of the well was characterized by “slip, convergence, suspension, adsorption, and lifting”. The slag flow in the discharge pipe exhibited the states of “high density, low flow rate” and “low density, high flow rate”, respectively. The multiphase fluid flow patterns in the well bottom and slag discharge pipe were horizontal and axial flows, respectively. The model test of the gas lift reversed circulation slag discharge and the theoretical model of the bottom hole fluid velocity distribution confirmed the accuracy of the multiphase coupling slag discharge flow field distribution model. The rotation speed of the drill bit had the most significant impact on the bottom hole flow field. Increasing the rotation speed of the drill bit can significantly enhance the tangential velocity of the bottom hole fluid, increase the pressure difference between the bottom hole and annular mud column, and improve the adsorption capacity of the slag suction port. These findings can provide valuable insights for gas lift reverse circulation well washing in western drilling shaft sinking.

Analysis of Potential Use of Freezing Boreholes Drilled for an Underground Mine Shaft as Borehole Heat Exchangers for Heat and/or Cooling Applications

Borehole engineering encompasses the part of mining that involves the process of drilling boreholes and their utilization (e.g., for research, exploration, exploitation, and injection purposes). According to legal regulations, mining pits must be closed after their use, and this applies to pits in the form of boreholes as well. The Laboratory of Geoenergetics at AGH University of Krakow is involved in adapting old, exploited and already closed boreholes for energetic purposes. This includes geothermal applications, as well as energy storage in rock formations and boreholes. Geoenergetics is a relatively new concept that combines geothermal energy with energy storage in rock formations (including boreholes). One type of analysed borehole is a freezing borehole. They are used, for example, in drilling mining shafts that are in the vicinity of aquifers and are drilled using the rotary drilling method with a reverse circulation of drilling mud, or in peat bogs. For borehole heat exchangers based on freezing boreholes for long-term mathematical modelling, several heating scenarios were considered with several thermal loads. The maximum average power obtained after one year of usage of four boreholes with variable temperatures was 11 kW. With the usage of 10 boreholes the power reached over 27 kW. The heat-carrying temperature was assumed to be 22 °C during early summer (June and July) and 2 °C during the rest of the year. When considering stable exploitation during a 10-year period with four boreholes with the same temperatures, a heating power of over 12 kW was obtained, as well as a power of over 28 kW when considering using 10 boreholes. The maximum amount of heat obtained during the 10-year period using 10 boreholes was over 8.8 thousand GJ. Once they have fulfilled their function, these boreholes lose their technological significance. In the paper, the concept is outlined, and the results of the analysis are described using the numerical program BoHEx.

Study, Regulation and Effective Use of Groundwater in the Piedmont Plains of Azerbaijan

The paper discusses the basics of methods for assessing groundwater in the foothill plains of Azerbaijan. When identifying groundwater reserves in mountainous areas, operational resources must be taken into account. In the process of exploration and exploitation of groundwater, it may be necessary to use exploration wells as exploration and observation wells, and vice versa. The transfer of wells from one category to another should be taken into account when planning geological exploration work. This can help improve the geological and economic efficiency of the work. The requirements for drilling and construction of hydrogeological wells of different categories are not the same. Methods for drilling hydrogeological wells are selected based on local geological and hydrogeological conditions, research objectives, design depths and diameters of wells and other factors. Reverse circulation drilling is used in conditions of deep groundwater (more than 3 m) and in continuous aquifers with a depth of 300 m or more and a diameter of 1000 mm or more. This method is used when it is necessary to drill exploration and production wells.

Characterization of a Metamorphosed Volcanic Stratigraphy and VMS Alteration Halos Using Rock Chip Petrography and Lithogeochemistry: A Case Study from King North, Yilgarn Craton, Western Australia

Despite countless advances in recent years, exploration for volcanogenic massive sulfide (VMS) deposits remains challenging. This is particularly the case in the Yilgarn Craton of Western Australia, where outcrop is limited, weathering is deep and extensive, and metamorphism is variable. At Erayinia in the southern Kurnalpi terrane, intercepts of VMS-style mineralization occur along ~35 km strike length of stratigraphy, and a small Zn (-Cu) deposit has been defined at King (2.15 Mt at 3.47% Zn). An extensive aircore and reverse circulation drilling campaign on the regional stratigraphy identified additional VMS targets, including the King North prospect. Through a combination of detailed rock chip logging, petrography (inc. SEM imaging), and lithogeochemistry, we have reconstructed the volcanic stratigraphy and alteration halos associated with the King North prospect. Hydrothermal alteration assemblages and geochemical characteristics at King North (Mg-Si-K enrichment, Na depletion, and high Sb, Tl, Eu/Eu*, alteration index, CCPI, and normative corundum abundance values) are consistent with an overturned VMS system. The overturned footwall stratigraphy at King North is dominated by metamorphosed volcanic rocks, namely the following: garnet amphibolite (tholeiitic, basaltic), biotite amphibolite (andesitic, calc-alkaline), chlorite–quartz schist (dacitic), and narrow horizons of muscovite–quartz schist (dacitic to rhyolitic, HFSE-enriched). The hanging-wall to the Zn-bearing sequence is characterized by quartz–albite schists (metasedimentary rocks) and thick sequences of amphibolite (calc-alkaline, basaltic andesite). An iron-rich unit (>25% Fe2O3) of chlorite–actinolite–quartz schist, interpreted as a meta-exhalite, is associated with significant Cu-Au mineralization, adjacent to a likely syn-volcanic fault. Extensive Mg metasomatism of the immediate felsic footwall is represented by muscovite–chlorite schist. Diamond drilling into the deep hanging-wall stratigraphy at both King North and King has also revealed the potential for additional, stacked VMS prospective horizons in the greenstone belt stratigraphy. The discovery of HFSE-enriched rhyolites, zones of muscovite–chlorite schist, presence of abundant sulfide-rich argillaceous metasedimentary rocks, and a second upper meta-exhalite horizon further expand the exploration potential of the King–King North region. Our combined petrographic and lithogeochemical approach demonstrates that complex volcanic lithologies and VMS alteration signatures can be established across variably metamorphosed greenstone belts. This has wider implications for more cost-effective exploration across the Yilgarn Craton, utilizing RC drilling to reconstruct the local geology and identify proximal halos, and limiting more costly diamond drilling to key areas of complex geology and deeper EM targets.

Air-lift characteristics of rock core mass in gas–liquid–solid mixed flow

The air-lift reverse circulation drilling method enables efficient and continuous core extraction. However, the flow characteristics of gas–liquid–solid mixtures during core mass transport are complex, and developing a model to predict performance remains challenging. The flow characteristics of gas–liquid–solid mixtures inside the drill pipe are numerically analyzed by calculating the mixing transport of the core during the airlift process. By solving the momentum equations for multiphase flow, the distribution of physical quantities of three phases and pressure along the depth was calculated, and the laws of influence of the operating parameters on the transport characteristics of the core were analyzed. The results show that the drilling performance is related to the geometric parameters of the pipe and core, drilling speed, and depth. When the submergence ratio is increased to 0.9, the maximum liquid-phase superficial velocity is increased by 109% compared with that when the submergence ratio is 0.6. The size of the annular space gap 67 formed between the core and the pipe wall is the key to the core's mechanical properties, and the differential pressure gradient force increases with increasing core diameter. An increase in well depth reduces the fluid flow. In addition, increasing the pipe diameter improves drilling performance due to reduced friction losses, which elevates the air flow rate required for air-lift reverse circulation operation.

A Feasibility Assessment of Heat Energy Productivity of Geothermal Wells Converted from Oil/Gas Wells

The mitigation of greenhouse gas emissions necessitates a shift from fossil fuel to environmentally friendly energy, such as geothermal energy. It is advantageous to retrofit end-of-life oil/gas wells for geothermal energy extraction. Prior to repurposing depleted wells into geothermal wells, it is imperative to conduct the heat-energy potential assessment. In this work, an analytical model was developed for this purpose. A case study was conducted using the model and the data from a well in North-west Louisiana for a feasibility assessment. A sensitivity study was performed with the model to identify major factors affecting well productivity. The result of the case study shows that reverse circulation is 35% more efficient than direct circulation for improving the heat-energy productivity of geothermal wells converted from oil/gas wells. The sensitivity analysis revealed that well productivity increases with higher injection rates and greater horizontal wellbore lengths. Additionally, well productivity rises in correspondence with reservoir temperature as well as the temperature of the injected water. However, well productivity decreases as the thermal conductivity of the tubing insulation increases. Counteracting this trend, well productivity increases with thicker tubing insulation layers. This study furnishes engineers with an easy-to-use tool for predicting the heat-energy deliverability of wells converted from end-of-life oil/gas wells.

Simulation and Analysis of a Split Drill Bit for Pneumatic DTH Hammer Percussive Rotary Drilling

Reverse circulation impact drilling has the advantages of high drilling efficiency and less dust, which can effectively form holes in hard rock and gravel layer. As integral reverse circulation drill bits used in the conventional down-the-hole (DTH) hammers are only suitable for specific formations, the whole set of DTH hammer needs to be replaced when drilling different formations. In this paper, several types of split drill bits for different drilling technologies are designed. The flow field characteristics of one of the split drill bits is analyzed based on the computational fluid dynamics (CFD) method, with four technic parameters considered, which are input flow rate, number of inlet holes, angle of injection exhaust holes, and diameter of injection exhaust holes, respectively. Three parameters are selected as indicators to evaluate the rationality and performance of the split drill bit, which are injection exhaust hole outlet mass flow rate, ratio of the mass flow rate out of injection exhaust holes to the whole inlet mass flow rate, and maximum pressure at the upper end of the split drill bit. According to the CFD analysis results, the above four technic parameters influence the flow rate and pressure in different rules. Considering the injection capacity, pressure loss, and bit strength, inlet holes of 10, injection exhaust holes with an angle of 50°, and injection exhaust holes with a diameter of 12 mm are recommended to obtain ideal reverse circulation. Different types of split drill bits were manufactured, and drilling experiments were carried out in unconsolidated formations. The maximum drilling rate can reach 1.5 m/min in the drilling experiments. The split drill bit proposed in this paper exhibits excellent adaptability for reverse circulation drilling in loose formations.

Sealing method and experimental study of large-diameter reverse circulation hole hammer

A reliable sealing structure is the key to achieving reverse circulation drilling technology for large- diameter reverse circulation down the hole hammers, and it is also a difficult point in the design of large- diameter reverse circulation down the hole hammers. The existing large-diameter reverse circulation down the hole hammers are designed based on the sealing structure of the bottom drilling tool body. This article proposes a joint sealing method for hole bottom and hole opening. Based on this sealing method, a bundle type reverse circulation down the hole hammer and hole opening sealing device with a diameter of 710/311mm were developed for hole expansion, and field tests were conducted with a double wall drilling tool with a diameter of 127/70mm. The method achieved good continuous reverse circulation slag removal effect, with an average mechanical drilling speed of 2.1m/h, which is 2.6 times higher than the conventional roller bit hole expansion method. The experimental results indicate that the joint sealing method between the bottom and the mouth of the hole is feasible and worthy of further promotion and application.

Development and application of power head for CBM vehicle mounted drilling rig

In order to meet the construction needs of surface coalbed methane extraction holes, cable holes, and mine surface rescue holes, a multifunctional power head suitable for coalbed methane vehicle mounted drilling rigs has been developed. The power head adopts a dual speed hydraulic motor to drive the spindle rotation through a first gear reduction, with a compact structure, high transmission efficiency, large spindle diameter, wide range of speed and torque adjustment, and spindle braking function. It can be applied to various drilling processes such as air down the hole hammer, air lift reverse circulation, and directional drilling. On site tests have shown that the power head has high capacity, efficiency, comprehensive functions, and is easy to operate, providing equipment support for efficient and safe drilling construction.

Rapid increase in warm‒wet compound extreme events with high health risks in southern China: Joint influence of ENSO and the Indian Ocean

High temperature and high humidity pose notable threats to the health and survival of humans, and the impact of compound extreme events involving multiple meteorological elements is usually greater than the sum of the impacts of individual extreme events. However, there is limited research on the compound extreme meteorological events, defined based on the extreme of health risks rather than just the extreme of meteorological elements, necessitating further investigation into their characteristics and underlying driving factors. Using daily records of emergency ambulance dispatches from selected Chinese cities, together with daily average temperature and relative humidity data, this study identified and quantified warm‒wet compound extreme events with high health risks (HRWWs) that occurred in southern China during 1979–2022. Results revealed that HRWWs were most prevalent in the coastal region of southern China. The annual frequency of HRWWs across China underwent a marked shift in 2014, with the rapid increase in recent years primarily contributed by the increase in summer HRWWs and advance and extension of the period of occurrence of HRWWs in summer. Further analysis indicated that the changes in HRWWs in southern China during summer were primarily regulated by the El Niño‒Southern Oscillation (ENSO) of the preceding winter and the springtime Indian Ocean basin-wide (IOBW) mode. El Niño and Indian Ocean warming force a reverse Walker circulation in the tropical Indian Ocean‒western Pacific, strengthening the Philippine anticyclone (PAC) in summer. This weakens convection in the northwestern Pacific and enables the western Pacific subtropical high to extend westward over coastal areas of southern China. The resulting abnormal atmospheric circulation causes prevailing subsidence over southern China, which is unfavorable for precipitation but conducive to maintaining high surface temperatures. Despite reduced precipitation, water vapor flux is increased owing to strengthened southwesterlies associated with the PAC that enhance regional humidity. Consequently, as temperature and humidity levels rise, HRWWs occur more frequently in southern China, as evidenced since 2014. Further analysis suggested that the contribution of intensification of IOBW warming to the sudden increase in HRWW occurrence over the past decade has been greater than that of ENSO.

Key parameters and mechanisms of ice cores autonomously breaking with air reverse-circulation drill systems

In recent years, a new ice-drilling method for continuous coring with air reverse circulation (CCARC) using a rapid air movement (RAM) ice drill system has been proposed that uses a dual-wall aluminum drill pipe. CCARC ice-drilling technology can effectively prevent compressed air circulation losses in snow-firn cover and continuously obtain ice cores using CCARC. When removing embedded ice cores without lifting the drill to the ice-sheet surface, the drilling operation remains uninterrupted; therefore, it can significantly improve the ice core production rate. However, a prerequisite for the realization of CCARC ice drilling is that the core splitter set on the internal surface of the drill bit inner tube can autonomously break ice cores of equal length. To further improve CCARC ice-drilling technology, key parameters such as the horizontal load and lateral displacement required to break ice cores with different diameters and lengths during drilling must be investigated because they are important for ice-coring drilling operations and drill design. In this study, the mechanism, and key parameters of the ice core breaking process under different conditions were theoretically calculated and experimentally measured. Subsequently, the influence of the ice core temperature, diameter, and splitting length on ice core breaking was quantified, and the feasibility of the ice core breaking mode was demonstrated.

Improving the outcome of distally based anterolateral thigh flap reconstruction: New classification and surgical guidelines

The distally based anterolateral thigh (dALT) flap is associated with a high incidence of venous congestion. This study aimed to investigate factors associated with vascular compromise to improve the outcomes. We retrospectively analyzed 41 dALT flap reconstructions performed between November 2010 and February 2023. The dALT flap was classified into type I, II, or III based on the origin (the descending, oblique, or transverse branch) of the chosen perforator. The distance from the pivot point to the superolateral patella, pedicle length, flap reach, complications, and loss rates were analyzed to identify different dALT flap characteristics. The type Ⅰ flap had a shorter pedicle length (type Ⅰ vs. type Ⅱ, p=0.000; type Ⅰ vs. type Ⅲ, p=0.000) that primarily reached closer regions (distal third of the thigh anterior/lateral knee). Pedicle lengths were similar between type Ⅱ and Ⅲ flaps (p=1.000), most of which reached more distal regions (medial/posterior knee or proximal third of the leg). However, the type Ⅲ flaps had a higher complication rate and flap loss rate, although no significant differences were observed (complication rate, p=0.094; flap loss rate, p=0.071). To achieve more desirable outcomes using the dALT flap, preoperative assessment of flap pedicle length and proper intraoperative maneuvers that avoid compromising the reverse blood circulation are necessary.

Justification of drilling parameters of a typical well in the conditions of the Samskoye field

In the Republic of Kazakhstan, there is a noticeable shortage of water resources, which is a consequence of the natural features of its territory and climate. In particular, there are big problems in the water supply to the Mangystau region. The main source of water in the region is the Samskoye groundwater field. In this work, the conditions of the Samskoye field are typified, the method and technological parameters for drilling a typical well are selected and substantiated. It has been established that rotary drilling with reverse circulation in the conditions of the Samskoye field has significant advantages. The maximum possible production rate of drilling with reverse circulation, taking into account the limited thickness of the aquifer, is 4.3 times higher than with rotary drilling with direct circulation and 2.5 times higher than with percussion drilling. With the same filter pipe diameter, the greatest possible thickness of the gravel pack layer in reverse circulation drilling is 15 times greater than for conventional rotary drilling and 3.7 times greater than for percussion drilling. Thus, the use of rotary drilling with reverse circulation will solve an important problem – the provision of domestic and drinking water supply to the area.

Temporal and Spatial Variation Characteristics of Hydrodynamic Forces in Urban Shallow Lakes

To study the temporal and spatial variation characteristics of hydrodynamic forces in Rule Lake, a two-dimensional mathematical model of shallow water lake was established based on MIKE 21, and the flow field characteristics of Rule Lake under the action of topography, wind field and inflow were simulated and analyzed. The results show that the spatial and temporal heterogeneity of hydrodynamics in the Rule Lake area is obvious, the velocity in the lake area presents a gradient change characteristic of high in the west and low in the east, and the velocity in the middle of the lake area is greater than that in the bends of shorelines on both sides of the lake area; Under the driving of wind field, there is a reverse circulation area in the lake area. The existence of the circulation area can disturb the dead water area at the shoreline bend and improve the local water mobility; The flow velocity in summer and autumn is slightly higher than that in spring and winter. It is suggested that during the operation and maintenance period, attention should be paid to the fluidity of the water body in the southwest of the lake area, the change in water quality and the timely removal of floating garbage on the water surface.

Experimental investigation and CFD simulation of multiphase flow behavior in air reverse circulation drilling

In reverse circulation (RC) down-the-hole hammer (DTH) drilling, hole cleaning has a great impact on reducing accidents and improving efficiency. There is a technical difficulty in RC drilling to select the minimum air influx while keeping cuttings discharged smoothly according to different water invasion conditions. A novel experimental device was used to study the physics of multiphase flow associated with the cleaning process. Air influx required for cuttings transport was measured under different conditions in Rate of Penetration (ROP), cuttings diameter, and water yield, and influence among three factors were revealed. Furthermore, the computational fluid dynamic (CFD) method simulated and analyzed multiphase flow behavior. The results show that factors of ROP, cuttings diameter, and water yield obviously impact minimum air influx during the cuttings transport process. The accuracy and credibility of CFD method have been confirmed on account of reasonable agreement with experimental data (a relative error of less than 14% is achieved). The CFD simulation of multiphase transport reveals that cuttings velocity and pressure drop could be influenced by ROP, cuttings diameter, and water yield. Therefore, these factors should be carefully characterized during air RC drilling and hole cleaning to maximize the efficiency of cuttings transport.