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Horizontal wells have been widely used to exploit unconventional oil and gas reservoirs across the world. Insufficient hole cleaning has been recognized as one of the main difficulties in drilling horizontal wells. Drilling incidents caused by insufficient hole cleaning increase unproductive drilling time, induce a great amount of additional drilling costs and may even lead to the loss of the well. Drilling a well while maintaining efficient hole cleaning is a systematic process that requires various parameters to implement hole cleaning and requires cooperative effort rather than separate work. Therefore, optimizing multiple parameters to achieve the best hole cleaning effect is of great importance. However, to the author's knowledge, few research studies in this area have been undertaken. The objective of this study is to develop a new method to optimize multiple hole cleaning parameters by introducing the ant colony algorithm. The flow rate, consistency coefficient in power law model and nozzle flow area, which are three easily-adjusted parameters to control the hole cleaning on drilling site, are selected as the optimization variables. The hydraulic constraints that affect hole cleaning optimization are proposed. The mechanism and procedures of ant colony algorithm optimization are described. The practical usefulness of the developed method is demonstrated with a field example. The effect of the selected parameters on hole cleaning is analyzed, and the hole cleaning result after optimization is compared to the data before optimization. The result of the optimization shows that hole cleaning is greatly improved and all constraints are satisfied after optimization. By analyzing the optimization results, it can be concluded that the ant colony algorithm can be used to optimize the hole cleaning problem for horizontal wells. Artificial intelligence can help optimize the drilling of horizontal wells to reduce the risk of unproductive time and decrease drilling costs. The flow rate, consistency coefficient and nozzle flow area should cooperate with one another to minimize the cutting bed height while satisfying all of the constraints. Increasing the flow rate is the most efficient way to reduce the cutting bed height. Decreasing the consistency coefficient and increasing the nozzle flow area can reduce the total pressure loss and enlarge the capacity for increasing the flow rate. Increasing the pressure-bearing capacity of the system is favorable for improving the hole cleaning of horizontal wells. The cutting bed height can be further reduced and the jet velocity can be further increased when increasing the pressure-bearing capacity of the system. [ABSTRACT FROM AUTHOR]

This study investigated the effects of secondary chlorination on bacterial regrowth, microbial communities (abundant and rare taxa) and bacterial functions of pipe wall biofilm and bulk water in simulated secondary water supply system (SWSS). Continuous secondary chlorination was more effective than short-term secondary chlorination to control the bacterial regrowth in both biofilm and water samples. Bacterial diversity slightly reduced after continuous secondary chlorination, and 19.27% of the total operational taxonomic units (OTUs) were shared by biofilm and water samples, with Bacillus as the dominant genus. Abundant and rare taxa exhibited different community structures. Proteobacteria and candidate division WPS-1 predominated in abundant and rare phyla were sensitive to chlorine, while Firmicutes, Acidobacteria and Bacteroidetes , exhibited relative strong chlorine resistance. The abundant genera in control sample (e.g., Bosea , Sphingobium and Gemmata) exhibited poor tolerance to chlorine, while Bacillus in biofilm and Defluviimonas in water were the main chlorine-resistant genera. Moreover, the composition of rare genera in each sample was obviously different. Furthermore, a total of 18 potential pathogens were detected with Pseudomonas as the dominant genus, most of which were significantly reduced after disinfection. There were mainly positive interactions among potential pathogenic bacteria, with Enterococcus , Legionella and Vibrio as the hub genera as revealed by network analysis. Similar bacterial functions in both biofilm and water were observed with metabolism as the predominant bacterial function, while, human disease function only accounted for 1.07% of bacterial functions. These results highlighted the importance of continuous secondary chlorination for controlling biosafety of SWSS and identified the dissimilar responses of abundant and rare bacteria to the disinfection, as well as the co-occurrence patterns among potential pathogens, improving our understanding of bacterial communities in SWSS. Unlabelled Image • Continuous secondary chlorination could effectively control bacterial regrowth. • The community structures of abundant and rare taxa were different. • Some chlorine-resistant and -sensitive abundant and rare genera were identified. • Hub pathogens mainly showed positive interactions with other pathogenic genera. • Bacterial functions included in human disease were predicted using PICRUSt. [ABSTRACT FROM AUTHOR]

[Display omitted] • AA-TFCW accelerated NH 4 +-N transformation with 6.68 mg/(L·h) in start-up phases. • Heterotroph and autotroph synergistically removed 74.2% TN at low temperature. • HN-AD bacteria achieved direct NH 4 +-N removal by nitrate assimilation pathway. • Ferribacterium and Nitrosomonas carried high-weight key genes for N removal. This study explored the quantitative mechanisms of heterotrophic nitrification-aerobic denitrification (HN-AD) in a pilot-scale two-stage tidal flow constructed wetland (TFCW). The TFCW packed shale ceramsite (SC) and activated alumina (AA) at each stage, respectively, and aimed to improve decentralized wastewater treatment efficiency. In start-up phases, AA-TFCW accelerated NH 4 +-N decline, reaching transformation rates of 6.68 mg NH 4 +-N/(L·h). In stable phases, SC-AA-TFCW resisted low-temperatures (<13 °C), achieving stable NH 4 +-N and TN removal with effluents ranging 6.36–8.13 mg/L and 9.43–14.7 mg/L, respectively. The dominant genus, Ferribacterium, was the core of HN-AD bacteria, simultaneously removing NH 4 +-N and NO 3 –-N by nitrate assimilation and complete denitrification (NO 3 –-N → N 2), respectively. The quantitative associations highlighted importance of nitrification, nitrate assimilation, and denitrification in nitrogen removal. HN-AD bacteria (e.g., Lactococcus , Thauera , and Aeromonas) carried high-weight genes in quantitative associations, including nap AB, nas A and glt BD, implying that HN-AD bacteria have multiple roles in SC-AA-TFCW operation. [ABSTRACT FROM AUTHOR]

• Simultaneous N and P removal was achieved in SC-AA-TFCW at low temperature. • SC-TFCW contributed 85.6% of particulate phosphorous removal. • ADNB were highest abundance denitrifiers compared with FADNB and AUDNB. • ADNB showed positive interactions with key genes related to N and P metabolism. • The synergy of porous substrates and ADNB was proposed in SC-AA-TFCW. A pilot-scale two-stage tidal flow constructed wetland (TFCW) with working volume of 0.46 m3/d packing with shale ceramsite (SC) and activated alumina (AA) was constructed (named as SC-AA-TFCW) for nutrients removal at low temperature (<15 °C). SC-AA-TFCW achieved stable removals of 78.1% nitrogen and 98.3% phosphorous. SC-TFCW contributed to 55.2% of organics and 85.6% of particulate phosphorous removal. Among 17 denitrifiers, the absolute abundance of aerobic denitrification bacteria (ADNB) was highest, followed by facultative anaerobic denitrification bacteria (FADNB) and autotrophic denitrification bacteria (AUDNB). Nitrogen assimilating into organic nitrogen, dissimilatory and assimilatory nitrate reduction and complete denitrification may be main nitrogen metabolic pathways. Some ADNB (e. g. Zoogloea , Pseudomonas and Acidovorax) showed positive interactions with various key functional genes related to nutrients removal. Dissolved oxygen and reducing elements were main environmental factors in changing ADNB compositions. This study highlights the importance of ADNB and their synergy to porous substrates in SC-AA-TFCW. [ABSTRACT FROM AUTHOR]

• High C/N ratios and effluent recirculation promoted SND process for N removal. • HNAD was the main nitrogen transformation pathway in TFCWs. • HNADB were the dominant functional genera related to nitrogen removal in TFCWs. • Some core HNADB showed positive interactions with other functional genera. • Tidal strategies contributed more to shifts in functional genera than C/N ratios. This study investigated the influence of C/N ratios and tidal strategies on nitrogen removal and bacterial communities in two pilot-scale tidal flow constructed wetlands (TFCWs) with simultaneous nitrification–denitrification process. Heterotrophic nitrification aerobic denitrification (HNAD) was the main nitrogen transformation pathway in both TFCWs. High C/N ratios and effluent circulation at low temperature promoted HNAD in TFCWs with high nitrogen removal efficiencies (72.6%–95.5% for NH 4 +-N and 70.9%~91.8% for TN). Effluent circulation had more influence on bacterial community structure and diversity than C/N ratios. Among 16 detected genera related to nitrogen removal, HNAD bacteria (HNADB) were abundant. Especially, some dominant HNADB (e.g. Aeromonas , Hydrogenophage and Gemmobacter) were core genera, showing positive interactions with other genera related to nitrogen removal. Tidal strategies had more contribution to the shifts in these genera than C/N ratios. This study highlights the importance of HNADB in pilot-scale TFCWs and their responses to C/N ratios and tidal strategies. [ABSTRACT FROM AUTHOR]