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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]

Two methods of coagulation and adsorption were used to pretreat a simulated micro-polluted ground water to study the relationship between ultrafiltration (UF) membrane and pollution levels of different water samples and analyze the effect of particles characteristics on flux decline. The experimental results indicate that powdered activated carbon could reduce the concentration of organics effectively, but the effect of wiping out turbidity is not obvious. Coagulation could reduce the turbidity of water effectively although it has low efficiency on organics removal. The coagulation pretreatment could improve the flux of raw water, but the adsorption has no influence on flux. The correlation fitting results of fouling index of turbidity and dissolved organic matter (DOC) show that fouling index of UF has an obvious correlation with turbidity, but no obvious correlation could be found with DOC concentration. The turbidity-causing pollutants are the major foulant under experimental condition. The colloidal and particles sized between 0.01 µm and 1.2 µm are the main pollutant which lead to flux decline, meanwhile, it is cumulatively on fouling index for turbidity-causing pollutants during UF process. [ABSTRACT FROM AUTHOR]

The high speed fluid jet for directly or indirectly breaking rock is one of the most effective ways to improve the deep penetration rate. In order to maximize the efficiency of energy use, the flow characteristics of different combinations of high pressure jet nozzles are analyzed through numerical simulations. According to the velocity vectors at the bottom and the bottom hole pressure diagram, the effects of the high pressure nozzle combinations on the flow structure and the penetration rate are analyzed. It is shown that the combination of three vertical edge nozzles is very efficient, but inefficient in cleaning the bottom hole and eroding the wall. The jet velocity is 400 m/s and the radius is 5 mm, with a center nozzle added, the problem can be solved, but the high-pressure fluid displacement would increase. The center nozzle’s jet velocity is 200 m/s and the radius is 8 mm, the combination of two vertical edge nozzles and a center tilt nozzle or that of a vertical edge nozzle and a center tilt nozzle would provide a flow structure favorable for drilling. The angle of inclination is 10°. To take advantage of high pressure jet energy to improve the efficiency of drilling, it is important to select a suitable nozzle combination according real conditions. [ABSTRACT FROM AUTHOR]