| China is rich in coalbed methane(CBM)resource.CBM’s extraction is of great significance to the sustainable development of China’s energy strategy.It has important strategic value in safety,energy and environmental protection.The technology of drilling horizontal wells has widely used to increase the gas production in China.The transport of cuttings is an important influence factor during the drilling of CBM horizontal wells.The drilling of CBM horizontal wells will not safe until the concentration of cuttings is in an appropriate range.The risk of drilling include sticking accident,hole collapse,and so on.The study of the law of large particle cuttings’ transport is very necessary because they will influence the whole cuttings transport.In this paper,a variety of related domestic and abroad literature is studied to summarize the mechanism of cuttings in the CBM horizontal well drilling and cuttings transport model.Cuttings transport force model is modified by the introduction of shape factor.The axial equation of motion and radial equation of motion are established.The CFD-DEM is appropriate for the study of the transport law of large particle cuttings through the comparison of the different simulation models.The method is proved applicative and accurate by compared between calculated result and experiment result.Then using numerical simulation method,considering the large particle cuttings’ different shape,the single large particle’s law of transport and its’ impact on the stability of the wall of the borehole are simulated and analyzed.Large cuttings of different shape and small cuttings’ transport are simulated to obtain the shape’s effect on transportation and its’ impact on the stability of the wall of the borehole by using the actual drilling data.The different cuttings’ trajectory is also obtained.Then the simulation of the content of large cuttings is conducted to gain the effect on the index of the carrying cuttings and the impact on the stability of the wall of the borehole.Finally,in this paper,critical diameters of different drilling fluid flow are calculated in vertical well.It provides theoretical basis for the CBM horizontal well drilling and cuttings transport.This paper offers four suggestions to improve the cuttings transport efficiency to ensure the safety of CBM horizontal wells drilling. |
