Analysis And Parameter Optiamization Of Drilling, Milling-grinding Techniques For Drilling Out Composite Bridge Plugs In Coiled Tubing In Horizontal Well

Shale gas is a kind of high-quality clean energy stored in organic shale strata.It is of great significance to optimize China's energy structure,promote energy consumption change and ensure energy security.In recent years,this technique about drilling out composite bridge plugs in coiled tubing has been used widely along with the large-scale development of shale gas at home and abroad.Through the coiled tubing downward grinding and milling tool,the downhole bridge plug can be drilled and milling,and the wellbore can be smoothed quickly.However,this technology is also faced with a series of engineering problems such as low drilling and grinding time,frequent downhole failures and so on.Therefore,it is very important to study the composite plug technology of coiled tubing drilling and grinding bridge to solve the practical problems of field engineering and improve the drilling and grinding time.This paper mainly studies the fluid mechanics in the construction of coiled tubing drilling plug,involving the parameter optimization in the drilling plug stage and the short lifting and washing stage of coiled tubing.The migration law of bridge plug debris is different from that of conventional rock debris.Through numerical simulation of short-lifting debris in coiled tubing,it is concluded that the causes of debris migration include: local complex turbulent flow near the shoe;increased turbulent intensity of annular fluid flow caused by coiled tubing lifting;and friction between coiled tubing lifting and debris particles.At the same time,the numerical simulation verifies that there is an optimum speed of chip-carrying effect under a certain displacement and the continuous upward speed is in a low speed range,and that too large or too small speed is not conducive to the upward movement of debris.Based on the movement characteristics of bridge plug debris in horizontal section,a stable slip model of debris particle accumulation in horizontal section is established,and the relationship between short lift velocity of coiled tubing and annular fluid flow velocity in well washing stage is explained theoretically.The experiment of debris migration under the condition of coiled tubing lifting is carried out,and the optimal lifting speed of different particle sizes of debris migration in horizontal and inclined sections under a certain displacement is determined,which has guiding significance for field construction.The effects of abrasive particle size,well deviation angle and water hole with or without drill bit on the optimal lifting velocity are analyzed experimentally.The optimization scheme of composite bridge plug for coiled tubing drilling and grinding is worked out,the displacement and drilling pressure during drilling and grinding construction are optimized,the construction pump pressure is predicted,and the optimal lifting speed of coiled tubing at a certain displacement in short lifting and washing stage is optimized.According to the optimization scheme,an application software for optimizing construction parameters of coiled tubing drilling and grinding bridge plug is developed,which is beneficial to the smooth implementation of field construction.