| Water jet technology has developed rapidly in the field of oil and gas exploitation because of its high efficiency,cleanness and low cost.It is widely used in drilling and completion operations such as jet drilling,perforation and fracturing,sand flushing and well washing.With the exploration and development of oil and gas resources is gradually moving towards the deep layer,the working condition of jet tends to be complex,and the application effect of jet is limited by factors such as bottom hole confining pressure.Predecessors have done a lot of research work on the characteristics of single nozzle jet,but the influence of confining pressure on the characteristics of jet is not clear.In order to explore the characteristics of water jet under confining pressure,this thesis takes the conical nozzle jet as the research object,and carries out the following research by combining theoretical analysis,numerical simulation and indoor experiment:(1)the jet characteristics under different confining pressure and displacement are tested by using the confining pressure jet comprehensive test system,and the effects of confining pressure and displacement on nozzle pressure drop,jet structure and dynamic pressure distribution under submerged conditions are analyzed;(2)Considering the compressibility of water,wall function,nozzle cavitation and other factors,a single nozzle high confining pressure jet model is established.The effects of confining pressure on nozzle cavitation,nozzle pressure drop,jet structure and pressure distribution are simulated and analyzed.Combined with the basic theory of water jet and indoor experimental results,the effects of displacement and confining pressure on the jet characteristics of conical nozzle are clarified;(3)Compare and analyze the numerical simulation and indoor experimental results,combined with the basic theory of water jet,analyze the influence of high confining pressure on jet characteristics,and carry out the numerical simulation of single nozzle rock breaking to verify the results.The results show that there is a critical value for the influence of confining pressure on the jet characteristics of conical nozzle.Under constant discharge,the changes of nozzle pressure drop and jet dynamic pressure are affected by nozzle cavitation.With the increase of confining pressure,the cavitation in the straight section of conical nozzle is limited,and the nozzle pressure drop and jet dynamic pressure gradually decrease when the confining pressure is less than the critical value;When the confining pressure exceeds the critical value,there is no cavitation in the straight section of the conical nozzle,and the nozzle pressure drop and jet dynamic pressure basically do not change with the confining pressure;The increase of displacement will enhance the cavitation degree of the nozzle and increase the critical value,resulting in the increase of the influence of confining pressure on the application effect of jet.When the displacement increases from18.38L/min to 33.00L/min,the critical value increases from 2MPa to 8Mpa.This thesis can provide a theoretical basis for efficient jet operation in deep and ultra deep wells. |
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