Numerical Simulation Of Rock Breaking By Porous Water Jet And Design Improvement Of Self-advancing Sprinkler

With the exploration and development of petroleum in the world improving,the petroleum production of high productivity wells decreasing,most of oil fields in our country came into the middle or later production periods,and the majority of production came from the old petroleum fields.However,it's difficult to recover them,oil recovery rate is low and the cost is very high.In recent years,the radial horizontal well technique has been applied more and more,which uses high pressure water jet to break the rocks.Moreover,it attracts more and more attention from all over the oil fields in the world.The core technique of the radial horizontal well is the nozzle of the high pressure water jet.According to the previous research,the radius of the bore which is drilled by multi-perforation water jet is large and deep,and the drilling efficiency is high.But the rock-breaking mechanism has not been studied in the practical working conditions.While in the daytime,most of the water jets in drilling wells must be drived by driving devices on the ground,which make it difficult to operate and increase the cost.Based on this situation,a new structure of water jet should be developed to move forward autonomously while breaking rocks with high efficiency.Therefore,the work in this research including:Firstly,based on the practical working conditions,studying on the rock-breaking mechanism because of multi-perforation water jet.An experiment without submerged confining should be established,which is used to simulate the rock-breaking effect with the multi-perforation water jet when the pump is opened to give it flow.Secondly,with the software called LS-DYNA,based on the contrast on experiment and simulation,a correct simulation model should be established.And,the correct simulation model is used to study the rock breaking in the practical condition,such as the stress distribution in the sandstone.Meanwhile,the rock-breaking process,the influence on water jet speed to the breaking effect and the propagation characteristic of stress wave in the sandstone and coal should be displayed.Then,a self-advanced and straight-rotating nozzle which is applied in the radial horizontal well should be designed.The water jet and straight-rotating water jet are built and simulated,which is used to contract their differences,and the structure parameters of optimal straight-rotating water jet should be found out.Finally,the water jet flow field model on the self-advanced and straight-rotating nozzle is built and simulated by the software Fluent.Some structure parameters of the nozzle which influence the fluid field should be found out.A best nozzle structure should be solved out through the judge index about water jet speed and self-advanced strength.The work of this thesis can make a process to know the mechanism of porous water jet to break rocks,find the stress distribution law of rocks under the high confining pressure and direct the construction of site.With the self-advanced and straight-rotating nozzle,the efficiency of radial horizontal well drilling can be improved,which solve the problems on sticking and long working time.