Study On Flow Structure Characteristics Of Self-propelled Jet Bit For Radial Horizontal Drilling

The radial horizontal well drilling has been proved to be an effective technique in marginal reservoirs,shallow reservoirs and unconventional reservoirs development with high efficiency and low cost.Researches on this has been a hot issue in oil and gas development fields.Self-propelled jet bit is one of the most important parts in radial horzontal well drilling system,which is tasked with rock breaking,reaming and assisting high-pressure hose drilling into the formation.The flow structure of self-propelled jet bit is closely related to the pulling force,well track straightness,radial horizontal well extending ability and hose pre-installed length,etc.Therefore it is important to study on the flow structure of self-propelled jet bit for application and development of the radial horizontal well technology.This paper focuses on such problems as the mechanism of self-propelled jet bit,sensitive factors of pulling force,the calculation and control method for jet bit with complicated structure and so on.To solve these,at first,the flow field characteristics of different self-propelled jet bits were researched by numerical simulation method.The self-propelled mechanism was analyzed in the microscopic point of view,and the influences of different factors(inlet flow rate,diameter of wellbore,spray distance)on the jetting force,the ejector force and the pulling force were also analyzed.In addition,the experimental researched influences of different factors on the pulling forces of self-propelled multi-hole jet bit and self-propelled straight-swirling integrated jet bit,in order to get the measured data and compared those results with the numerical simulation ones.At last,a multi-condition calculation method of the pulling force of self-propelled straight-swirling integrated jet bit was established.The control means of pulling force were proposed.The results showed that the pulling force provided by the difference between jetting force and ejector force of the jet bit,and the pressure-reducing effects of forward and backward jet.The inlet flow rate and diameter of wellbore were key factors which can influence the pulling force.With the inlet flow increasing,the pulling force increased linearly;with the diameter of wellbore increased,the pulling force increases firstly,and then it reduces;an optimal wellbore diameter range exists to a designated inlet flow rate.With taking the pressure-reducing effect and flow sensitivity coefficient into consideration,a multi-condition calculation method of the pulling force of self-propelled straight-swirling integrated jet bit was established.This method is in line with changes in the measured pulling force.In the practical applications,the pulling force can be adjusted by increasing flow rate,optimizing the forward and backward flow ratio,and adjusting backward nozzle tilt angles.