Structure Design And Research Of A Milling Fishing Tool For Repairing Wells

There are many domestic oil and gas fields with the characteristics of ultra deep burial,high temperature,high pressure,high methane content and small borehole diameter.With the deepening of oil and gas exploitation,many oilfields have entered the middle and late stage of exploitation,and the overhaul operations caused by falling objects in the well and casing deformation are increasing year by year.When the workover fishing is carried out after the above problems occur in the ultra deep and small-sized hole,due to the small space gap of the small hole ring and the difficulty of handling,the conventional workover tools cannot meet the fishing requirements due to the limitation of the hole size and the tool strength,so at present,the fishing for the ultra deep and small-sized hole is to first run a set of milling tools to handle the fish at the bottom of the hole,and then run a fishing tool to handle the fish The generated debris can complete the workover for ultra deep and small-sized wells and resume production.Although the above treatment method can achieve workover,the workover cycle is long and the cost is high.In view of the above problems,this thesis develops an integrated tool for milling and fishing,which can fit the requirements of ultra deep and small-sized well environment.The tool can be used to mill,fish and drill in ultra deep and small-sized wells,and collect bottom hole debris by using the mechanism of local reverse circulation of workover fluid in the tool,this tool can improve fishing efficiency and shorten workover period.In this thesis,firstly,we study the structure of the high-speed nozzle which is installed inside the tool to form a high-speed jet,From the three kinds of nozzle structures,the nozzle structure with the best effect of forming high-speed jet is selected.After determining the most suitable nozzle structure,the orthogonal test method is used to study the structural parameters that affect the performance of the nozzle,and the structural parameters of the nozzle are optimized with the performance of the high-speed jet produced by the nozzle as the goal and the size as the constraint..After determining the structure and parameters of the nozzle,the annulus flow path between the inner wall of the casing and the tool and the inner flow path of the tool are extracted and simplified,and then we set the solid particles in the bottom area to simulate debris and small size fishings in the bottom hole.Then,the numerical simulation of solid-liquid two-phase flow is carried out.Based on the pressure and velocity distribution nephogram of the annulus and the fluid inside the tool,the feasibility of designing the fishing mechanism of the tool and some factors affecting the fishing performance of the tool are analyzed.At the same time,according to the calculation results,the distribution of bottom hole debris in the tool under the impact of workover fluid under different time steps is simulated and analyzed,which shows the fishing process of the device in the well directly and verifies the feasibility of the tool.After determining the fishing mechanism feasibility of the design tool,we study the parameters that may affect the fishing performance of the tool,which are mainly divided into two categories: structural parameters and working condition parameters,the structural parameters including the number of nozzles,nozzle arrangement angle,debris collection chamber length;the working condition parameters are divided into inlet flow,ambient temperature and ambient pressure.According to the above six parameters,the control variable method is used to study respectively.After comparative analysis,we can select the optimal number of nozzles and nozzle arrangement angle,and we can determine the effects of debris collection cavity length,inlet flow,environmental temperature and environmental pressure changes on the fishing performance of tools.At the same time,according to three different specifications of debris collection cavity,the available range of each specification of debris collection cavity is determined.It can provide some reference for making the prototype of the tool and putting it into actual production.