Research On Casing Window Opening And Rock Breaking Technology Of Branch Wells Based On Jet Technology

With the continuous development of oilfield resources,China’s oil resource exploitation has entered the middle and late stage.It is the top priority for the development of China’s oil industry to efficiently exploit three low oil fields and remaining oil fields.Three low oil fields refer to the oil fields with low permeability,low production and low pressure.The remaining oil fields refer to the oil fields that have not been fully exploited.Branch well technology based on jet is one of the methods to efficiently exploit three low oil fields and remaining oil fields.This technology not only has the characteristics of economy and high efficiency,but also can build a new wellbore from the original well wall,increase the gas injection pressure and water injection of three low oil fields and remaining oil fields,and improve the oil field production.The core of branch well technology is to remove the casing at the window so that the injection mechanism can contact the oil layer.This process is called "window opening";Then continue to drill a new wellbore from the original wellbore,which is the rock breaking process.In order to make up for the shortcomings of traditional downhole windowing methods,abrasive water jet technology is gradually applied to this field.Abrasive water jet technology is to strengthen the cutting ability of the jet by forming a high-speed flow of high-pressure water and high hardness particles mixed into it through the nozzle.As a cold working technology,it has the characteristics of high efficiency,no burr and simple nozzle structure.According to the characteristics and size of the current hydraulic jet rock breaking equipment and based on the actual underground application,if a 30 mm * 50 mm window is opened,the formation can be sprayed continuously to realize one-time window opening and rock breaking.The specific contents of this paper are as follows:(1)This paper introduces a branch well technology based on jet,introduces the function of core equipments,and explains the connection mode and operation process of branch well technology.Design the nozzle test on the ground,and introduce the test system,equipment,materials and methods.(2)According to literatures,considering the characteristics of nozzle jet and the failure mechanism of casing material,LSDYNA software is selected to simulate the nozzle under different structures.According to the determined wedge nozzle structure modeling,the casing erosion windowing simulation is carried out,and compared with the experimental results,its parameters are modified to make the simulation results of the software calculation model consistent with the experimental results,and the second experiment is used to verify the model.Analyze the pressure distribution of the workpiece in the window,and use the determined simulation model to design the nozzle that can cut the window with the size of 30 mm * 50 mm,so as to save the test cost.Finally,the design is optimized on the basis of simulation results,and three nozzle structure schemes are proposed,including wedge nozzle structure,movable nozzle structure and round head nozzle structure,and their advantages and disadvantages are summarized.The failure mechanism of plastic materials is verified.When the abrasive water jet impacts at an inclined angle,the failure mode is ploughing,which is consistent with the analysis results.(3)The control variable method is used to control the single factor variable,and the other parameters are the same.Using FLUENT software,the pressure and velocity nephogram of the erosion surface under the single factor are analyzed to obtain the influence law of jet flow,abrasive concentration and abrasive particle size on the cutting speed of abrasive water jet,and summarize the approximate range of data applicable to the field,so as to provide theoretical support for the field application.It is concluded that the jet flow should be appropriate,the abrasive concentration should be 6%,and the abrasive particle size should be 0.6mm.(4)Simulate the failure process of rock under a single nozzle,establish the simulation model of rock failure with LSDYNA,summarize the law of rock failure process,and draw the conclusion that the curve of cutting depth with calculation time is fast first and then slow.At the same time,it shows that the existence of water cushion will weaken the cutting energy of abrasive water jet.Using fluent to observe the distribution and movement track of abrasive particles in the flow field during rock failure,the failure mechanism of rock is obtained,and the conclusion that when the pressure value of rock exceeds the shear strength of rock,the rock will be damaged.