Study On The Mechanical Properties Of Expansion Casing And Special Thread Design

In the process of oil and gas exploration and development,there are a large number of deep wells,ultra-deep wells and special wells with complicated formations.The depth of casing entering the casing increases with the increase of well depth,resulting in the continuous decrease of wellbore diameter and lack of follow-up working space.In order to effectively reduce the loss caused by borehole reduction and provide more space for follow-up work,an expansion sleeve technology is produced.The principle is to utilize the metal plastic strain characteristics of the expansion sleeve,and to expand the sleeve under the expansion shaft The radial expansion is carried out by means of cold extrusion and expansion to achieve the purpose of expanding the borehole and expanding its diameter to meet the engineering requirements.The disadvantage of this technique is that the thread often undergoes severe deformation during expansion,resulting in the thread connection strength Reduce and seal performance damage.When the expansion casing threaded connection is damaged,it will aggravate the corrosion and failure,to the oil and gas wells operations incalculable losses,showing the thread connection is the most important expansion casing technology,therefore,to improve the casing after the expansion of the thread The connection strength and sealing performance are the problems to be solved urgently in the expansion sleeve technology.In this paper,the mechanical properties of the expansion casing thread will be studied in this paper.From the analysis of the material model under the corrosion condition and the influence of the expansion rate on the thread,the special design of the mechanical properties of the expansion sleeve thread with improved thread connection strength and sealing performance Expansion sleeve thread.Specific research content:(1)The mechanical properties of the casing are analyzed,and the material parameters are the basis of the model.Firstly,the casing of the corrosion failure is analyzed macroscopically and microscopically.The main corrosion products of the casing were observed from the macroscopic observation.Then the corrosion parts were analyzed microscopically.The corrosion range,corrosion pits and so on were observed by scanning electron microscopy.The main products of corrosion were obtained by energy spectrum analysis.On the basis of the experimental conclusions The main factors of casing corrosion occurred;and then through the indoor test ratio of etching solution;Finally,the use of high-temperature autoclave casing corrosion test,the corrosion before and after the sample tensile test,weight loss and mechanical properties of the material parameters The relationship between.(2)Based on the mechanical properties of different corrosion degree of the material,the corrosive material model of the non-thread and thread part of the casing was established.The relationship between the material parameters and the corrosion degree was input into the casing model.The casing and the thread were made by the corrosive material model The feasibility and the applicability of the corrosive material model are verified,and the mechanical behavior of the casing is studied based on the corrosive material model.(3)The mechanical properties of the extended casing thread are analyzed and the corrosion conditions Three-level expansion index of casing expansion operation.(4)According to the research results of the mechanical properties of the expansion sleeve under the corrosion condition,this paper puts forward the corresponding measures to protect the casing.First,the expansion sleeve is recommended to use bimetallic composite pipe,and through the research to obtain the best anti-corrosion material,the anti-corrosion material as the bimetallic expansion casing of the inner layer of bimetallic expansion casing forming mechanical behavior of a simple study,The range of material parameters of the outer layer of the bimetallic casing is obtained,and the initial gap should be set between the inner and outer layers during the composite operation.Then,the optimal size of the thread protection device is designed by drawing on the forming theory of the bimetallic expansion sleeve,And the best fit size of the thread protection device with the sleeve.(5)This paper designs a three-stage special thread for the problem of reduced strength and sealing performance after expansion casing expansion.Firstly,the variable pitch thread is designed for the problem of reduced strength after thread expansion.Then,the variable pitch gap is designed for the problem of reducing the sealing performance.Finally,considering the expansion working condition,the expansion of the three special thread,The best allocation of the number of threads at all levels.In this paper,the experimental results show that the three-stage special thread designed in this paper not only improves the joint strength of the expanded thread but also ensures the sealing integrity of the screw after expansion.In this paper,And in the expansion casing before and after the expansion can meet the requirements.On the basis of the experimental results,this paper has optimized the tooth profile of the three special thread,and obtained the best grade three special thread.The method of establishing corrosive material model in this paper is also applicable to other downhole columns under corrosive conditions,which has strong theoretical significance for the mechanical analysis of pipe string under corrosion conditions.The three-stage expansion index,The design of the special thread,variable pitch thread can not only be applied to the casing,but also can be used in tubing,drill pipe,etc.,on the downhole pipe thread design has a good engineering application value.