Development Evaluation And Application Of Special Thread Connections

In oil and gas exploitation,tubing and casing are connected together to down in the oil well,and the best way of connection is threaded connection.API round threads and Buttress threads are widely used now.The joint efficiency of API round threads is only 60-80% of the pipe body.At the same time,the loading surface of this thread form is 30 degrees,which is easily to skip and slip.The Buttress threads are composed of complete threads and vanish threads,and the vanish threads are extended to the outside surface of the pipe,so the thickness of the connection part is not reduced to thin;And the threaded loading surface is 3 degrees,which is not easily to slip,so the joint strength can be the same as the pipe body.But according to triangle position,the Buttress threads are made up,the torque is unpredictable.For all API threads,the maximum contact pressure generated by the make up with maximum torque will inevitably lead to a high stress level of the joints,which will easily lead to stress corrosion and easily to bond.At the same time,for API round threads,there is a spiral leakage channel between the top and bottom of the thread connection.For API Buttress threads,the spiral leakage channel exists not only between the top and bottom of the teeth,but also between the side of the teeth.The development of new drilling technologies,such as casing drilling,horizontal drilling,multi-branch drilling,extended reach drilling,slim hole drilling and so on,requiring higher and higher requirements for the whole string and the threaded joints to have good strength and sealing performance.This paper mainly completed the following work :1.To investigate and analyze the application background of special thread joint,the basic characteristics of special thread structure,and the development process of special thread technology at home and abroad.2.Studied the processing technology of the special threaded joint,developed the processing technology of the special threaded joint,compiled the processing program,developed the tools and measuring tools for the special threadedjoint processing,and evaluated the technical characteristics of the special threaded joint.3.Developed special threaded joints and evaluated their safety and reliability by finite element analysis and physical test.The finite element analysis method is mainly used to analyze and evaluate the designed structure,calculate the fit and interference of thread parameters,the stress and strain distribution law of thread joint under the top buckle torque and top buckle state,and the stress and strain distribution law of thread joint under compound load.The actual test mainly refers to iso13679-2002 "test method for casing and tubing joints in the petroleum and natural gas industry" to develop the evaluation method and procedure for special threaded joints,and the full-size evaluation test is carried out on the samples,and the samples meet the technical indicators of each working condition.4.TO study the operation of special threaded joints,compile the "service manual of special threaded joints" and "site repair program of special threaded joints",and conducte on-site tracking service for the use of follow-up products.