An analysis and evaluation method for gas sealing threads of tubing in high temperature and high pressure gas wells

Abstract

The invention discloses an analysis and evaluation method for hermetic seal thread of a tubing of a high-temperature high-pressure gas well. The hermetic seal applicability of a limit tolerance samplein the condition load and stress correction environment under different make-up torques is tested and evaluated by analyzing the make-up torque of the hermetic seal thread according to down-hole workenvironment characteristics of the high-temperature high-pressure gas well and structural characteristics of the thread; according to analysis on the make-up torque of the hermetic seal thread, the limit tolerance and torque are selected to analyze hermetic seal finite elements under the condition load spectrum, and the down-hole condition load spectrum sealing after make-up of the hermetic sealthread is analyzed; and thread dynamic-load anti-fatigue analysis in the gas production process of a down-hole tubing string is analyzed, an applicability test and evaluation process is determined according to links likely to fail in analysis, and the applicable reliability of the thread is evaluated and analyzed comprehensively. The method can be widely applied to high-temperature high-pressure gas wells as well as unconventional multi-segment high cracking gas wells, especially to evaluate selection and applicability of threads of well-completion tubing strings of deep and ultradeep wells inTarim and southwest oil and gas fields.

Description

technical field [0001] The invention belongs to the technical field of petroleum and natural gas development, and in particular relates to an analysis and evaluation method for gas sealing threads of oil pipes of high-temperature and high-pressure gas wells. Background technique [0002] The representative oil and gas fields of high temperature and high pressure three super gas wells in China are Tarim and Southwest China. For oil and gas wells with such complex working conditions, the representative method for the detection and evaluation of tubing string threads is the four-level test evaluation (CALIV) of ISO13679; Numerous leaks and broken failures. Compare and analyze the difference between the actual downhole working conditions and the evaluation method: [0003] 1) Thread make-up: According to the ISO test standard, for sample 1# with the worst air-tightness of the thread limit tolerance, make-up according to the minimum torque, according to the minimum contact leng...

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Problems solved by technology

[0003] 1) Thread make-up: According to the ISO test standard, for sample 1# with the worst air-tightness of the thread limit tolerance, make-up according to the minimum torque, according to the minimum contact length and pressure of the main seal after make-up (that is, the worst sealing performance) , to detect the sealing performance under the 1# sample load; without considering the screw thread plastic deformation of the make-up torque change in the oil field, the failure of the stress corrosion gas seal and the failure of the vibration fatigue gas seal and fracture under the environment medium of the downhole working condition;

[0004] 2) Load air seal: ISO standard adopts A-series full-envelope and B-series half-envelope load spectrum, that is, tension or compression (bending) + pure external pressure (liquid) or pure internal pressure (gas) to detect the gas of the thread The sealing ability is called the sealing efficiency according to whether the thread sealing ability reaches the performance of the pipe body; it does not consider the influence of the axial load and the coexistence of internal and external pressure on the air seal under the actual downhole working conditions, due to the coupling of the special thread The tooth height of the internal thread is about 0.2mm higher than that of the external thread, and the thread forms a fluid channel, which directly acts on the position of the main seal, causing the contact pressure of the main seal to drop, which may easily lead to the failure of the internal pressure and gas seal of the downhole thread;

Does not consider the temperature and load changes in different operating stages of the actual downhole working conditions; fracturing low-temperature stretching, production high-temperature compression and gas flow-induced vibration under pipe string buckling, resulting in thread seal failure or fatigue fracture

In view of the above comparative analysis, it can be seen that the current representative standard detection method is not applicable to the working conditions of high temperature and high pressure gas wells, and the analysis and evaluation methods need to be supplemented and improved:

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