Experimental Study on Sealing Failure Mechanism of Injection-Production String in Underground Gas Storage under Cyclic Loading

Abstract

In order to clarify the impact of cyclic loading on the mechanical properties and sealing performance of threaded connections on pipe string under the injection-production conditions of gas storage and the airtight threaded connections suitable for the actual working conditions can be preferred, the sealing failure of injection and production tubular strings of several domestic gas storages was investigated comprehensively. It was found that the airtight threaded connections with different performance may leak during the service of tubular strings. Existing standards and testing methods have limitations, which are not fully applicable to the working environment of gas storage wells and the production mode of forced injection-production and cannot reflect the operation characteristics of multiround injection and production. Based on the stress analysis of the tubular string during injection and production, a full-scale simulation testing of 30 cycles of gas seal cycle under alternating load was proposed. The cyclic loading test results of two P110·13Cr tubing in domestic gas storage showed that after 30 cycles of cyclic loading, the yield strength, internal pressure strength, collapse strength, and compressive bearing capacity of tubing were all decreased; the compression efficiency of the joints should be fully considered when selecting the gas-sealed thread.