Small-scale Experimental Research on the Key Parameters Affecting Metal-to-metal Sealability

The harsh service environment of high pressure and high temperature (HPHT) gas well have posed great challenge to the seal integrity of the casing string thread connections. All the time, due to the complexity of metal-to-metal sealing mechanism, there is no uniform reliable sealability criterion in the Finite Element Analysis process of the casing premium thread, so a systematic research on the sealing mechanism of the casing premium thread metal-to-metal seals. In this paper, a series small-scale metal-to-metal seal tests considering different influence factors were conducted, the results showed that the average contact stress at the leakage threshold increases with gas pressure, thread compound and metal roughness has significant influence on the metal sealing property, tests with fine surface roughness (<0.05um) and without thread compound show the lowest critical average contact stress value. Based on the test results, the key parameters for calculating the sealability criterion model were calibrated, and the sealability criterion is recommended for use in high-pressure applications.