Failure risk assessment of deepwater HTHP well completion test string based on uncertainty analysis

Abstract

In deepwater HTHP well completion test, the stress of the test string changes violently under the influence of HTHP environment, which is easy to cause the string failure. To solve this problem, the test string is simplified as a thick-wall cylinder model with uniform loads under the influence of high temperature. Then, the failure risk assessment method of the string is established based on the generalized stress-strength interference theory, and the influence of gas production, bottom hole pressure and test fluid density on the failure risk of a case well are analyzed. The results show that the failure mode in this well is internal pressure resistance failure, and the risk positions are mainly concentrated near wellhead. Gas production increasing leads to the intensification of radial heat transfer, increases the annular pressure and reduce the pressure difference of the string, resulting in the reduction of failure risk. Increasing the bottom hole pressure will increase the positive pressure difference of string, which will increase its internal pressure resistance failure risk. The test fluid density has low impact on failure risk. This method can provide theoretical reference for ensuring the reliability of deepwater HTHP well completion test.