Seal Qualification and Single-Trip Lockdown Sleeve Reduces Risk Through Innovative and Advanced Technology

Abstract

The oil and gas industry continues to face the need to reduce risk and the overall cost of operations as a means to compensate for lower oil prices. Conventional designs and methods are economically infeasible when drilling offshore in the current economic environment pushing the manufacturer to re-evaluate how to reduce risk and drive down costs. This paper describes a new and advanced way to drive down cost and reduce risk while drilling by reducing the number of trips into the well, adding significant value to the end user. The subsea wellhead system functions in a dynamic, complex environment; however, the qualification process of this system commonly employs relatively static test fixtures. These critical seal/casing hanger barriers within this wellhead system are presented, discussed and shown with exhaustive validation efforts necessary to evaluate relevant failure modes. Within the wellhead system, loads are typically resultant of a combined state including pressure and temperature. The validation of these components is aimed at defining the performance of the system in these states while detailing the limitations that one performance aspect may have on another. (Brown, 2017) This wellhead system offers reduced cost, simplified installation procedures and lower operational risk. Traditionally, a wellhead system would require a drilling lockdown sleeve during the drilling operations; however, prior to running the lockdown sleeve, many additional trips are made into the well to verify the position of the hanger in the wellhead. By eliminating the lockdown sleeve, the operator will save multiple trips into the well, therefore, reducing NPT and cost of operations. This is proven by performing well-defined subsea seal/casing hanger testing validation to accurately simulate the installed configuration. Because of this innovative seal assembly design, development of a single trip lock down sleeve was designed for wellhead systems requiring extremely high lock down requirements. The lock down sleeve does not require a trip with a Lead Impression Tool to clean the wellhead and measure the position of pre-installed equipment. This allows the user to save trips previously required by legacy designs, reducing time spent down hole and reducing overall cost. The antiquated claims of not being able to provide metal-to-metal sealing in dynamic applications are dispelled based on performed validation testing of a metal-to-metal seal (with no elastomeric/thermoplastic elements) which accurately represents field scenarios, in which combined pressure/temperature, load and hanger movement are applied. Therefore, the need for costly trips into the well is shown to be unnecessary with the installation of the single trip lockdown sleeve and/or high capacity casing hanger/seal assembly.