Salt Creeping Analysis on Deepwater Wells Submitted to Cooling Operations on Trapped Annular

Abstract

Abstract This paper presents the finite element analysis of salt-creep behavior on deepwater wells with trapped annulus, considering cooling effects caused by injection operations. In addition, this effect was considered coupled with salt-creep behavior and its influence on casing collapse design under transient and steady state well operation. The scenarios of injection flow rate and temperature profile were analyzed using the coupled approach, for salt creeping and thermal trapped annulus. The wellbore profile is a typical Pre Salt Brazilian Offshore, where rock salt layer is confined under two casing shoes. The injection wells operation results in a pressure decrease in a confined annulus due to thermal cooling between casing and salt formation. Due to this pressure drop on the trapped annulus, the salt creeping behavior tends to increase, and proper casing stress verification must be done. The finite elements analysis for salt creeping was modeled using commercial finite elements software package, and thermal profile for transient and steady state injection was obtained using thermal casing design software. The coupled effects were evaluated using commercial casing design software. Preliminary studies have shown that there is a great influence on the salt creeping response on confined annulus when subjected to a pressure decrease due to thermal cooling on trapped annulus, caused by water injection operation. It is observed that there is a growth of the confined annular pressure due to salt creeping effects and that there is an acceleration in this phenomenon. The analysis also shows that casing collapse safety margin is time dependent considering a given operation. After well shutdown, the natural heating of the confined annulus occurs due to geothermal effects, and this pressure is added to the trapped annulus, increasing the pressure of trapped annulus. The final pressure is the sum of the salt pressure build up accelerated by the cooling steady state regime and geothermal pressure build up, during shutdown. The worst case scenario could be during restart the well injection, in that way, this kind of situation must be analyzed, so that it does not lead to critical situations on the casing design. Historically, according to literature review, only the annular pressure build up with production heating is analyzed. This work is a novel approach where annular pressure drop off, caused by cooling operations, was investigated including coupled salt-creeping and thermal phenomenon.