Thermal Shock Transient Analysis for Well Integrity Through Operational Envelope

Abstract

Abstract A physical evidence of an injector well failure caused by transient thermal behavior in cooling operations has lead to technical actions in order to provide a safe operational envelope. A modified thermal analysis was developed to predict the transient thermal behavior that can result in a cascade casing collapse. The as built approach was applied in a number of wells already constructed in a Brazilian offshore field resulting in a better way for selecting which mitigation method can be appropriate for each case. One of the main results from the study was to establish a controlled injection flow rate in order to avoid a cascade casing collapse due to thermal shock in the wellbore. In some cases, it was necessary to provide an annulus pressure communication in the wellhead using a ROV for bleeding off the excessive pressure in C annulus. With these actions, the wells studied were able to present a safe operational envelope. The approach commonly employed in the industry takes into account just steady state injection operations, which are not enough to describe what is happening in the field and also are not sufficient to support a suitable casing design. The industry must put efforts to develop and consolidate a methodology based on transient thermal analysis to deal with thermal shock events in the well, as proposed in this paper. Furthermore, this work also proposes four alternatives to mitigate the well integrity loss based on the transient thermal simulations and a comprehensive well risk assessement.