Use of Novel Test Setup to Simulate WAGI Well Flow Conditions for Corrosion Management
Authors: Kumar Amit , Willingham Thomas , Wang Zhihua , Kohata Akihiro , Alsowaidi Alunood , AlDaghar Tareq , Troshko Andrey , Fischer David , Pacheco Jorge 
Published: January 2020

Water-alternating-gas-injection (WAGI) pilot wells are planned to be drilled in a giant offshore oil field in Abu Dhabi. To minimize pilot well cost, carbon steel is considered as one of the potential materials. Planned WAGI wells will have extremely long horizontal completions, and the incomplete displacement of water during gas,water displacement cycle may lead to significant corrosion. This paper describes the corrosion management methodology used to make material selection and corrosion control related decisions for pilot WAGI wells.

A key aspect of the methodology is its structured approach that combines science-based corrosion modeling with field-specific laboratory testing and surveillance data. The corrosion models have been extensively validated with laboratory and field data, and are applied in conjunction with flow models to enable full wellbore corrosion predictions. Computational Fluid Dynamics (CFD) was used to simulate gas,water displacement efficiency. The laboratory testing was conducted in specialized high pressure, high temperature autoclave test cells. A corrosion testing program was created to reproduce corrosion conditions during incomplete gas-water displacement. Corrosion inhibition effectiveness as part of corrosion control strategy was also evaluated.

During the WAG gas injection cycle, the hydrocarbon gas contains CO2; hence, there is the potential for corrosion due to water hold up in the well from either incomplete displacement of injected seawater or due to cross flow from the reservoir. Any damage to completion due to corrosion may affect the injection profile and may result in an underperforming injector. Moreover, deposition of corrosion products may lead to a reduction or even a complete loss of injectivity in some zones.

Lab test results show that corrosion due to a long term gas-water wellbore mixing can lead to completion corrosion within few WAG cycles. Effect of water splashing and intermittent wetting on corrosion due to high gas flow during gas,water displacement cycle was also evaluated. Results show that submerged (continuous) and splashing (intermittent) exposure to CO2-containing seawater under WAG cycle conditions can create a very high corrosion risks for carbon steel. However, corrosion due to incomplete gas-water displacement mixing can be mitigated by injecting an optimal corrosion inhibitor prior to WAG switchover.

Test setup demonstrates an innovative approach to replicate anticipated flow environment in WAGI wells in the laboratory. CFD model incorporates the key physical drivers envisioned in the WAGI process and includes modeling of the gas-water interface evolution and gas leaking into the formation. Learnings from this study will be deployed in the field in form of a corrosion management strategy, deployed completion design and surveillance plans to manage corrosion risks, extend well-life and ensure long-term WAGI reliability.