Establishing Best Practices for Well Abandonment in CCS

Abstract

Abstract In CO2 storage sites, wells located within the predicted area of review, and that penetrate the confining zone, may become a leakage pathway out of the injection zone if not properly abandoned. Prior to injection, the abandonment focus is on existing (legacy) wells. After injection has concluded, the focus will expand to include storage development wells, e.g., injector and monitoring wells. Unlike oil and gas developments, where formation fluids are produced, Carbon Capture and Sequestration (CCS) projects inject CO2 into downhole formations, creating a plume that must be contained within the target reservoirs for periods of time that are longer than oil and gas wells’ life span. These differences make it necessary to develop CCS-specific well abandonment practices. The authors have analyzed industry-accepted well abandonment standards, abandonment recommendations and requirements from regulators for CCS projects, and several case studies and laboratory experiments on well integrity to develop an understanding of the challenges and probable solutions for CCS well abandonment. Then, a recommended practice for well abandonment in CO2 storage sites that addresses isolation of the confining and reservoir zones, the effects of a CO2-rich environment on well materials, and corrective action for legacy wells will be presented. Most of the existing regulations and standards on CCS establish expectations and objectives for well abandonment without providing detailed guidelines that can be consistently applied across projects. Without consistent rules for CCS well abandonment, project teams will conduct design or planning exercises that will have varying outcomes as they adapt conventional well abandonment guidelines to CO2 storage site requirements. This may result in under- or over-designing the well abandonment; which could translate into compromised well integrity, impact on project value; and an ever-changing technical standpoint. The aim of a recommended practice is to establish simple high-level principles with which to approach well abandonment in CO2 storage sites to facilitate the work of project teams and to have an acceptable level of consistency on abandonment plans. This paper will demonstrate a comprehensive abandonment strategy for CCS and legacy wells. The strategy addresses CCS-related containment concerns and local applicable abandonment regulations for all other sources of inflow not related to CCS. It discusses how the ability of a confining zone to stop the flux of CO2 through it, that depends on its permeability, thickness and capillary pressure; is relevant for establishing CCS abandonment principles.