Plug and abandonment of oil and gas wells – A comprehensive review of regulations, practices, and related impact of materials selection
Augustine Okechukwu Chukwuemeka, Gbenga Oluyemi, Auwalu I. Mohammed, James Njuguna
Abstract
This paper reviews the state of research in permanent barrier materials for plug and abandonment of oil and gas wells to identify key strengths and weaknesses of each barrier material and understand the impact of reservoir conditions and fluids on barrier failures. The influence of regulatory requirements on P and A practices and the impact of selected barrier material on possible repurposing of depleted reservoirs for hydrogen and CO2 storage are also discussed. This review reveals that previous studies in these areas have focused primarily on improving plug placement and durability without significant consideration of the potential for long term development of leakage paths in the old wellbore infrastructure (cement and casing) whose surfaces remain exposed to reservoir fluids below the permanent plug after conventional P and A. The need for a new approach to plug and abandonment materials selection and reengineering of materials placement methods to ensure permanent isolation of reservoir fluids from existing well infrastructure is herein identified especially as the stock of wells nearing their end of life grows on a global scale. A summary of studies in the accelerated degradation of Portland cement in the presence of corrosive reservoir fluid under high temperature and pressure conditions is also presented. This will significantly drive research in materials selection for alternative barrier as HPHT wells mature for permanent abandonment.