Understanding Leakage Rates in Permanently Abandoned Wells by Studying Natural Hydrocarbon Seepages

Master's thesis in Petroleum engineering.Permanent plug and abandonment (PP&A) of wells is steadily becoming more important on the Norwegian Continental Shelf (NCS), as a large number of fields are approaching end of their productive life. Combining operational, material, and qualification challenges, it is evident that risk of leaks exists from permanently abandoned wells. To ensure the protection of our environment, well integrity standard NORSOK D-010 constitutes zero leak acceptance criteria; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. To evaluate the fate of leaking oil and/or gas from abandoned wells, two real cases from the NCS, one historical gas leak (Field A) and one theoretical oil leak (Field B), have been subject to fate analysis, executed using software from SINTEF Ocean’s Marine Environmental Modeling Workbench (MEMW). For Field A, it is found that approximately 95 to 99% of the leaking gas dissolves while rising through the water column. The fraction of gas transported to atmosphere is a function of the initial gas bubble size and ambient temperature. The fate of oil is more complex than gas, but results show that due to its persistent nature, released oil will be able to travel more than hundred kilometers away from the release point. Due to this dispersion, concentrations, the main factor controlling toxicity, will be greatly diluted. Fate of oil is dependent on chemical composition; lighter compounds will evaporate to the atmosphere, while heavy compounds will be deposited on the seafloor. Evaporation, sedimentation and biodegradation are the main contributing mechanisms in fate analysis of oil

The fate of hydrocarbon leaks from plugged and abandoned wells by means of natural seepages

When a well reaches the end of its productive life, it is permanently plugged and abandoned. Even though new technology and verification methods are being evaluated, it is evident that operational, barrier material and qualification challenges together contribute to risk of leaks from abandoned wells or wells to be abandoned in future. Most regulatory authorities constitute zero leak acceptance criteria to protect the environment; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. In this study, we conducted a theoretical comparison between leaking wells and natural seeps and suggest conducting a fate analysis is appropriate to provide necessary data for evaluating environmental implications of leaking wells. Two case studies were analyzed using SINTEF Ocean's OSCAR (Oil Spill Contingency And Response) software; one historical gas leak (Field A) and a theoretical oil leak (Field B). It is found that for releases of natural gas, 95–99% dissolve in the ocean, and the fraction of gas reaching the atmosphere is dependent on the initial gas bubble size. Fate of oil is more complex than gas, but evaporation, sedimentation and biodegradation are the main contributing mechanisms in the fate of hydrocarbon analysis.publishedVersio

The fate of hydrocarbon leaks from plugged and abandoned wells by means of natural seepages

When a well reaches the end of its productive life, it is permanently plugged and abandoned. Even though new technology and verification methods are being evaluated, it is evident that operational, barrier material and qualification challenges together contribute to risk of leaks from abandoned wells or wells to be abandoned in future. Most regulatory authorities constitute zero leak acceptance criteria to protect the environment; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. In this study, we conducted a theoretical comparison between leaking wells and natural seeps and suggest conducting a fate analysis is appropriate to provide necessary data for evaluating environmental implications of leaking wells. Two case studies were analyzed using SINTEF Ocean's OSCAR (Oil Spill Contingency And Response) software; one historical gas leak (Field A) and a theoretical oil leak (Field B). It is found that for releases of natural gas, 95–99% dissolve in the ocean, and the fraction of gas reaching the atmosphere is dependent on the initial gas bubble size. Fate of oil is more complex than gas, but evaporation, sedimentation and biodegradation are the main contributing mechanisms in the fate of hydrocarbon analysis

The fate of hydrocarbon leaks from plugged and abandoned wells by means of natural seepages

When a well reaches the end of its productive life, it is permanently plugged and abandoned. Even though new technology and verification methods are being evaluated, it is evident that operational, barrier material and qualification challenges together contribute to risk of leaks from abandoned wells or wells to be abandoned in future. Most regulatory authorities constitute zero leak acceptance criteria to protect the environment; however, natural hydrocarbon seepages are occurring all over the world on a daily basis. In this study, we conducted a theoretical comparison between leaking wells and natural seeps and suggest conducting a fate analysis is appropriate to provide necessary data for evaluating environmental implications of leaking wells. Two case studies were analyzed using SINTEF Ocean's OSCAR (Oil Spill Contingency And Response) software; one historical gas leak (Field A) and a theoretical oil leak (Field B). It is found that for releases of natural gas, 95–99% dissolve in the ocean, and the fraction of gas reaching the atmosphere is dependent on the initial gas bubble size. Fate of oil is more complex than gas, but evaporation, sedimentation and biodegradation are the main contributing mechanisms in the fate of hydrocarbon analysis