Abstract The decommissioning of oil and gas wells at the end of their economic life is a critical operation in the oil and gas industry. Decommissioning sees an increased scrutiny regarding its long-term environmental impact. It requires full isolation across the entire wellbore including the formation to casing and across all annuli or tubing. To improve time- and cost-efficient abandonment and to provide ‘rock-to-rock’ isolation, the decommissioning requires data and expertise across a large number of areas. The decommissioning process starts with assessing the wells to understand the asset current conditions and potential risks. The planning for abandonment starts with the analysis of the last operating years operations and well productivity. Followed by a detailed log evaluation to identify existing annular isolation, lack of isolation and potential casing corrosion. Based on this data, an abandonment plan is created to fulfill any internal and regulatory requirements. The plan includes cement plugs to provide isolation across potential hydrocarbon zones and aquifers; casing retrieval / casing cutting; placing appropriate well barriers; and ends with a location restoration and monitoring. The primary objective is to create a seal that will prevent fluids from migrating past the reservoir sections based on the well depth and geological conditions. To improve efficiency, a detailed plan is prepared to set the cement plugs and required remediations using most of the time specialty tools like perforate, wash and cement in stretches showing poor isolation behind the production casing, casing patches, cement squeezes, down hole tools, among others. Plug lengths and plug placement are always optimized to limit the wait on cement but at the same time to identify, address any operational risks and comply with any necessary isolation testing. Cement plugs are placed in a method to reduce and eliminate the need for costly aqueous fluids left in the wellbore after the well decommissioning which includes corrosion inhibitors, oxygen scavengers, stabilizers for different depths and temperatures. Proprietary software is utilized to minimize fluid contamination and simulation results are used to optimize lab testing. A detailed validation of well barriers is agreed to comply with regulations to provide long term isolation after the well abandonment and avoid leakage of formation fluids and gases to the atmosphere or surface. This new process has now been standardized by various operators in the region. As wells are safely and responsibly plugged and abandoned, leaving no concerns regarding the long-term environmental impact of retired assets, particularly those close to social centers and with any risk of unplanned formation fluid emissions. The novel and optimized approach has provided both a time saving of 36% time and by optimizing the fluid requirements and logistics, the total well abandonment costs has reduced by 28%.
Hurtado et al. (Mon,) studied this question.