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Hundreds of thousands of documented and undocumented orphaned oil and gas wells exist in the United States (U.S.). These wells have the potential to contaminate water supplies, degrade ecosystems, and emit methane and other air pollutants. Thus, orphaned wells present risks to climate stability and to environmental and human health, which can be reduced by plugging. To quantify environmental risks and opportunities of well plugging at the national level, we analyze data on 81 857 documented orphaned wells across the U.S. We find that > 4.6 million people live within 1 km of a documented orphaned well. 35% of the documented orphaned wells are located within 1 km of a domestic groundwater well, yet only 8% of the wells have groundwater quality data within a 1 km radius. Methane emissions from the documented orphaned wells represent approximately 3%–6% of total U.S. methane emissions from abandoned oil and gas wells, but this estimate is based on measurements at < 0.03% of U.S. abandoned wells. 91% of the documented orphaned wells overlie formations favorable for geologic storage of carbon dioxide and hydrogen, meaning that orphaned well plugging can reduce leakage risks from future storage projects. Finally, we estimate plugging costs for documented orphaned wells to exceed the $4.7 billion federal funding by 30%–80%, emphasizing the importance of prioritizing federal spending on wells with large remediation benefits. Overall, environmental monitoring data are not extensive enough to quantify risks, especially those related to air and water quality and human health. Plugging orphaned wells can provide opportunities for geologic storage of carbon dioxide and hydrogen and geothermal energy development, thereby facilitating efforts to transition to net-zero energy systems. Our analysis on environmental risks and opportunities of orphaned wells provides a framework that can be used to manage the millions of documented and undocumented orphaned wells in the U.S. and abroad.

Hydrated bentonite is considered an alternative subsurface sealing/plugging material for deep geo-energy wells. However, the knowledge related to this application and the corresponding properties of bentonite is still lacking. This includes the mechanical properties at the interface of bentonite plugs with the adjacent materials (surrounding rock or casing steel) and the mechanical stability of plugs under downhole in-situ conditions. In this work, we performed experiments investigating the interface shear properties and shear strength of a bentonite plug under various settings for deep geo-energy applications, such as hydrocarbon and geothermal wells. The interface’s shear properties against various adjacent materials and fluid conditions were characterized. The influence of chemical exposure, the salinity of the curing fluid, fluid pH, pressure, and temperature on bentonite’s mechanical stability was evaluated in a small- and large-scale setting. The latter was performed using realistic casing sizes and placement methods, relevant for the field application. The experimental results show that the averaged shear strength of the bentonite plug interface is 13.3 kPa and 9.1 kPa when cured in freshwater and seawater, respectively. The increase in strength with increasing curing pressure, temperature, and fluid pH was characterized for the first time. The interfacial properties of cohesion and friction angle vary with different surrounding materials. They are also influenced by the saturating condition and salinity of the saturating fluid. Based on the experimental results, a bentonite plug with a minimum length of 15–43 m placed in casings of 7–5/8″ to 13–3/8″ would be sufficient to meet the necessary criteria of the Dutch regulators as an isolating material for well abandonment.HighlightsThe bentonite’s mechanical stability for plugging operations in deep geo-energy wells and the properties of the bentonite interface are evaluated under different in-situ downhole conditions..The interfacial shear strength of bentonite plugs cured in freshwater and seawater is approximately 13.3 kPa and 9.1 kPa.A bentonite plug with a minimum length between 15 and 43 m, varied with casing sizes, would comply with the verification requirement of the Dutch regulators to seal deep geo-energy wells permanently.

The continuous exploration and development of oil wells increases the risk of leakage from abandoned wells and brings challenges to the traditional plugging and abandonment technology. In order to overcome the above problems, a thermite plugging and abandonment technology is proposed in this field. The technology uses the aluminothermic reaction to melt the original or set material for sealing. The natural convection under different confinement conditions directly affects the heat flux transfer in the heat transfer process. In order to study the melting effect of the thermite reaction on sandstone, based on the heat conduction theory, a heat conduction model based on the temperature release law of the thermite reaction was established. The numerical simulation results show that the surrounding heat transfer conditions are the key factors affecting the heat transfer effect in the axial and radial directions without considering the particle size and dosage of the thermite itself. This work is of great significance for studying the temperature law of thermite reaction release and the future research of thermite plugging and abandonment technology.

A three-dimensional finite element model of stratum-cement ring-casing-cement plug was established for the failure analysis of the cement plug seal in the abandoned oil and gas wells. The mechanical parameters, length, bottom fluid pressure and casing swaging length of the cement plug under non-uniform ground stress conditions were analyzed. The results showed that when the bottom of the cement plug was subjected to fluid pressure, the stress at the interface between the cement plug and the casing increased, and thereby the cement plug at the bottom and the cementation of the casing failed, resulting in a the decrease in the sealing performance of the cement plug, which may be sealed under fluid corrosion. As the modulus of elasticity and the radius of the cement plug increased, the cement plug stress and the cement failure length increased. As the cement plug length increased, the cement plug stress and the cement failure length decreased, while Poisson's ratio for the cement plug stress and the cement failure length increased. The increase of the bottom fluid pressure could increase the cement plug stress and the cementation failure length. In the abandoned well, where the casing was forged and then grinded after the casing was forged, the length of the casing milling increased, the plug stress of cement reduced. These findings can provide insightful potentials for the parameters of cement plugs when the cement plugs are closed in the offshore oil and gas wells.

A wave of oil and gas wells drilled in the last 50 years are reaching the end of their useful life. These wells require attention to be plugged and abandoned in a safe manner to avoid costly liabilities for oil companies. However, plugging and abandonment represent an unwanted but necessary cost to the industry. Any improvements in efficiency and reduction of cost in this activity would deliver significant financial benefits to the oil companies and the tax payers, since in many cases these activities are subsidized through government fiscal regimes. A traditional section milling job is time-consuming. Typically, it takes 10 days to 14 days to perform a 50-m (164-ft) section milling operation using an expensive drilling rig.