Written By Kennedy Metcalf August 22, 2023
Introduction:
Plug and abandonment is a critical aspect of the life of an oil well. When wells are no longer economic or productive, operators should begin drawing up engineering plans to permanently retire the well and decommission the associated facility. The objective of plugging a well is to isolate the producing formation and any other hydrocarbon-bearing zones from the surface, groundwater table, and other potential aquifers downhole to prevent contamination of potable water sources or surface areas. Plugging wells can be complex and calls for collaboration between landmen, engineers, geologists, and the field operations team. As more funding has been devoted toward addressing orphaned wells across the United States, the need for plugging wells correctly and efficiently has only increased.
This graphic is from Saskatchewan Research Council
The Process of Plugging:
Plugging wells can be a difficult task as Taylor Heffner, a petroleum engineer with Carbon Shield explains, each well has a unique set of circumstances that require careful consideration and sound front-end engineering plans. Wells may vary in depth, orientation, location, age, number of hydrocarbon-bearing zones and aquifers present, type of artificial lift at the surface and downhole, and the condition of surface infrastructure, to name a few. All plugging efforts are subject to federal and state regulations (US DOL). Plugging regulations may vary from state to state but all typically require a combination of mechanical and/or cement plugs to be placed within the wellbore to prevent the migration of hydrocarbons and produced water from one formation to another (US DOL).
Once a well has been identified as in need of plugging:
· The first step is to remove all infrastructure from production that may be present. Additionally, all necessary equipment like workover rigs, pumps, tanks, wireline trucks, and cement trucks need to be in place for the operations.
· Then, it is essential to clear or blow down any remaining pressure in the well to ensure that the wellbore conditions are near static before rigging up. Flowback incinerators or enclosed combustion devices may be required to prevent the release of hydrocarbons and other gases into the atmosphere. Freshwater or mud is then pumped into the well to eliminate any remaining pressure on the well.
· Next, the workover rig will disassemble (nipple down) the wellhead and install (nipple up) the blowout preventer, or BOP, before removing any tubing that is left in the casing. A mechanical and/or cement plug is usually set above the producing formation to provide zonal isolation and allow for the casing to be pressure tested before continuing with P&A operations. Pressure tests are an important step in ensuring casing integrity and confirming that the plugging procedure may be executed as planned. Prior to setting any plugs downhole, it is necessary to review the cement bond log, or CBL, of a well that displays the extent of the cement that exists behind the production casing that was set when the well was originally drilled or during remedial operations afterward. Existing cement behind the pipe will largely determine the method and depth at which cement and/or mechanical plugs are set during plugging operations.
· Plugging procedures may vary widely from well to well, but typically involve a combination of cement and/or mechanical plugs set at specific intervals throughout the wellbore to provide adequate zonal isolation between all hydrocarbon-bearing zones and potential aquifers further up hole. In any case, all plugging procedures must adhere to state regulations and federal regulations where applicable.
· Once zonal isolation from the producing formation, hydrocarbon-bearing zones, potential freshwater aquifers, and groundwater has been achieved, operators are required to submit subsequent plugging documentation to the appropriate regulatory body confirming that the well was plugged according to state and/or federally approved plans. Documentation may include cement and wireline tickets, cement bond logs, pressure test records, and daily rig reports.
This image is from The Colorado Sun. Pictured is a workover rig on a well.
Plugging Orphaned Wells:
It typically takes about a week to plug a well once the rig and associated plugging equipment arrives on location. However, with orphaned wells, plugging may be much more time-consuming. Heffner mentions that orphaned wells can often be more costly and require more time to plug than wells that were productive within the last year. This is oftentimes due to the degradation of the infrastructure within the well, settling of solids within the liquid column on top of downhole equipment, or buildup of paraffin or other solids. Some orphaned wells have been sitting for decades (Webb 2023), which can pose unique problems for plugging operations. The metal casing inside the well may deteriorate with time and exposure to hydrocarbons and other produced fluids. Depending on the condition of the well, plugging operators may need to address several issues, whether downhole or at the surface, which could prolong plugging and decommissioning activities.
Conclusion:
Plugging wells safely, effectively, and efficiently is a vital step toward reducing the potential for danger associated with inactive wells. Orphaned wells especially pose a risk to people as they could pollute water sources and emit methane and other harmful compounds. The process of plugging a well may vary considering the nature of the specific well, but regulation requires certain safety measures to ensure that after a well has been plugged, zonal isolation provided during well plug and abandonment will prohibit the migration of hydrocarbons or other formation fluids.
References:
Jaffe, Mark. Najmabadi, Shannon. 2022. “An Oil and Gas company wants to plug four idle wells. The wells could end up owned by the troubled Colorado Operator instead.” Accessed July 31, 2023. https://coloradosun.com/2022/01/20/kp-kauffman-oil-gas-transfers/
SRC Communications. 2019. “Drilling Through Advancements in Oil Production”. Accessed July 31, 2023.https://www.src.sk.ca/blog/drilling-through-advancements-oil-production
United States Department of Labor. N.d. “Oil and Gas Well Drilling and Servicing”. Accessed July 31. 2023. https://www.osha.gov/etools/oil-and-gas/abandoning-well
Webb, Shelby. 2023. “States Struggle to Plug Oil Wells with Infrastructure law cash”. Energy Wire News. Accessed July 31, 2023. https://www.eenews.net/articles/states-struggle-to-plug-oil-wells-with-infrastructure-law-cash/
