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Examples of Well-Plugging Prioritization Considerations: Evaluating Wellbore Integrity and Subsurface Conditions

INTRODUCTION

The second session of the workshop was moderated by workshop planning committee member Mileva Radonjic, Oklahoma State University. It focused on examples of strategies to prioritize well-plugging projects by evaluating wellbore condition (with consideration of integrity issues, historical records, and available data) and subsurface geology (including subsurface fluids surrounding the wells).

EXAMPLES OF PRIORITIZATION CONSIDERATIONS FOR MANAGING PERMANENT END-OF-LIFE SOLUTIONS FOR MARGINAL, IDLED, ORPHANED, AND OTHER WELLS

Dan Arthur, ALL Consulting, explained that understanding the varied risks of marginal, idled, orphaned, and other wells is critical for prioritization efforts. Prioritizing the plugging of more than 3.5 million idled and orphaned wells in the United States is complicated, he continued, owing to challenges related to the Permian Basin water crisis; fresh water shortages; historic plugged-well failures; produced water disposal; development of new resources (e.g., geothermal); and new, complex projects (e.g., carbon dioxide sequestration and hydrogen storage). He explained that understanding the interconnectivity of these and other issues (e.g., methane leaks, groundwater contamination, and oil seepage) might be one of the most significant challenges that the industry and regulators have faced. Furthermore, many discrepancies remain between the number of wells that have been inventoried and the number of wells that exist. For example, he said that in one area of Tulsa, Oklahoma, for every documented well, three to five undocumented wells exist. And within a 20-foot radius, one could expect to find one well but instead find five to six wells drilled to different depths right next to each other.

Given that the first commercial gas well was drilled in 1821 and the first commercial oil well was drilled in 1859, Arthur highlighted the importance of understanding the impacts of corrosion over time. He noted that learning about historical and pre-regulation environments, practices, and standards—and combining that historical knowledge with current perspectives—may help with understanding which wells to address first.

Exploring the prioritization process in more detail, Arthur observed that location is a key factor. He shared an anecdote from 1954 about a Tulsa home filling with gas from an unplugged abandoned well beneath it; additional unplugged wells were found beneath the local elementary school and nearby surface lots. Many oil and gas wells were drilled in now-populated urban areas, including economically disadvantaged communities, and many urban development areas encroached on highly developed oil and gas fields. For instance, in Kellyville, Oklahoma, 275 idled and orphaned wells—many of which are emitting methane—are within only 2 miles of four schools. In more populated areas, he underscored that the problem is even worse.

Arthur indicated that addressing and mitigating the impacts of methane leaks is a serious concern in the United States. He shared images captured by a forward-looking infrared camera from a well on his own property in Hectorville, Oklahoma, with methane leaking through the fittings and valves and migrating through the soil. In some applications, multiple methane flow meters of different ranges are required. He stressed that there is not necessarily a “one-shot fix all” approach, but new technologies are being developed that do volumetrics.

Arthur summarized that well-plugging prioritization is difficult owing to potential impacts to surface water or groundwater; well depth, age, and condition; threats to public health and safety; threats to the environment and wildlife; proximity to people and critical infrastructure; impacts to land and land use; soil impacts, leaks, and spills; and environmental justice issues. He underscored that well-plugging and site restoration is complicated and potentially dangerous work.

ORPHANED WELL-PLUGGING PRIORITIZATION IN WYOMING

Tom Kropatsch, Wyoming Oil and Gas Conservation Commission (WOGCC), provided a brief overview of oil and gas production in Wyoming. Since the first well was drilled in 1884, more than 118,000 wells have been drilled on federal, state, and private lands. Wyoming is ranked seventh overall in oil production and ninth overall in gas production in the United States. With ~60% of the mineral estate in Wyoming owned by the federal government, he noted that significant coordination occurs between state and federal agencies.

The WOGCC was created in 1951 and has operated an orphaned well program for several decades. Since 1997, this program has plugged more than 6,200 oil and gas wells on state and fee land. Since 2013, 500–600 wells have been plugged each year, and since the initial Infrastructure Investment and Jobs Act (IIJA) grant was awarded, 959 wells have been plugged. Kropatsch added that 335 more orphaned wells are under contract to be plugged by the end of 2024, and another 550 orphaned wells will need to be plugged using other funds.

Turning to a discussion of well prioritization, Kropatsch explained that requirements are set by state regulation:

The Supervisor shall establish and maintain a well plugging schedule which prioritizes wells for plugging through an assessment of the well’s potential to adversely impact public health [and] public safety [i.e., well proximity to public, which is less common in Wyoming], surface or ground waters [i.e., environmental impacts, which often can be prioritized first in more remote areas of the state], surface use [i.e., landowner loss of use or impact to operations], or other mineral resources. (055-3 Wyo. Code R. §§ 3-16(f))

He noted that prioritizing based on issues of well integrity involves understanding field and well history. For example, wells in the same field typically exhibit integrity issues at the same depths. Well construction, completions, geology, and fluids interact to contribute to these integrity issues. However, he pointed out that wells drilled later might not have the same cement and formation issues if knowledge from earlier wells was used to change drilling and completion. Understanding all of these factors is important in prioritizing plugging efforts, he continued, especially for wells that have had or may eventually need remedial work. In addition to understanding known issues and any changes made to a drilling program, he pointed to the importance of knowing the operator and how issues were handled, as well as whether routine mechanical integrity tests are being conducted.

Recognizing an area’s geology is another key aspect of understanding well integrity and prioritizing wells for plugging, Kropatsch remarked. For example, salt zones in certain fields can cause casing to collapse, and sour gas zones can create safety issues for workers and the public as well as issues in the casing. He suggested that historical well records, production records, knowledge of nearby problem wells, and knowledge of the type of fluids in a wellbore all help to understand these well-integrity issues and to prioritize appropriately.

Kropatsch indicated that issues of well integrity impact plugging operations because equipment could get stuck in the well; cement squeezes may be necessary to remediate a failed casing; and obstructions, fill, and casing collapse could prevent access at the right depth. Such issues could increase the cost and time required to complete a project as well as decrease the effectiveness of a plug. Therefore, he emphasized the usefulness of understanding the impact of integrity issues on the environment, public health and safety, downhole issues, and plugging conditions prior to prioritization. Wildlife, weather, timing, landowner access restrictions, and surface issues are also considered. Wyoming then uses a ranking system to prioritize plugging wells with the highest potential impacts. He suggested that lower-priority wells of similar type, geography, and plugging requirements could be added to a plugging project for a higher-priority well to help ensure efficient use of funds.

ORPHANED AND ABANDONED WELL-PLUGGING IN PENNSYLVANIA

Don Hegburg, Pennsylvania Department of Environmental Protection (DEP), reiterated that to begin prioritizing wells for plugging, it is important to understand the state’s history of drilling and associated regulations. In Pennsylvania, the first oil well was drilled in 1859. Wooden plugs were used in the early 20th century before modern standards for plugging with cement emerged in the 1950s; currently, Pennsylvania has cement plugging requirements through oil- and gas-producing and coal extraction zones but does not have standards for protection/isolation of other formations that might be useful for mineral extraction or storage/disposal of fluids and gases.

Hegburg noted that DEP’s current inventory includes ~173,000 conventional wells, and its well-plugging program was established in 1985 to plug oil and gas wells without an identifiable responsible party. As mentioned in the first session of the workshop, DEP has documented more than 27,000 abandoned wells and plugged ~3,400 wells over the past 40 years.

Before IIJA funding was available, Hegburg explained that an average of 21 wells were plugged and about $1 million was spent per year in Pennsylvania. Now, the IIJA funding will provide ~$400 million to Pennsylvania to plug orphaned and abandoned wells through 2031, and the budget is expected to be ~$50 million per year for the next 4 years. While the average plugging cost under state contracts from 2014 until 2023 was ~$50,000 per well, he said that since the IIJA contract was issued, that cost has increased to ~$106,000 per well. With the initial IIJA grant, Pennsylvania has plugged 199 wells and plans to plug 26 more wells by the end of 2024.

Hegburg then moved to a discussion about downhole challenges that affect well-plugging. For example, oil and gas wells vary from single to multistring casing designs; some wells are more than 100 years old, without reliable records; and well integrity is often compromised, which causes problems with retrieving casing, reaching total depth, and placing cement plugs. In one example, he cited a pH of 1 to 2 in groundwater in some areas, which would completely deteriorate casing. Several surface challenges also exist, and well access can be a significant cost.

Historically, Hegburg continued, well-plugging priority was determined after conducting site investigations that included assigning a numeric score based on a well’s risk. The primary risks of abandoned wells in Pennsylvania include stray gas migration into homes and private water wells, fugitive methane emissions or hydrogen sulfide releases into the atmosphere, liquid releases into surface water and groundwater resources, casing deterioration through interaction with acidic mine-influenced water, and well communication events during new well completions.

With the IIJA funds, however, Hegburg indicated that the prioritization process for plugging wells is changing. Instead of prioritizing only emergency well-plugging activities, additional funds may allow for the prioritization of methane monitoring and quantification; environmental remediation; undocumented well (estimated around 300,000 in Pennsylvania) discovery with record review, georeferencing, drone surveys, and field verification; environmental justice outreach, including public meetings; and

workforce development. Pennsylvania’s new priority scoring system was developed using ArcGIS Survey123.¹ The scoring system includes 8–10 categories and 20–30 subcategories—for example, proximity to sensitive receptors, buildings, water supply, or sensitive habitats. Inspectors can enter data into the Survey123 app, which the central office can then access and begin to score to inform priority rankings. He stressed that Survey123 is a transparent and justifiable way to support decision-making, and DEP’s public-facing website² tracks project progress and costs and provides emissions data (see Figure 3-1).

RAILROAD COMMISSION OF TEXAS: STANDARD PRACTICES FOR PLUGGING ORPHANED AND ABANDONED WELLS

Danny Sorrells, Railroad Commission of Texas (RRC), noted that the RRC’s well prioritization process has four categories—well completion; wellbore conditions; well location with respect to sensitive areas; and unique environmental, safety, or economic concerns—with subcategories and scores for each. When determining how to score wellbore conditions, for example, he said that an ideal well is one from which the pump, rods, and tubing can be pulled and for which the casing has integrity—a rare find in Texas. Unforeseeable issues include pumps that are stuck downhole, collapsed casing, parted rods or tubing, holes in the casing, and debris in the hole. When determining how to score wells in sensitive areas, one primary concern may be proximity to the public.

Sorrells explained that the RRC’s scoring within these four categories results in a ranking of 1, 2H, 2, 3, or 4 for prioritization; a score of 1, which represents a leaking well, is automatically prioritized for plugging. Inspectors view wells periodically to evaluate whether scores and rankings should be updated.

Sorrells indicated that standard plugging requirements in Texas are based on the Texas Administrative Code (TAC);³ for example, “Wells shall be plugged to ensure that all formations bearing usable quality water, oil, gas, or geothermal resources are protected” (16 TAC §3.14(d)(1)), and “cement plugs shall be set to isolate each productive horizon and usable quality water strata” (16 TAC §3.14(d)(2)). He explained that the tagged plug is the most important plug in the well; the deepest water plug is required to be tagged by tubing, drill pipe, or approval by the district director for wireline (16 TAC §3.14(d)(2)). Furthermore, “plugs shall be placed by circulation or squeeze method through tubing or drill pipe” (16 TAC §3.14(d)(3)), and “all cement for plugging shall be an approved API [American Petroleum Institute] oil well cement without volume extenders” (16 TAC §3.14(d)(4)). Although exceptions may be granted in some cases, the regulations also state that “mud-laden fluid of at least 9 1/2 pounds per gallon with a minimum funnel viscosity of 40 seconds shall be placed in all portions of the well not

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¹ For more information about this tool, see https://www.esri.com/en-us/arcgis/products/arcgis-survey123/overview?srsltid=AfmBOorht1YqAGsGtx8ZdFNs4T_IG9nStnFGZT4CgbE42iU6FRbPxlpZ.

² DEP’s project tracker is available at https://padep-1.maps.arcgis.com/apps/instant/portfolio/index.html?appid=064e373125c34182b2e132dd50d7c619.

³ To view the TAC, see https://texreg.sos.state.tx.us/public/readtac$ext.TacPage?sl=R&app=9&p_dir=&p_rloc=&p_tloc=&p_ploc=&pg=1&p_tac=&ti=16&pt=1&ch=3&rl=14.

filled with cement,” and the wellbore must be static prior to placing the cement plug (16 TAC §3.14(d)(9)). Additionally, “all cement plugs, except the top plug, shall have sufficient slurry volume to fill 100 feet of hole, plus 10% for each 1,000 feet of depth from the ground surface to the bottom of the plug” (16 TAC §3.14(d)(11)) to mitigate potential contamination or pressure issues.

Sorrells also discussed several challenging issues that emerge during well-plugging projects and potential solutions. First, owing to various geological characteristics, specialty cement and mud may be necessary and circulation issues may arise. Second, crossflow, which can be determined with an ultrasonic log or a hydrophone, might require squeezing. Third, pressure issues may necessitate the use of kill mud, cement retainers, or packers. Fourth, cement retainers could be necessary for leaks in casing, while casing mills can help repair collapsed casings, and alignment tools and casing patches can help repair parted casings. He added that leaks often appear not only in the casing but also in packers or tubing, and “push plugs” can be used to address leaks that occur below the required squeeze zone. Sharing a series of project photographs, he emphasized that no single approach to well-plugging exists, and unique issues materialize with each well.

EVALUATING WELLBORE INTEGRITY AND SUBSURFACE CONDITIONS IN ALASKA’S ORPHANED WELLS

Bryan McLellan, Alaska Oil and Gas Conservation Commission (AOGCC),⁴ explained that Alaska’s first known wells were drilled in 1901, and the AOGCC was founded in 1958. Thus, most of the ~50 confirmed or suspected orphaned wells on state and private lands pre-date the AOGCC. Although Alaska did not have a state-level orphaned well program prior to the IIJA, he noted that the Bureau of Land Management (BLM) Legacy Well Program (which does not use IIJA funds) has been plugging a few wells per year in the National Petroleum Reserve–Alaska over the past 5–10 years.

McLellan highlighted the AOGCC’s objectives for plugging wells, including to plug wells according to AOGCC regulations;⁵ ensure that hydrocarbons and freshwater are confined to their indigenous strata and prevented from migrating into other strata or to the surface; prevent contamination of fresh water; and prevent waste of hydrocarbon resources. He stressed that achieving these objectives helps to prevent any risks to public safety. Therefore, one of the AOGCC’s primary goals in allocating IIJA funds is to plug known wells to prevent additional contamination, methane emissions, or waste of hydrocarbons; then, if funds remain, subsequent goals are to remove or remediate reserve pits and remove debris from the sites, and to remediate existing soil or water contamination.

To select which wells to plug first, McLellan indicated that the AOGCC has modeled its scoring and ranking system after the RRC’s, with categories that align with

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⁴ For more information about the AOGCC, see https://www.commerce.alaska.gov/web/aogcc/.

⁵ For more information about the AOGCC’s regulations, see https://www.commerce.alaska.gov/web/aogcc/StatutesandRegulations.aspx.

Alaska’s specific issues. Similar to many other states’ systems, Alaska’s prioritization is risk-based, with leaking wells always being addressed first and efficient use of funding taking precedence (i.e., plugging all wells in a particular area instead of just those at high risk). He explained that wells are ranked and scored based on wellbore condition, reservoir risk, well location with respect to sensitive areas, and logistical and landowner considerations.

McLellan remarked that the first steps in evaluating wellbore integrity and subsurface conditions are to search the AOGCC’s database for records, search U.S. Geological Survey or BLM files for wells drilled before Alaska’s statehood in 1959, search museum records and historical photographs, conduct a title chain search and converse with landowners, and perform site visits. Key questions to consider include whether a well was plugged adequately and how deep the plugs should be. To determine minimum plug depth, he suggested using the pore-pressure/frac gradient tool (see Figure 3-2). In brief, if one starts with the pressure at the depth of the hydrocarbon reservoir and follows a gas gradient (grey line, which represents the pressure inside the wellbore, assuming the wellbore is full of gas) up to the point where the gas gradient intersects the frac gradient curve (orange line, which represents the fracture pressure in the formation outside the wellbore), this point of intersection represents the shallowest safe plug depth. If the plug is set shallower than this depth and the casing corrodes and develops a leak, the pressure inside the wellbore can fracture the rock outside the casing allowing gas to bypass the plug and leak to shallower zones or to the surface via the fractures. Ideally, then the plug would be set below that point, where the pressure inside the well could not exceed the fracture pressure, he said. Even if a leak occurred in the casing below the plug, the gas would likely stay in place (assuming there is annular cement outside the casing) because the rock strength can withstand the pressure below the plug.

The next step before placing plugs, McLellan continued, is for geologists to review mud logs and petrophysical data. To determine subsurface risk and priority, they aim to pinpoint where the freshwater is, if significant hydrocarbons and sources of overpressure exist, where the confining zones are, and how the pore-pressure/frac gradient curves can help. He noted that this geological analysis is then compared with wellbore conditions to understand risk and plugging priority, by reviewing cement records and bond logs, considering the location of existing plugs, and reviewing the well site survey of methane measurements and active leaks or signs of contamination.

PERSPECTIVES FROM THE BUREAU OF LAND MANAGEMENT

Matthew Warren, BLM, conveyed that BLM manages more than 245 million surface acres and more than 700 million subsurface acres across the United States. It has a trust responsibility for managing oil and gas on Indian lands, except for those of the Osage Nation. BLM is also the permitting agency for all federally managed minerals onshore under all surface estates (including those that are privately owned). He noted that BLM’s orphaned well-plugging program emerged in 1976 when it started managing the U.S. onshore oil and gas program, and BLM currently manages more than 95,000 unplugged wellbores, including 8,500 federal idled wells, and 70 unplugged federal orphaned wells.

Warren indicated that prioritization begins with consideration of the downhole integrity of idled wells, which the IIJA defines as those that have been inactive for 4 or more years and have no future beneficial use. BLM’s 2020 Instruction Memorandum Idled Well Reviews and Data Entry⁶ provides policy and guidance for conducting idled well reviews. He remarked that the highest priority generally is given to wells that have been idle for at least 50 years, followed by those that have been idle for 25–50 years. In the first half of fiscal year 2024, 427 idled wells were plugged or reclaimed; 252 idled wells were returned to production; and 609 new wells were added to the idled well count, resulting in a net decrease of 70 idled wells. He explained that BLM office staff are required to review 20% of idled wells each year via policy, and BLM field inspection staff review 40% of idled wells rated as highest priority each year.

Although BLM dedicates much time to idled wells, Warren said that BLM also plays a role in plugging orphaned wells. The IIJA defines orphaned wells as those with no “liable party”⁷ responsible for plugging, which BLM must plug and reclaim. BLM also has agreements with Wyoming and New Mexico to plug wells, and BLM’s 2021 Instruction Memorandum Orphaned Well Identification, Prioritization, and Plugging and Reclamation⁸ provides policy and guidance for the identification and prioritization of orphaned wells. This document includes priority rankings—for example, whether the well is leaking at the surface or a problem with pressure exists, whether the wellbore configuration is known or unknown, how old the well is, whether surface contamination exists, if additional equipment or existing infrastructure are present, whether hydrogen sulfide is present, how close surface waters and water wells are, and whether a National Environmental Policy Act review has been completed.

BLM’s specific regulations for plugging oil and gas wells can be found at 43 CFR 3172.12. Warren remarked that minimum requirements include that “all formations bearing usable-quality water, oil, gas, or geothermal resources, and/or a prospectively valuable deposit of minerals shall be protected”; that “cement is the default isolating medium”; and that, according to BLM processes, plugging operations must be approved by BLM prior to starting operations.

Before closing, Warren provided a brief overview of issues related to bonding. BLM’s most recent leasing rule includes new bonding amounts: $500,000 for every statewide bond and $150,000 for every lease bond. BLM also maintains federal bonds and reviews Indian land bonds at the request of the Bureau of Indian Affairs. He pointed out that idled wells increase the amount of bond required, depending on an operator’s percentage of idled wells.

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⁶ This Instruction Memorandum is available at https://www.blm.gov/policy/im-2020-006.

⁷ For BLM, liable parties’ responsibilities date back to when the well was drilled, even if the lease rights were sold or transferred, which differs from many states and may take a couple of years to pursue previous owners.

⁸ This Instruction Memorandum is available at https://www.blm.gov/policy/im-2021-039#:~:text=This%20IM%20defines%20an%20orphaned,cost%20for%20permanent%20well%20plugging%2C.

OPEN DISCUSSION

Radonjic moderated a discussion among the workshop speakers and participants. An online participant inquired about public partnerships for well-plugging activities in Pennsylvania. Hegburg replied that community outreach and engagement will be a key use of IIJA funds; his team has identified potential partners such as nongovernmental organizations and university extensions and will be conducting outreach sessions to discuss future plans, highlight the “plugging 101” process, and gather input.

James Saiers, Yale University, observed that some states prioritize plugging wells that exhibit a threat to groundwater or are in close proximity to water supply wells for households. He wondered if any states are conducting far-field monitoring of groundwater quality in areas with compromised wells. Kropatsch said that Wyoming is not currently conducting this kind of monitoring, primarily owing to the remoteness of its wells and their distance from water wells. Warren added that BLM is not conducting far-field monitoring either, but if indications are available from nearby wells, those become part of an analysis for prioritization. Hegburg explained that in Pennsylvania, wells are inspected as contracts are prepared. When a water supply is located nearby, pre-drill sampling is conducted to prepare for any issues that might arise during plugging. Eric van Oort, University of Texas at Austin, encouraged the use of data to make prioritization decisions and suggested incorporating artificial intelligence (AI) and machine learning to determine which wells are currently or could become problematic with leaks. Arthur mentioned that the Department of Energy is working on AI solutions for prioritization.

An online participant posed the following question: If a well operator is prevented from managing a well and Pennsylvania declares that well abandoned, does that operator have the right to rehabilitate the well instead of plugging it? Hegburg responded that stringent rules exist to declare a well “abandoned,” and the landowner will be notified if a well deemed abandoned is going to be plugged. He urged operators to maintain familiarity with all state rules and regulations.

Dwayne Purvis, Purvis Energy Advisors, asked what data are helpful for labeling an orphaned well “documented” versus “undocumented” and whether some wells could be labeled “partially documented.” Hegburg noted that he refers to the Department of the Interior’s guidelines, which are based on locational data, to determine whether a well can be considered “documented.” Workshop planning committee member Mary Kang, McGill University, added that data provided by the states on documented orphaned wells are often missing information on depth, type, and last production date. Purvis proposed developing a common taxonomy with clear thresholds by which wells can be counted as documented, undocumented, and partially documented. However, Radonjic highlighted the value of flexibility because states have different practices, cultural foci, and historical issues that affect what data can be collected.