4

Examples of Procedures and Best Practices for Wellbores

INTRODUCTION

During the third session of the workshop, moderated by workshop planning committee member Nathan Meehan, Texas A&M University, experts from industry shared examples of lessons learned and best practices for plugging orphaned wells.

CHALLENGES TO PLUGGING ORPHANED WELLS

Steve Plants, Plants and Goodwin, Inc., commented that while well-plugging may not be the most exciting part of the oil and gas industry, it is an important process for operators and regulators to avoid potentially costly mistakes. He also highlighted a historical disconnect between the industry and regulators and between the industry and environmental activists. However, he pointed out that the orphaned wells problem has improved cooperation and collaboration significantly, which could enable greater success.

Plants next discussed four challenges that contractors face when plugging orphaned wells. The first challenge relates to access. For example, as discussed in the previous session of the workshop, the surface owner is often not the same person or entity as the mineral rights owner, especially in the Appalachian Basin. Therefore, when orphaned wells are on private land, contractors’ interactions with landowners are critical. Overhead power lines present another access issue when plugging wells, as utility companies may be hesitant to shut off power and relocate lines, especially given the associated high costs. Underground utilities (e.g., gas lines, water lines, sewer lines, fiber optic cable) also pose challenges. Furthermore, environmentally sensitive areas are important to consider when plugging wells, many of which were drilled long before people were concerned about preserving wetlands, for example. He added that topography (e.g.,

steep or remote areas) also creates access challenges, as do road stability (i.e., with equipment that weighs 100,000 lb per piece) and aboveground structures.

A second challenge that plugging contractors confront relates to well control, which Plants suggested is not discussed enough. Some of the elements of well control include casing integrity, a functioning wellhead, use of hot taps to access wells with unknown pressure, creation of barrier policies that protect contractors, and use of kill fluid.

Plants highlighted wellbore obstructions as a third challenge for contractors. In other words, not having well records; dealing with older wells; working with an open well casing that allows access to passerby who throw things in the well; finding unknown equipment left in the well at abandonment; encountering circulation issues; and lacking fishing, milling, and other specialty tools can all create difficult well-plugging situations.

Finally, cost is likely a significant challenge for contractors, and Plants explained that access issues, well control issues, and wellbore obstructions all increase cost. He suggested that cost per foot is an ineffective unit of measurement to determine the cost of plugging a well; for example, a shallow well might have more problems and thus cost more to plug than a deeper well. He proposed that a more effective strategy to determine cost starts with considering the goal—whether that means plugging wells at low cost, plugging wells only once, keeping workers safe, and/or meeting minimum standards (i.e., developing erosion and sediment controls, testing cement, tagging plugs, tracking waste disposal, and conditioning wellbores).

Plants suggested the following example operating procedure for plugging and abandonment: (1) verifying that all required permits are in place; (2) making notifications; (3) developing an emergency response plan; (4) conducting a pre-construction site visit; (5) completing access road and well pad construction; (6) assessing wellhead/cellar; (7) move the plugging rig and ancillary equipment on to the site and set up for operations; (8) cleaning out to total depth; (9) cementing bottomhole plug; (10) conducting wireline logs, cut casing, and/or shoot perforations based on well construction; (11) pulling uncemented casing; (12) pumping remaining cement plugs; and (13) reclaiming the location and access road.

EXAMPLE LEARNINGS FROM GULF OF MEXICO PLUGGING AND ABANDONMENT EXPERIENCE

Drew Hunger, Seashore Petroleum, LLC, reaffirmed Plants’s comments on the challenges confronted by plugging contractors. For example, between 2011 and 2013, upon entering 10 wells plugged and abandoned by a previous operator that were leaking, he found at least 1,000 psi in four of the wells. In particular, the Gulf of Mexico has many temporarily abandoned wells with sustained casing pressure. He described two catastrophic failures related to carbon dioxide floods from previously plugged and abandoned wells in Louisiana and Mississippi, multiple plugging and abandonment failures in West Texas, and a significant well blowout in Colorado in 2023. He shared his concern that the number of plugged and abandoned wells now leaking across the United States is indicative of a significant problem.

Hunger then highlighted the importance of “bubbles.” He explained that bubbles migrate upward due to buoyancy, regardless of pressure and fluid in a plugged and abandoned well. As bubbles migrate upward from a leaking lower plug and collect under an effective shallow plug, problems and risks arise. The bubbles build pressure equivalent to the reservoir pressure over time (in weeks or in decades) as the trapped gas volume increases and pushes fluid out of the well. Well control kick calculations indicated that if a stray zone has a 10 lb per gallon environment at 10,000 ft, 4,435 psi and 160,000 lb of force could build under a 7 5/8-inch plug if the fluids have been mostly displaced by gas. Therefore, he stressed that a well that leaks all the way to the surface is not nearly as concerning as one that leaks from the bottom to the top but has no surface expression. He also described sources for a high-pressure leak, including zones recharged from water drive, stray hydrocarbon zones at initial pressure, or future carbon dioxide injection zones. He added that the Gulf of Mexico does not have a frac gradient at shallow depths, which can increase the risk of failure.

With these issues in mind, Hunger pointed to the following suggestions for effective plugging and abandonment:

• Keeping hydrocarbons out of the wellbore from the start to prevent bubbles from forming in the well with this best accomplished by cementing productive zones;
• Designing for a long-term hydraulic seal, not just a mechanical plug;
• Preparing the pipe with surfactant to ensure a cement bond;
• Recognizing the benefits of cement additives and cement testing;
• Leaving the well alone until the cement reaches compression strength;
• Considering the impact of cool temperatures on cement and how long it takes to set;
• Checking the top of the cement after every plug;
• Never assuming that steel will maintain its pressure integrity over time;
• Never assuming that a mechanical barrier that relies on elastomers for a seal is a permanent barrier, as elastomers will fail eventually;
• Conducting a “bubble test” after every cement plug;
• Replacing plugs where they fail during the plugging process;
• Solving annular bubble problems deep in the well; and
• Avoiding the use of mud because it breaks down over time, loses its hydrostatic properties, and hinders the achievement of a hydraulic seal.¹

Furthermore, to prevent plugged wells from leaking, Hunger suggested that well-plugging and abandonment be a recognized specialty for which people are well trained and that people designing plugging and abandonment plans as well as those pumping the cement be trained in cement and cement placement and understand the importance

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¹ Hunger later offered clarification that mud is not used often in the Gulf of Mexico owing to reliance on a rigless plugging and abandonment approach and a dual barrier approach, with two cement plugs being placed before any open work is done with the well.

of going beyond the regulations with best practices. Hunger reported that most plugs in the Gulf of Mexico use Class H “neat” cement (i.e., no additives) and that more design should go into the cement. Echoing Plants, he noted that contract strategies that create an urgency to “rush to save” are dangerous (e.g., not waiting for the cement to reach compression strength). He also suggested that increased operator priority and oversight as well as strong regulations and inspections could be beneficial. By following this guidance, he suggested that high-cost, high-risk interventions could be avoided, thereby protecting the oil and gas industry’s reputation as well as protecting key regions such as the Gulf of Mexico and inland waterways.

THE PROCESS: EVALUATION, PLANNING, AND EXECUTION

James Bolander, JLB Engineering, LLC, offered guidance from an operator’s perspective but pointed out that in the case of orphaned wells, the operator’s role and the regulator’s role overlap. He highlighted three key stages of plugging orphaned wells: (1) evaluation, after identifying the well and the wellbore construction; (2) plan development, with particular attention to understanding the state regulatory structure for plugging and abandonment operations and identifying technical support and best practices; and (3) project execution, followed by inspection and post-completion monitoring.

Exploring these stages in more detail, Bolander first discussed the critical components of well identification, including age, drilling method, and purpose; well site location and condition; surface equipment, including the wellhead; and wellbore and subsurface conditions, including type, fluids, depth, and pressure. Potentially useful sources of this information include well histories, logs, and regulatory filings such as drilling reports, plugging permits, and plugging reports. When data are not available, he said that offset well evaluations and visual inspections of the well site could be useful. To evaluate well construction, he suggested gathering information on the casing use (e.g., conductor, surface, intermediate, or production) and casing depth (i.e., whether it meets state regulations), the perforated interval(s) and what can be isolated, the cement (i.e., whether the top of the cement is above areas that require isolation such as potential flow zones, usable water, producing zones, and corrosive zones), and other equipment in the well (e.g., tubing, packers, or casing equipment).

If the appropriate information has not been acquired during the well identification and wellbore construction evaluation to prepare a plugging plan, Bolander indicated that one could identify gaps and next steps, such as by conducting further inspections of the well and performing active testing. He suggested consideration of whether remediation is necessary prior to plugging the well (e.g., fish in the wellbore, casing repair). During the planning stage, he noted that states review the regulatory structure and determine zones that require isolation; review cement quality standards by type and compressive strength; determine placement, including plug type and use of the squeeze method; determine the thickness of the plugs; and consider static wellbore requirements to maintain well control. States also consider technical best practices from industry. For example, the American Petroleum Institute’s (API’s) Recommended Practice 65-3 discusses formations that require isolation as well as material considerations for bar-

riers (e.g., environmental issues like the effect of temperature on cement). Industry Recommended Practice 27 identifies steps and best practices to perform permanent well abandonment, including a helpful pro/con list of barrier types. Lastly, the Ground Water Protection Council’s Well Integrity Regulatory Elements for Consideration² discusses plugging operations, inspection elements, flexibility to use alternative methods and materials, and reporting requirements.

Reflecting on best practices for cement, Bolander suggested that the cement used for plugging and abandonment would ideally be of the same quality as the cement used for the primary cement job—that is, it would conform to API specifications, tailor to local conditions, meet compressive strength requirements, and meet free fluid content standards to minimize the potential for channeling. Meeting standards for mix water quality is also critical, he continued. To achieve operational success, he proposed following procedures for conditioning of the wellbore and requirements for maintaining static wellbore conditions prior to plug placement, including tagging or testing requirements for specific plugs, and tailoring plug placement based on varying well configurations. He suggested that flexibility in planning is key.

Finally, Bolander reiterated that inspection and monitoring play an important role in the project execution stage. Operators can consider when to be on site during the plugging process (e.g., for setting, tagging, and/or testing plugs), when corrective action is warranted, and what type of monitoring is appropriate (e.g., long-term monitoring in certain geographic regions and in active operating areas).

OPEN DISCUSSION

Meehan moderated a discussion among the workshop speakers and participants. He asked Hunger to elaborate on the relationship between hydraulic seals and mechanical plugs. Hunger explained that a mechanical plug will prevent any movement caused by shearing forces acting on the cross-sectional area of the plug along the interface between the cement plug and the pipe. A hydraulic seal will then prevent transmission of pressure or flow through the cement or at the interfaces of the cement plug and the pipe.

Bryan McLellan, Alaska Oil and Gas Conservation Commission, posed a question about how to reenter a well where the pressure below a shallow plug is unknown. Hunger said that after a dangerous experience, he learned never to enter an already-plugged well without controlling the pipe and the pressure and being prepared for a volume of gas to emerge. Thus, he began using a large-diameter coil tubing unit and, most importantly, started pilot milling through the cast iron bridge plugs to check for pressure. He pointed to these two actions as allowing for control of the pipe and control of the gas (at a lower volume).

Nick Gianoutsos, U.S. Geological Survey, asked how long well plugs could last, based on current standards. Thomas Lopez, ExxonMobil, explained that if the caprock is restored, a plug could last many thousands of years. Hunger suggested that plugs could

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² To read this guidance, see https://www.gwpc.org/wp-content/uploads/2021/03/Well_Integrity_Elements_Revised_1_19_2021_002.pdf.

last until the geology heals itself (i.e., until the shales encroach and collapse the well); however, the cement may not last that long. Meehan elaborated that chemical processes that begin over the long-term help with solidification; however, unknown future issues (e.g., fault migration, carbon dioxide injection) could be problematic.

Workshop planning committee member Mary Kang, McGill University, suggested that if states recognize that some plugs will fail within 50 years, they could then develop a risk ranking system for long-term monitoring. Lopez expressed his support for this idea but emphasized how challenging it would be to predict which plugs will fail in the future—tens of thousands of wells are plugged in a lifetime, and finding leaking wells is very difficult. Michael Hickey, Colorado Energy and Carbon Management Commission, explained that, in some cases, plug failure could actually be a failure to place plugs. Danny Sorrells, Railroad Commission of Texas, noted that a “Railroad Commission plugger” is always on location from the start to the finish of a project in Texas to weigh plugs and monitor and document the process.

An online participant wondered how seasonality affects the plugging process. Plants described this as a critical issue in the Northeast because many of the roads where wells are located are secondary rural roads not built for heavy loads. Such roads are particularly vulnerable to damage during the “freeze/thaw” period, which might last from February through May, so projects located off of state highways that are less vulnerable to damage are conducted during that timeframe instead. He emphasized the value of well-developed plugging plans that consider seasonality to avoid unnecessary costs.

Karl Haase, U.S. Geological Survey, wondered if states or regulatory agencies are cataloguing the designs and technologies used for plugging wells. Hunger remarked that operators in the Gulf of Mexico have to submit wellbore sketches with their proposed plugging and abandonment procedures (and updates any time a change is made) as well as a weekly operations report and an end-of-operations report. Jesse Frederick, WZI, commented that California’s WellSTAR system requires before-and-after diagrams of formations and cement calculations. Bolander noted that all states have these types of requirements, but Greg Lackey, National Energy Technology Laboratory, elaborated that although the records exist, they are not always in databases, and large-scale queries often require a review of paper records.

Adam Peltz, Environmental Defense Fund, inquired about training programs for members of the plugging industry. Bolander replied that Texas’s regulations require that plugging contractors have specific qualifications. Plants said that the governor of Pennsylvania has set aside money for formal training; furthermore, Plants and Goodwin, Inc., has a rigorous program that includes 6 months of short-service training and mentorship, after which competency has to be demonstrated before work in the field can begin. Hunger described Superior Energy Services’ hands-on training program in the Gulf of Mexico as an exceptional model. It had a test well, temporary living quarters, and all the necessary plugging and abandonment equipment in a fenced-in area, where new employees worked 14 days on, 7 days off to train for future offshore work. He suggested that such a model also helps prevent continuous turnover in the industry. Meehan observed that drilling courses at Texas A&M do not dedicate much time to decommissioning, and opportunity exists to expand educational offerings in general.