Report Summary Improving Abandonment Processes. Revision: 0A (Draft)

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1 Report Summary Improving Abandonment Processes Revision: 0A (Draft) Prepared for: Canadian Society for Gas Migration Avenue Southwest #370, Calgary, AB T2P 3H7, Canada Prepared by: Robert Walsh and Dru Heagle Project Number: Document ID: _TRM Wellbore Abandonment_Summary_R0b.docx June, 2016

2 1 INTRODUCTION Production wells that that are no longer economically viable, or that have wellbore issues requiring closure, must be plugged to prevent reservoir fluids (oil, gas, brine, etc.) from migrating upward over time and possibly contaminating other formations or freshwater aquifers. Plugging and abandonment work takes capital to complete and provides no obvious return on investment for the oil and gas companies, so there is economic pressure to ensure that most wells are plugged at the lowest possible cost while following the requirements set forth by the oil and gas regulating agencies. There are strict regulations. In Alberta, these regulations are intended to isolate non-saline (<4000 mg/l TDS) groundwater from deeper saline water and to isolate or cover all porous zones (AER, 2016). However, despite these good intentions, leaky abandoned wells remain a problem. The issue of leaky wells, during production and post-abandonment, is fueling opposition to new oil and gas development. Images of flaming tap water in movies such as Gasland do not help the public perception of the fossil fuel industry, although the presence of natural gas in water wells is very often a natural consequence of shallow gas-rich rocks that also provide groundwater. Beyond the issue of societal acceptance, as older oil and gas fields are re-entered to exploit bypassed reserves or to develop reserves previously considered uneconomical, plugged and abandoned wells within these fields may become a potential problem. If technologies such as water or CO 2 flooding are applied, the reservoir pressure will increase, increasing the chance that the formation fluids will bypass the wellbore plugs (in poorly plugged wells) and migrate upward. Thus, in addition to social and environmental impacts, there may also be latent and long term economic consequences to inadequate wellbore plugging and abandonment. The purpose of a technology roadmap is to identify knowledge and technology gaps that are barriers to realizing a change, or, in other words, how do we get from the current state to a desired state. This technology roadmap focuses on wellbore abandonment. This document presents a high-level overview of the methods and materials used to plug and abandon wells, a synopsis of plugging and abandonment research, and the issues that impede the development of new and improved technologies. 2 ABANDONMENT PRACTICES The goal of wellbore abandonment is to restore the low permeability of the caprock formation preventing fluid migration in the wellbore. An abandoned wellbore commonly comprises a surface casing that extends below the base of groundwater protection and a production string, or multiple production strings, that access the target formation. The annular spaces between casing and formation, and between different casing strings, are cemented or at least partially cemented. The overall abandonment approach is to emplace plugs (within the casing if it has been installed) consisting of tailored cement types supported by mechanical plugs. The well operator must design an abandonment program that identifies wellbore integrity issues, oil and gas zones, groundwater zones, and the cement integrity. The first step of the abandonment process is to remove tools from the wellbore such as production tubing, downhole pumps, and packers. If downhole equipment cannot be removed then the wellbore abandonment strategy may need to be changed and the new abandonment strategy may require special permission. June,

3 Following removal of downhole equipment, the borehole must be cleaned, typically by flushing the wellbore with a circulation fluid capable of controlling borehole pressures, which may contain numerous additives to achieve the proper fluid properties. If sealing an uncased well, it is important to remove the mud and mud cake from the zones of the wellbore where cement will be emplaced as mud retards the set of cement and may cause poor bonding to the walls. Mud-contaminated cement must be displaced from the desired zone to ensure the proper cement is allowed to isolate the zone. In a cased borehole, hydrocarbons should be removed to ensure the casing is water wet, allowing cement to bond. Cement plugs in open holes or within cemented production casing (liners) are emplaced under a variety of well conditions and, depending on the well conditions, can be emplaced by different methods. Cements can be placed in single or multiple stages in the borehole depending on the needs of the scenario. The most common method used for the placement of cement plugs is the balanced plug method. An important component of cement plugs is their compressive strength development. For the purposes of inhibiting wellbore leakage, the plug must have enough strength to inhibit gas migrating through the cement during the gelation phase. Compressive strength testing shows that cement development times can be from three to five times longer with as little as 10% mud contamination. Most cement plugs fail because of fluid flow in the borehole including cross flow of formation fluids, a density or viscosity mismatch between a balanced plug and wellbore fluids or failure to stop the momentum of the plug being inserted into the wellbore. For cases where there is no cement behind a casing or the cement has been identified as inadequate it may be necessary to remediate the cement between the casing and the formation to isolate permeable zones. The cement squeeze method is used to accomplish this. The squeeze method involves perforating the casing or liner and pumping cement into the perforations where cement will presumably fill permeable pathways to form and impermeable barrier. Perforating the casing is a means to establishing access to permeable zones or gas source zones. Casings are typically perforated using shape charges and bullet guns, although abrasive methods (high pressure sandwater slurry) and other alternative methods have also been used (e.g. laser, electrical, mechanical). In addition to cement plugs, mechanical plugs such as bridge plugs and cement retainers, which are installed directly below the cement plug, play a role in stopping fluid flow in a wellbore. Both surface casing vent flows and gas migration scenarios are repaired in the same manner. The regulatory body requires the gas source to be identified and sealed to eliminate gas flow from the reservoir Cement Plug Evaluation Testing is required to ensure that the plug is placed at the proper level and provides adequate isolation of permeable zones. The plug can be verified by tagging its top, pump pressure testing or swab testing. Pressure tests can be carried out by applying pressure to the cement to test the seal. While this approach does identify the effectiveness of the plug it may damage the plug or cause damage elsewhere in the casing. Swabbing the wellbore to remove fluids will result in a loss of pressure in the wellbore. The fluid level recovery in the wellbore can be monitored to determine the effectiveness of the plug. This is a time consuming method. Both pressure application tests and fluid level recovery tests may not be deterministic if fluid can enter the wellbore from other zones. June,

4 2.1.2 Identifying Wellbore Leakage Abandoned oil and gas wells may develop wellbore leakage either over time or relatively soon after abandonment. In Alberta, prior to conducting a surface abandonment a surface casing vent flow test is conducted to determine if gas, liquid, or any combination of substances is escaping from the casing vent assembly. If gas is present the vent flow must be determined to be serious or non-serious based on the criteria in Interim Directive (AER, 2003). Gas Migration (GM) is defined as a flow of gas that is detectable at surface outside of the outermost casing string (often referred to as external migration or seepage). A serious GM is defined as a fire or public safety hazard or off-lease environmental damage, such as groundwater contamination. Leak identification methods are discussed in the Source Identification TRM document Repair Requirements The Alberta Interim Directive requires the well to be tested for SCVF within 90 days of drilling rig release. Testing for GM must also be carried out within 90 days for specified areas in Alberta as indicated in the Interim Directive. The licensee of a well with a serious SCVF/GM problem must repair the problem before 90 days from discovery of the problem. Non-serious SCVF/GM problems must be addressed at the time of well abandonment. Repair and remediation are addressed in a separate TRM document. 2.2 Abandonment Practices in Other Subsurface Industries The emergence of deep geological storage of carbon dioxide and nuclear waste has resulted in research into the performance of abandonment techniques for boreholes in carbon dioxide reservoirs and potential nuclear waste repositories. Boreholes associated with carbon dioxide sequestration must resist degradation by low ph groundwater and maintain an adequate gas seal over a long period of time. Nuclear waste repositories have a similar problem because some wastes types decay to produce pressurized gas in the repository that may move up poorly sealed boreholes. Deep borehole disposal has been proposed as an alternative to radioactive waste repositories, and clearly requires effective sealing of disposal boreholes. It may be possible to apply the work carried out in carbon dioxide and nuclear waste sequestration to provide workable and economic solutions to abandonment practices in the oil and gas industry. As a result of greater regulatory and public scrutiny, substantial resources have been directed to the long-term sealing of permeable pathways in and near nuclear waste repositories. In particular, assessments of hydromechanical behavior, chemical weathering, and longevity of sealing materials have been performed. In nuclear waste context, sealing materials must have adequate mechanical strength, ductility, low hydraulic conductivity, long term stability, swelling capacity, thermal conductivity, and workability/pumpability. Because no single material can satisfy all of these requirements, borehole sealing approaches typically follow a multi-component seal design. Materials considered for sealing boreholes include compacted bentonite, sand-bentonite mixtures, bentonitemagnetite slurry, barite, API Class G cements, expanding cements, low ph cement and grout with silica fume additives, cement stabilized quartz sand, magnesia cement (for boreholes in evaporate), saltwater grout and salt concrete (for salt formations), and others. June,

5 3 ISSUES WITH CURRENT PRACTICE Inadequate sealing of the annular space in natural gas production wells is an old and as yet unresolved issue. Jackson (2014) provides an excellent summary of case histories, providing substantial evidence of gas leakage in active and abandoned hydrocarbon wells. According to Bexte et al. (2008), public data at that time suggested that there were leaky wells in Alberta alone. Dusseault and Jackson (2014) report that 4.6% of the wells in the Alberta database have reported problems with surface casing vent flow or gas migration. Watson (2005) also reported a significant incidence of surface casing vent flow and gas migration in Alberta oil and gas wells. Bourgouyne et al. (1998) reported gas migration in over casing strings in 8000 offshore wells in the Gulf of Mexico. Bruffato et al (2003) stated that there is a 50% probability that a well will have a measurable sustained casing pressure by the time it is 15 years old. Kang et al. (2014) measured methane emission in abandoned oil and gas wells in Pennsylvania, finding that methane flows from abandoned wells likely account for 4-7% of anthropogenic methane emissions in Pennsylvania. Gas migration and vent flow in wells is primarily the result of poor mud displacement during cementing, gas migration into cement during setting, stress crack formation during operation, or autogenous shrinkage during cement hydration, which leads to the formation of a micro-annulus (Oyarhossein and Dusseault, 2015; Zhang and Bachu, 2011). Nygaard (2010) observed that cased wells seem to be more prone to leakage than drilled and abandoned wells, and injection wells were more leakage-prone than production wells. Duguid et al. (2013) examined the condition of five wells using ultrasonic and sonic logging tools, performed permeability testing outside the casing, and completed permeability testing of cased-hole sidewall cores. The wells ranged in age from 6 to 25 years old, and used a light, pozzolan, Class G cement. In this experiment, bond logs indicated generally good cement quality and bond, and sidewall cores indicated that cement was undegraded, with a low permeability (averaging approximately m 2 ). However, vertical interference tests in the same locations measured much higher in-situ permeabilities in the cemented annuli (approximately m 2, or three to four orders of magnitude higher than cement core samples). Gasda et al. (2013) added one additional well to the dataset, finding an average intact cement permeability of approximately m 2 and annulus permeability of m 2. Crow et al. (2009) did a similar analysis of a 30 year old CO 2 well, finding that intact cement cores had low permeability (approximately m 2 ), while vertical interference testing returned permeabilities on average three orders of magnitude higher than the cement sidewall cores (10-14 m 2 ). Together, these results suggest that permeable interfaces (micro-annuli) or problems with cement placement are responsible for the creation of permeable flow pathways in the annulus cement. Cement placement in a deep borehole, particularly in the annular space outside the casing, is difficult. There are a large number of things that can go wrong, leading to poor sealing against gas movement. Short term issues affecting the cement sheath include improper drilling mud and cement slurry design, inadequate mud removal, eccentric casing placement, and invasion of gas or liquids during cement setting (Dusseault et al., 2014). Long term issues affecting the cement sheath include operating stress (cyclic loading sand thermal stress), cement shrinkage, casing corrosion, and cement degradation (Halliburton, 2015). These problems may be exacerbated in certain geographical areas, in deviated wellbores, and in cased wells, (as opposed to drilled and abandoned). Even if the bridge plug set June,

6 inside the casing never degrades, the cement plug inside the casing provides a durable seal, and the casing never corrodes, an inadequately sealed cement sheath will allow gas to migrate. 4 IMPROVEMENTS WITH EXISTING SCIENCE AND TECHNOLOGY Existing technology can be used to improve the performance of abandoned wells, and this begins during installation of the casing, long before the well is abandoned. Eccentric casing placement, or poor centralization, seems to contribute to gas leakage in many wells, especially deviated and horizontal wells. The solution to this problem is evident. According to Dusseault et al. (2014), Shell Canada has been using one centralizer per casing joint in vertical sections of its wells in the Montney and Duvernay plays in Alberta and British Colombia, improving the quality of primary completions. Improved completions would also improve the ease and effectiveness of plugging and abandonment operations, and reduce remedial requirements. Dusseault et al. (2014) commented that better centralization may be the most cost-effective method to reduce wellbore leakage in new wells. According to Bexte et al (2008), a combination of improved cementing techniques can greatly reduce the incidence of gas seepage and surface casing vent flow (by roughly a factor of 10, however, the authors did not assess long-term performance). Many of the problems identified in Section 3 are well documented. The primary difficulty seems to be education of engineers, supervisors, and stakeholders on the issues, including mud contamination, cement design, gas invasion during setting of cement, and adequate centralization. This is addressed in the section of the TRM covering Communication of Best Practices. Coupled with educational efforts, updated regulations might improve plugging and abandonment(p&a) There is currently no requirement in regulatory directives (at least in Alberta) for supervision and/or testing by a third party during P&A. As noted in Watson and Bachu (2009), when a small number of abandoned wells were re-entered for production purposes: Generally, the cement cap placed on top of the bridge plug was not evident, even though a tour-report review indicated that the cement had been dump bailed on the bridge plug. Tour reports are logs of daily operations in well drilling and completion. This finding seems to indicate that adequate accountability and supervision during plugging and abandonment may be a problem. Regulators should consider requiring that a responsible engineer, perhaps independent of the cementing contractor, confirm all abandonments, indicating that the work has been completed according to specifications. Perhaps recognizing that many of the problems in wellbore abandonment occur behind the casing, a number of authors have suggested that milling out or otherwise removing a section of casing and annulus cement should become a standard practice in wellbore abandonment. As early as 1999, Husky Oil (Saponja, 1999) proposed an economical cap rock repair solution to the problem of gas leakage. Operational simplicity was achieved by ignoring possible multiple source locations, and placing a seal in a relatively shallow, impenetrable formation. Using hydro-jetting, two 110 slots were cut through the casing, cement sheath, and formation, followed by two offset 110 slots 0.3 m shallower, to achieve 360 degree coverage. Cement was then pumped into these slots, to induce horizontal fractures cutting off gas migration, regardless of the local stress regime. Gray et al. (2007) and Carlsen and Abadollai (2007) both recommend removing part of the casing and sheath before abandonment. Research and development in milling techniques is ongoing, with recent patent applications including a hydrojetting system using cement slurry (Halliburton, 2015), a novel June,

7 mechanical milling system (Bansal et al. 2015), and a system for cutting casing and cement using explosive charges (Statoil, 2015). Other researchers, inventors, and oil service companies are proposing alternatives to cement, based on the application of heat and/or molten materials to create an impermeable seal. Nygard (2010) proposed using a molten metal alloy which expands slightly upon cooling for sealing wells at the Wabamun CO 2 Sequestration Project. Kunz (2016) proposed the use of a molten eutectic salt (low melting point salt mixture) as a seal for borehole abandonment. Bisn Tec (2014) proposed use of a thermite heat source to melt eutectic Bismuth/Germanium alloys to form plugs in deep boreholes. Baker Hughes (2015) propose the use of a high powered laser run in on a wireline to melt casing, cement, and formation rock such that it becomes molten and flows onto a pre-installed plug, eventually cooling to form a solid, impermeable mass. Interwell (2015) are developing a method in which they ignite a heat-generating thermite mixture generating temperatures of up to 3000 C, this melts casing, cement sheath, and a great proportion of the surrounding rock, which eventually solidifies, forming a seal. Approaches involving molten rock have also been assessed for sealing wells for deep well disposal of radioactive waste. Gibb and Travis (2015) describe the development of a rock welding technique, in which downhole electrical heating was used to melt crushed granitic rock taken from the host formation. According to these authors this is forms a continuous seal, virtually identical to the host rock. 5 KNOWLEDGE GAPS AND RESEARCH RECOMMENDATIONS As highlighted in the previous section, there are many methods, techniques, and materials which hold promise for improving wellbore abandonments to reduce gas leakage rates. There are many proposed techniques, customized cements, epoxy and elastomer based seals, use of molten materials which have been proposed as effective solutions for borehole abandonment. Some methods are relatively new, but even alternative approaches which have existed for some time have not gained wide adoption. This suggests that there is a certain amount of conservatism and perhaps skepticism among operators and regulators, and that this may be inhibiting progress in improving abandonment methods. This skepticism may be warranted by a lack of independent and publicly available assessment of the claims made by commercial oilfield service companies. A major open question involves durability of sealing materials and methods. Ideally, a plugged and abandoned wellbore should be able to reliably prevent fluid migration and restore the natural integrity of the formation in perpetuity. Which materials and techniques work the best, and are most durable in the in the long term? These issues point to the need for independent assessment of field trials using well designed testing programs, as occurs in the nuclear-waste disposal industry. This work should also be used to develop and validate numerical models, which can be used to predict the long-term evolution of wellbore P&A systems. 6 REFERENCES Alberta Energy Regulator (AER), Interim Directive ID , 1) Isolation packer testing, reporting, and repair requirements 2) surface casing vent flow/gas migration testing, reporting, and repair requirements 3) casing failure reporting and repair requirements (January 2003). June,

8 Alberta Energy Regulator (AER), Directive 020, Well Abandonment (March 2016). Baker Hughes Incorporated, Laser Plug and Abandon Method. United States Patent Application Publication US 2015/ A1, United States Patent Office, Washington, D.C. Bansal, R.K, et al Milling System for Abandoning a Wellbore, United States Patent Application Publication US 2015/ A1, United States Patent Office, Washington, D.C. Bexte, D.C., M. Willis, G.G. De Bruijn, B. Eitzen, and E. Fouillard Improved cementing practice prevents gas migration. World Oil 229, no. 6: Bisn Tec Ltd Heat Sources and Alloys for Use in Downhole Applications, International Patent Application WO 2014/ A2, World Intellectual Property Organization, Geneva, Switzerland. Bourgoyne, A.T., S.L. Scott, and W. Manowski Review of Sustained Casing Pressure Occurring on the OCS (Outer Continental Shelf). Submitted to the Minerals Management Service, US Department of the Interior, Washington, D.C. Brufatto, C. et al From mud to cement building gas wells. Schlumberger Oilfield Review 15, no. 3: Carlsen M. and Abdollahi, J., Permanent, abandonment of CO2 storage wells, Sintef report Crow, W., D.B. Williams, J.W. Carey, M. Celia, S. Gasda Wellbore analysis of a natural CO2 producer, Energy Procedia 1: Duguid, A., R. Butsch, J. W. Carey, M. Celia, N. Chugunov, S. Gasda, T. S. Ramakrishnan, V. Stamp, J. Wang Pre-injection baseline data collection to establish existing wellbore leakage properties, Energy Procedia 37: Dusseault, M. and R.E. Jackson Seepage Pathway Assessment for Natural Gas to Shallow Groundwater During Well Stimulation, Production and after Abandonment, Environmental Geosciences 21(3): Dusseault, M., R.E. Jackson and D. MacDonald Towards a Road Map for Mitigating the Rates and Occurrences of Long-Term Wellbore Leakage. Downloaded from: Gasda, S., M.A. Celia, J.Z. Wang, A. Duguid Wellbore permeability estimates from vertical interference testing of existing wells, Energy Procedia 37: Gibb, G.F. and K.P. Travis Sealing Deep Borehole Disposals of Radioactive Waste by Rock Welding, Conference on International High Level Radioactive Waste Management, Charleston, SC, April 12-16, June,

9 Gray, K., Podnos, E. and Becker E., Finite Element Studies of Near-Wellbore Region During Cementing Operations: Part I. Production and Operations Symposium, 31 March April 2007, Oklahoma City, Oklahoma, U.S.A. SPE Halliburton Energy Services Systems and Methods for Using Cement Slurries in Hydrajetting tools, International Patent Application WO 2015/ A1, World Intellectual Property Organization, Geneva, Switzerland. Interwell Technology AS Method of Well Operation, United States Patent Application Publication US 2015/ A1, United States Patent Office, Washington, D.C. Jackson, R.E., A.W. Gorody, B. Mayer, J.W. Roy, M.C. Ryan, D.R. Van Stempvoort Groundwater Protection and Unconventional Gas Extraction: The Critical Need for Field-Based Hydrogeological Research, Groundwater 51, no. 4: Jackson, R The integrity of oil and gas wells, PNAS 111 (30): Kang, M., C.M. Kanno, M.C. Reida, X. Zhang, D.L. Mauzeralla, M.A. Celia, Y. Chen, and T.C. Onstott Direct measurements of methane emissions from abandoned oil and gas wells in Pennsylvania, PNAS 111, no. 51: Kunz, D Eutectic salt abandonment plug for wellbores, Canadian Patent Application CA A1, Canadian Intellectual Property Office, Ottawa-Hull, Canada. Oyarhossein, M. and M. Dusseault Wellbore Stress Changes and Microannulus Development Because of Cement Shrinkage, presented at the 49th US Rock Mechanics / Geomechanics Symposium held in San Francisco, CA, USA, 28 June- 1 July Nygaard, R Well Design and Well Integrity Wabamun Area CO2 Sequestration Project (WASP), Energy and Environmental Systems Group, University of Calgary. Saponja, J Surface Casing Vent Flow and Gas Migration Remedial Elimination New Technique Proves Economic and Highly Successful, Journal of Canadian Petroleum Technology, Special Edition (13), paper Statoil Petroleum AS, A method of plugging a well. United States Patent Application Publication US 2015/ A1, United States Patent Office, Washington, D.C. Watson, T. (2005). Investigation of wellbore leakage for CO2 storage: Part II. Alberta Energy Regulator. Watson, T. and Bachu, S., Evaluation of the potential for gas and CO leakage along wellbores. SPE Drilling and Completion, 24(1): SPE Zhang, M., and S. Bachu Review of integrity of existing wells in relation to CO2 geological storage: What do we know? International Journal of Greenhouse Gas Control, 5, June,