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Introduction ....................................................................................................................... 3 Main impressions .............................................................................................................. 4 Regulations and Norsok requirements to plug and abandonment of wells ....................... 6 Challenges related to permanent plugging in general ..................................................... 10 4.1 General challenges ..................................................................................................... 10 4.2 Knowledge of well status ........................................................................................... 10 4.3 Ability to log cement quality through multiple casing .............................................. 10 4.4 Competent formations ................................................................................................ 10 4.5 Collapse...................................................................................................................... 11 4.6 Maximum pressure exposure ..................................................................................... 11 4.7 Observations during the operational phase ................................................................ 11 Challenges related to the permanent plugging of wells with vessels .............................. 12 5.1 Securing good cement behind casing ......................................................................... 12 5.2 Plugging of wells with control lines .......................................................................... 12 5.3 Need for pulling tubular and equipment .................................................................... 12 5.4 Need for section milling............................................................................................. 12 5.5 Operations without riser ............................................................................................. 12 Proposed recommendations for improvement ................................................................. 13 6.1 Topics that should be addressed by the industry ....................................................... 13 6.2 Topics that should be addressed in standards ............................................................ 15 Check list ......................................................................................................................... 16

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1 Introduction The Norwegian Petroleum Safety Authority (PSA) has conducted a seminar addressing plug and abandonment of wells. The choice of topic is based on the encounter a new phase in the petroleum activities in Norway, where we will see a large amount of abandonment of wells having reached the end of its life. The number of applicable wells over the next 10 to 20 years is high, and provides a basis for some reflections: • We are facing what the industry refers to as a "Plug Wave". • Recent studies and experience suggests that the duration of the operations can be time consuming, and run up to 35 - 40 days. • One should take into account that this work is an outright expense and will not generate any income. o It is expected that the future will bring a strong focus on developing effective solutions that will compete to a lesser degree with the resources that are used for drilling and completion of new wells. o The companies appear to be conscious that this is a commitment they have, and the need to plug and abandon the wells in a safe and prudent manner. o Cost of current technology is high, but there can be substantial savings in promoting new technologies and methods. • In view of this, one may expect the use of mono-hull vessels or special vessels for plug and abandonment activities, operated by contractors emerging in the market. o This is also the experience from the UK sector. • The extent of plug and abandonment of platform wells is about 4 times higher than the number of subsea wells, but this seminar will focus on the abandonment of subsea wells. Operators and suppliers were invited to present the following topics: • Requirements and challenges related to the plug and abandonment of wells with vessels • Industry experience from actual field operations • Available and future technologies to meet current challenges • Regulatory requirements and practices in the UK • Plugging material • Cement height / plug length • Verification of barriers • Categorization of wells • Input with respect to the well design to facilitate subsequent plugging of wells Wellbarrier have been asked to document the proceedings and discussions in the seminar. This report is based on statements that have emerged in addition to the presentation materials that were given. Following the seminar, the author, with input from PSA has made a summary to highlight factors that one believes should be focused on and addressed by the industry in the future. The statements in the report should be used with a degree of caution as they may have been a party’s point of view or taken out of a context. The external report does not contain the presentations or company specific statements.

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2 Main impressions The following main impressions were given during the seminar: • We are facing a work task that will require a lot of resources. • There is a lot of missing information on the status of existing wells. • There is a discussion whether to categorize wells to be plugged back so that one can group the work ahead into categories where one uses different techniques or methods to do the job effectively and safely. However, there is some disagreement in the industry to the benefit of this. • There is a need to develop improved or new equipment in a number of areas. o Logging  In low density fluid  In high densities fluid  Through several tubular  Through tubular with more than 0.8'' wall thickness  More reliable log interpretation methods o Milling without having to take the shavings to the surface (there are already prototypes) o Ability to enter wells with collapsed tubular o Ability to perform plug and abandonment without pulling tubular o Handling of cables and control lines in the wells (possible leak paths) • There is a need for better post monitoring of plug and abandoned wells, as the U.S. has experienced that previous work has not been satisfactorily done. • Through presentations of plug and abandonments with vessels on the UK Continental Shelf, there is left an impression that there is uncertainty about how well cementing / isolation on the outside of the casing is established when the plug is set inside the tubulars of the well. • The importance of good cement behind the casing is well known, but there seems to be little evidence that this is actually in place. Much of the work that is performed on the UK Continental Shelf indicate that they are working hard to put cement inside the well, while there is little said about what they have done to verify the cement external to the casing. This may be a challenge when an Operator engages a Contractor to plug back the well without the Operators own presence. • There is great variety in the world with respect to the requirements for cement heights to act as a barrier. From alleged 7.5 meters in Canada to 100 meters (tested) / 200 meters (job well done) in Norway. • There will be a need for greater focus on shallow formations and plugging of these, not only the main formation from which the well has produced in its lifetime. • It is important to plan for plug and abandonment from the start of the well design. • It is important to look at the well design as a whole, from drilling top holes to P&A - and consider the consequences of the choices one makes in a life time perspective. • It is important to know where you have competent formation that is capable to sustain any formation pressure. • It is important to take into account the fact that companies will be net present value (NPV) driven, this is not likely to change, as such the P&A activity is an operation that will give no financial return (although companies apparently fully accept that this is an obligation and must be done properly). • There are a lot of questionable cement jobs done in the past. • Many people will acknowledge that former cementing techniques have been inadequate, and that verification has been of varying quality. Verification of job execution and interpretation of logs in the past have been questionable. We also recognize that we have come a long way in these areas today, yet it seems that many people are prepared to use old

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presence of cement as a barrier without further verification. This must be regarded as uncertain and doubtful. There seems to be some issues related to the experience of plugging and abandonment from vessels that makes experience transfer and comparison difficult: o Different durations of operations are quoted; this may be caused by operations consisting of different phases being performed by different vessels. o Many wells on the UK sector are quoted as plugged with durations of less than three days, this seems optimistic, and is assumed to be a result of not including activities prior to, and after establishing two well barriers inside the well. o In the final documentation of permanently abandoned wells there are rarely clear descriptions on how one has ensured that the cement in the annulus is verified before setting the internal plug. o One recognizes that the quality of logs and interpretation of old logs is uncertain, yet this seems to be the basis for plug and abandonment of wells (there is little mentioning of this in in the final P&A well reports). When setting plugs and their required pressure capacity, this is usually derived from a reservoir pressure less the hydrostatic column. However, there appear to be uncertainties as to how to calculate this hydrostatic column. Should this be based on oil, gas, formation fluid or a combination thereof? The well life does not end when it is plugged and abandoned, it also covers the long-term effectiveness of the plugging, and assurance that the well holds tight “forever” There are some parties that are very active and work focused on identifying problems, solve them and develop the technology. There also seems to be quite a few that is "sitting on the fence" and waiting for solutions to appear.

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3 Regulations and Norsok requirements to plug and abandonment of wells The below text is extracts from the regulations, guidelines to these and Norsok D-010 addressing well design for plug and abandonment: The facilities regulations:

The activities regulations:

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The guidelines to the regulations are referring to Norsok D-010 rev. 3: Norsok D-010 rev. 3 extract:

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4 Challenges related to permanent plugging in general Below are listed and briefly discussed some topics that are particularly relevant for plug and abandonment of wells on a general basis.

4.1 General challenges There are a number of challenges related to the expected future "plug wave" that one sees coming; • • •

Available technology Available resources (rigs, vessels, personnel) Time Aspects o When should a temporarily plugged well be permanently plugged? o What is the expected duration of the operation of permanent plug operations?

The volume and scope of the work ahead suggests that there could be great benefits to be gained by improving and optimizing the technologies and methods to help shorten the operation time.

4.2 Knowledge of well status Data from old wells can sometimes be inadequate. In particular, the information about cement quality behind the casings is an important parameter. It is also important to have knowledge of any pressure buildup in the annulus of subsea wells in general, this is a challenge as these annuli cannot be monitored, and the casings have to be perforated and annulus checked for pressure before casing and wellhead can be pulled. If the well has been suspended for many years, there may be uncertainties related to what is the actual status of corrosion and pressure build-up in certain parts of the well. Lack of knowledge of the well's status will necessitate preliminary investigative work before starting the plug and abandonment operation. Alternatively, this force the use of a rig with conventional BOP and riser to be able to do the job with the best possible pressure control readiness.

4.3 Ability to log cement quality through multiple casing The ability to log cement or isolation qualities through multiple pipes, either multiple casing or through the casing and tubing, will be an important contribution to providing understanding and confirmation of the existence of good cement / isolation behind the casing in the area where there are competent formation, and where the internal cement plugs will be set.

4.4 Competent formations It must be identified where there are formations which has sufficient formation strength to withstand pressure from a below reservoir. In old wells this knowledge is not necessarily available and this must then be obtained as part of the plug and abandonment operation. For this purpose it may be necessary to do physical tests of the formation below the point where one wishes to establish the well barrier.

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The requirement for competent formation applies: • • •

both primary and secondary barrier for shallow formations that have flow potential even if they have not been produced earlier sufficient strength to withstand the reservoir pressure to the level it will build to in an eternal perspective (corresponding to the virgin reservoir pressure?)

4.5 Collapse Many wells are located in fields where formation or seabed has been subject to subsidence due the depletion during the field/wells life. This may result in shear stresses in the well which can cause the tubing and casing to collapse or shear, and prevents one from entering the well below depths where the damage has occurred. If it is necessary to set isolation plugs below this level to achieve sufficient formation strength, this will be a major challenge for plugging and abandoning of the well in a safe manner.

4.6 Maximum pressure exposure The maximum pressure an isolating plugs set in the well may be exposed to, must be established with reasonable certainty. This will normally consist of two elements. 1. What pressure the reservoir will build up to having been shut in for a long period (10 - 50 100 years or more?). This may at worst be virgin reservoir pressure or higher(?) if the field has been the subject of gas or water injection. 2. Hydrostatic column from the top reservoir to the isolating plug (both primary and secondary plug). Whether this hydrostatic column could be free gas must be carefully considered.

4.7 Observations during the operational phase It is important that lessons learned from operations are made available for those who plan to plug and abandon the well. •



The annular pressure, or lack thereof, may be indications that the cement in the annulus may be insufficient as isolation, or that it confirms that the cement is fulfilling its purpose as a pressure barrier. Indications of sudden changes in production may indicate that the well have been exposed to mechanical collapse.

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5 Challenges related to the permanent plugging of wells with vessels Below are listed and briefly discussed some topics that are particularly relevant for plug and abandonment of wells using vessels. These issues are also present when plugging platform wells, but will represent a particular challenge when performed from a vessel.

5.1 Securing good cement behind casing Even if one wants to make a simplified plug and abandonment by use of a vessel, it is important to know the condition of the cement behind the casing in the area where the internal plugs should be set. This may mean that such verification must be done from the vessel and one may have to wait for interpreting results before proceeding with the operation. Old cement logs and job reports should not be solely used as basis for establishing the setting depth for the barrier when doing the plug and abandonment.

5.2 Plugging of wells with control lines When performing plug and abandonment of wells from a vessel it will be highly desirable to avoid having to pull the pipe from the well. If the tubing has control lines attached, especially in the deeper regions where one would want to set isolation plugs, this may be a challenge. There may be a challenge when cementing the A-annulus past the cable clamps, and the control line itself may constitute a leak path, either through the internal bore or through degradation of the plastic encapsulation.

5.3 Need for pulling tubular and equipment If the operation requires pulling tubular or equipment out of the well, this is much more demanding than if the steel can remain in the well. This may require large pulling forces and pipe handling. If one pull completions with low-radioactive deposits this is also a handling and exposure issues. Generally speaking, if one can avoid pulling pipe, this will be an important basis for the premise of making it easier to make plugging and abandonment from a vessel.

5.4 Need for section milling If the cement behind the casing is inadequate or it is not possible to confirm it’s condition, it may be necessary to mill away portions of the casing in order to insert good transverse cement plugs in the well. Taking milling shavings back to the surface to a vessel without risers will be a challenge, and will benefit from a solution that allows leaving the shavings in the well below the milled section.

5.5 Operations without riser When running operations from a vessel it is desirable to avoid the use of risers as this is costly, time consuming to install and requires a lot of deck space. This means that the cementing of the well will have to be made through hoses for pumping of the cement and return of the mud/fluid. There will also be a need for arrangements placed in the wellhead area to allow fluid to be pumped in and out of the well through a common mechanism. Several such systems exist in the market. Pumping cement through hoses connected to the well control equipment must be planned and implemented with care so that the cement cannot impair pressure control equipment capacity and the ability to shut in the well in an emergency. Side 12 av 16

6 Proposed recommendations for improvement As a result of the presentations and discussions held, and the subsequent assessment some suggestions for follow-up may be considered. The following recommendations will help to establish a better foundation for future work in this area

6.1 Topics that should be addressed by the industry A number of issues are presented below where the industry should improve technology and methods. This may be appropriate to address through Norwegian Oil & Gas (former OLF) and PAF (Plug and Abandonment Forum). Scientific approach to required cement height The current requirement to cement height appear to be largely based on empirical figures, and there is a difference from country to country. It is recommended that a more scientific approach is applied to establish necessary cement height to serve as a well barrier. The approach should consider necessary cement height to withstand a given pressure differential duly taking into account cement height, implication of vertical versus measured depth, impact of offset pipe in borehole, hole ID/pipe OD dimensions, bonding, and parameter for accepting the cement log quality. Requirements to document competent formation There should be clear requirements for documentation that shows that the formation is competent to withstand the pressure that can occur below the established barrier, this applies to both primary and secondary barriers (including barriers set at shallower depths). Requirements to document good cement behind casing / plugged section There should be clear requirements to demonstrate that there is cement with good bond / isolation between the casing and the formation in the areas where you want to set internal cement plugs. The recommendation of method for verification of cement or other isolation materials should be made clearer. Consideration should be made from well to well whether old logs or job data is sufficient verification to proof good isolation behind casing at the depth where the internal plugs are to be set. The value of no annulus pressure in old wells If one can prove that there is no annulus pressure build-up, can this then be taken as evidence that the cement in this annular space is an acceptable well barrier? If one could make such a decision, what should then be the condition for stating that this isolation is good? Improve logging tools and interpretation methods Logging and interpretation of cement logs has always been a challenge. There are many limitations in existing equipment, thickness of the steel one can log through, ability to log across several annuli, restrictions on the density of the liquid where the logging tools are run. Furthermore, the interpretation of logging data is often linked to personal judgments, and the expertise to make such assessments seems to be very limited and often localized to the suppliers. One should in this context, encourage vendors to come up with tools that have greater capacity and provide clearer results that are less dependent on highly specialized expertise to interpret. Side 13 av 16

Qualification of formation as a well barrier What should be the basis for qualifying formation as a competent well barrier, should physical tests be performed at the actual depth, or can it be accept that qualification is done based on log data and formation properties? The industry should consider mapping and description of formation types that are suitable to act as a well barrier given that they have the ability to collapse onto the casing or can be activated with additives. Monitoring of geology In certain fields, there are experience with geology and formations giving special concern for the wells, this is especially true in relation to subsidence and tectonic shifts that can lead to deformation or shear in the casing / tubing with subsequent difficulty in getting sufficiently deep into the well to set the necessary barriers at a depth with sufficient formation strength. The industry should consider plans for monitoring of the properties of the overburden with respect to pressure development and tectonic movements. Could this be monitored in any way, and which acceptance criteria should be established to determine whether the continued operation of the well can be justified, or whether the well should be worked over while still having full access to the well path? In this context one should also have plans to monitor and ensure that there is no accidental pressure buildup in shallower zones caused by migration, and that there is a competent formation that can withstand such migration, or that there are clear criteria for managing such migration, or that the well is plugged back while this is still possible in a prudent manner. "Sensors" in cement One should consider whether it is possible to use "additives" in the cement making it easier to interpret the logs, particularly with respect to homogeneity and bonding between the formation and the casing, and possibly also for tracking any pressure build-up within the cement column. Qualification of new isolation materials There should be established qualification criteria for alternative materials to cement. Several parties are presenting and considering new isolation materials (Sandaband, Bismuth plugs, etc.), the industry will thus be better served if there is a standardized format for how such a qualification should be performed. Oil & Gas UK has such a qualification plan in its "Guidelines on qualification of materials for the suspension and Abandonment of wells, Issue 1, July 2012" Integrated planning of plug and abandonment of wells One should consider to possess internal dedicated expertise (at least for the major companies that have larger well portfolios) on plug and abandonment of wells, and let this be an integral part of the well planning in the original well design. One should already in the early planning have a clear idea on how the well is to be plugged back in 10 to 15 years, and have a handle on the costs and resources required to make such a plug and abandonment.

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Establish a list of wells to be abandoned in the foreseeable future The number of wells to be abandoned by the individual operators should be considered (a similar study was done in the UK in 2008). In this context, there should be established a categorization so that one can visualize the scope and complexity of the work ahead Encourage training institutions to address the industry's actual problem The industry should see it as part of its responsibility to assist educational institutions to identify and work with the challenges that actually exists in the industry. The industry should also provide speakers to present situations from the real world so that those who are in education are introduced to the challenges of tomorrow as well as relevant current practice. The industry should encourage employees to pursue Master Degrees and higher education.

6.2 Topics that should be addressed in standards In the section below there some issues that should be addressed by standards such Norsok D-010 to ensure that the methods are being standardized in the (Norwegian) industry. Establish categorization of wells to be abandoned Categorization of wells to be abandoned has been used in the UK sector; in Norway it seems to be a reluctant attitude to establishing such a categorization. It is possible that the parties feel that they have too little experience with permanent abandonment to create such a system (particularly subsea wells). It should nevertheless be considered to establish such a system in order to have a clear guideline for when to use a vessel, either operated by a contractor versus using a more full-featured drilling rig operated by an Operator. Requirements for calculating maximum pressure exposure There should descriptions on how to derive maximum pressure the reservoir can built up to in the eternal perspective, or simply state that one should use virgin reservoir pressure for this purpose. Guidance for calculating the hydrostatic column There should be a guidance on when to use which type of fluids to derive the hydrostatic column, are there situations where one may / must use the reservoir fluid to define the hydrostatic column, such as in formation with free gas, or is this unreasonable if one look at migration in a micro annulus as a result of inadequate cementing?

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7 Check list The below table provide a list of items that should be addressed as part of the permanent plug and permanent abandonment of wells. Subject Flow zones

Flowing medium Cement behind casing Cap rock

Future reservoir pressure

Exposure pressure

Future utilization Consistent use of barriers Control lines in the well

Low-radioactive tubular

Description In addition to the original producing formations, there must be identification whether there are other formations in the well at shallower depths that have flow potential. Necessary isolation of these zones must also be taken care of. What is the flowing medium from potential zones? I.e. saturated or free gas? It shall be identified where and how long adequate cement columns can be found to set corresponding internal cement plugs. It shall be identified where suitable cap rock with sufficient capacity to withstand a formation pressure is located for all identified flow zones (also where this is used as a secondary barrier). Describe expected future shut-in reservoir pressure that the reservoir will rise to in a future perspective and what is the basis for such calculations. Artificial gas or water injection may have to be taken into account. It shall be explained how the maximum exposure pressure for primary and secondary barrier is derived as a function of the source reservoir pressure and any hydrostatic column. Can the field be the subject to future utilization as new development or CO2 storage? Are all wells in the field isolated across the same cap rocks to avoid cross-flow between the wells? Are there control lines in the well that must be removed in order to set the primary and secondary isolation plugs in the well? Can cable clamps preclude setting cement plugs on the outside of the tubing? If there are indications that it is low-radioactive deposits on the pipe to be pulled, precautions must be taken for handling and storage.

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The checklist should be further developed with more items as experience is gathered.

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