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The Operator of a subsea field in the UK North Sea studied the optimum process for the permanent plugging and abandonment of a number of subsea wells which included a campaign of downhole data gathering and safe suspension of selected wells using a Light Well Intervention vessel (LWI) prior to the arrival of a mobile drilling unit. The criticality of this phase of the operation was to enter already shut-in wells, and to establish access to wells which had not been accessed or worked over for over 20 years. This meant limited data was available for the condition of the casings and completions. In order to safely suspend the wells after the campaign, the wells had to be plugged above the reservoir and the envelope of the well had to be pressure-tested to confirm the integrity of the barriers. Once the well envelope and barriers were successfully tested in accordance to established industry criteria the wells could be safely suspended. It is to be noted that in this phase of the operation the tubing needed to remain in place and was not be retrieved, as the retrieval of the tubing would require a drilling rig. However, the main envelope of the well which had to be pressure-tested is located behind the tubing. In order to assess the condition of the casing behind tubing an Electro-Magnetic (EM)pulselogging tool was run in the well to determine the condition of the casing and to determine the level of the corrosion. This then assists the Operator to design the pressure test values for the operation. The major steps of the operation were as follows: Multi -Finger Caliper (MFC) and EM pulse logging tool to be run inside the tubing using electric wireline to assess the integrity and corrosion condition of the tubing as well as the casing behind tubing.Deep-set plug to be set at the bottom of the tubing to isolate the reservoir.Deep-set plug to be pressure-tested to ensure the plug is set properly.Tubing to be punched to circulate the tubing and A-annulus fluid.The envelope of the well i.e. Completion Jewellery – Casing, Packer, Deep-set plug, etc. to be pressure tested. Prior to pressure testing the EM pulse logging data would be utilised to determine the pressure test values.Successful pressure test would mean successful isolation and suspension of the well, however, in the event of a failed pressure test the root cause of the failure would be investigated using Spectral Noise Logging technique to detect and identify the leak point, e.g., casing leak, packer leak, plug leak etc. This specific logging tool was kept on board as a contingency service in case of a failed pressure test. This paper describes briefly the physics of the measurements for EM pulse logging as well as Spectral Noise Logging in the context of this campaign followed by case studies which illustrate specific well data. The paper also includes a description of additional sensors which were utilised in the campaign in combination with EM pulse logging and Spectral Noise Logging (SNL) to explain how these multiple sensors complement each other to assist with corrosion assessment and leak investigation.
The Operator of a subsea field in the UK North Sea studied the optimum process for the permanent plugging and abandonment of a number of subsea wells which included a campaign of downhole data gathering and safe suspension of selected wells using a Light Well Intervention vessel (LWI) prior to the arrival of a mobile drilling unit. The criticality of this phase of the operation was to enter already shut-in wells, and to establish access to wells which had not been accessed or worked over for over 20 years. This meant limited data was available for the condition of the casings and completions. In order to safely suspend the wells after the campaign, the wells had to be plugged above the reservoir and the envelope of the well had to be pressure-tested to confirm the integrity of the barriers. Once the well envelope and barriers were successfully tested in accordance to established industry criteria the wells could be safely suspended. It is to be noted that in this phase of the operation the tubing needed to remain in place and was not be retrieved, as the retrieval of the tubing would require a drilling rig. However, the main envelope of the well which had to be pressure-tested is located behind the tubing. In order to assess the condition of the casing behind tubing an Electro-Magnetic (EM)pulselogging tool was run in the well to determine the condition of the casing and to determine the level of the corrosion. This then assists the Operator to design the pressure test values for the operation. The major steps of the operation were as follows: Multi -Finger Caliper (MFC) and EM pulse logging tool to be run inside the tubing using electric wireline to assess the integrity and corrosion condition of the tubing as well as the casing behind tubing.Deep-set plug to be set at the bottom of the tubing to isolate the reservoir.Deep-set plug to be pressure-tested to ensure the plug is set properly.Tubing to be punched to circulate the tubing and A-annulus fluid.The envelope of the well i.e. Completion Jewellery – Casing, Packer, Deep-set plug, etc. to be pressure tested. Prior to pressure testing the EM pulse logging data would be utilised to determine the pressure test values.Successful pressure test would mean successful isolation and suspension of the well, however, in the event of a failed pressure test the root cause of the failure would be investigated using Spectral Noise Logging technique to detect and identify the leak point, e.g., casing leak, packer leak, plug leak etc. This specific logging tool was kept on board as a contingency service in case of a failed pressure test. This paper describes briefly the physics of the measurements for EM pulse logging as well as Spectral Noise Logging in the context of this campaign followed by case studies which illustrate specific well data. The paper also includes a description of additional sensors which were utilised in the campaign in combination with EM pulse logging and Spectral Noise Logging (SNL) to explain how these multiple sensors complement each other to assist with corrosion assessment and leak investigation.
Production casings of Cyclic Steam Stimulation (CCS) or steam-assisted gravity drainage wells are exposed to significant temperature variations which in many cases resulted in casing breaks in the weakest part which are typically connection joints. The paper focuses on the new downhole logging approach, in monitoring and detecting production casing connection breaks through tubing without requirement for tubing retrieval. The metal well barriers can be assessed by utilizing electromagnetic (EM) pulse defectoscopy. This is done by running multiple coaxial sensors downhole in tandem. Each sensor generates EM pulse and then records EM decay from surrounding metal tubes. Modeling of recorded EM decay enables precise assessment of metal loss or metal gain in up to four concentric barriers. However, the tool had never been used previously to detect minor defect features as casing breaks through the tubing. To identify casing breaks several yard and field tests have been conducted and new methodologies were developed. The last one included the recognition of specific patterns of raw EM responses, analysis of hole sensors and utilization of data from all coaxial sensors utilized during the downhole survey. The new approach including downhole EM pulse tools and new data analysis have been implemented to detect casing connection breaks in over a hundred Cyclic Steam Stimulation (CCS) and SteamAssisted Gravity Drainage (SAGD) wells. The paper demonstrates the testing of the application feasibility in a comprehensive yard test and extends to real field examples. All detected breaks were confirmed after tubing removal and were successfully repaired. Paper highlights detection challenges due to different casing connection break types: minor breaks, partial breaks (contrary to fully circumferential), and casing breaks aligned with tubing connections. The technology has helped Operators to fulfil the objectives of connection break detection without tubing removal through a non-intrusive, safe, quick and economical approach. Today, CSS and SAGD Operators should confirm casing integrity repeatedly prior to each subsequent steam cycle through the time and resource consuming approach of tubing removal and checking the casing integrity mechanically. Utilizing through tubing electromagnetic diagnostics, enables Operators to pick up multiple casing connection breaks in a single run without tubing retrieval.
Planning and execution of the well plug and abandonment(P&A) requires detailed knowledge of the downhole barrier's integrity status and position of its downhole completion elements.[Maxim Volkov] This input is utilized for the determination of zones for permanent plugs, casing cuts and retrieval procedures. The last one can be significantly optimized if conducted across the zones with minimal total wall thickness. Cutting the casing across casing collars, fins or casing decentralization may extend the operation requiring more time and resources to achieve success. However, the detailed completion information is not always available due to several well handover. This may result in casing cut performed blindly, based on the position of the first casing collars revealed by caliper or ultrasound surveys. This may result in an increase of the RIG operation timing from few hours to few days. The paper shows results of downhole scanning during three subsea wells P&A campaign at the stage of environmental plug deployment. This included cutting and pulling out of casing wellhead elements (casing stumps) after milling works, before setting environmental cement plug in seabed zone. Casing wellhead design may include the first 13 3/8" and 20" casing joint welded fins to centralize casings. Typical casing joint with fins (rigid type) is shown in figure 1. The abandonment program included milling of these casings and the cutting through the minimal or nominal wall thicknesses with avoiding fins and collars of the casings. The depth of the cutting window initially was set from the available well diagrams, which were not available in all the wells. Thus, the main role of the scanning was to verify and optimize the casings cut window depth to perform the process with minimal issues. Figure 1 Casing joint with rigid centralizers-fins.
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