Summary A technological breakthrough within the application of wireline technology has been achieved. In August 2008 on an offshore platform on the Norwegian continental shelf, a wireline tractor and a new wireline milling system were used to mill and remove a permanent bridge plug at 4,147 ft measured depth (MD). The operator decided to mill out the plug on electric wireline and worked closely with the service company to develop this novel solution. Having developed and tested several bits and milling tools, results showed that by combining the wireline miller with hydraulically provided weight on bit (WOB), it would be possible to mill out the retaining rings of the plug, which would cause the plug to collapse. The milling-control unit allows the WOB to be adjusted for each application and also controls the reactive torque—the force generated when the milling bit engages the plug. The service company was able to develop the solution within the client's parameters and in accordance with the timeline set out for this project. The offshore operation was completed in 3 days, to the operator's satisfaction. In another platform well, a permanent bridge plug had been set in 2003 in the sealbore between two screen sections [3-ft seal- bore, 67° well angle, 4.75-in. inner diameter (ID)]. The plug was set in order to isolate the somewhat higher water cut in the lower reservoir zone to prolong oil production from the well. In 2006, the well drowned after a 2-week-maintenance period. Two years later, a coiled-tubing (CT) gas lift operation was carried out with good results. It was then decided to remove the permanent bridge plug to reopen for production before another CT gas lift operation was carried out. A method for milling the permanent bridge plug was developed on the basis of lessons learned from the other plugmilling operation and by extensive testing at the service company's facilities. The operation was completed successfully in 13 days. This new application for milling completion hardware and other wellbore obstructions offers a cost-efficient alternative to existing methods. The success of the milling operation is a significant achievement and has pushed the limits for what is possible on electric wireline. This paper will examine two cases of milling bridge plugs on electric wireline and the technical challenges that had to be overcome in offshore operations.The first case used the well stroker as WOB, and the second cased used the well tractor as WOB.

In recent years, the number of subsea wells has increased steadily; a 2011 report estimated more than 5,500 worldwide. One of the key challenges the industry faces with subsea wells is generally lower recovery factors compared to wells with surface access. A key reason for this difference is because workover activities to improve recovery rates in subsea wells has traditionally required use of large rigs, risers, jointed pipe or coiled tubing (CT), with high operating rates. The high costs of these operations can make it difficult to achieve the necessary increases in production rates and revenue to justify the workover investment, even with increasing oil prices; therefore, operators often forgo production-improvement workovers. However, a growing global population and soaring energy demand means that operators are facing increasing pressure to maximize production and value from mature assets. These challenges have spurred development of alternative, lighter weight, more cost-effective intervention methods to enhance recovery rates in deepwater, subsurface wells. These alternative technologies include electric-line tools that can be run from smaller, dynamically positioned light well intervention vessels, instead of large workover ships with risers. These rigless and riserless light well interventions (RLWI) improve scheduling flexibility and reduce costs, thereby reducing barriers to performing subsurface well interventions and enabling subsea operators to realize oil recovery rates of 50% or more. Today many industry companies have a clear tendency to migrate towards lightweight, more cost-effective alternative solutions. But for some, misperceptions still exist and skepticism remains for using RLWI for deepwater subsea wells. However, over the past decade, RLWI has achieved a solid track record of demonstrated value and is an inherently safer method for subsea well interventions, compared to conventional heavier methods. This paper describes the opportunities to improve recovery rates in subsea wells using the lighter, more efficient and ultimately more productive RLWI methods. Using these techniques has enabled operators to conduct routine planned access to subsea producing assets, improve surveillance and management of interventions, and, ultimately, increase recovery rates. Several case histories and examples are presented. Introduction Challenge: The Need to Increase Production from Existing Assets to Meet Growing Global Demand for Energy. Looking at peak oil production from a number of the major oil producers shows that many of them have reached peak oil production over the last ten years (Table 1) the industry is striving to find new resources to replace diminishing reserves and to meet increasing global demand; these factors are moving exploration and development into deeper water offshore, where currently more new fields are being developed subsea than from platforms (Strategic Offshore Research Ltd. 2012).

A further evolution of wireline intervention technique has emerged allowing mechanical manipulation in horizontal wells using a combination of Wireline Stroker and field proven Wireline Tractor technology - best described as Well Construction on wireline in a highly deviated well. This technology represents a cost-efficient method for setting and retrieving of specific downhole hardware (i.e. plugs and straddles) as a resource-efficient alternative to existing technologies. This paper will present the following case history and the benefits of the operation, particularly in deviated wells, where tractor technology in combination with the Wireline Stroker exemplify the advantages of this technology. In a well offshore Norway, producing since 1995, completed with 2 Sliding Side Doors (SSD) to control zone production, attempts had been made to close both SSD's in October 2003, but only the upper SSD was possible to close. A two-piece straddle was sat above the lower SSD, which however showed no change in production. PLT results showed an internal leakage in straddle and tubing; straddle was therefore retrieved in February 2006 and the well temporarily plugged. Later in 2006, it was decided to perform a new intervention in order to remedy the situation and a Tractor/Stroker combination was considered optimal for performing the operation, as an alternative to a Coiled Tubing operation. Introduction Well P-24 is an oil producer at Snorre A. It is a 5 ½" monobore deviated well completed in 1995 with perforations in the Upper and Lower Statfjord sands in both the Western Fault Block (WFB) and in the South Western Fault Block (SWFB). The well has produced 4.6 mill Sm3 oil since it came on production in 1995. In 2003 the water cut level was increased to more than 80%, the GOR was 2100 and the oil rate had dropped to 100 Sm3/day. It was anticipated that the high water cut and GOR mainly came from S1 and S2 in the WFB. The P-24 completion design allows these sands to be isolated by two mechanical sleeves and in 2003 an intervention was planned to close the sleeves in order to shut off the production from these zones. However, this intervention was not successful as only the upper sleeve was closed. A 2-section straddle was installed across the lower sleeve using tractor on wireline, but the well production profile remained unchanged. A PLT log indicated a leakage in the straddle.

A technological breakthrough within the application of wireline technology has been achieved. In August 2008, on an offshore platform in the Norwegian Continental Shelf, a wireline tractor and a new wireline milling system were used to mill and remove a permanent bridge plug at 4,147 ft MD. The operator decided to mill out the plug on electric wireline and worked closely with the service company to develop this novel solution. Having developed and tested several bits and milling tools, results showed that by combining the wireline miller with hydraulically provided weight on bit (WOB), it would be possible to mill out the retaining rings of the plug, which would cause the plug to collapse. The milling control unit allows the WOB to be adjusted for each application and also controls the reactive torque, the force generated when the milling bit engages the plug. The service company was able to develop the solution within the client's parameters and in accordance with the timeline set out for this project. The offshore operation was completed in three days to the operator's satisfaction. In another platform well, a permanent bridge plug had been set in 2003 in the sealbore between two screen sections (3 ft sealbore, 67 degree well angle, 4.75" ID). The plug was set in order to isolate the fairly higher watercut in the lower reservoir zone to prolong oil production from the well. In 2006, the well drowned after a two week maintenance period. Two years later, a coiled tubing (CT) gas lift operation was carried out with good results. It was then decided to remove the permanent bridge plug to re-open for production before another CT gaslift operation was carried out. A method for milling the permanent bridge plug was developed based on lessons learned from the other plug milling operation and by extensive testing at the service company's facilities. The operation was successfully completed in 13 days. This new application for milling completion hardware and other wellbore obstructions offers a cost-efficient alternate technology to existing methods. The success of the milling operation is quite an achievement and has pushed the limits for what is possible on electric wireline. This paper will examine two cases of milling bridge plugs on electric wireline and the technical challenges that had to be overcome in offshore operations. The first using the well stroker as WOB, the second using the well tractor as WOB.

The combination of increasing global energy demand, known reserves being depleted, and the offshore locations of new oil and gas discoveries is pushing drilling and production into deeper and deeper waters. As a result, the number of subsea wells has increased steadily over the years to more than 5,500 by the end of 2012. Unfortunately, due to their location in deep water, interventions in subsea wells have typically required drilling rigs. Thus operators have been reluctant to perform interventions on these wells. This problem has only been exacerbated as drilling rates increase and sourcing rigs becomes more and more difficult. Thus, recovery factors are much lower-typically 10% to 30% lower-than recovery rates of dry-tree, platform-based wells. Therefore, cost-effective riserless light well interventions (RLWI) are crucial if subsea operators are to realize the full potential of 50% oil recovery (or more) from their subsea fields. This becomes increasingly true as wells age without proper maintenance.Many opportunities exist to increase recovery rates in brownfields. From milling scale and debris to cutting tubing without using explosives to setting packers and manipulating or changing downhole hardware-all these and much more can be done with RLWI. As proof of concept, several case studies of specific interventions and the resultant productivity increases will be discussed. We will also discuss how adoption and use by North Sea operators has let them increase recovery from 36-46%. For example, Statoil estimated that in 2010, the contribution of RLWI interventions was in the range of 15 billion NOK (2.5B USD).In addition, we will show the increasing effect pro-active interventions have on recovery rates over time, for selected Norwegian fields. Finally, we will discuss how increased use has made these operations much more routine while also providing opportunities for the technology to evolve. This is a trend that will only continue as operators request additional services in increasingly challenging environments, particularly outside the North Sea.