Flow assurance problems in flowlines and pipelines include hydrate formation/blockage, paraffin wax deposition, asphaltene deposition and scale formation on the walls of pipelines, all of which impede the flow of produced hydrocarbons and associated well fluids. Conventional means for pipeline remediation to remove these restrictions include periodic and extensive pigging (either through flowline pigging loops or from subsea pig launchers), chemical injection through umbilicals and high performance thermal insulation (syntactic foam, pipe in pipe, and/or pipeline bundles).This paper presents a review of the types of pipeline restrictions and blockages, and innovative solutions for remediation, including remediation planning techniques, chemicals, debris pick-up gels and intrusive intervention. The intrusive pipeline intervention system conveys fluids directly to the area of any particular problem, using composite coiled tubing and a pipeline tractor. Two significant factors that restrict the use of an intrusive flow remediation system are the design of the production facility and the reach capability of coiled tubing. Past and current flowline designs have not considered the use of intrusive remediation systems, and to-date the use of coiled tubing as the conduit for an intrusive system has not been practical beyond a total distance of 9000 feet. Advances in composite technology have enabled the manufacture of high performance light coiled tubing, which eliminates or reduces the flowline-to-coiled tubing drag force, allowing for longer distance intervention with existing tractors. Subtle flowline design changes enable intrusive blockage remediation systems to yield significant benefits.Maintaining flow of oil and gas through production flowlines is vital to successful offshore and onshore operations. Flow assurance engineering has become a significant part of the feasibility and conceptual design stage of projects, and systems such as active heating employing either electric power or heated fluids have been considered as a method for assuring optimum flow. The application of the flow assurance solutions adds substantially to project CAPEX. In the case of chemical injection or pigging, OPEX is increased, and in most cases operational pigging causes a reduction in production during the pigging operation. In deepwater oil and gas developments the additional cost can be significant, particularly for long tiebacks. The remediation solutions presented herein obviate the need for these high CAPEX and OPEX solutions, without increased risk of long term flowline blockage.

This paper describes an operational subsea wireline system that is self-contained and flexible and offers a safe, economical, and proven method for riserless re-entry into any subsea well. IntroductionApproximately 400 subsea wells currently exist worldwide, and most predictions indicate a doubling of this number within the next decade.Being time-consuming and costly, conventional methods of reentering subsea wells with wireline are not consistent with the lowcost profile required by many subsea developments. This factor has predominantly driven the development of cost-effective subsea wireline systems.The system discussed here was developed over a number of years and has been used to carry out a comprehensive range of wireline tasks from floating vessels in the North Sea. Although generally deployed from a diving support vessel (DSV), the system has been successfully used from a drilling rig to conduct wireline operations in a well, simultaneously with workover operations in an adjacent well, on a subsea template.It is important to realize that any function that can be achieved by conventional means can also be carried out by subsea wireline. Subsea wireline has been used to pull and run surface-:controlled subsurface safety valves (SCSSV's), to set and pull plugs, to pull and run gas-lift valves in side-pocket mandrels, and to run production logging tools and electronic memory recorders.

An important factor in the overall success and cost of an offshore well intervention depends significantly on the choice of the equipment including downhole tools and surface units. Using a conventional workover rig for well intervention is expensive and may not be appropriate in many circumstances. Additionally, intervention of a subsea well can further increase the costs due to the requirements of a floating vessel and subsea systems to access the wellbore.This paper systematically categorizes downhole applications that are performed during well intervention. It reviews techniques such as Wireline, Coiled Tubing (CT) and Hydraulic Workover (HWO) that do not require use of a conventional workover rig and have capability of performing downhole applications in live (under pressure) wells. Included are guidelines for selection of these rigless techniques for the various downhole applications.The rigless techniques are further reviewed in relation to subsea well intervention. The emphasis is placed on selection of a floating vessel along with subsea systems to connect to the well. The paper includes a discussion on market trends that are directed towards either reducing intervention costs or minimizing its frequency.

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