Pumpdown (TFL) Technology For Subsea Completions II
Authors: Arendt Hank , Heard Tom , Williams Carlyle 
Published: December 2007

Abstract
Subsea completions are gaining in popularity as oil production moves into deeper and less accessible waters. Pumpdown or TFL (through flowline) methods are a practical means of servicing these wells.
The relative low cost of completing new or existing exploration or development wells at the seafloor and bringing each on stream as it is completed provides for a comparatively low initial investment and a quick cash flow. A simple completion designed to maximize production rates makes this package even more attractive. Utilizing TFL for well servicing maintains this attractiveness since no surface service vessel is required and resulting production downtime can be minimized.

Introduction
As petroleum production has moved into deeper and less hospitable waters, costs for production facilities and well maintenance have increased dramatically. For a field to be profitable under these conditions, wells simultaneously must produce large volumes, require minimal maintenance, and be able to generate an early, steady cash flow. Subsea systems can make all this possible.
There are many reasons that operators have turned their attention to TFL for subsea completions. Platform requirements for TFL service are few, thereby substantially reducing costs and concern for depth of operating waters. TFL systems can increase early production and cash flow since drilling and completion can take place while production facilities are being constructed. Service tools can be pumped from the TFL production facility, through the flowlines, and into the tubing. As a result, surface service vessel delays and costs can be eliminated.
There is less hazard of storm and vessel damage with subsea TFL systems. Satellite wells generally may be drilled vertically - an easier, faster, and less expensive method than directional drilling. Where weather conditions could restrict ease of vertical access, TFL subsea well service from a remote location can minimize costly production downtime.
Important to environmentally sensitive areas, congestion is lessened with TFL systems since the only necessary surface facility is a central gathering/production structure. TFL service also offers a measure of safety not otherwise available since personnel need not be in the vicinity of wellheads or production manifolds during service operations. Tree valves can be closed at any time, such as in the event of an emergency shutdown, since there is never a wireline in the well.
Ease of operation, added measures of safety, time savings, and a marked reduction of costs are a few of the more important results from the use of TFL systems.

Applications
There are a variety of existing and potential applications for TFL subsea completion systems. TFL service can produce unique solutions to the operational problems, monetary drawbacks, and safety dilemmas presented by traditional production methods.
Operationally, TFL methods are suited for deep or hostile waters, existing platforms, high sea traffic areas, iceberg regions, deviated wells, and other conventional or unusual conditions. Where prevailing weather or congested waterways would ordinarily hamper servicing by other methods, TFL systems can be designed to operate from remote locations. Therefore, virtually every type of existing subsea production system is adaptable to TFL well service (Reference 7). There are TFL service systems which can operate most producing wells. Examples include wet tree systems with wey-block assemblies, full wellhead loops, and flowline connectors; simple diver-assist trees with entry loops connected directly to the tops of the trees; and hybrid wet/dry systems (see Fig. 1).
Subsea templates that combine a number of well systems provide another area for TFL application.