Subsea TFL Systems - A Technology Update

Abstract

This paper presents and analyzes equipment development and testing, completion procedures, and maintenance operations using through-flowline (TFL) methods on five subsea wells in 100 to 200 ft (30.5 to 61 m) of water offshore Brunei. These wells, installed in 1974-76, presently are operated by Brunei Shell Petroleum and include both single-and dual-string (multizone) completions. Introduction In the early 1970's, Shell Internationale Petroleum Mij. (SIPM) undertook a series of studies aimed at the development of systems for producing deepwater oilfields beyond the continental shelf. An important building block in deepwater production systems would be the underwater completed (UWC) well. A principal objective was that the UWC wells would be drilled, completed, produced, and serviced using remote control and servicing techniques. Downhole servicing of the well would be done by pumpdown TFL techniques. Single-Zone Well In 1971 it was envisaged that the UWC wells would have to be large producers for an economical deepwater field development. The terms of reference established for a diverless deepwater subsea completion resulted in these basic requirements and assumptions:the well must be a prolific producer of 5,000 to 10,000 B/D (794.9 to 1589.8 m3/d);no artificial lift by gas lift would be needed;sand production would not be present;completion would be as simple as possible, preferably with a single production string probably 4 1/2 in. (114.3 mm) OD; androutine well servicing by TFL. It was decided to install a pilot UWC (Fairley 16) offshore Brunei (Borneo) in relatively shallow water, permitting easy intervention by divers if necessary. For this purpose a project team was set up in Brunei. Since at that time TFL tools and ancillary equipment had been well-developed only for 2 3/8-in. (60.3-mm) tubing, SIPM approached Otis Engineering Corp. in Oct. 1971 to set up a program for developing and testing TFL capability in the larger tubing size [4-in. (102-mm) nominal size tools].Subsequently Otis designed and constructed the TFL tool string and service tools, a surface-controlled subsurface safety valve suitable for TFL, a Sliding Side-Door (SSD), and a standing valve. The equipment was tested in the Otis test well in Dallas from Aug. to Oct. 1972. A number of modifications were made to the equipment. It became apparent that the "reach rod" approach using conventional sucker rods led to unacceptable friction resistance in the TFL loops. ("Reach rod" refers to an operation whereby a flow control may be installed in a nipple below the TFL circulation point by using rods or bars to span the distance between the flow control running tool and the TFL piston units, which must remain above the circulating point.) To counter this friction, knuckled spacer bars approximately 3 ft (1 m) long were introduced and later tested successfully. JPT P. 1538＾