This paper details Vetco's floating subsea production system experience during the Petrobras Enchova/Bonita Template project. Specifically, it considers the following aspects:
Template system design to accommodate Wellheads, trees and a subsea manifold.
Tubing hanger and subsea tree installation procedures.
Simultaneous workover and production operations.
The intent is to emphasize the operational considerations. The overall system design ought to accommodate all likely operations with ease. Careful preplanning is required and a strong interaction between operator and equipment supplier is an absolute necessity for success.
Template System Design
Wellheads and Tubing Hangers
Control Umbilical System
Simultaneous Workover and Production.
The Enchova/Bonito Production System is located in the Campos Basin area, 250 kilometers north east of Rio de Janeiro and approximately 90 kilometers distant from the Brazilian Coast. A combination of six template trees and four satellite trees produce through a retrievable template mounted manifold system and a single 8" flexible production riser to a semi-submersible processing facility (Penrod 71). After processing on board the floating production facility (FPF), the oil is sent to one or another of two CALM type single buoy tanker loading facilities. Again, a single 8" flexible line is used. Gas is also compressed and sent to a subsea pipeline to shore through a flexible 8" flowline.
The six template trees are located directly beneath the FPF In 192 meters (620 feet) of water.
Three of the satellite wells originally produced directly to the Penrod 72 via flexible flowlines/risers. The Penrod 72 was another FPF located 3 kilometers from the template. In March 1983, these wells were disconnected from the Penrod 72. Their flowlines were re-laid and connected to the template system. Thus all satellites currently produce through the manifold to the Penrod 71. This illustrates the system's inherent flexibility.
The template specification called for a cluster of wells with provisions for laying in satellite wells, a subsea manifold and a production riser system that would permit simultaneous workover and production by the FPF, located directly over the template. The final design included:
Six well slots
Four satellite well flowline connections
A subsea manifold base for ten wells and two flexible risers
Integral piping between the well slots and the manifold base
Integral control lines (two) between each wellhead slot and the hydraulic control umbilical receptacle.
Integral electric cables between each wellhead slot and the electric umbilical receptacle.
Major components installed on the template had to be designed for easy retrieval and would be recovered to surface for maintenance and repair. As back-up, these components were also designed for atmospheric diving system maintenance (ADS).
The template was built in Brazil while final delineation was continuing. It is constructed from 30 inch OD by 0.625 inch wall tubulars as illustrated in Figure 3. Several sections of the structure were left buoyant to ease trimming during installation. Overall dimensions were 20 meters by 10 meters by 4 meters high. The template weight in air was 220 tons and installation was completed in December 1979 by crane barge.