During 1995, Subsea Offshore Ltd and their Brazilian partners Consub, in a Cooperation Agreement with the Brazilian National Oil Company PETROBRAS, developed the MAC Manifold concept The design comprises a conventional production manifold containing manually operated valves and a retrievable control system that actuates these valves under the command of the host platform By separating the actuators from the valves, considerable cost and weight savings are made with increased long-term system reliability A prototype system was built which underwent comprehensive factory testing followed by accelerated lifetime testing offshore Brazil to demonstrate reliable operations over a 5-year period
PETROBRAS are recognised as one of the world leaders and innovators in deepwater production systems, having considerable experience in producing oil from their MARLIM and ALBACORA fields in the Campos Basin in water depths ranging from 100m to depths greater than 600m Production from these deepwater fields is by semisubmersible Floating Production Systems (FPS) which collect the output from a number of wellheads through flexible flowlines and then export the production via flowlines to shore or by offloading to tankers In their quest for lower operating costs, higher efficiency and expertise in operating even deeper fields, PETROBRAS are continually developing new technology through research and development programmes such as the PROCAP 2000 Programme The MAC Manifold concept has emerged from the studies into improving production efficiency related to the use of subsea manifolds to combine and control wellhead output on the seabed prior to delivery to the floating production platform
The two main deepwater fields currently in production - MARLIM and ALBACORA - represent huge reserves and correspondingly large development potential The development programmes for both of these fields are organised in different phases, with the MARLIM and ALBACORA fields expecting to each have approximately 150 wells producing at their conclusion
The economics and indeed the practicalities of producing from such a large number of wellheads directly to the FPSs has led PETROBRAS to the preferred use of subsea production manifolds that combine the output from several wells and therefore reduce the number of export flexible flowlines required Two such manifolds have been recently installed in the ALBACORA field
Typical subsea production manifolds comprise a number of connection points for the flowlines from the wellheads and a set of isolation and choke valves for each This enables
output from each of the wellheads to be regulated using the production choke valve
control of gas-lift pressure by the setting of the gas-lift choke valve
output routing to production or test headers
complete isolation of wellhead(s)
There are additional services provided on the manifold such as chemical injection lines and optionally a service line for pigging operations The process valves on the manifold are fitted with hydraulic actuators that allow their remote operation under the command of the control system
