In the last part of this decade production targets have moved to deep and very deep-water environments. Petrobras, for instance, is preparing to start producing oil in waters as deep as 2000 m (6560 ft) in the fields of Roncador and Marlim Sul, still in 1999. Drilling wells and deploying production facilities in such harsh environments are already feasible. The major concern of operating companies is then how to carry on production in the most economical way. These developments should encompass highly productive wells delivering fluids to the least possible number of high flowrate floating or stationary production units. As a consequence, the use of long subsea flowlines and manifolds are expected to increase. This, in association with the cold environment at the sea floor, will worsen the wax deposition scenario. Also, due to the high pressure necessary to overcome these depths, flow conditions are certain to be, for a vast number of cases, inside the thermodynamic hydrate formation envelope. Methods to prevent and correct both classes of problems should be available in the design stages and be at hand when these production systems come into operation. This paper covers some of Petrobrasâ?? efforts in tackling the Campos Basin flow assurance issues, from design considerations to operational experiences, in the past three years. A description of Phase I and Phase II of the Flow Assurance Project is given.
From 1992 to 1996 Petrobras conducted the Flow Assurance project1, under the auspices of PROCAP-2000 Program. Its main objective was to make available methods of predicting, preventing and removing wax deposits occurring in subsea flowlines, pipelines and equipment. Understanding and developing predictive tools for hydrate deposition were the secondary targets of this project.
Many Petrobras offshore fields, which were developed prior to the Flow Assurance project (Phase I), were designed without proper subsea layout and facilities to prevent and mitigate wax. Among those, Albacora and Marlim, the two giant fields discovered in mid 80's, became the most troublesome ones to be operated. Their development strategies relied on the use of nonpiggable subsea X-mas trees, and production and service flexible flowlines of different diameters. This hindered the use of conventional pigging.
Therefore, the main concern of the first Flow Assurance project was to investigate technologies to mitigate wax problems in this specific scenario, aiming at these two fields. They were:pipeline thermo-hydraulic calculation tools, pigging, SGN? process2, wax chemical inhibitors, pipeline heating/insulation, and magnetic tools. Of those, pigging and SGN, as the preventive and the corrective measures, respectively, became the main ones to be implemented in large scale, in existing and new production systems.
For the pipeline thermo-hydraulic calculation (flowrate, pressure drop and temperature gradient predictions), an in-house steady-state multiphase computer simulator had to be re-written. Commercial packages, although becoming very popular at the time, were not as adapted as required for the typical well design, subsea layout, flowlines materials, and equipment used in Brazil. For dynamic wax prediction two approaches had been taken: developing proprietary single-phase oil flow model, and taking part in a JIP for the development of a more complete two-phase model. Although both codes were made available at the end of the project, the computer simulator produced by each of these endeavors did not become popular among the technical staff. Apparently, this was because they required special input data, unavailable in the