Pigging In Subsea Flexible Flowlines

ABSTRACT Subsea flowline pigging is a difficult task because the access to installations involves complex and costly operations requiring high reliability in equipment and procedures. The problem of paraffin build-up in flowlines installed in cold sea bottoms is a permanent challenge. In this paper the Albacora field illustrates the work PETROBRAS have been doing in these scenarios. Through the example of the Albacora field in Campos Basin, we will see the multiple aspects of an evolving project, and the different perspectives and possibilities for subsea pigable installations. INTRODUCTION Production flowline pigging which is a common usage for many oil fields, on land and shallow waters, turned into a challenge for deep offshore scene, due to accessibility problems and the complexity of subsea operations. With water temperatures around 5° C at the sea bottom, paraffins and asphaltenes of high molecular weight in the oil, the Albacora field presents the problem of deposits in flowlines with dramatic decrease in production of wells of high potential. The Albacora field in Campos Basin discovered in 1984, is located on the continental slope, approximately 250 Km northeast of. Mo de Janeiro and about 100 Km from the coast, has its limits within 200 and 2000 meters of-water depth (figure 1). The present layout of installations in the field, first phase in an development which envisage three phases, consists of a floating production platform and 14 producing wells, 13 of which gathered in two subsea manifolds and one connected directly to the platform. An export line is connected to two monobuoys via a subsea manifold which permits continous loading of produced oil in shutle tankers. The associated gas is transported to Garoupa platform situated 50 km away, through an 16 in pipeline. An schematic flow diagram for this first phase is presented in figure 2. In October 1987, the production of Albacora field began, and two months later, an accumulation of paraffin in the production separators was observed. In July 1988, due to operational difficulties, the separators were opened and 800 liters of paraffin removed. At this time a reduction in the flow rate of well RJS- 329 and RJS-330 was noticed. After unsuccessful tries with circulation of solvent, the replacement of the flowlines, brought back initial production. Such problem has been occuring frequently since then, and some flowlines were retrieved for cleaning before the thermochemical cleaning process became operational for flowlines. So PETROBRAS, facing the problem of internal build up of paraffin in subsea Q flowlines at Albacora Field, create a group to study and develop possible methods to prevent and remove the wax. Among other methods, the use of paraffin inhibitors, the development of the thermochemical process Nitrogen Generation System (NGS) and the use of scrapers were privileged, nevertheless studies on thermal insulation, electrical heating were continued and the research on the mechanism of paraffin deposition was intensified to provide theoretical suport for these approaches.