Siri Pilot Project: First Offshore Extraheavy and Viscous Oil

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 20134, ’Siri Pilot Project - First Offshore Extra Heavy and Viscous Oil (12.3 API) Ever Produced,’ by Alexandre Dutra Sayd, Andre Luiz B. Moco, Celso C.M. Branco, Edson T. Kato, Ivan Parreiras de Carvalho Jr., Joao A. Rosseto, Jose Augusto da Silva Neto, Josiane L. Diniz, Marcelo Brennand, Marcelo Guarda, Miguel Pittella Franco, and Thomas Edison Brasil, Petrobras, originally prepared for the 2009 Offshore Technology Conference, Houston, 4-7 May. The full-length paper describes the appraisal and pilot testing of a large, offshore highly heterogeneous carbonate 12.3ºAPI reservoir in 100-m water depth. The successful pilot production started on 31 March 2008 to the floating production, storage, and offloading (FPSO) vessel Cidade de Rio das Ostras (Fig. 1). Since then, pilot production has been monitored closely by permanent-down-hole-gauge (PDG) and electrical-submersible-pump (ESP) sensors used to update a reservoir-simulation model. Preliminary results show more-viscous oil than initially expected in a more complex reservoir. Introduction In the early stages of exploration and production of the Campos basin offshore Brazil in the late 1970s and early 1980s, a shallow (900-m true vertical depth) Siri carbonate reservoir was discovered in water depths of 100 m. Although the volume in place was large (currently estimated at more than 300 million m3), it was considered noncommercial because of the 12.3°API oil gravity and 320-cp viscosity. At that time, there was an abundance of lighter oils to be developed beneath the same area. In addition, the technology for extracting such heavy and viscous oil in an offshore cold environment had not been developed yet. In 1993, a vertical development well, designed for the deeper reservoir, tested and collected a bottomhole oil sample. Operational problems during the well test, including water production, made it difficult to quantify reservoir parameters. In 2002, new studies were made, which led to the drilling and testing of a pilot vertical well, later sidetracked to a long-horizontal-section (2000 m) well, revealing a better-than-expected reservoir scenario. An ESP-aided flow test in the vertical well produced an impressive productivity index. In this context, the Siri reservoir appeared as a candidate for a pilot production project. Many other heavy- and extraheavy-oil discoveries were made in Campos basin, which caused additional interest in testing and development technologies.