SIRI Pilot Project - First Offshore Extra Heavy Oil (12.3 API) Ever Produced
Authors: Sayd Alexandre Dutra , Moco Andre Luiz Bueno , Branco Celso Cesar M. , Kato Edson Tsuneo , Carvalho Ivan , Rosseto Joao , da Silva Neto Jose Augusto , Diniz Josiane , Brennand Marcelo , Guarda Marcelo , Pittella Miguel , Brasil Thomas Edison 
Published: July 2009

Some of the heavy and extra heavy oil accumulations offshore Campos Basin have been known since the beginning of the development of the basin, in the 80's, but they never had a chance of being developed due to the technology challenges involved. The maturation of lighter oil fields, associated with recent technology developments has boosted the interest for these heavy oil resources which have been set aside for many years.

This paper describes a case history on the strategy for the appraisal and pilot testing of a large offshore shallow highly heterogeneous carbonate 12.3 API reservoir, at 100m water depth. The pilot was justified aiming at obtaining static and dynamic information of the reservoir behavior such as: volume in place connected by the well, reservoir permeability, presence of internal barriers and reservoir connectivity, aquifer support, effectiveness of long horizontal well (2000m) completed with slotted liner performance, high power electrical submersible pump (ESP) behavior.

The successful pilot production started in March, 31, 2008 to the FPSO Cidade de Rio das Ostras. It has been since closely monitored by permanent down-hole gauge (PGD) and ESP sensors used to update a reservoir simulation model. Some unexpected shut downs in the processing plant shut have created a series of build-ups followed by flow periods which have given the opportunity to better investigate the reservoir although putting some risk in the ESP/VSD operation. Preliminary results show more viscous oil than initially expected in a more complex reservoir (possibly a double porosity/permeability system). Well effectiveness and productivity is also below estimated values nevertheless it has shown a promise for a definitive production plan. Pilot information will be employed in the definitive development plan expected to be implemented in 2011.

1) Introduction

In early stages of exploration and production of the Campos Basin offshore Brazil, that was in the late 70´s and early 80´s, a shallow (900 m TVD) the so called Siri carbonate reservoir was discovered in water depths of 100 m. Although the huge volume in place - presently estimated in more than 300 million m3 - it was considered noncommercial owing to it´s oil properties: specific gravity of 12.3 API reservoir viscosity of 320 cP in the reservoir (this value was obtained more recently based on single-phase PVT quality oil samples). At that time there were plenty of lighter oils beneath the same area to be developed, the technology for extracting such heavy and viscous oil in offshore cold production hadn't been developed yet (1). In 1993, a vertical development well, designed for the deeper reservoir, tested and collected a bottom-hole oil sample. Operational problems during the well test, including water production, made it very difficult to quantify reservoir parameters.