Subsea Processing at Parque das Conchas (BC-10): Taking Flow Assurance to the Next Level
Authors: Iyer Sada , Lang P. , Schoppa Wade , Chin Y. Doreen , Leitko Alan 
Published: July 2010

The Parque das Conchas (BC-10) development located in the deepwater BC-10 block offshore Brazil - comprises of relatively low-energy, low-API reservoirs (Ostra, Argonauta B-West) and one high-GOR field (Abalone) - tied back subsea 9 to 34 km to an FPSO. To enhance production and maximize recovery, an innovative subsea separation and boosting technology has been employed, consisting of a shallow well conductor that contains a caisson where liquid and gas are separated prior to transport to the surface. In the case of Ostra/Abalone, separated gas flows naturally to the FPSO via a dedicated, un-insulated gas flowline. Separated single phase fluids at the bottom of the Caisson are boosted via an electrical submersible pump (ESP) located within the caisson, and transported to the FPSO in a wet insulated flowline. The heavier B-West fluid is separated and recombined in the caisson and pumped as a multi-phase mixture.

The addition of the Caisson/ESP (C-ESP) subsea separator and pumping system has significantly reshaped the flow assurance challenges and analysis processes typically applied to deepwater subsea tieback developments. For instance, several of the traditional flow assurance concerns - such as hydrate control, slug management, sand handling, and emulsion/foam tendency - will now involve a different set of design and operability requirements. Additionally, " ensuring the flow?? in the C-ESP system itself involves several unique design and operability challenges, associated with separator design and control and mitigation of separation inefficiencies.

This paper describes some of the new challenges and analysis tools to be encompassed by flow assurance engineering, as this new area of subsea processing emerges in deepwater developments. The role of the flow assurance engineer will expand to include subsea " process systems engineering?? - i.e. the application and extension of traditional process engineering approaches to the design and operability of subsea separation and artificial lift systems.

Introduction

The Parque das Conchas development is located in block BC-10, approximately 74.5 mile South West of the coast at the city of Vitoria in Brazil in water depths about 5,900 ft. Shell is the operator with a 50% working interest, in a joint venture with Petrobras (35%) and ONGC (15%). Phase 1 of the development includes three fields - Ostra, Abalone and Argonauta B-West, each with different fluid properties. Argonauta O-North is currently in planning for development in Phase 2. Ostra and Abalone fields use the concept of subsea separation and boosting. B-West uses a novel non-separated boosting system in which the multiphase fluids from the well are separated and then recombined and boosted using a conventional ESP.

The Ostra field will be produced via six horizontal wells. The oil has an API of 24 and a GOR of 274 scf/sbbl. Abalone has an API of 44 and a GOR of 3,800 scf/sbbl and behaves like a gas condensate. B-West has a heavier oil with an API of 16 and a GOR of 194 scf/sbbl. An additional challenge at B-West is the unusually high viscosity of the fluids, especially below the bubble-point.