SS:Subsea Processing - Subsea Processing and Boosting - Building Blocks for PETROBRAS Scenarios
Authors: Euphemio Mauro Lopes , Kuchpil Cassio , Figueiredo Mauricio Werneck 
Published: July 2009

In the last 30 years or more PETROBRAS discoveries offshore were predominantly in deepwater. The successful history was supported, among other pillars, on a policy of investing aggressively on R&D projects through its R&D Programs like PROCAP-3000, among others. Specifically, Subsea Technology and Process have done much to unlock the non-conventional deepwater and heavy oil resources offshore Brazil and will continue to do so. High levels of activity in these areas will remain necessary with increased technology content. In particular, the shift to Subsea Processing is becoming more marked as a means to: 1-anticipate production, 2-improve reservoir recovery, 3-debottleneck high water flow rate field platforms and 4-allow marginal fields development.

Actually, after successful implementation of several - technology projects, on subsea boosting and processing, the leading operators in these technologies have demonstrated that subsea processing is definitely a field development tool as predicted decades ago. Bearing in mind the above considerations, this paper introduces the updates on PETROBRAS most recently subsea boosting and processing efforts. The work hereafter includes applications and developments on the following technologies: Subsea Raw Water Injection, High Power ESP, Subsea Gas-liquid and Oil-Water Separation, Subsea Multiphase Pumping, Seabed ESP. It examines the main hurdles for applying these technologies Offshore Brazil on long tie-backs and ultra-long tie-backs (for instance: producing subsea to beach or very long tie-backs - 150 km or more).

Introduction

One can say that boosting technologies will permit to construct the subsea to shore system; nevertheless these are just part of the technological puzzle. There are still several technologies to come out of the box to construct an oil or gas subsea to shore. Some of the hurdles are complexities for instance on the conventional issues like: flow assurance, corrosion protection, chemical injection, emulsion handling, water production and slugs. Additionally it is necessary also to carry out new technology developments on electric power, on deepwater oil-water separation, on multiple emulsion formation.

Actually the subsea to shore concept comes to compete mainly as an alternative to offshore platforms where no existing infrastructure is present. The high prices (and the time schedule) for constructing new platforms and the raising prices of operational expenditure scores heavily for the subsea to shore and stimulates efforts, studies and technology developments to achieve it.

Nevertheless, new developments that configure a typical scenario for the subsea to shore approach are not easily found these days. Petrobras operated oilfields, on the other hand, present several opportunities to develop some important components either on boosting or on subsea processing, to improve recovery of mature fields, making use of subsea installations to overcome limitations imposed by the existing infrastructure. Small fields where old floating units can be replaced by subsea systems or fields where subsea boosting or processing systems optimize the production are the predominant scenario. These equipment developments, together with additional studies, are intended to provide the necessary tools to be applied on most scenarios.

Petrobras applications nowadays are dominated by fields producing oil with associated gas and along the discussion on the main issues involved in subsea boosting and processing systems we will be updating the information about the company efforts on its projects.

External Energy for Flow: alternatives

When extremely long tie-backs for oil wells are mentioned, one always thinks either in high DeltaP seafloor multiphase pumps or reboosting stations. Long distances does not necessarily mean that the friction losses on the subsea pipeline are the highest. It is not uncommon the cases where the pressure drop due to hydrostatic column may be five to ten times higher than the pressure drop on the horizontal flow. This can be reached for instance with 250 km tie-back, with a 28 degree API on 18" pipeline. So it is not always necessary a reboosting system along the pipelines, on extremely long pipelines.