Material Selection for Brazilian Presalt Fields
Authors: Henriques Carlos C.D. , Joia Carlos-Jose Bandeira , Guedes Flavia , Baptista Ilson Palmieri 
Published: April 2012

One of the most important oil discoveries of the last 10 years, in the wholeworld, was made in Brazilian offshore deep waters. The so called BrazilianPre-salt province comprises reservoirs below a layer of variable thickness ofsalt, which can reach up to 2,000m. Since 2006 several oil fields werediscovered in this province and the initial evaluation shows that the oilreserves of the fields evaluated so far may, in the future, double the currentBrazilian proven oil reserves.

Among the technological challenges that are being faced to put these hugereserves into production, an important one is the material selection forcorrosive environments. High pressures coupled to variable CO2 contents makethe use of carbon steel in wells, risers and topsides pipings nearlyimpossible, requiring extensive use of Corrosion Resistant Alloys (CRAs).

This paper describes the work that was done to optimize the material selectionfor the initial pre-salt production development projects. This includes effortsto simulate the corrosive environment in wells, which are subjected toextremely high pressures and variable concentrations of CO2. Interactionbetween fatigue and corrosion in deep water risers and the materialsrequirements for the topside of floating production units had also to be takeninto account, as well as materials to withstand extremely low temperatures thatmay occur in the piping of the CO2 compression plant for injection in thereservoir, due to situations of depressurization (one important assumption inthe pre-salt development is not to vent the CO2 produced with the associatedgas. This CO2 will be reinjected in the reservoir, improving the oil recoveryor disposed in aquifers close to the producing reservoirs).

In parallel with the materials selection process, a great effort is beingcarried out on research and development, aiming to optimize and improve thematerials used in the production systems. The most important lines of researchare:Development and test of new metallic alloys for production wells;Test of coatings for water and gas injection well tubing;Alternative routes for fabrication of metallurgically bonded pipes;Use of non-metallic materials for risers.

Introduction

The impact of Presalt Discovery Offshore Brazil

The Brazilian offshore province began to attract the attention of the oilindustry a couple of decades ago. Since then, the development of giantdeepwater fields in Campos Basin such as Marlim, Albacora and Roncador haveproved the basin potential (Ref.1, 2). But this potential seems to have reacheda new scale in 2006, with the huge Tupi discovery (later on renamed as LulaField, complying with to Brazilian Law that requires that oilfields take thenames of sea animals). The Lula field is located in Santos Basin deep waters(2,200m), south of Campos Basin, below a salt layer which, in some locationsreaches more than 2,000m thick (Fig. 1). The Lula Field alone has estimatedtotal reserves of more than 6 billion boe and. other discoveries in SantosBasin adjacent explorations blocks, such as Guará, Iracema (located in the sameexploration block as Lula), Carioca and others, have confirmed how prolificthis new province was. Moreover, as the salt layer extends north of SantosBasin, into Campos and EspÍrito Santo Basins (Fig. 2), several discoveries weremade in Presalt layers of these Basins, including areas where oil was alreadybeing produced (from post-salt reservoirs) such as Jubarte Field, in EspÍritoSanto, allowing fast connection of the new pre-salt wells to existingproduction facilities.