PETROBRAS Experience on Water Management for Brown Fields
Authors: Lara Anelise Quintao , Nunes Giovani Cavalcanti , Figueiredo Laura , Melo Marcel , Luz Junior Euripedes Barsanuplho , Motta Rogerio , Lage Ronaldo 
Published: May 2011

Brown fields usually associate high volumes of produced water with old and reduced performance units. Because most of Petrobras fields have been producing for more than 20 years now, delivering specified oil and gas has become an increasingly more difficult task. To guarantee operational and economical sustainability debottlenecking is an option but because most of its production comes from offshore fields, the cost of revamping and maintenance of such units can be prohibitive. Alternative options such as sending off-spec oil for onshore treatment, subsea separation, produced water reinjection, infill drilling or even relocating units have been analyzed. Environmental restrictions as well as economic limitations create a huge challenge for which new technologies play a big role. This work presents Petrobras experience with Brown fields and its approach to problem solving. The produced water perspectives are shown and future trends with the use of innovative technologies are explored.

1- Introduction

Initial exploitation of offshore fields in Brazil date back to the 80s when fixed leg platforms were used to produce shallow waters accumulations in Campos Basin. Central units were designed to treat its crude as well as the oil collected from sattelite platforms. The oil was then pumped to the continent through pipelines.

Subsequent discoveries were made in deeper waters. Fields such as Marlim, Roncador and Albacora had a water depth ranging from 500 to 800 meters. In such cases the cost of fixed leg platforms was prohibitive and semisubmersibles were adopted. Once again pipelines were used to send the oil to the continent.

During the 90s as new discoveries were made in greater depths a variety of alternative concepts were considered: semisubs, FPSOs, TLPs and SPARs. A strategic decision was made to go for FPSOs, taking advantage of the great availability of low cost oil tanker hulls at the time. The cost of converting such units paid off when compared to buying new hulls. A complex logistic system of shuttle tankers was created to handle the oil offloaded from such platforms. Pipelines were no longer considered and for those semisubmersibles whose construction had already started FSOs were used to store their oil.

For platforms with bottlenecks in their water treatment systems it has been pondered the installation of an Oil Treatment Station. This water would have to be pumped through pipelines to an onshore Oil Treatment Station to be able to be treated and disposed properly. However this kind of approach would bring a risk because it would also result in a high corrosive potential to the submarine pipelines. To reduce this risk, the premise was that all produce water should be treated at the origin at the Static Production Unit, preventing the transport by pipelines and keeping the integrity of the ducts.

Further preventive measures would have to be taken, such as, injection of corrosion inhibitors and corrosion monitoring coupons.

With the availability of ships such as Petrobras VLCCs: Cairu, Vidal, Henrique Dias and Jose Bonifacio, those would be used as an alternative instead of upgrading offshore processing plants, which would require costly operation interruptions. Besides, that would also reduce the use of pipelines.

These FSOs would be equipped with a Turret system that would replace the " monobóias?? that often had operational problems. The alternative with FSOs became interesting, because it would ensure tankage to reprocess oil whenever necessary (operational problems at treatment plants).