Evaluation of Floating Liquefied Natural Gas Units for Brazilian Scenarios
Authors: Teles Ana Paula Fonseca , de Abreu Andre da Silva , Saad Arthur Curty , de Mello Darley Carrijo , Campos Flavio Barboza , Silva Juliana Pereira , Quintanilha Leandro Fernandes Nolasco , Ferreira Marcos Donato Auler da Silva 
Published: July 2010

The lastest discoveries of oil and gas reserves in the Brazilian offshore area present new challenges on gas transportation due to their location, far away from the coast. For these new scenarios, Floating Liquefied Natural Gas (FLNG) units may be a good solution for a natural gas volume production around 2.5 MTPA. It is worth saying that this technology hasn't been proved yet. So, there are many challenges to overcome to turn the FLNG into an economically and technically feasible solution for these new scenarios.

One of the main challenges for establishing a LNG (liquefied natural gas) offshore unit is the definition of the liquefaction process technology to be used. Characteristics such as motion effects, footprint, robustness, operational flexibility and asiness, safety, maintenance and availability must be considered when the main differences between the processes are being identified. Depending on the capacity to be attended, liquefaction processes may use hydrocarbon refrigerant mixtures or inert refrigerant fluids.

Due to the environmental conditions in Brazilian waters, side-by-side offloading operations are not possible, as the operational availability would not be large enough. Therefore, LNG offloading would only be achieved through the tandem operational mode. Since the technology available for this kind of operation uses aerial hoses, it will be necessary to provide a bow loading system (BLS) installed on the LNG carrier and also a dynamic positioning system (DP) may be needed for an accurate control of the positioning and maintenance of a relative heading. The study indicates that the cargo containment system (CCS) should fulfill some constraints: let free upper deck area for topsides facilities; withstand any partial filling condition (sloshing impacts); have a good track record; and its configuration should allow inspection and maintenance in the offshore environment.

This paper reports the Petrobras findings on the evaluating of the FLNG technology. Petrobras considers the FLNG unit an attractive option for its scenario, although many sub-systems still present important challenges in order to achieve a good overall performance. The choice of the best technology for each sub-system is still on-going, aiming the largest reliability and the minimum cost possible.

Introduction

The international natural gas market has been growing at a very high rate in the last decades. The mature technologies for natural gas bulk transportation are pipelines and the LNG considering a supply chain based on onshore liquefaction plants and LNG carriers.

The natural gas consumption in Brazil has been growing since 2000. The Brazilian Government's goal for the natural gas participation in the energy matrix is 10% by 2010. PETROBRAS is the main company for Natural Gas (NG) production, transportation and supply in Brazil.