Investigation of a Floating-Liquefied-Natural-Gas Unit for Brazilian Waters
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 20677, ’Evaluation of a Floating Liquefied Natural Gas for Brazilian Scenarios,’ by A.P.F. Teles, A.S. de Abreu, A.C. Saad, D.C. deMello, F.B. Campos, J.P. Silva, L.F.N. Quintanilha, and M.D.A.S. Ferreira, Petrobras R&D Center, originally prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed.

The latest discoveries of oil and gas in the Brazilian offshore area present new challenges for gas transportation because of their distance from the coast. For these new scenarios, floating-liquefied-natural-gas (FLNG) units may be a good solution for the natural gas volume produced. Because this technology has not been proved yet, there are many challenges to overcome to turn FLNG into an economically and technically feasible solution.

Introduction

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

The latest discoveries of oil and gas in the Brazilian offshore area present new challenges for gas transportation because of their distance from the coast. Offshore pipelines are economically feasible for short or medium distances, depending on water depth. The concept of an FLNG combines a tailor-made vessel with isolated cryogenic tanks in the hull, a liquefaction plant on the topside, and offloading systems on the deck. Because the FLNG concept combines existing and proven onshore and offshore technologies, integration is a critical issue.

Development Issues

LNG. LNG is obtained when a stream of suitably treated natural gas is cooled to −160°C, at atmospheric pressure. The gas-to-liquid phase change reduces the gas volume 600 times. LNG is the chosen technology for sea transportation in carriers of large quantities of natural gas to distant markets when a pipeline is not feasible.

The LNG sea-transportation model has, basically, four items: the field processing plant, the baseload liquefaction plant, the carriers, and the regasification terminal. The field processing plant receives the reservoir production, does the primary separation, and treats the gas to avoid hydrate formation in and corrosion of the exporting pipeline. The baseload liquefaction plant further treats the gas to remove heavy hydrocarbons and impurities, adjusting the natural-gas composition to the process requirements and to the LNG sales specifications. This plant usually is placed near a marine terminal where special carriers, with isolated cryogenic tanks, are filled with LNG. These carriers transport the LNG to the regasification terminal commonly placed near a marine terminal.

Liquefaction Technology

The baseload LNG industry has more than 40 years experience, with the first plants consisting of simple liquefaction technologies based either on cascade or mixed-refrigerant (MR) processes with train capacity less than 1 million tons per year.