Gas FPSO - How Soon to Reality?
Authors: Wagner Jan , Cone Stan 
Published: October 2008

Today's FPSO applications primarily process oil production while associated gas is re-injected where there is no gas pipeline infrastructure available. Remote dry gas fields, however, no matter their size, often fail to be produced because of either technical or economic factors. Production of remote dry gas fields would require a "gas-only FPSO" (GFPSO). A GFPSO would essentially be a floating gas production and conditioning facility. Principal export products from a GFPSO would be a LPG liquid, a C5+ condensate liquid and pipeline quality residue gas. Transport of the residue gas remains the biggest problem facing implementation of a GFPSO.

Gas can be transported or readied for transport by one of four generic methods. These are:by gas-phase pipeline;by reducing gas volume through liquefaction or compression (LNG, CNG);by conversion to another form of energy such as electric power orby converting the "methane molecule" to a liquid product (methanol, GTL).

The paper compares four of these options, Pipeline, CNG, Power and LNG technically and commercially using a simple pay back economic analysis approach. The paper examines each option based on a rate of 400 MMSCFD of feed gas. This volume was selected because the weight of topside facilities necessary for this flowrate can be carried by commonly available hull sizes. The Power option, at this gas rate, could generate 2000 MW of power which would require more turbine generators than hulls of the size contemplated here could accommodate and is therefore discussed only on its technical merits.

Under the assumptions used here the CNG option demonstrates the lowest overall investment for the operator. This is only true however on the assumption that CNG ships are available. Since none of these ships has yet been built the economics of the initial CNG projects will reflect the capital costs of the ships in some manner not considered here.

The Pipeline and LNG options tend to show a tradeoff beginning at about 2000-km distance from the market. The actual economic justification and transportation method chosen for a specific project will depend on the unique combination of parameters facing that project development. What this analysis shows is the concept of a GFPSO is technically and commercially feasible and there are technically proven options available for production of stranded dry gas reserves. A GFPSO project can be expected in the not too distant future.

Introduction

Today's FPSO applications primarily process oil production while associated gas is re-injected where there is no gas pipeline infrastructure available. Processing of associated gas to recover NGL liquids has been performed on floating facilities in a few installations but the residue gas is still re-injected. Technology developments in gas utilization processes, continuing discovery of both oil and gas reserves in remote and/or deepwater locations, increasingly strict regulatory requirements and changing market pressures all combine to drive both technical and commercial aspects of recovery of associated gas in remote locations. The result will inevitably be combination of traditional oil production facilities and gas utilization facilities on a single vessel. Some observers consider this option as technically feasible now.