Summary
Liquefied natural gas (LNG) has yet to be deployed in the development of
offshore fields in spite of several detailed studies completed and offshore
technology development demonstrating its technical feasibility. The perceived
risks associated with deploying unproven technology in a high construction cost
and volatrile gas price environment have so far inhibited offshore liquefaction
projects. The potential deployment of such technologies is of paramount
importance considering the massive volumes of natural gas currently deemed as
“stranded” and the exploitation of which is compelling not only because of the
inherent economic benefit but also because of the otherwise adverse impact on
oil production. It is conceivable that deep water offshore locations may
contain quantities of natural gas rivalling those of onshore locations. Such a
statement cannot even be confirmed because drilling for offshore natural gas
reservoirs, expected to be found considerably deeper than oil reservoirs, has
been unattractive exactly because of the absence of coherent exploitation
strategies. If anything, the mere presence of large natural gas deposits even
in the form of solution gas in oil is now often considered as largely
undesirable because of the cost of just handling non-monetized natural gas.
This paper discusses potential offshore LNG processes and reviews natural gas
liquefaction cycles in the context of compactness, ease of operation, process
safety, and efficiency.
Particular attention is paid to the lower-efficiency turboexpander processes
for plant capacities up to 3 million tonnes per annum (MTPA, approximately 0.43
Bcf/d). These cycles offer several advantages over the alternative optimized
cascade and mixed refrigerant (MR) liquefiers for offshore applications.
Introduction
Increasing global demand for natural gas is supporting the rapid growth and
diversification of worldwide LNG production capacity. As demand continues to
grow and the value of natural gas remains high in the major consuming markets,
the impetus to monetize more difficult and remote gas resources also grows.
There is a drive to develop stranded gas fields that have remained undeveloped
for many years to satisfy the thirsty energy markets with a cleaner fuel than
coal or oil (in terms of lower emissions of greenhouse gases and other
pollutants) that has kept the industry keen to develop the technology that will
enable it to ultimately deploy floating liquefaction facilities on a commercial
basis. Unfortunately it was the major international oil companies that
conducted most of the early research, development, and feasibility studies,
focused on deploying large-scale facilities to develop the very large gas
reserves that are material to them. There are, however, very few giant gas
fields located in remote offshore regions available to the majors for such
deployments.
The future potential to deploy floating liquefaction probably lies in medium
size gas fields, or aggregations of smaller fields with associated gas,
developed by medium sized independent companies. However, the restrictions of
more stringent no-flaring rules being introduced in many countries (e.g.
Nigeria and Angola) may prompt some existing offshore producers of giant
volatile oil and wet gas fields to aggregate gas from several such fields and
develop large-scale (> 4 MTPA capacity) floating liquefaction as an
alternative to building and operating expensive gas re-injection facilities.
The potential to unlock offshore gas reserves without the need to invest in
capital-intensive pipeline infrastructure, infield platforms, and onshore
infrastructure and to minimize exposure to geopolitical and security risks is
also attractive to upstream LNG operators.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
25 May 2007
- Meeting paper published:
14 November 2007
- Manuscript approved:
17 August 2007
- Version of record:
20 December 2007
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