A Revolutionary Hybrid Solution to the Grand Challenge of Developing Deepwater Stranded Gas
- Richard Moore (SubCool Technologies Pty Ltd)
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 1-4 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2017. Offshore Technology Conference
- 4.5 Offshore Facilities and Subsea Systems, 1.6 Drilling Operations, 4 Facilities Design, Construction and Operation, 5 Reservoir Desciption and Dynamics, 4.1.4 Gas Processing, 4.5 Offshore Facilities and Subsea Systems, 4.2.3 Materials and Corrosion, 5.3.4 Integration of geomechanics in models, 7.2.1 Risk, Uncertainty and Risk Assessment, 4.5 Offshore Facilities and Subsea Systems, 6.3 Safety, 5.3 Reservoir Fluid Dynamics, 4.5.9 Subsea Processing, 4.3.1 Hydrates, 7.2 Risk Management and Decision-Making, 7 Management and Information, 1.6.9 Coring, Fishing, 4.1 Processing Systems and Design, 4.1.2 Separation and Treating, 4.2 Pipelines, Flowlines and Risers
- subsea processing, subsea dehydration, FLNG alternative, Hybrid Concept, Gas development
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Many deepwater gas fields remain stranded in the current economic environment. Conventional surface solutions result in large facilities that are heavy and costly. Subsea solutions are challenged when confronted with long distance tie-backs. While the FLNG option initially looked promising, high CAPEX and very high OPEX have limited its potential application, with four potential FLNG projects being cancelled in Australasia in the last two years.
A revolutionary new solution, a proprietary ‘Hybrid Concept’ has emerged to solve this grand challenge of developing deepwater gas fields. It is not surface, not subsea, but the ultimate combination of both, offering fundamentally more efficient and hence lower cost processing.
The concept incorporates several principals that have been overlooked to date, namely:-
Fundamental differences in cost between surface liquids and surface gas processing
There is a key distinction and granularity between the costs for surface processing of liquids and surface processing of gas. Liquids can be processed on the surface relatively efficiently. It is the high pressure surface gas systems that have a disproportionate impact on size, weight and cost of surface facilities.
Fundamental Processing differences for liquids and gas
Cold temperatures are required for gas processing and this is efficiently found near the seabed. In contrast, liquids processing requires heat both to efficiently separate and stabilise the components.
Dehydration is the core unit operation to allow long distance pipeline transfer by preventing hydrates and corrosion. Dehydration has been almost universally applied to onshore and fixed platform processing facilities, thus allowing dry, single phase pipeline transfer.
Existing subsea gas developments rely on either adding chemicals or heat and insulation to avoid hydrate formation and reduce corrosion. While successful across short to medium distances, across longer distances and in deeper waters these methods prove far less efficient and much more costly.
The Hybrid Concept fully processes the high pressure gas on the seabed in two stages. The first stage includes active cooling and bulk water separation and removal. In the second stage, the gas is processed with liquids removed to achieve full subsea dehydration. All liquids are directed to a simple and compact, low pressure surface unit. This surface unit provides support to the subsea processing, reducing complexity, costs and project risk.
The result is significantly lower development CAPEX and lower OPEX, with a minimum of complexity, giving an acceptable project risk. Importantly all components are proven and require a minimum of technical development. Safety is significantly improved with no high pressure gas on the surface and a significantly reduced permanent offshore workforce required.
The details of this concept, along with its significant advantages are discussed in this paper.
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