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Downhole gas compression

Based on gas bearings and direct drive, permanent magnet, high frequency synchronous motors, downhole gas compression offers a technically feasible solution for accelerating production and increasing the ultimate recovery from depleting gas fields.

The oil and gas industry has long recognised that pressure boosting in gas fields by placing a compressor at the optimum location in close proximity to the source reservoir can lead to major economic gains in hydrocarbon recovery beyond that which is possible using conventional central gas compression alone. A Feasibility Study completed by CORAC in 2002 concluded that Downhole Gas Compression (DGC) based on its patented gas bearings and direct drive, permanent magnet, high frequency synchronous motors, offers a technically feasible solution for the acceleration of production and increase in ultimate recovery from depleting gas fields. An important outcome of this study was the realisation that the introduction of downhole gas compression earlier in the production cycle of maturing gas fields can produce very significant improvements in financial returns through accelerated revenue streams and increased UR (Ultimate Recovery). It will extend the production plateau of producing gas fields by bringing forward tail-end production, thus delaying the need for investment in new facilities or the development of new fields. From the reference fields studied, incremental production gains of between 28% and 42% were found to be possible with only very modest pressure boosting ratios. In addition, by accelerating production rates and increasing ultimate recovery by lowering the reservoir abandonment pressure, downhole gas compression is seen to offer a potential solution for the development of otherwise sub-economic gas assets. The technology also has the potential to fundamentally alter the production strategy for natural gas recovery. It can lead to a significant reduction in the number of wells drilled and encourages the use of large bore casing schemes to further increase the installable power downhole and thereby, hydrocarbon recovery. The key benefits DGC is able to bring to brownfield sites include a substantial acceleration in production rates and maximised ultimate recovery (UR) by lowering reservoir abandonment pressure. The technology achieves this through improved vertical lift performance and increased well draw down, stimulating reservoir flow. Taking these conclusions from the Feasibility Study as its starting point, a Joint Industry Project (JIP) was established with the objective of undertaking a phased and tollgated development programme over a period of 36-42 months, leading through detailed design engineering and a comprehensive test programme to a field trial in a live gas well by 2007. The phases of the project are: PHASE 0: Feasibility Study - complete PHASE 1: Technology Verification - complete PHASE 2a Detailed Design: The scope of work for this Phase is addressed under the following main headings: Preliminary Engineering, Axial Compressor aero design, Bearing system design, Bearing gas off-take and booster compressor design, Inlet homogeniser design, Discharge liquids/fines trap and NRV arrangement, Permanent magnet motor design, Electrical Power Delivery System Design, Command and Control, Commutation and Speed Control System Design, Design Review and Manufacturing Drawings. PHASE 2b Component Testing: The scope of work for this Phase is addressed under the following main headings: Procurement and Building of Test-rig Assemblies and Components, Component Rig Tests. PHASE 3a Manufacture Prototypes PHASE 3b Development testing in a flow loop PHASE 4: Field Trial: The downhole gas compression concept involves the coupling together of a number of axial compressor modules in a single compression train for installation in the well bore in close proximity to a gas reservoir. In this location, a modest uplift in pressure results in a very significant increase in gas production compared with conventional methods using surface compression alone, thereby accelerating gas production and cash flow from a producing asset. The most important contribution of the project is an increase in efficiency in the production of gas fields. This translates into an increase of the gas reserves and a better use of the natural resources. This in turn, allows for the reduction in usage of more contaminant fuels, therefore reducing the negative impact on the environment. Keywords: gas extraction, gas compressor, gas field recovery.
Acronym: 
DGC
Project ID: 
3 669
Start date: 
01-05-2006
Project Duration: 
36months
Project costs: 
7 490 000.00€
Technological Area: 
Energy production, transmission and conversion
Market Area: 
Oil and Gas Exploration and Production

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