Subsea Multiphase Compression System Estimated to Boost Averaged Natural Gas Production by up to 30% While Halving Energy Consumption

Published: 11/02/2022

Photo of OneSubsea and Shell workers observing transportation of the subsea multiphase compression module.

The objective

The giant Ormen Lange Field is located 120 km [75 mi] off the Norwegian coast in 900 m [2,955 ft] of water. Natural gas production started in 2007, and at its peak, the field supplied about 20% of the UK's gas requirements, playing a key role in reducing the amount of coal in the country’s energy mix.

From the beginning, Shell and its license partners were interested in using subsea instead of topside compression to boost production. Compression is a mechanism for transferring energy to the production stream to overcome losses during extraction and transport. Compared with the option of lowering the near-end pressure using topside technology, compressing gas near the start of a long production flowline (where gas pressure is higher) is significantly more energy efficient—with correspondingly lower CO2 emissions—over the productive life of the asset. However, the technology’s high costs and lack of maturity made it unfeasible at the time.

30%
Averaged production increase
30–50 billion m³
Incremental gas recovery
85%
Recovery factor
Graph shows higher production, recovery, and field life with subsea compression.
Subsea multiphase compression will increase both production and total recovery.

The solution

Interest was rekindled in 2017, when OneSubsea commissioned the world’s first subsea multiphase compression system in Equinor’s Gullfaks South Field in the North Sea. The system has demonstrated a high level of reliability and reached Technical Readiness Level (TRL) 7 in early 2019.

OneSubsea’s award-winning subsea multiphase compressor is the world’s first and only true subsea wet gas compressor. Conventional compressors require perfectly dry gas to operate safely and efficiently. Complex equipment is necessary to eliminate any liquids and pump them separately, which makes the marinization of conventional technology complicated and expensive.

The subsea compression system from OneSubsea, on the other hand, can operate with the unprocessed multiphase well stream—including condensates, produced water, and MEG—with liquid fractions ranging from 0% to 100%. It also tolerates sand and solids. As a result, the size and weight of the solution decreases by about 60%, with a corresponding reduction in cost. Fewer components also mean increased reliability. In addition, core components, such as the motor, bearings, and seals, are part of OneSubsea’s proven boosting portfolio, which has delivered more than 4 million hours of operating time. All these factors led to Shell awarding an integrated EPCI contract to Subsea Integration Alliance; OneSubsea will supply the compression system while its partner, Subsea 7, will perform the installation.

Schematic of Ormen Lange subsea multiphase compression system.
Dotted blue lines represent the low-pressure well streams that commingle at the manifold and are split to the two compression stations. The compressed multiphase gas (solid blue lines) is then sent back to the manifold and routed to shore via the production flowlines.

The results

The system includes two compression stations, each containing two compression modules. Each compressor can provide up to 50-bar differential pressure (DP), and they are initially configured in parallel for a large volumetric flow capacity. As production declines, higher DP and compression ratio become beneficial, and the compressors can then be easily configured in series, enabling up to 100-bar DP.

The record-breaking 32-MW subsea multiphase compression system will use onshore VSDs located 120 km away, an industry first. Eliminating subsea VSDs or a topside floating alternative improves project economics. The solution’s technical feasibility was validated using OneSubsea’s state-of-the-art umbilical simulator and multiphase flow loop. Installation is scheduled for completion in 2024.

The recovery factor is expected to increase from 75% to a world-class 85%, with up to 30% (up to 50 billion m3) of additional gas production. An added benefit is the estimated reduction in power consumption of >50% per unit volume of gas produced, compared with a conventional topside solution. Once the system is commissioned, Subsea Live data-driven performance service will use remote monitoring and data analysis to optimize subsea asset performance through AI, automation, and OEM expertise, providing prescriptive health, operational, and production insights.

Location
North Sea, Europe, Offshore
Details

Streamlined, cost- and energy-efficient subsea system is projected to increase the recovery factor of the mature Ormen Lange Field by 10% and deliver 30–50 billion m3 [1,060–1,765 billion ft3] of additional gas.