Subsea Compression: Developing Solutions To Keep Gas Flowing

Subsea exploration is needing to take place in increasingly extreme harsh environments, as the oil and gas reservoirs are no longer easy to find close to the shore. At the same time, the industry faces several key challenges, such as high costs and risks, low efficiency, and reliability and nonsustainable issues.

New technology that goes beyond today’s current capabilities is required to go deeper and farther than ever before. In an oil or gas field, the more depleted the existing reservoir, or the more inaccessible it is due to distance, the greater the need for subsea pumps and compressors and the technology that powers them. This is especially crucial to extending the operating life of existing fields.

Subsea compression
Producing oil and gas from reservoirs located at long distances from land is a costly proposition that presents many challenges to offshore operators. Subsea installations situated far from shore or remote platforms can be a very cost-efficient solution, as it may eliminate the need for a fixed or floating topside installation.

Moving the required pumps and compressors from the topside installation to the seabed increases the effectiveness of oil and gas extraction. Compressors are used to maintain output by restoring reservoir pressure at gas-producing fields as it drops over time. Traditionally, they have been installed on platforms above sea level, but with subsea compression, the compressor can now be placed on the seabed. Putting the compressor on the seabed near the wellheads improves recovery rates, reduces costs and minimizes environmental impact. Additionally, it reduces the number of people working in harsh environments offshore, cutting labor costs and enhancing safety at the same time.

Jansz-Io compression project
The Jansz-Io Field is located about 200 km offshore on the northwest coast of Western Australia at about 1,350 m below the surface. It is a part of the Chevron Australia-operated Gorgon Project, one of the world’s largest natural gas developments. Here, subsea compression is applied to enhance the recovery and maintain a longterm natural gas supply of 17.1 ton per year to LNG and domestic gas plants on Barrow Island. The system increases the pressure close to the wells and pushes the gas toward the large LNG plants onshore.

ABB is collaborating in the delivery of a subsea compression system with Aker Solutions and MAN Energy Solutions for Chevron, where the compression system will boost recovery of gas more cost-effectively, leaving a smaller environmental footprint than the traditional use of semisubmersible compressor solutions. ABB’s role in the FEED of a subsea compression station is designing the electrical power system that will distribute onshore power to the subsea compression station. It needs to be designed in the right way and tested under many different scenarios to ensure power is delivered to the compressor reliably and is controlled and optimized. This subsea power will go deeper and farther with reliable communication, monitoring and control.

From Åsgard to Jansz-Io
The Jansz-Io offshore field in Australia is the first location outside of Norway to use subsea compression technology. ABB has been involved in the development of subsea equipment and systems for three decades.

This collaborative project is an outcome of several years of joint work that includes landmark developments such as the 2015 delivery of the world’s first subsea compression system for the Åsgard Field offshore Norway, where the operator had discovered that the internal pressure of the well was dropping rapidly, although there were considerable resources remaining. New ways of boosting the pressure were investigated with subsea compression.

Although Jansz-Io represents the first time subsea compression has been used outside of Norway, there is the potential for subsea compression to be used globally, wherever the environment requires it. The company’s collaborative work combines strengths in subsea, power and automation technologies to develop solutions that will improve oil and gas production for the global energy industry.

There are many challenges in optimizing and extending the life of the fields in Jansz-Io. Not only are we building a resilient and reliable system to maintain high levels of production, but the company also is using its expertise to design them in a robust way to withstand the harsh environment. The company also needs to plan and manage the installation, as there are lots of components that all need to work together. For example, the equipment is lowered to the seabed and integrated with the technology without causing damage. Long power cables also require careful handling. The company needs to enable maintenance in hostile environments and not forget about handling the data securely and intelligently.

Benefits of subsea compression
The main benefit at Jansz-Io will be the enhanced recovery and maintained long-term natural gas supply. This also brings economic benefits, as increasing the amount of oil and gas that can be recovered from new and existing fields by deploying compression or pumping systems at the seabed decreases overall costs per unit. Looking at the Åsgard project, the world’s first subsea gas compressor system, as an example, it is predicted to enable an additional 306 MMboe, corresponding to a medium-sized field on the Norwegian Continental Shelf. It also will extend the field’s life to 2032.

The systems also are more reliable and come with less risk as cables and transformers that have been rigorously tested are being used. Maintenance is decreased and decommissioning is reduced to towing the substation away and replacing it with another. With a reduced environmental impact, the solution is also more sustainable for operators, with a lower carbon footprint. It uses less energy as compressors are closer to the gas reservoir in the Jansz-Io Field.

The deeper and farther afield the location of the subsea compression is, the higher the corresponding economic benefits with this approach. There is also less downtime, as there are no or minimal modifications to be made to existing infrastructure. Removing the need for local power generation means it uses less energy to produce the same amount of gas. It can be up to eight times more energy-efficient. Overall, this represents a considerable leap as the industry looks to a new digital future for the industry toward autonomous operations.

Have a story idea for Operator Solutions? This feature highlights technologies and techniques that are helping upstream operators overcome their challenges. Submit your story ideas to Group Managing Editor Jo Ann Davy at jdavy@hartenergy.com.