Advancing recovery

Gregory Hale

March 1, 2015

Greg Hale takes a look at subsea electronic modules.

“Doom and gloom,” and “scaling back” are phrases not heard in the industry in the last five years. But, now there is an opportunity to wring more productivity and profitability out of existing assets.

Åsgard project. 
Images from Aker Solutions.
 

Norway’s Åsgard field, about 125mi off the coast, has been producing gas since 2000, but its supply dwindles. Operator Statoil created the first subsea gas-compression facility to boost rates. The facility will become operational this year and Statoil says it should increase recovery by about 278 MMboe and also help keep production running into 2050.

Statoil needed a control system for high availability and reliability. They want to cut down on production stoppages that end up costing big bucks, said Pete Skipp, engineering manager applied technology at Rockwell Automation.

With real estate at a premium, control systems will reside in subsea electronic modules (SEM).

“Most oil and gas producers opt for control systems that have already been proven in topside applications,” Skipp said. “We scaled these systems down to Eurocard circuit-board format to fit into existing SEMs. Right-sizing the control system to an existing, subsea-qualified SEM is less expensive and less burdensome than designing, building and testing a completely new SEM. It’s also crucial that all electronics used in subsea systems be hardened in every practical sense and thoroughly tested for the environmental challenges they’ll face, including extreme temperature fluctuations and severe vibrations.”

This architecture provides a small equipment footprint while providing high availability and high integrity (up to safety integrity level (SIL) 3). Subsea systems can also reduce overall operating costs by as much as 50% compared to the costs of building, staffing, operating and supplying a topside platform, Skipp says. Because subsea installations are also unmanned, they offer inherent safety benefits. This presents opportunities to expand production to more inhospitable locations. Subsea production facilities also can recover as much as 20% more from producing fields compared to topside facilities, because less pressure ends up required to pull the product out.

Two SEMs coordinate using secure “black channel” communications links. While performing no direct safety function, the links are purely communications vehicles. The SEMs carry out peer-to-peer communications on these channels, exchanging diagnostic, status and input/output (I/O) information, while also relaying the status of field devices.

If a single device or I/O module fails on one SEM, the presence of multiple data paths ensures continued operation using data from the same device on the second SEM, Skipp says. Subsea operations would only come to a halt if the same two devices failed on both SEMs or if topside communications were lost to both SEMs.

This “hot-swappable” architecture can only occur if the two SEMs are physically separate from each other and provide enough space for a remotely operated underwater vehicle to remove the decommissioned SEM without touching or interfering with the operational SEM.

A subsea control system should use a standard programming environment to ensure easy integration, regardless of which manufacturer’s equipment the controls integrate with, Skipp says. The control systems also should have a minimum 25-year lifecycle to support decades of production. The controls should have a demonstrated ability to operate “no touch” for a minimum of five years. Additionally, control systems based on commercial off-the-shelf technology will reduce time spent on customized programming and engineering.

Understanding details

As more sophisticated equipment deploys to the seabed, diagnostics becomes even more vital. Details have to delve deeper than just knowing something is wrong. Diagnostics should provide knowledge of the problem, what it is, and why it happened, so operators can understand the specifics of a failure and build a response plan.

Detailed diagnostics can support overall system management and more accurate troubleshooting. Diagnostics also plays a crucial role in a subsea system’s SIL coverage. Basic diagnostics is adequate for SIL 1, but additional comprehensive diagnostics is a must to achieve the more demanding rating of SIL 3. The addition of a second processor to an architecture increases diagnostic coverage and can provide SIL 3 fail-safe coverage.

Using technology can not only boost safety, but keep profit levels increasing during an industry downturn.



Gregory Hale
is the Editor and Founder of Industrial Safety and Security Source (ISSSource.com) and is the Contributing