DNV GL is proposing a joint-industry project (JIP) for a hybrid-power concept for offshore units using batteries in combination with traditional power generation equipment. The concept has already delivered multiple advantages in the maritime and automotive industries but has not yet been applied in the oil and gas industry. “You reduce fuel consumption, which is a direct cost saver, but you also get a significant performance benefit because the whole power system is much more responsive,” Christian Markussen, Subsea Business Development Director at DNV GL Oil & Gas, said during a press conference at the 2014 OTC in Houston on 7 May.
The concept that DNV GL is proposing is similar to that used in the automotive industry, for example in the Toyota Prius. The maritime industry started to adopt this technology five years ago not just because of the environmental benefits, but also because it adds financial value and performance benefits. In the automotive industry, there is typically about a 20% fuel saving with the use of a hybrid system. In some maritime applications, there is up to a 40% saving, and DNV GL expects to see the same for the oil and gas industry. Currently, there are 17 hybrid ships either in operation or being built, plus one electric ferry. DNV GL studies show that the payback period is typically only about two years for the maritime application.
The reduced size of the power generator is a major advantage with a hybrid approach, Mr Markussen said. Three gas turbine generator sets, plus a spare one for redundancy, typically power a conventional offshore facility. The total installed power is dimensioned according to the peak power requirement but is normally operated at a much lower power level. In addition, the gas turbines are operated at low partial-load to have reserve capacity to be ready to react to sudden power demands. This results in low power generation efficiency, and thus the fuel consumption and CO2 emissions are higher per unit of power.
“With a hybrid system, the power generation becomes optimized for an average load rather than a peak load, and hence the power generation capacity can be reduced. A battery, like those used in maritime vessels, will act as a buffer and supply power when needed or charge up when demand is low,” he explained.
For more information about the JIP, please contact Mr Markussen at Christian.Markussen@dnvgl.com, +47 94831307.
A separate, ongoing JIP on wellhead integrity is expected to deliver a recommended practice (RP) later this year to complement current codes and standards and improve methodology to assess the integrity of an important well barrier. DNV GL began the project in Norway with Statoil in 2005, and it now has 16 participating operators from the US, Europe, Canada and Australia. “A trend we see today is that BOPs are getting larger and larger, and the wellhead size, which is about 36-in., has remained the same. Imagine you have an 800-ton BOP on a 36-in. conductor,” Partha Sharma, Head of Riser, Umbilical, and Mooring at DNV GL, said at the press conference. “This has become a problem because now the sixth-generation rigs are designed to stay for over 200-to 300-day drilling operations, and it has significant impacts on the fatigue of the wellheads.”
This second phase of the JIP will fund various studies to increase industry knowledge on key parameters affecting wellhead fatigue. In addition, the JIP will benefit from work-in-kind contributions. Current best practices for fatigue life assessments will be documented in the RP, which will be publicly released as the JIP progresses. It is envisaged that the JIP will continue with subsequent phases, which will be completed in the first half of 2015.
Subsea report on technology, safety and future trends
DNV GL has issued a report, “Subsea – Technology Developments, Incidents and Future Trends” on behalf of the Norwegian Petroleum Safety Authority. The number of installed subsea Christmas trees is currently about 800 on the Norwegian Continental Shelf and approximately 5,000 globally, and these numbers are forecasted to increase. “The report aims to raise awareness and share knowledge within safety, industry cooperation, degradation mechanisms, failure modes, monitoring, integrity management and incident-related information,” Bjørn Søgård, DNV GL’s Segment Director for Subsea Technology, said.
“Based on data, there’s no evidence that incident frequency is increasing due to the age of subsea facilities,” Mr Søgård said at a press conference at OTC. “Most failures are due to quality issues resulting in early life failures or more random failures.”
The report describes the current status of the industry and future trends. Mechanisms related to degradation and aging, and the effect these have on the robustness in operation, are also described. Click here to read the report.