Extending offshore platform life by producing renewable crude oil from seaweed
Arnold Keller, Sustainable Transportation Fuels
As oil field production declines, offshore platforms eventually reach the end of their useful lives. Several potential scenarios may follow, including repurposing the platforms for renewable energy production (if near shore), decommissioning and sinking for artificial reefs, or complete disassembly and removal. The choice of decommissioning method depends on various factors, such as environmental regulations, platform condition and potential for repurposing. However, all typical options result in a loss of value for a company that has already invested heavily in fabricating, installing and operating the platform throughout its useful life.
PROPOSED SOLUTION: OIL PLATFORM LIFE EXTENSION
Sustainable Transportation Fuels, LLC (STF) has developed an innovative technology (patent pending) that can extend the life of an offshore oil platform by producing renewable crude oil from harvested seaweed (macroalgae). The declining oil flow from the reservoir is augmented with bio-crude oil made on the platform from seaweed, so the platform's productivity is maintained. The bio-crude oil can be stored and shipped separately or hydrotreated on the platform for compatibility, mixed with the fossil crude, and then piped or shipped to shore facilities.
The bio-crude oil produced from seaweed enjoys significant government subsidies when processed into renewable transportation fuels, ranging from liquefied petroleum gas (LPG) to sustainable aviation fuel (SAF), enhancing the economic viability of this solution.
THE PROCESS
STF's patent-pending process integrates two separate technologies—hydrothermal liquefaction (HTL) and gasification—and allows heat integration between them for improved yield and efficiency. The process starts by making a concentrated biomass slurry in water, which is heated and pressurized. Conversion occurs when the slurry is further heated to near the critical point of water, causing the biomass to depolymerize into bio-crude oil, along with by-products such as aqueous products, synthesis gas and solid residue (hydrochar).
The output of hydrochar is not minimized, as is the typical case with the HTL process, but instead, our process utilizes it as a feedstock for the integrated gasification process. Gasification produces additional synthesis gas, which can be cooled to provide the heat required for the HTL process, enabling free heat integration between the two processes.
While gasification technology is well-established, HTL faces challenges scaling-up. STF's patent-pending process includes modifications to overcome these challenges, enabling the kind of large-scale commercial operation that is essential for meaningfully reducing transportation greenhouse gas emissions by displacing fossil crude with biomass-derived bio-crude.
OFFSHORE PLATFORM
For offshore platform implementation, the complete terrestrial process may need simplification, due to platform limitations in space and equipment weight. The platform-based process need not be optimized for yield, as seaweed biomass near the platform is abundant. Additionally, bio-crude produced from seaweed may require desalting, a process already employed in some oil refineries for fossil crudes contaminated with salt.
The concept is not so complicated, but the devil is in the details. Sustainable Transportation Fuels, LLC has developed technology originally most suited to terrestrial processing, using a biomass that grows continuously under optimum conditions in a climate-controlled building. To take this technology and adapt it to offshore application requires a thorough redesign.
Our process features the Hydrothermal Liquefaction process, which has been established at a low scale. Our design seeks to employ the HTL technology and make it suitable for large-scale biomass conversion, so that it applies as an adjunct to the oil industry and can be incorporated on a commercial scale. The availability of government subsidies in the U.S. makes the technology economically viable. We are putting more resources into tweaking the basic HTL process, so that we can capitalize on improving the yield and reducing equipment space and weight, to accommodate the constraints of the offshore industry.
We have noted that at ultimate, full-scale replacement of fossil crude, using bio-crude made from seaweed would require vast quantities of seaweed. Platform owners are not in this “aquaculture” business and will require significant adjustments to their business practices and will inevitably encounter resistance to adoption of the concept. STF is also not in the aquaculture technology business, and so we need to explore who can help bring the needed technology. Fortunately, there are thriving businesses all over the globe that have developed farming techniques for seaweed that can be adapted for use by the oil industry, if they are able to invest adequate resources and if the size of the prize is worth the effort.
One of the challenges is maximizing the seaweed production using automation, as personnel on platform rigs are very limited. Sea drone technology is one promising method.
The Climate Foundation is at the forefront of farming seaweed. See Figure 1, extracted from the following link: https://thefishsite.com/articles/can-submersible-seaweed-platforms-help-regenerate-ecosystems-and-provide-economic-returns-marine-permaculture
SARGASSUM OCEAN BLOOMS: ADDRESSED BY FPSO
Since 2011, nearly every year, there have been significant sargassum blooms affecting coastal states in the U.S., particularly during the warm months, with peaks in June and July. These events have impacted coastlines in the Caribbean, Gulf of Mexico, and Florida (Fig. 2), causing environmental and economic challenges. Before 2011, such large-scale blooms were not a regular occurrence. A significant narrative on the impact and formation of Sargassum in the Atlantic can be found in the following link: https://earthobservatory.nasa.gov/images/151188/a-massive-seaweed-bloom-in-the-atlantic
A massive seaweed bloom in the Atlantic. This is the opposite problem of insufficient seaweed near a production oil platform, which would require seaweed farming. In the case of sargassum bloom, there is an excess of seaweed that is a free-floating nuisance that can be converted to bio-crude oil.
This leads to an interesting variation to the application of a modified STF process on a repurposed oil tanker operated as a Floating Production Storage and Offloading (FPSO) unit. A commercial-scale HTL system on an FPSO could navigate alongside sargassum blooms, processing the seaweed from the deck and converting it into bio-crude oil. This approach simultaneously mitigates the environmental and economic challenges posed by sargassum blooms affecting coastal communities, while producing valuable bio-crude oil.
The presence of the sargassum bloom is identified by satellite observation. The size of the bloom dictates its ability to generate more sargassum. The larger the bloom, the larger the new daily production of sargassum. If the sargassum bloom is detected early, it may be contained with the capacity of the equipment aboard the FPSO. If the size of the bloom is too large, then the capacity of one FPSO is inadequate to process the daily production of sargassum.
REFINERY INTEGRATION AND RENEWABLE FUEL STANDARD COMPLIANCE
The Renewable Fuel Standard (RFS) requires U.S. refineries to include a proportion of biomass-derived oil in their feedstock. Refineries can incorporate modest amounts (5–10%) of bio-crude with minimal disruption or equipment upgrades. As the displaced fossil crude amount increases, more significant changes are needed to address the higher oxygen and nitrogen content in bio-crude, requiring hydrotreatment—preferably with green hydrogen.
The STF process can convert a portion of the produced synthesis gas into green hydrogen via a water-gas shift reaction and CO2 removal. The economics of the process are further enhanced by the value of Renewable Identification Numbers (RINs) associated with the bio-crude oil, which is higher than the cost of crude oil, making the STF process highly profitable at the refinery scale.
CONCLUSION
The proposed solution by Sustainable Transportation Fuels, LLC offers a novel approach to extending the life of offshore oil platforms by producing renewable crude oil from harvested seaweed. The patent-pending process integrates hydrothermal liquefaction and gasification technologies, enabling heat integration for improved efficiency. By adapting the process for offshore platforms or FPSO units, this solution maximizes the return on investment for aging infrastructure, while providing an environmentally sustainable source of renewable crude oil eligible for government subsidies. Furthermore, the process can aid in refinery compliance with the Renewable Fuel Standard and potentially mitigate the impact of sargassum blooms on coastal communities.
Sustainable Transportation Fuels, LLC is looking for partners interested in exploring the potential solutions outlined in this article. Every production platform operator is unique, and there is not a standard one-size-fits-all configuration. The right combination of processes must be tailored to the production platform. Please contact the authors of this article to discuss if this is a possible solution to your situation.
REFERENCE
ARNOLD KELLER is a process engineer with over 50 years of practical front-end design experience in the fields of gas processing, gasification, and synthetic fuel production via Fischer Tropsch and methanol conversion through zeolite catalysis.
