SNF’s Oil & Gas Division presents:
POLYMER ENHANCED OIL RECOVERY: THE BEST OF BOTH WORLDS! as published in the Exploration & Production section of the Winter 2023 OG Innovation Magazine.
The full article can be read below:
Polymer Enhanced Oil Recovery:
The Best of Both Worlds!
What if there was a magic bullet that reduces your carbon footprint whilst economically allowing you to add more recoverable reserves to your portfolio? You would take it, right? But that can’t possibly exist! Or can it? Surprisingly, polymer Enhanced Oil Recovery (EOR) can not only do this in theory but is actually a globally deployed technology in over 350 projects that has shown to be highly effective in sustainably recovering more oil. Whilst more common onshore, what have been the barriers to implementation in the offshore environment? Higher risk perception, cost, retrofitting limitations and increased complexity have all been contributing factors, but with more and more offshore projects now being sanctioned and successfully executed there is perhaps no better time to evaluate polymer EOR. For the North Sea in particular, the energy transition and the requirement to reduce all carbon emissions to zero by 2050 (Net Zero) will require operators to maximise their recoverable reserves whilst doing so within a carbon-neutral environment.
So, what makes polymer flooding so attractive? Globally, 60% of all oilfields are currently using water-flooding as a way to maintain reservoir pressure but this only recovers 20-40% of the oil in the reservoir. The lower viscosity of the water leads to poor sweep leaving most of the oil within the reservoir. Additionally, once this injected water breaks through at the production wells, a rapid increase in water-cut is often observed with the resulting production issues that follow (scale, separation etc) requiring additional chemical treatment. In the North Sea, this water must be treated before being reinjected at great cost to the operator. Adding polymer to the injected water increases the viscosity of the water phase, reducing the mobility of the water resulting in higher recovery factors.
Figure 1 (left) highlights the increase in oil recovery for water-flooding vs polymer EOR for over the same project lifetime (15 years). Over this period polymer flooding recovered around twice the number of barrels as water-flooding alone. Another way to view this data is that in order to recover the same amount of oil, it takes twice as long under water-flood.
Just as important to the improved oil recovery factors is the reduction in the amount of water being injected, produced and treated. The majority of associated carbon emissions from oil production can be directly attributed to the energy required to run the water-flood. Therefore, it stands to reason that if you can reduce the overall amount of water that you have to handle, you will reduce the carbon footprint of your operation.
Figure 2 highlights the relationship between water cut and the resulting carbon intensity to produce a single barrel of oil. As the water cut rises to 80% and above, the carbon intensity begins to rise exponentially. With an ageing basin such as the North Sea, reducing the water cut would have a substantial benefit to the future of the industry there. Water injection requires high amounts of energy to inject the water, often from burning produced gas in gas turbines which contributes significantly to a company’s emission calculations. Reducing the amount of produced water will decrease the amount of lifting energy required to produce a barrel of oil, often via electrical submersible pumps (ESP) or gas lift operations, further reducing carbon emissions. Figure 1 (right) shows that when adjusted to the same oil recovery values (~32,000,000bbls), the amount of CO2 emitted is around half that for the polymer EOR project than water-flooding.
Figure 3 shows an example of a full carbon emissions calculation of a water-flood vs. polymer flood. The carbon intensity to recover 1 barrel of oil during water-flood was calculated as being 26kg CO2/bbl in this example. The polymer flood calculation shows a slight increase in energy usage for the running of the polymer injection unit (PIU) and manufacture/transportation of the chemicals, but these are almost negligible compared to the energy savings due to the reduction water handling. Overall, the carbon intensity is reduced from 26 to 7 kg CO2/bbl of oil produced, a saving of ~70%. This magnitude of reduction in carbon intensity falls within the average values of the polymer flood operations that SNF have implemented and studied in the field as demonstrated in Figure 4.
In order to maximise the environmental benefit, it is imperative to ensure that all steps are being taken to minimise the carbon footprint contributions from the manufacturing and transport logistics. SNF not only constantly adapt and improve our formulations and processes to ensure that the least amount of energy is consumed during manufacture, but we also strive to reduce the carbon emissions associated with transportation. This is demonstrated by our investment in our manufacturing plant in the Teesside area, purpose-built to serve the future needs of the North Sea. Previously our products were manufactured in France and transported by road to Aberdeen for shipping to the offshore installation. This shorter supply route (~460km vs. ~1900km) represents greater than 4x reduction in the carbon footprint in transport alone (80kg CO2/ton vs. 325kg CO2/ton). Planned refinement of the supply route via rail or sea transportation to suit the chemical requirements of the North Sea will reduce emissions further.
As mentioned above, many offshore EOR projects have been ruled out in the past following initial evaluation due to many factors including injectivity, product quality, asset retrofit, produced water issues and economics. SNF have continued to innovate in this area in order to minimise these risks. For example, by dewatering our liquid emulsion polymers, commonly used offshore for ease of deployment, the volumes required have been drastically reduced meaning better product stability (less water) and a reduction in the size of the required storage facilities on the platform or FPSO due to lower volumes of bulk emulsion being required. Advances in emulsion technology mean that good injectivity is routinely achieved. On the economics side, new research from Heriot-Watt University looking at the way in which polymer works at the pore scale to produce oil, demonstrates that relatively low dosages of polymer can achieve highly profitable results even in heavy oil reservoirs. So, projects previously ruled out due to unfavourable or marginal Net Present Value (NPV) calculations due to high polymer loading may now be greatly beneficial. In fact, it has been calculated that polymer EOR adds only $4-6 per incremental barrel to the overall economics of a water-flood project. This is no more apparent than with Ithaca in the Captain field where wells at the limit of their economic benefit due to extremely high water-cuts are now some of the most profitable on the asset due entirely to the polymer flood project. Finally, back-produced polymer has always been a topic of great concern to operators, fearing process upsets and poor water quality for reinjection. Advances in this area have also been made in recent years with bespoke products for polymer-containing systems being developed to enable better separation and aid water clean-up.
In summary, the time has never been more primed to evaluate (or re-evaluate) polymer EOR for North Sea deployment. Reducing carbon emissions and maximising production will ensure the longevity of the North Sea oil and gas industry to enable us meet the changing energy demands of the future. In essence, polymer Enhanced Oil Recovery gives us the best of both worlds – sustainable, profitable oil production!
If you would like to know more about the topics discussed in this article, or would like to know more about SNF’s solutions, please contact them at: