The impact of infusing two chemical agents for better oil recovery into oil shale has been investigated by Skoltech researchers. As it turned out, neither of the fluids under investigation water solutions of nanoparticles or a compound resembling soap known as a surfactant is a viable alternative for shale oil operations.
In actuality, these substances might prevent the oil from being recovered by trapping it underground. The scientists advise that the effectiveness of additional drugs should now be investigated while keeping that danger in mind. Their findings are reported in Energy & Fuels.
The pressure pushing oil to the surface steadily decreases during the course of an oil well’s existence. By infusing steam, chemicals, and other substances into the reservoir, so-called enhanced oil recovery techniques eventually make further extraction impractical. Enhanced recovery is frequently required to start with for shale deposits because they are more difficult to remove from.
Enhanced recovery encompasses three main approaches: Thermal injection heats the oil in the reservoir using preheated water, air, etc., which reduces its viscosity and increases its mobility. By combining the oil with gases such as carbon dioxide and natural gas, gas injection expands the oil and increases its mobility.
Last but not least, chemical injection is a catch-all name for a variety of methods that increase oil recovery by using a variety of water-based fluids with a variety of modes of action.
We have shown that water or surfactant injection, a relatively cheap and effective enhanced oil recovery technique for conventional reservoirs, is not as appealing as it seems and bears considerable risks when it comes to oil shales in general and the Bazhenov Formation in particular. Further research is necessary to identify alternative surfactants and other enhanced oil recovery techniques perhaps, gas injection that might prove suitable for shale oil reservoirs.
Elena Mukhina
Oil shale is a profitable source of hydrocarbons that enables nations and businesses to access resources that were previously inaccessible. When applied to shale reservoirs, however, the impacts of improved oil recovery techniques that have been tried and tested on conventional deposits are not well understood. Finding out what works and what doesn’t is a key to unlocking this valuable resource.
A research team from Skoltech Petroleum featuring Junior Research Scientist Alexandra Scerbacova and Senior Research Scientist Elena Mukhina the lead authors of the study and the project’s principal investigator Alexey Cheremisin ran a numerical simulation and two complex and unique lab experiments on oil shale samples to determine if it is feasible to inject water solutions containing silicon dioxide nanoparticles or a soaplike substance called a surfactant into shale oil reservoirs to enhance recovery.
“Our study considered 13 fluids and two were selected for tests on cylinder-shaped samples of oil-saturated rock from the Bazhenov Formation of Western Siberia,” Alexandra Scerbacova commented. “First we injected brine water with a very high salt content and measured an oil recovery factor of about 53%. This is roughly analogous to being able to extract about half of the oil in the reservoir. That figure served as the baseline value for assessing the efficiency of the two agents in the experiment, although the value under actual reservoir conditions would be lower.”
Technically speaking, the surfactant that the researchers used is known as sodium fatty acid methyl ester sulfonate. Even though it increased the oil recovery factor, the final value was still 53%, the same as with brine injection, making it apparent that this particular agent is not economically feasible because it is much more expensive than the freely accessible water.
Surfactant injection was tested on a real rock sample as well as through numerical simulation. However, while the simulation correctly predicted the oil recovery factor, it did not take into account the unfavorable experiment result: some of the rock’s pores became clogged, limiting its permeability. This highlights the importance of experimental studies.
The experiment showed that the issue of decreasing rock permeability was significantly worse with the other, nanoparticle-based treatment. “Due to the small size of rock pores and channels which do not exceed the size of nanoparticles … the filtration of nanofluids may eventually lead to critical damage to the shale rock,” the study warns.
“We have shown that water or surfactant injection, a relatively cheap and effective enhanced oil recovery technique for conventional reservoirs, is not as appealing as it seems and bears considerable risks when it comes to oil shales in general and the Bazhenov Formation in particular. Further research is necessary to identify alternative surfactants and other enhanced oil recovery techniques perhaps, gas injection that might prove suitable for shale oil reservoirs,” Elena Mukhina concluded.
