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The planet has run out of light oil, so we need to make oil light
In the early 2000s, leading experts in the oil and gas industry proclaimed the era of the end of «light oil», i.e. oil that can be extracted in relatively simple and inexpensive ways. Since that time, 65-70% of oil and gas fields (even the legendary Saudi Gavarra) have been classified as hard-to-recover reserves (HRR) to one degree or another. Technologies that require oil and gas corporations to be literally at the forefront of technological progress began to come into the limelight. Methods that had not been used before began to return from oblivion since the level of technology development in the past years prevented them from being implemented.
Carbon dioxide. Not only for making soda
For the first time, the injection of carbon dioxide or other inert gas into the reservoir took place back in 1917. It was especially actively conducted at the Nobel fields in Baku and Grozny. The oilmen of that time focused on increasing reservoir pressure rather than increasing oil recovery, which was a secondary task. At that level of technological progress, it was a very expensive and unproductive activity. The compressors were too imperfect and low-power at that time. Carbon dioxide was replaced everywhere by water. Gas methods had to «make room» in the technical arsenal until the 1950s when the oilmen of Bashkiria and Tatarstan began to actively experiment with injecting associated petroleum gas into the reservoir. APG, as part of a water-gas mixture, entered the reservoir, making it difficult to penetrate into areas with high permeability. It mixed with residual oil in hard-to-reach pores, thereby ensuring its displacement into the well, reducing waterlogging and increasing the oil recovery coefficient (ORC). The same effect is produced by the injection of carbon dioxide.
APG is too expensive and valuable a product for petrochemistry to be pumped back into the well. However, the properties and characteristics of carbon dioxide make it optimal for this technological procedure, despite some inconveniences that accompany it.
Pros
Cons
As you can see, along with the positive aspects of injection, oil workers will also face negative ones due to the properties of carbon dioxide. But are they so fatal?
CO2 dissolved in water is able to create carbonic acid, which in theory leads to corrosion. However, carbonic acid, firstly, is one of the weakest acids in its properties. Secondly, it is very unstable and easily decomposes again into carbon dioxide and air, under some conditions forming salts and esters that are not a corrosive agent. Thirdly, an extensive line of carbon dioxide corrosion inhibitors has already been developed, effectively protecting the fittings, equipment and infrastructure of the well. Moreover, in sand reservoirs, carbonic acid (H2CO3) will dissolve the formation rock, increasing its permeability, which will also have a positive effect on increasing the ORC. Laboratory experiments conducted at BashNIPIneft have shown that the permeability of sandstones can increase by 5-15% – and that of dolomites even higher, from 6 to 75%. That is, this is already becoming an advantage and not a disadvantage of this method! Therefore, as we can see, this factor is possible but very unlikely.
Separation and capture of carbon dioxide from APG is not the only way to produce CO2 in the field. As part of the decarbonization of the economy, when humanity faces the global task of reducing greenhouse gas emissions into the atmosphere, their injection into the reservoir and disposal in the Earth’s crust is the best way out. It allows to solve several problems simultaneously, therefore carbon dioxide will be delivered to the well as a technological product subject to official and mandatory disposal.
The use of seals made of metalized rubber with a metal cord and flexible inserts installed in the cascade solves the problem of stability and pressure preservation in the equipment and well. The same applies to asphaltenes, which are successfully combated by the corresponding inhibitors, whose formulations effectively prevent their loss.
Intensification of Oil Production with Carbon Dioxide – Fiction or New Horizons?
So, we have established that the injection of carbon dioxide into the reservoir is a very promising direction in oil and gas production, due to the properties of carbon dioxide, which it exerts on the reservoir and its characteristics. First of all, it is:
To date, more than 140 injection projects have already been implemented in the world, on oils of different densities and viscosities. In the case of highly viscous bituminous oil, carbon dioxide additionally acts as a solvent agent, which reduces the density and improves the fluidity of the oil. On the Athabasca oil sands in the Canadian province of Alberta, its use gave an increase in ORC by 2-3 times (with a standard 11-15%). Obviously, a complex combination, for example, with thermal methods will increase these indicators.
The most effective injections are in the form of injection cycles with subsequent exposure and commissioning of the well. In English-language literature, this technique is called Huff and Puff. This term came from the arsenal of thermal methods of influencing the formation when steam (or a vapor-air mixture) was injected into a well with high-viscosity oil. Replacing the steam-air mixture with carbon dioxide gives a similar (if not better) result without the side effects associated with steam-gas (steam-air) methods, even on an inactive and low-capacity fund. In 2017, RITEK (part of PJSC Lukoil) conducted a cyclic injection of carbon dioxide at an inactive well of the Maryinsky field (Samara region). In total, about 300 tons of food-grade carbon dioxide were pumped at a pressure of 10.3 Mpa with an exposure after treatment for 21 days. The result was the output of the well to a daily flow rate of 8.6 tons per day with a decrease in viscosity by more than 10 times. The most important thing is that the well was put into the operating production fund with profitable economic indicators.
As we wrote above, the injection of gases into the reservoir at the dawn of the development of the oil industry was replaced by water. But to combine flooding with simultaneous treatment with carbon dioxide as a complex procedure came to mind only in the mid-1950s – and even then, as an empirical experiment. When flooding with carbon dioxide, the first step is to pump water into the reservoir, which causes an increase in reservoir pressure. When there is sufficient pressure in the reservoir, the next step will be to inject CO2 through the same injection wells. The gas is pumped into the tank for contact with the oil. This creates a mixing zone that is easier to move into the production well. Usually, the injection of carbon dioxide alternates with the injection of water and the water moves the oil towards the production area. This method has become the second most common method of tertiary recovery and is being actively developed by all oil companies.
Hydraulic fracturing, which has been actively used by all oil companies since the late 1990s, causes no less damage to nature than carbon dioxide in the atmosphere. The reason for this is the use of special gels, acids, fillers, etc., which expand cracks in the oily rock. After wedging the crack with proppant (ceramic or glass beads with a diameter of 0.3-1 mm), the gel hardens, preventing the crack from closing. Once in aquifers, the substances included in the gel can have a negative effect on their composition. The use of water-based fracturing fluids causes a change in the properties of the formation, since it provokes swelling of the clay rocks forming it, can form stable emulsions with reservoir fluid and also saturates the pore space, reducing their relative permeability to target fluids, which in combination has a strong negative effect on permeability and its productivity. To reduce the negative effect, clay inhibitors and demulsifiers are necessarily included in the formulation of hydraulic fracturing fluids and the quality of destruction of the viscous structure of the liquid is carefully monitored for its efficient removal from the reservoir. However, the effectiveness of these measures is far from always high. Besides, some formations, due to their physicochemical properties, remain incompatible with aqueous liquids. To solve this problem, since the beginning of the development and popularization of hydraulic fracturing technology, work has been underway to introduce anhydrous hydraulic fracturing fluids. At the moment, as an alternative, there is experience in the use of hydrocarbon-based liquids and foam-nitrogen liquids. Both of these technologies have been mastered in the Russian oil and gas industry and are successfully used in various fields, if appropriate. However, Western experience in the field of hydraulic fracturing using liquefied carbon dioxide (Liquid CO2) remains unexplored.
Hydraulic fracturing using liquid carbon dioxide was mastered in Canada in the early 1980s. By the end of the 20th century, Canadian companies had successfully completed more than 1,200 fracturing operations using carbon dioxide. The use of carbon dioxide for hydraulic fracturing involves using it in liquefied form as a fracturing fluid – and a sand carrier fluid to place proppant in the created crack. A feature of carbon dioxide for hydraulic fracturing is its physical property of phase transition (from liquid to gas) during injection into the reservoir. It occurs at a temperature of — 304.1K (30.1°C) and pressure above 7.38 MPa and gives the substance intermediate properties between liquid and gas. Thus, hydraulic fracturing using liquid carbon dioxide is unique in that it performs two functions at once: fracturing fluid and then, after conversion to gas, improving the fluid and its displacing properties. And if you consider that carbon dioxide is also disposed of and does not enter the atmosphere, the prospects are simply stunning.
Gas for Gas Production or Condensate Block Removal
During gas production, a condensate shaft is formed, especially when the pressure in the well falls below the value corresponding to saturation. For formations with low permeability, this phenomenon is critical since formation damage resulting from a decrease in effective permeability around the borehole can cause a decrease in production or the formation of a condensate plug, which completely blocks production and leads to damage to the well. This situation is considered to be an emergency, the well is put under repair, pumps for pumping liquid and condensate are installed, a complex drainage system (siphon tubes) is installed or chemical compositions with surfactants (not always environmentally harmless) are injected. The injection of carbon dioxide leads to the displacement of water and a drop in the liquid level in the pipe, with a simultaneous increase in bottom-hole pressure, which causes a phase transition in the gas condensate and pumping it to the surface. As a result, the flow of gas into the well is restored without the use and implementation of expensive and lengthy procedures.
Conclusions
Without a doubt, at the moment we are witnessing the development of a new direction in the fuel and energy complex, which is directly related to the creation of infrastructure and a new universal direction in the production of hydrocarbons, including hard-to-recover reserves. The advantages of this method will be:
The relevance of this technology is evidenced by the growing number of implemented projects for the capture, storage, transportation and use of carbon dioxide, including in oil production with refining (steam reforming to produce hydrogen, etc.). According to the United Nations Economic Commission for Europe, as of 2016, 55 such projects were implemented worldwide (31 in Europe and 24 in the USA). In 2006, there were only 3 of them.
We invite customers and partners interested in further development of carbon dioxide intensification technologies to constructive mutually beneficial cooperation.
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