Scientists from Kazakhstan National Research Technical University named after K.I. Satpaev performed a series of lab tests to assess the potential of using gas to enhance oil recovery at the fields featuring heavy oil. East Moldabek was the oilfield, where the studies took place. The pay zones of this filed contain very high viscosity oil. Such reservoirs are especially difficult to develop: the oil is poorly filtered, moves very slowly along the pores in the rock, and practically does not respond to traditional displacement methods including water flood. As a rule, the significant part of such reserves remains in the reservoir inaccessible for the recovery.
To understand the potential effectiveness of gas-based recovery methods in such conditions, the researchers simulated the reservoir development process in the lab environment. Core samples were prepared containing rock from the pay zone, they were treated and saturated with stratum fluids. The tests were performed under the temperature and pressure values close to real conditions of the reservoir. At first, oil was displaced from the core samples with water, as it is done in reality. Then gas was injected into the same core samples — carbon dioxide (CO₂), азот (N₂), methane (CH₄) or propane (C₃H₈). This allowed to determine, which one of the agents allows for better recovery of the residual oil from the rock.
CO₂ turned out the most efficient: its injection resulted in the oil recovery factory increasing by more than 5% vs flooding. This effect is explained by the ability of carbon dioxide to be dissolved in oil decreasing its viscosity and surface tension. Due to this, oil becomes more moveable and comes through the pores easier. On top of that, CO₂ causes oil swelling thus improving the filtration. Such mechanisms allow for gas to penetrate into previously inaccessible sections of the reservoir and to involve additional oil volumes into the development.
On the contrary, nitrogen practically does not dissolve in oil and does chemically interact with the rock. Its effect is limited to physical displacement of oil (like a piston). The efficiency of this method is lower (the recovery growth was only 2.5–3.6%), however, it has certain advantages: nitrogen is accessible, easy to handle and does not cause corrosion of the equipment. This may be an important factor for selecting the technology in the conditions of strictly limited budget or lack of the infrastructure required for handling CO₂.
Methane and propane demonstrated interim results. Propane was especially interesting: due to its high solubility, it provided for the recovery growth of up to 3.6%. Methane turned out less efficient. However, both gases may be applied in practice, if the associated petroleum gas is available at the field — it may be used as a source decreasing the costs and increasing the cost-effectiveness of the development.
Thus, the research demonstrated the high potential of using gases to enhance oil recovery in difficult conditions typical for fields with heavy oil. Subject to smart engineering, such methods allow for significant increase of recoverable reserves and to extend the time of active development of mature or poorly drainable reservoirs.
