The exploitation of heavy, extra-heavy and bitumen crude oils has been possible by the application of thermal recovery methods such as steam injection. The efficiency of these technologies is constantly limited under certain reservoir or fluid conditions, such as deep reservoirs and reservoirs with high water saturation. As a potential alternative, different investigations and studies about experimental tests and numerical simulations have considered supercritical water injection as a new enhanced oil recovery method.
Water is supercritical above its critical point (22.1 MPa and 374 ° C), where the gas-liquid phase interface disappears and most of the hydrogen bonds are broken. Under these conditions, supercritical water has advantages in terms of process intensity, energy consumption and distribution of the injected fluid. Supercritical fluids have characteristics of both liquid and gaseous fluids. In this way, supercritical water can flow more easily into micro and nanopores than hot water because there is no surface tension, and it favors heat transport and mass transfer compared to steam due to its higher density.
As an organic solvent, supercritical water also provides a homogeneous environment for upgrading reactions and thermal cracking of heavy oil (insitu upgrading). Furthermore, the properties of supercritical water can be adjusted to a wide range of temperatures and pressures, making possible the promising implementation of the process in reservoirs under different conditions.
Based on the above description, supercritical water injection would generate miscible, thermal and chemical recovery mechanisms. The thermal are reflected in the viscosity reduction both by the increase in temperature and by the permanent compositional change of the hydrocarbons. Supercritical water acts not only as a heat carrier but also as an organic solvent, thus heating and dissolving heavy oil to form a miscible displacement. Heavy components, including asphalt, move into rather than accumulate in the reservoir. Preliminary results indicate that this technology has better injectability and thermal capacity than conventional steam injection, reflected in higher fluid production. These studies are preliminary evidence of a promising strategy for heavy oil recovery, through high efficiency, energy savings and environmental sustainability.
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