Scientists Estimate Volumes of "Escaping" Oil in Western Siberia

Scientists at the Gubkin Russian State University of Oil and Gas (Gubkin University) have developed a digital hydrodynamic model that enables more accurate calculation of oil movement within the residual oil saturation zone of reservoirs. Until now, this factor had not been taken into account when formulating oil production strategies. The model created by the researchers will help reduce oil losses during extraction in Western Siberia.

Experiments using the model revealed the amount of oil that migrates into the formation and remains there during conventional extraction methods. Under certain geological conditions, properly accounting for the residual oil saturation zone allows for the recovery of up to 2–5% of mobile reserves that would otherwise be lost; furthermore, selecting an appropriate development system can actually increase recoverable reserves.

"The essence of the new model lies in accounting for oil not only above the oil-water contact—as is currently the practice—but also within the transition zone between that contact and the free-water level. Although the oil in this zone is immobile, accounting for it is crucial during the design phase, as it influences hydrodynamic processes and fluid flow during field development. Experiments have shown that during waterflooding, some oil can migrate downward, below the oil-water contact, and become immobile," explained Pyotr Pyatibratov, Dean of the Faculty of Oil and Gas Field Development and Head of the Department of Oil Field Development and Operation at Gubkin University.

By correctly defining the oil distribution across the entire height of the formation—rather than just within the main reservoir body—from the outset, the model can more accurately predict production volumes and identify areas where potential losses might occur. This makes it possible to adjust the waterflooding system so that oil is directed toward production wells rather than being displaced into the water-bearing zone.

"This development is particularly relevant for Western Siberian fields with extensive oil-water contact zones. The large surface area of ​​these contact zones, the complex geological and physical characteristics of the reservoir, and the pressure differentials created during development can collectively lead to significant losses of mobile reserves," the scientist explained.

Water was present in Western Siberian reservoirs when the rock formations themselves were being created. Oil migrated into these traps later, rising from deep underground through fractures and faults. Consequently, oil and water became trapped in the same reservoirs; as a result, hydrocarbon extraction inevitably brings up water, which must be constantly managed.

"Traditional 'light' Siberian oil is largely depleted, so new, effective extraction methods are needed. On one hand, this involves seeking technologies for hard-to-recover reserves and unconventional resources; on the other, it requires a highly careful approach to developing fields where the necessary infrastructure is already in place," explained Pyotr Pyatibratov.

An experiment using data from a Western Siberian field demonstrated that the new calculation approach allowed for a more accurate assessment of oil losses in contact zones. The discrepancy amounted to approximately 40,000 cubic meters for an average-sized oil field.

"The 40,000-cubic-meter difference is a specific example. For larger fields, the figures could be higher, depending on geological and physical characteristics, the field's geological structure, and the technologies employed." "Accounting for the man-made processes occurring in reservoirs during development is the path to formulating sound project decisions and increasing the oil recovery factor," the researcher concluded.