«Geology, geophysics and development of oil and gas fields»

ON THE LEGALITY OF THE EXISTING THEORETICAL JUSTIFICATION OF CYCLIC FLOODING TECHNOLOGY PRODUCTIVE FORMATIONS

UDC: 532.546+622.276
DOI: 10.33285/2413-5011-2021-6(354)-57-60

Authors:

¹ Oil and Gas Research Institute Russian Academy of Sciences (OGRI RAS), Moscow, Russian Federation

Keywords: cyclic waterflooding, layered heterogeneous formations, capillary mass transfer, enhanced oil recovery

Annotation:

The current scientific substantiation of technologies for cyclic water injection into productive formations is that reservoir pressure fluctuations caused by periodic shutdown of some injection wells lead to activation of mass transfer processes between layers of different permeability in layered heterogeneous productive formations. At the same time, a correct mathematical analysis of such mass transfer processes shows that the crossflows of formation fluid between layers, caused by periodic changes in reservoir pressure, are in fact negligible and cannot cause any noticeable increase in oil recovery during their cyclic waterflooding. It has been established that the real mechanism of enhanced oil recovery during cyclic waterflooding is a change in the directions of filtration flows in the reservoir, leading to the displacement of oil pillars in stagnant zones of the reservoir into zones with higher displacement pressure gradients. It is also shown that the displacement of oil-saturated zones in layered heterogeneous layers increases the intensity of vertical capillary mass transfer between high and low permeability layers. At the same time, it was found that the cyclical nature of the waterflooding process leads to a periodic displacement of oil-saturated zones in the opposite direction, which leads to a completely irrational zigzag movement of oil pillars to the producing wells. Hence it follows that to achieve the maximum possible effect of changing the directions of filtration flows in the reservoir, it is necessary to abandon the cyclical waterflooding in favor of a single, optimally calculated change in the injection modes. It should be noted that the optimal injection option presupposes incomplete shutdown of a part of injection wells, which leads to an increase in the trajectory of oil movement to the producing wells due to its bending, and the most rationally selected ratio of the volumes of injected water in injection wells, ensuring the maximum increase in oil recovery of productive formations.

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