Considerable portion of Russian oil fields, including the Volga-Ural region, are at the late stage of development and are characterized by production decline. This decline is attributable to depletion of active oil reserves with the resultant increase in the share of residual oil trapped in unswept zones. Other contributing factors are increase in water cut of complex terrigenous reservoirs and substantial reservoir compartmentalization. Such reservoirs are typically developed using waterflooding method. This well-proven and relatively cost-effective method still has its limitations. Different viscosities of crude oil and displacing agent, and their immiscibility as well as reservoir heterogeneity are the primary factors affecting water-oil displacement efficiency.
Target oil recovery factor can be achieved through improvement of water (displacing agent) displacing ability or reservoir sweep efficiency. Various flow diversion technologies have been implemented and applied in Tatneft PJSC. Of these, gel-forming compositions, dispersion systems and sedimentation agents have gained wide acceptance. However, application of such compositions can cause total blockage of high and medium permeability intervals that contain considerable oil reserves despite high water saturation. This puts such intervals out of operation for a long time to the extent that the entire reservoir becomes non-producing. At the same time restoring production from blocked intervals requires complex and costly operations. Consequently, permanent shut-down of individual reservoirs cay result in increase of the share of hard-to-recover oil reserves and decrease of ultimate oil recovery. In light of the above, application of low-impact flow diversion technologies becomes urgent. These technologies enable temporary blockage and suppression of water flow in flushed high- and medium permeability reservoir zones. The common practice is to use hydrocarbon-based emulsion compositions exhibiting the above properties. Emulsion compositions improve sweep efficiency and facilitate conformance control to prevent rapid breakthrough of injected water towards production well due to high viscosity of the emulsion. Adjustable viscosity enables penetration of emulsion composition into flushed high-permeability zones, redistribution of injected water to lower permeability zones and complete oil recovery from unswept reservoir zones.
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