Review of Formation Mechanisms, Localization Methods, and Enhanced Oil Recovery Technologies for Residual Oil in Terrigenous Reservoirs

Inzir Raupov, Mikhail Rogachev and Egor Shevaldin ()
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Inzir Raupov: Department of Oil and Gas Fields Development and Operation, Empress Catherine II Saint Petersburg Mining University, 2, 21st Line, 199106 St. Petersburg, Russia
Mikhail Rogachev: Department of Oil and Gas Fields Development and Operation, Empress Catherine II Saint Petersburg Mining University, 2, 21st Line, 199106 St. Petersburg, Russia
Egor Shevaldin: Department of Oil and Gas Fields Development and Operation, Empress Catherine II Saint Petersburg Mining University, 2, 21st Line, 199106 St. Petersburg, Russia

Energies, 2025, vol. 18, issue 21, 1-35

Abstract: Residual oil (RO) in terrigenous reservoirs formed after waterflooding can exceed 60% of the original oil in place; approximately 70% is trapped at the macro-scale in barriers and lenses, whereas about 30% remains at the micro-scale as film and capillary-held oil. This review aims to synthesize current knowledge of RO formation mechanisms, localization methods and chemical recovery technologies. It analyzes laboratory, numerical and field studies published from 1970 to 2025. The physical and technological factors governing RO distribution are systematized, and the effects of heterogeneities of various types, imperfections in pressure-maintenance (waterflood) systems and contrasts in oil–water properties are demonstrated. Instrumental monitoring techniques—vertical seismic profiling (VSP), well logging (WL), hydrodynamic well testing (WT) and geochemical well testing (GWT)—are discussed alongside indirect analytical approaches such as retrospective production-data analysis and neural-network forecasting. Industrial experience from more than 30,000 selective permeability-reduction operations, which have yielded over 50 Mt of additional oil, is consolidated. The advantages of gel systems of different chemistries are evaluated, and the prospects of employing waste products from agro-industrial, metallurgical and petroleum sectors as reagents are considered. The findings indicate that integrating multi-level neural-network techniques with instrumental monitoring and adaptive selection of chemical formulations is crucial for maximizing RO recovery.

Keywords: residual oil (RO); terrigenous reservoirs; reservoir heterogeneity; localization of reserves; polymer gel systems; physico-chemical enhanced oil recovery (EOR); optical well logging; neural-network forecasting (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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