Mobilization mechanisms and enhanced oil recovery of hydrocarbon gas injection in offshore low-permeability reservoirs after water flooding based on LBM
In offshore low-permeability reservoirs,a significant amount of residual oil remains trapped in the pore spaces after water flooding.Hydrocarbon gas injection offers a potential method to enhance oil recovery,but its mobilization mechanisms remain unclear.This study focuses on the WZ12-1 Oilfield in the Beibu Gulf of the South China Sea.Based on pore characteristics extracted from cast thin section experiments,microscopic simulations of hydrocarbon gas injection after water flooding were conducted using the lattice Boltzmann method(LBM).The study investigated the distribution characteristics of residual oil,the mechanisms of mobilization by hydrocarbon gas injection,and the effects of different gas injection methods on oil displacement efficiency.Results indicate that residual oil after water flooding primarily exists in parallel channels,as membrane-like oil,in dead-end pores,and in micropore throats.Hydrocarbon gas injection can mobilize residual oil through dissolution and extraction,oil expansion,and improved flow pathways,thereby increasing sweep efficiency.When hydrocarbon gas and crude oil achieve miscibility,the gas breakthrough time is delayed by 25.29％,and the sweep efficiency improves by 24.87％.Among various gas injection methods,water-alternating-gas(WAG)injection proved most effective,as water injection effectively blocked high-permeability channels,improving gas utilization efficiency.A 1∶1 WAG ratio increased gas utilization by 41.43％.This research provides theoretical guidance for the development of hydrocarbon gas injection in offshore low-permeability reservoirs after water flooding.
LBMoffshore low-permeability reservoirspore scalemiscibilityhydrocarbon gas injection
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