Study On Influence Factors Of Foam's Blocking Ability On Flow Channels In Low-permeability Oil Reservoir

Nowadays,the demand for profile control and oil displacement technology in low-permeability oil reservoirs is becoming increasingly urgent in China.Because of its good injection ability and blocking ability,foam system is one of the best choices.However,there are many problems in its application.To solve these problems,this paper carried out a research on the influence factors of foam system's blocking ability on water channeling in low-permeability oil reservoirs to provide a basis for improving the foam system's blocking ability and oil displacement effect in low-permeability reservoirs.Under target reservoir's conditions,12 foaming agents were chosen based on solubility.By using Waring Blender method,the best concentration of the foaming agents was determined based on initial foam volume and foam stability.1 strong foaming ability agent and 1 strong foam stability agent were selected through compounding experiments.The effect of gas-liquid surface tension on foaming ability and stability was studied.Results show that in the extent of high surface tension,with the decrease of the surface tension,foaming ability of the foaming agents enhances while foam stability goes otherwise.In the extent of the low surface tension,foaming ability and foam stability have no obvious relevance with the surface tension.This indicates that in low surface tension range,the main control factors of foam properties aren't merely the surface tension.It may be decided by multiple factors.By foam injecting experiments in long homogeneous cores and oil displacement experiments in heterogeneous cores,the influence of foaming ability and foam stability on foam system's blocking ability and oil displacement effect were studied.Experimental results show that the foam agent(0.3%LAO+0.5%OA-12)with strong foaming ability and relatively weaker stability has better blocking ability and oil displacement effect than the foam agent(0.3%LAO+0.5%AES)with weak foaming ability and strong stability.Through foam injecting experiment in long homogeneous cores,the influence of the permeability,fracture and reservoir heterogeneity on foam blocking ability were studied.The experimental results show that the relationship between the foam's blocking effect on water channels and the permeability has a critical value(kc).In the range of permeability which is lower than the kc,the higher the permeability,the better the blocking effect.When permeability is higher than kc,the higher the permeability,the poorer the blocking effect.Foam blocking selectivity experiments were conducted in heterogeneous parallel cores.Under the experimental conditions,in the heterogeneous parallel cores of permeability contrast 37.1,97.1 % of the foam system flows into high permeability core.During subsequent water flooding process,high permeability core flow rate percentage declines from 95.1% to 55.9%.Whether the heterogeneity of parallel cores is too strong or too weak,foam blocking effect for high permeability cores becomes poorer.The influence of injection speed,injection volume and injection slug concentration on foam blocking and oil displacement effect were studied by foam injecting experiments in homogeneous and heterogeneous cores.It shows that increasing injection rate appropriately help to improve foam blocking strength.But the too high injection rate is easy to lead to gas channeling and blocking ability will decline.When foam injection volume is lower than 0.6PV,increasing injection volume can improve the foam flooding effect.When higher than 0.6PV,the foam oil displacement effect doesn't rise obviously with injection volume addition.Decrease of foaming agent concentration will reduce foaming effect in deep reservoir and foam strength goes down sharply,so improving deep displacement and sweep efficiency cannot be achieved.Therefore,the actual foaming agent concentration should be greater than that of the experimental optimization to avoid adsorption and dilution of foaming agent in the reservoirs.