Phase Behavior And Oil Displacement Mechanism Of An Alkali-Induced Mild O/W Emulsion

The depression of the current global oil market makes the majority of chemical EOR projects worldwide nearly unprofitable,especially in China.Therefore,economic alternative methods and technologies must be quickly developed.This proof of concept research evaluates a chemical flooding method using pre-formed mild O/W emulsions,which were produced by saponification between a low-cost alkali(NaOH)and a petroleum acid-rich oil.Our focus was first given to the dynamics of the saponification with an aim to quantify alkali consumption.Afterward,the composition of the crude oil before and after the reaction was characterized using a Fourier transform ion cyclotron resonance mass spectrometer(FT-ICR MS)to determine the preferred compounds in saponification.The physiochemical properties of the generated emulsions were further investigated through direct measurements of rheology,morphology,particle size distribution,and stability.Particular attention was placed on the relationship between emulsion stability,dropt particle/pore radius matching,and EOR efficiency.The oil displacement mechanisms of the emulsions at pore level and an alkali-induced oil/water(O/W)emulsion stabilized with cellulose nanofibrils(CNFs)was proposed to advance the development of EOR approach.This can provide us a theoretical and experimental basis for the development of economic and high efficiency chemical flooding methods.Our focus was first given to the dynamics of the saponification with an aim to quantify alkali consumption.The composition of the crude oil before and after the reaction was characterized using a Fourier transform ion cyclotron resonance mass spectrometer(FT-ICR MS)to determine the preferred compounds in saponification,and the physical properties of O/W emulsions.The results showed that 1.0 mLof the crude oil neutralized 0.71 mg of sodium hydroxide.C16 and C18 fatty acids(DBE=1,DBE represents equivalent double bond number)were predominantly saponified,which accordingly produced mild O/W emulsions(pH?7.0).The viscosity,morphology,and stability of the emulsions were found to strongly depend on the oil-water ratio.To investigate flow behaviors,oil displacement efficiency and oil displacement mechanism of the emulsion,core flooding tests and macroscopic displacement experiments were conducted.The core flooding tests proved that due to the Jiamin effect,the injection pressure of the stable emulsion significantly increased when flowing in the core,and the unstable emulsion experienced oil-water separation,leading the injection pressure to change insignificanty.As the consequence,the oil recovery factor was further improved by 6-17%.High matching factor and emulsion stability accounted for more significent EOR effect.The displacement dynamics of three stable emulsions observed in a visual micromodel revealed that the O/W emulsion flooding can enlarge the sweep area and also notably reduce the residual oil saturation when employed as an EOR mode.Emulsification/entrainment,blocking,and stripping were three dominant pore level driving forces for this emulsion flooding.Finally,nanocelluses(L-CNF and CNF)were introduced as stabilizer to stabilize O/W emulsions.The results showed that the introduction of L-CNFs and CNFs were irreversibly absorbed at the oil/water interface forming a solid "armor" on the drops with 63.1%of the oil water interface being covered by CNFs.This finally led to the generation of highly stable O/W emulsion.In summary,alkali-induced mild O/W emulsion can be used in enhanced oil recovery technologies because of their unique properties,indicating the potential in enhanced oil recovery technology and significance of research.