Studies On Adsorption And Activation Mechanisms Of Hybrid Fluorinated Surfactants At The Ultra-low Permeability Reservoir Interface

In China,low-permeability,ultra-low-permeability,and ultra-low-permeability reservoirs with complex lithology have large reserves and widely distributed,accounting for more than 76%of total oil and gas reserves.Ultra-low permeability reservoirs account for a large proportion of the remaining reserves of complex lithological reservoirs and have extremely high mining value.However,due to the low permeability,poor connectivity of pore throats,and strong hydration of clay minerals of such reservoirs,causing many problems such as high water injection pressure and difficult water injection during the exploitation process,the average recovery is only about 25%.This article designed and synthesized a hybrid fluorinated surfactant that can be applied to ultra-low permeability reservoirs.By analyzing and designing the molecular structure of the active agent,the hydrocarbon chain structure,fluorocarbon chain length,and hydrophilic structure were determined.Then used perfluorohexyl ethanol and vinyl benzyl chloride as raw materials,through the enbenylation and sulfonation reaction,a new hybrid fluorosurfactant（PFVB6）was synthesized,which can greatly reduce the oil-water interface tension,and can significantly enhance the non-wetting of the water on the rock surface also,which can play a role in reducing pressure and increasing injection.In this paper,the control variable method was used to investigate the effect of various reaction parameters on the yield,getting the optimal synthesis conditions of PFVB6.The molecular structure was characterized by ¹H-NMR,¹⁹F-NMR,and FT-IR,which confirmed that the target active agent was synthesized;By studying the performance of PFVB6 and the composite system PFVB6/sodium dodecylbenzene sulfonate（SDBS）,PFVB6/petroleum sulfonate（PS）,the relationship between the molecular structure and performance of the active agent,and the interaction law between PFVB6 and the commonly used hydrocarbon active agents SDBS and PS in the oil field were revealed;Visible absorption spectra,fluorescent probes were used to study the aggregated structure of the PFVB6 solution,and the molecular aggregation mechanism in the solution,the relationship between the solution properties and the micellar structure were obtained also;Through the study of displacement properties,the oil displacement mechanism of low-molecular fluorine-containing activator PFVB6 in ultra-low permeability reservoirs was obtained;Through the study of adsorption properties,the adsorption mechanism of PFVB6 molecules in natural cores and the influence of various factors on the adsorption amount were obtained.PFVB6 had excellent surface and interface properties,and could significantly enhance the non-wetting of the water phase on the surface of hydrophilic rocks.In aqueous solution,the critical micelle concentration（cmc）of PFVB6 was 0.4 g/L.At this concentration,the surface and interfacial tensions of the solution were 21.7 m N/m and 3.78 m N/m,and the contact angle of the water phase wetting（θ）was 76.54°;In the 30 g/L Na Cl solution,the cmc of PFVB6 was 0.2 g/L.At this concentration,the surface and interfacial tension of the solution were 17.6 m N/m and 1.71 m N/m,θwas76.19°;PFVB6 had excellent temperature and salt resistance.When the concentration of PFVB6 was 0.4 g/L,the anti-Na Cl concentration was higher than 60 g/L,and the anti-Ca Cl₂ concentration was higher than 6 g/L.In the composite system of PFVB6 with two kinds of common hydrocarbon active agents in oil fields,sodium dodecylbenzene sulfonate and petroleum sulfonate,the solution performance and salt resistance of PFVB6/SDBS system are stronger than PFVB6/PS system.In aqueous solution,the optimal compound concentration of the PFVB6/SDBS system is（0.4 g/L PFVB6）/（0.08 mmol/L SDBS）,0.08 mmol/L SDBS is 0.028 g/L SDBS.At this time,the interfacial tension is 1.87 m N/m andθis 74.82^o;In 30 g/L Na Cl solution,the optimal compound concentration is（0.2 g/L PFVB6）/（0.08 mmol/L SDBS）,the interfacial tension at this time is 0.07 m N/m,andθis 71.59^o;the anti-Na Cl concentration of this system is higher than 60 g/L,anti-Ca Cl₂concentration is higher than 6 g/L.Micellar thermodynamic studies had found that the Gibbs free energy(（35）_mG^（48）)of PFVB6 solution was less than-37.53 k J·mol^-1 when the temperature ranged from30°C to 55°C,and its absolute value is significantly lower than the hydrocarbon active agent,and the absolute value of（35）G _m^（48）increased with the increase of temperature,indicating that the formation of micelles in PFVB6 solution was a spontaneous process,and the micellization process was an entropy increase process.The dissertation used sand-filled pipes for displacement experiments to simulate the permeability and formation environment of an ultra-low permeability reservoir in Changqing Oilfield.The permeability was below 1.0×10^-3μm²,the formation temperature was 70°C,and the total mineralization of formation water was 27.25×10³mg/L.The study founded that for ultra-low permeability reservoirs,when the interfacial activity was higher than a certain interfacial activity,the effect of the non-wettability of the oil phase of the oil displacing agent on the depressurization effect was significantly better than the interfacial activity.The PFVB6/SDBS composite system was better than the single-component PFVB6 in depressurization and recovery,while the single-component SDBS with the best interface activity was the worst.In this composite system,when the concentration of PFVB6 was 0.03 g/L and the concentration of SDBS was 0.02 g/L,the pressure reduction effect and recovery rate are the highest,the pressure drop rate of active water flooding is 43.48%,and the water phase permeability increases 76.92%,the recovery rate increased by8.14%.The dynamic and static adsorption studies of PFVB6 and SDBS solutions showed that the adsorption loss of hydrocarbon active agent was higher than hybrid fluorine-containing active agent.The addition of fluorine-containing active agent can reduce the loss of active agent oil displacement system on the rock surface.In the PFVB6/SDBS composite solution,when the concentrations of PFVB6 and SDBS were both 0.03 g/L,the static adsorption capacity was 235.40μg/g,while the static adsorption capacity of the single-component PFVB6 solution with the same concentration as the total active agent was only 145.00μg/g.At the optimal displacement concentration（PFVB6:0.03 g/L,and SDBS:0.02 g/L）,the dynamic adsorption capacity of the composite system was 50.70μg/g,while the dynamic adsorption capacity of the single-component PFVB6 with the same concentration as the total active agent was only 34.24μg/g.