| Foam flooding is one of the tertiary recovery technologies for improving fluidity ratio,expanding sweep efficiency and improving oil displacement efficiency.It is of excellent temperature resistance and salt tolerant ability,and is very suitable for enhancing the recovery factor of deep ordinary heavy oil reservoirs.The pilot experiment of foam flooding in LKQ oil field achieved good application effect in increasing crude oil production.However,with the expansion of the test area,gas-liquid separation and gas breakthrough appeared in the reservoir.This paper is based on further increasing the application effect of foam flooding and expanding the reservoir adaptation range of LKQ oil field and similar deep ordinary heavy oil reservoir.Aiming at the problems of different types of foam flooding in the field,according to the theory of foam creation,attenuation and percolation,the improvement systems were constructed by mixing different foaming agents and hydrophobic association polymer.The mechanism of foam performance improvement was revealed by the theoretical and experimental studying on the surface and bulk phase properties of foaming fluid.The seepage characteristic of different foam systems in porous media was determined by core flow experiments.Then the adaptability of different foam systems to the reservoir was obtained by numerical simulation.The main research results are as follows:According to the optimization of the foam system,a composite system with strong foaming performance and good stability was constructed using 0.105 wt%CHSB+0.045 wt%AES+150 mg/L tetraethanol.On the basis of the composite system,1200 mg/L PAAO-1,a kind of hydrophobic association polymer,synthesized using AM as the main chain monomer,OA as hydrophobic monomer and AMPS as the heat and salt resistance structure monomer,was added to construct an enhanced system with considerably improved stability.The foam performance test results show that the temperature resistance,salt resistance and oil resistance of the composite system and the enhanced system are better than the original system(single foaming agent).Under the conditions of temperature 80?,salinity 160000 mg/L and oil content 30 vol%,the foaming volume,foam half-life and composite index of the composite system are increased by 27%,109%and 165%,respectively,compared with the original system.In addition,the stability of the enhanced system is greatly improved,the foam half-life and composite index are increased by 449%and 383%,respectively,while the foaming volume decreased by 12%.The results of the foaming solution properties show that the synergistic effect of the composite system and the enhanced system is presented,which makes the surface tension decrease and the surface dilatational modulus increase,and greatly improves the foam properties.The relationship between foam properties and foaming agent properties shows that the foaming property of the original system is mainly affected and controlled by surface tension,and the foam stability is influenced by the surface tension and the surface dilatational modulus.The foaming property of the composite system is controlled by surface tension.When the foaming agent concentration is low,the foam stability of the composite system is negatively correlated with the surface tension,and positively correlated with the surface dilatational modulus at high foaming agent concentration.What's more,foaming ability of the enhanced system is negatively correlated with the apparent viscosity of the foaming solution and foam stability is positively correlated with the surface dilatational modulus.The foam diameter observation results show that the average foam diameter of the original system and the composite system is 175?m and 152?m,respectively,while the average foam diameter of the enhanced system is 218?m.The core displacement experiment results show that the enhanced system is of the strongest plugging ability,but the 45%pressure drop is mainly concentrated in the middle of the core,which indicates that the foam migration ability is poor.The plugging ability of the original system and the composite system increase with the increasing of permeability when the permeability is less than 1500×10-3?m2 and 2000×10-3?m2,respectively,while the plugging ability of the enhanced system is the highest when the permeability is 4500×10-3?m2.However,the foaming ability of the enhanced system is poor due to the influence of foaming mode and injection rate.The critical foaming flow velocity of the enhanced system is 0.12 m/d.The single core oil displacement experiment results show that the non-foam flooding of the enhanced system improved oil recovery factor by 7.43%.When the foam flow velocity is greater than the critical foaming flow velocity,the EOR of the enhanced system is increased to 13.67%by foam flooding.Because foam flooding can not only improve sweep efficiency,but also achieve excellent fluidity control,and improve oil displacement efficiency.However,when the flow velocity of the enhanced system is less than the critical foaming flow velocity,the EOR is only8.62%due to the low shear rate and poor foaming.The experimental results of heterogeneous parallel core flooding show that when the permeability ratio is greater than 2,both the composite system and the enhanced system increase the EOR by more than 15%,and the liquid separation rate can also be modified by more than 35%.In particular,the enhanced system is of the strongest profile improvement ability and the highest EOR when the permeability ratio is 10,which indicates that the enhanced system ideally increases the swept efficiency of the reservoir with severe heterogeneity.A local equilibrium model of foam flooding was built,and the sub-models affecting the foam performance were solved by using MATLAB programming and linear regression method,and the values of parameters representing the performance of different foam systems were obtained accurately by fitting.The dimensionless effective migration distance(RD)and dimensionless gravity differentiation index(GI)were proposed to describe the characteristics of foam migration and distribution on the reservoir scale.The numerical simulation results show that the injection rate has a great influence on the RD and GI of the enhanced system,while the reservoir thickness has the greatest effect on the RD of the original system.The EOR by foam flooding of the enhanced system and the composite system are both higher than that of the original system.The enhanced system improves oil recovery even when the gas/liquid is wide(0.5:1-4:1),the oil viscosity is relatively high(<1000 m Pa·s),and the dominant channel is well developed(the permeability is 5000×10-3?m2),but it is greatly affected by injection method,alternate period and injection rate.However,the composite system is not affected by injection rate and has a similar effect to the enhanced system in EOR under other conditions.According to laboratory experiment and numerical simulation,it is concluded that the enhanced system is of strong stability,good foam performance and favourable EOR on the basis of complete foaming,and is suitable for reservoirs with developed dominant channels,concentrated streamlines and sufficient foaming energy to solve the foam flooding problems in rapid fingering and gas channeling.The composite system is of strong foaming ability,good stability,long migration and penetration distance in the reservoir,which can overcome the problems of viscous fingering and gravity differentiation of foam flooding in heterogeneous reservoirs.In this paper,the relationship between the foam properties and the foaming fluid properties is studied profoundly,and the reservoir adaptability of different foam systems is obtained,which provides a set of theoretical basis and technical methods for the economical and efficient large-scale application of foam flooding. |
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