Study On In-depth Profile Control And Displacement Of Soft Micro Gels In Offshore Heterogeneous Reservoirs

Offshore oilfield has a strong heterogeneity.Conventional polymer flooding in low permeability layers will cause the suction hydraulic pressure difference gradually decreases,the inversion phenomenon and the effect of limiting the precipitation polymer flooding.While the size distribution of soft micro gel particle is concentrated,which can only partially enter into the pores that is matched to their particle size in the displacement process.Then the carrier fluid stream diverts and occurs in small pores,ultimately expands swept volume and improve oil recovery.Thus,in this paper,performance evaluation,reservoir adaptability research and profile control mechanism research are carried out for the SMG(soft micro gel)system,main work and results are as follows:Using a particle size analyzer,rheometer and aging tank to study the expansion,shear resistance and long-term stability of the SMG.The results showed: SMG micro gels had a good swelling property,which multiple expandable increased with the increase of temperature,and the particle size of sub-millimeter SMG at reservoir temperature was larger than that of micrometer SMG.SMG system had lower apparent viscosity,while the viscosity at high shear rate curves showed certain Newtonian fluid characteristics.SMG system can maintain a good morphology and particle size for a long time at reservoir temperature.By core experiments,optimization experiments of injection parameters,parallel three-pipe oil displacement experiments and the reservoir adaptability of the SMG system was explored.The results showed that: the best matching coefficients of submillimeter SMG and micron SMG were between 0.98-1.40 and 1.32-2.07,respectively.The profile control and flooding of classification and grading method,including continuous polymer gel system and dispersed SMG system,had the highest recovery rate,which can reach 22.3%.based to the optimization experiments,the optimal injection rate was 1 mL/min,and the injection volume of the main slug SMG was 0.2 PV.The displacement experiments proved that the optimized parameters can effectively improve the diversion rate and recovery factor of the low and medium permeability cores.Through long core experiments,low-field NMR experiments and relative permeability experiments,the in-depth profile control and flooding mechanism of SMG system was studied.The results showed that: the profile flooding method can block the dominant channel one by one and start the low permeability area.After SMG flooding,the displacement fluid can be sufficiently startup throat apertures residual oil,and increased integrated recovery by 22.0%,where in the large pore recovery by 5.6%,and 12.1% in the medium pores,and 4.2% in the small pores.With respect to water flooding relative permeability curves,SMG displacement relative permeability curves shifted to the right.The residual oil saturation decreased from 33.8% to 19.0%,and the two-phase region saturation increased from 39.8% to 54.8%.At the same time,the anhydrous oil production period of SMG flooding was longer than that of water flooding.Results of this study help us to understand the oil displacement characteristics and oil displacement mechanism of the dispersed displacement system in offshore heterogeneous reservoirs,which can lay the experimental and theoretical basis for the oil displacement work in actual reservoirs.