Research On Influence Law Of Imbibition Process And Mechanism Of Matrix Crude Oil Migration By Slick-water Fracturing Fluid In Tight Reservoirs

During the fracturing process of tight reservoirs,fracturing fluid will invade the matrix pores and have a complex effect on the matrix.Due to the lack of systematic research on the effect of fracturing fluid to the reservoir matrix,the article starts with the research on the basic performance of the fracturing fluid.By clarifying the influence law and action mechanism of fracturing fluid on the crude oil imbibition process in tight reservoir,which can provides technical support and scientific basis for optimizing of the fracturing fluid formulation,majorization injection process and increase productivity after fracturing.This paper aims at the EM30 slick-water fracturing fluid system as the research object and takes the Chang 7 block in the Ordos Basin as the target reservoir to conduct research.Explore the basic performance of the EM30 slick-water fracturing fluid.Macroscopically analyze the influence of different factors on the performance of imbibition and fluidity of the fluid in the matrix through the imbibition experiment and physical simulation experiment.Through nuclear magnetic resonance analysis and scanning electron microscopy,explore the nano-microporous fluid migration rules and changes of pore wall morphology.The experimental results show that the concentration range of drag reduction agent in EM30 slick water fracturing fluid system is 0.15 ~ 0.30wt%,the optimal concentration of cleanup agent is 0.25wt%,and the optimal concentration of clay swelling inhibitor is 0.50wt%.Base fluid of fracturing fluid has a strong ability to improve the interface performance and has the effective ability of reducing the hydration swelling,and its imbibition recovery rate is 54.37%.By adding drag reduction agent to the base fluid and configuring it as a fracturing fluid,the recovery ranges from 10.40% to 48.69% under different imbibition conditions,which is generally much higher than the simulated water imbibition recovery factor,indicating that it has significant performance of imbibition and displacement.Core permeability decreases after imbibition process.The physical simulation experiment results show that the imbibition process of the fracturing fluid can cause damage to the core matrix.The core permeability has the most significant effect on core damage.The decrease in core permeability caused by solid damage accounts for more than 35% of the total damage,and increases significantly with the increase in the concentration of drag reduction agent,which is the main controlling factor.Through nuclear magnetic resonance to explore the fluid migration characteristics in matrix pores during the imbibition process and analyze the displacement space.The study found that oil in small pores has the highest utilization degree,which is more then 50%.Medium pores are most seriously damaged by solid phase,with the lowest utilization rate,mostly below 30%.The utilization degree of large pores is between small pores and medium pores,mostly between 30% and 40%.By simulating the fracturing and soaking process,combining macro analysis and micro research,the study clarified the influence law and mechanism of the slick water fracturing fluid on the utilization of crude oil of low-permeability tight reservoir.The fracturing fluid be imbibed into the matrix under the action of capillary force and well pressure,which has a positive effect on improving the recovery of tight reservoirs.Meanwhile,because the composition of the fracturing fluid is relatively complex,it will affect the fluid migration process,and has the negative effect of blocking the matrix flow channel.The fracturing fluid significantly improves the utilization of matrix pore crude oil through imbibition,which is conducive to increasing production in tight reservoirs.