Investigation On Plugging Fractured Water Layer With Nanoparticle In Fracturing Process

There are abundant natural fractures in china’s low-permeability fractured reservoirs,which are possible to communicate with the water layer.During the fracturing of this kind of reservoir,some of the cracks opening may communicate with the water layer,causing a sharp increase in moisture content.For prevent the occurrence of this phenomenon,a selective plugging agent can be added to the fracturing,plugging the water flow cracks without plugging the oil flow cracks.However,due to the small size of micro-fractures in low-permeability fractured reservoirs and the large size of conventional water-shutoff agents which can only be plugged in near-wellbore areas and cannot enter the deep layers of the formation to block water in micro-fractures effectively.Therefore,we are targeting at nano plugging agent which has small size.Recently,nanoparticle is generally applied to profile control for small pore blocking more,few people use it for fracturing technology to block water micro-cracks.Therefore,swellable nanoparticle has been chose as plugging agent for sealing performance experiments to crack.The basic properties of nanoparticles,the plugging mechanism,the plugging performance to cracks is analyzed,and a set of on-site construction scheme is recommended.On the basis of static experimental study,the basic performance evaluation of nanoparticles were carried out,including nanoparticle size and shape,dispersibility,compatibility,swelling,and salt resistance.The evaluation results show that the initial size of nanoparticles are small,which are far less than the width of micro-fissures,and meet the requirement of blocking agent “going in”.It has good dispersibility and compatibility with standard salt water and oil,and has strong ability to resist mineralization.In pure water,it has good water-swelling property.The expansion performance of the nanoparticle is poor in the main production layer with an oil saturation of more than 60%.Based on the analysis of conventional blocking agent blocking mechanism,the mechanism of nanoparticle blocking was systematically analyzed.Based on the blocking mechanism of particle bridging,the matching relationship between particle size and micro-cracks after expansion of nanoparticles was studied.The results show that the blocking mechanism of nanoparticles on water flow cracks is electric-level adsorption mechanism,water swelling mechanism,and polar adsorption mechanism.According to the particle bridging sealing mechanism,the particle size forming clogging in cracks need to be greater than 1/7 times the fracture size,and particles with initial size of 100-150 nm need to expand more than 20 times to form plugging in crack.Through indoor core flow experiments,the selective plugging performance,injection performance,and erosion resistance of nanoparticles were analyzed.Studies have shown that nanoparticles has good selective plugging performance,which can block the water flow cracks without blocking the oil flow cracks.The nanoparticle has good injection performance with low viscosity and injection pressure,which is equivalent to standard saline.The erosion resistance is good after being expanded for 4 days in the water flow cracks.Aiming at the site of the process,a set of construction solutions for blocking the fractured water layer in the fracturing process was recommended.The research results of this paper contribute to fill in gaps of the nanoparticles blocking the water flow cracks,and provide theoretical support for the study of the nanoparticles blocking the fractured water layer in the fracturing process,and provide reference for the on-site construction.