Study On Imbibition Mechanism Of Low-damage Non-flowback Guargum Fracturing Fluid In Tight Reservoir

Large-scale spatial fracture-network-formed fracturing of horizontal wells has become an important measure of tight reservoir development.There are some problems during the fracturing process.A large number of fracturing fluids remain in the reservoir because of the large scale and low flowback rate,causing damage to the formation,so it is particularly important to make rationally use the gel-breaking fluid to increase recovery.At present,the study of guargum fracturing fluid imbibition under confining pressure is very few,and its mechanism is not clear.This research used the samples of natural cores from HL tight oil block in Ordos Basin,and conducted imbibition experiments under confining pressure,and compared the spontaneous imbibition effects of conventional guargum fracturing fluid and low-damage non-flowback guargum fracturing fluid under different confining pressures.Next,0.3wt% of anionic surfactant FSLF-04 was selected as a low-damage guargum fracturing fluid's imbibition promoter by contact angle test,interfacial tension test and imbibition effect evaluation test.The influence of main controlling factors such as permeability,wettability,temperature and salinity on surfactant-assisted imbibition under confining pressure was evaluated and analyzed.Finally,the microscopic mechanism of surfactant-assisted guargum fracturing fluid imbibition under confining pressure was analyzed by nuclear magnetic resonance(NMR)technology and pressure pulse attenuation method.It is found that with the increase of confining pressure during 0.101-10 MPa,the imbibition recovery of guar gum fracturing fluid increases gradually,core permeability and effective pore radius decrease exponentially.Compared with the atmospheric spontaneous imbibition experiment,the imbibition recovery in small pore and throat increases obviously.After adding the imbibition promoter to gel-breaking fluid,the imbibition effect is improved obviously.The main mechanism of surfactant-assisted imbibition of guar gum fracturing fluid under confining pressure includes improving core wettability,reducing oil-water interfacial tension and reducing the adhesion work of oil droplets on rock wall.It is found that the action of surfactant causes oil droplets to peel off the rock wall and forms a layer of water film on the rock wall,which greatly reduces the viscous resistance of oil droplets to migrate in porous media.The differential pressure exists at both ends of the small pore and throat with poor connectivity and complex structure under confining pressure.In addition,the confining pressure increases the stress of core skeleton,and the pore compression drives the migration of oil droplets.At the same time,because of that surfactant reduces the interfacial tension between fracturing fluid and crude oil,it further enhances the ability of crude oil deformation to break through pore throat,and increases the imbibition recovery.