Study On Mechanism And Influencing Factors Of Fracturing Fluid Imbibition Displacement In Chang 8 Reservoir In Heshui Area

With the development of oil and gas exploration and development from conventional to unconventional,the development technology of tight reservoir has been paid more and more attention.In order to achieve industrial productivity,compact reservoirs must be reformed by fracturing.Because of the small pore radius and high capillary force,fracturing fluid retention is easy to occur after fracturing,which results in low fracturing fluid backflow rate.In view of the low fracturing fluid backflow efficiency of Chang 8 reservoir in Heshui area,the mechanism of imbibition and displacement of Chang 8 reservoir and its main influencing factors are revealed from microscopic scale by combining laboratory experiments with NMR technology.The results show that with the decrease of crude oil viscosity,the efficiency of imbibition flooding and the rate of imbibition increase.The interfacial tension mainly controls the efficiency of imbibition and displacement through the influence of small to medium pore.With the decrease of interfacial tension,the efficiency of core imbibition and displacement shows a downward trend.By comparing the imbibition efficiency and imbibition rate of different salinity of the same core,it is found that the imbibition displacement efficiency and imbibition rate are higher when the salinity of the imbibition fluid is 35000mg/L.The efficiency of core imbibition and displacement is increased by 70.3%,57.7%and 43.9%respectively before and after pulsed core with three different permeability grades.The efficiency of core imbibition and displacement with pulsed core imbibition is improved obviously when the permeability is less than 0.1×10^-3?m².Through the study of the oil displacement efficiency and contribution rate of pore imbibition at different scales in different imbibition periods,it is found that the phenomenon of imbibition appears in the pore of different scales.With the extension of imbibition time,the oil displacement efficiency of pore imbibition at different scales rises as a whole.Due to the migration of crude oil in different scales of pore,the contribution rate of pore imbibition and displacement will change at different scales.