The Imbibition Characteristics Of Jilin Tight Gas Reservoir And Its Relationship With Reservoir Damage

According to statistics,China has abundant unconventional natural gas resources,but unconventional reservoirs have dense pores and low permeability,so hydraulic fracturing is an effective method to increase production.In the process of hydraulic fracturing,a large amount of fluid often causes serious reservoir damage after being injected into the formation,but in practice,the productivity of some unconventional reservoirs increase with the increase of retention.It shows that we need to find a new method to evaluate unconventional reservoir damage.During the process of infiltration,the reservoir properties changes with the increase of the seepage volume.Analyzing the dynamic changes of physical properties after the fracturing fluid enters the reservoir is helpful to understand the reservoir damage and its mechanism.According to that,in practice workers can optimize the fracturing scheme.This paper focuses on the tests of physical properties,permeability,conductivity,water sensitivity and water lock of the tight gas reservoirs in Songliao Basin of Jilin Province based on the laboratory core test.The imbibition volume,permeation rate and diffusibility of the cores were determined by spontaneous imbibition test.The ion diffusibility was determined by conductivity test.The distribution process of the solution after it entered the core was obtained by nuclear magnetic resonance.The dynamic change process of the reservoir permeability during imbibition was studied by the relationship between permeability and physical properties of the reservoir.Main types and influencing factors of reservoir damage were studied by water sensitivity and water lock test.The relationship between initial water saturation,permeability,diffusibility,clay and reservoir damage was analyzed.The micro-mechanism of reservoir damage and water lock relief potential were studied by nuclear magnetic resonance and centrifugal experiments.The study shows that the main damage mechanism of tight sensitive gas reservoirs in Songliao Basin of Jilin Province is water sensitivity and water lock.The reservoir damage is mainly due to the fact that the fracturing fluid permeates the matrix pores.The clay,pore structure,water saturation,formation water salinity and imbibition time of the reservoirs affect the core permeation,diffusion,fracture generation and clay expansion,on which the reservoir damage and damage relief potential depend.The lower water saturation of the tight gas reservoir leads to the stronger fluid absorbility and diffusibility.Although the permeation causes serious static water lock damage,the dynamic water lock release ability is also enhanced.The water lock damage of different areas in the studied block is analyzed and evaluated by this method in order to give the tight sensitive gas reservoir damage mechanism and its control factors,which is significance for the fracturing reconstruction of reservoirs in the studied block.