Study On Physical Properties And Fracturing Fluid Imbibition Of Atmospheric Shale Gas Reservoir In Pengshui Area

With the increasing shortage of oil and gas resources,shale gas has become an important unconventional energy.There is a phenomenon of"low flowback and high production"in the exploitation of shale gas reservoir in Pengshui area.Due to the special physical properties and pore structure characteristics of shale,a large amount of fracturing fluid remains in the formation,and the main absorption mode of fracturing fluid in the reservoir is infiltration,so it is necessary to study the physical properties and the law of infiltration and absorption of shale reservoir.Taking Longmaxi formation shale in Pengshui area as the research object,through a series of experiments,such as porosity and permeability test,capillary force curve test,low temperature nitrogen adsorption test,shale permeability and absorption test,nuclear magnetic resonance test,we have a certain understanding of the pore structure,physical parameters,permeability and absorption law of Longmaxi formation shale in Pengshui area,and have studied the factors affecting the permeability and absorption effect,such as pressure,temperature The distribution of the liquid in the pores during the process of imbibition is analyzed.The results show that:?1?The permeability and porosity of shale are very low,usually at nanometer level,and the porosity is lower than other lithology.There are pinnecked pores in shale,which are arranged in series with micropores and mesopores,with small pore throat,poor connectivity and pore structure.The isotherms of core are all IV isotherms,and the adsorption curve of isotherms is not consistent with the desorption curve.The"tensile strength effect"of hysteresis loop can be observed.?2?The process of shale core imbibition is mainly divided into three stages.In a certain range,with the increase of pressure and temperature,the imbibition effect of shale is enhanced to a certain extent.In the early stage of imbibition,the imbibition rate of gel breaking fracturing fluid is significantly higher than that of non gel breaking fracturing fluid,and the fractures in the reservoir can promote the imbibition of fracturing fluid.Cationic surfactant can reduce the capillary force and surface hydrophilicity of shale,and then reduce the permeability of shale;KCl solution can reduce the permeability of shale by inhibiting the hydration of clay.?3?The T₂ spectrum of shale shows obvious double peak characteristics,and its left peak area is far larger than its right peak area.At the initial stage of shale spontaneous imbibition,the liquid first fills the macropores or fractures rapidly,and then the liquid first imbibites into the micropores,and gradually fills them,and the spontaneous imbibition of slightly macropores increases slowly.New microcracks appear in the process of imbibition.A large amount of fracturing fluid in microfractures can not be flowback,resulting in low flowback rate of fracturing fluid,and a large number of fracturing fluid is detained in shale reservoir.At the same time,the results of NMR are consistent with those of shale permeability experiment.Through basic test,experimental research and result analysis,the pore structure and physical property parameters of Longmaxi formation shale in Pengshui area are understood,the mechanism,law and influencing factors of fracturing fluid imbibition are revealed,and the distribution of fracturing fluid in pore throat is analyzed,which provides theoretical basis for understanding reservoir and evaluating the imbibition effect of fracturing fluid,as well as for shale gas fracturing reconstruction and shale gas fracturing high efficiency gas exploitation is of great significance.