Research On Microcosmic Laws Of Fracture Fluid Imbibition And Mechanisms Of Productivity Enhancement By "Shut-in" In Unconventional Hydrocarbon Reservoir

The imbibition of the fracture fluid by reservoir and the effects on the capacity is a key issue in the hydraulic fracturing development of unconventional oil & gas resources.But most of the relevant studies are focused on macroscopic characteristics of the imbibition,the micro characteristics of the imbibition inside the pores of the rock is insufficient in research.Besides,the traditional formation damage theory drew by conventional spontaneous imbibition experiments can`t explain the phenomenon that gas production of some well in field increased after "shut-in".And the microcosmic mechanisms of displacement by imbibition,the mitigation of the formation damage and the increase of the production are still not fully understand,the influence factors need further study.The ion exchange between fracture fluid and fracture faceduring hydraulic fracturing lacks sufficient attention,the internal rules,mechanisms and effect on production are still unknown.Base on the existing problems,we developed a testing method which combined the advantage of traditional imbibition spontaneous and NMR technology.Using this testing method,starting from different size of pores,we analyzed the imbibition and migration of fracture fluid in different size of pores,and we discussed the micro mechanism of imbibition displacement and mitigation of formation damage.The micro mechanisms of gas production enhancement by "shut-in" are primarily explained.Based on the imbibition experiments,we used conductivity and NMR technology,analyzed the ion exchange and migration in pores,the effects on reservoir conditions were also analyzed.At last we summarized the micro mechanisms of gas production enhancement by "shutin",and anlaysed the formation conditions that suitable for the "shut-in" operation.Basically the following achievements are got in our study:(1)Based on NMR technology and traditional imbibition experiment,we designed an experimental methods,which can analyze the imbibition characteristic inside of the pores,defined the micro mechanism of imbibition displacement.And we found that the imbibition speed in small pores are faster the that of the larger pores,and the saturation in small pores is higher than that of the larger pores,which drives the oil and gas in smaller pores to larger pores;(2)Based on NMR technology and traditional imbibition experiment,we designed an experimental methods,which can analyze the migration characteristic of fracture fluid inside of the pores,defined the micro mechanism of formation damage mitigation.And we found that fracture fluid migrates from larger pores to smaller pores,which decreases the water saturation in larger pores,and increases the permeability of the formation;(3)Based on imbibition experiments and NMR technology,we designed an experimental methods,which can analyze the ion-exchange characteristics fracture face and pores of the formation,and we defined the micro mechanism of ion exchange on methane parsing in formation;(4)We preliminarily analyzed the micromechanisms of productivity enhancement by "shut-in",and discussed the application conditions of "shut-in".