Evaluation Of Microscopic Pore Structure Characteristics And Flow Mechanism Of Shale Oil Reservoirs

Our country has a large amount of shale oil resources and great development potential.However,due to the limitation of development technology,the recovery rate of shale oil is not high.This paper took shale cores in the Qikou Sag and Raoyang Sag of the Bohai Bay Basin in Eastern China,Qianjiang Sag in Jianghan Basin,and Changling Sag in Songliao Basin as the research object.On the one hand,shale rocks were formed through nuclear magnetic resonance.Quantitative identification methods for different pore types and different pore fluids,on the other hand,through pressure imbibition physical simulation experiments to study the flow mechanism under volumetric fracturing water injection development conditions in shale oil reservoirs.It is an effective method for shale oil reservoirs,which provides theoretical basis for the developement.The following main research results have been achieved:1.In shale rock samples,the proportion of nano-pore throat space is high,while the proportion of micron and sub-micron pore throat space is low,there are parallel plate-shaped slit-shaped pores and ink bottle-shaped pores.Compared with tight sandstone with the same permeability,the maximum mercury saturation of shale rock samples is more than 30%lower,the displacement pressure is more than three times higher,and the specific surface area is more than 5 times higher.These indicate that compared with tight oil,shale oil has a greater solid-liquid interaction in the reservoir,and fluid production is more difficult.2.The formation of shale rock samples organic pores,inorganic pores and different types of fluid porosity quantitative nuclear magnetic resonance testing method.Based on the fact that the inorganic porosity of shale samples in the Raoyang Depression is greater than the organic porosity,the samples tend to be hydrophilic.The saturation of movable fluid in shale samples and the proportion of large pore throat(T₂>100ms)in movable fluid are positively correlated with permeability.3.Pressurized imbibition mainly uses sheet pore throats(T₂>100ms)and matrix pore throats(4<T₂<20ms),so the initial effect is higher.While spontaneous imbibition mainly uses matrix microporous throats(T₂<4ms)and small pore throat,the initial stage of imbibition is much weaker than pressure imbibition.Whether it is spontaneous imbibition or pressure imbibition,the existence of cracks has a greater impact on the imbibition effect of shale oil cores.During spontaneous imbibition,the imbibition efficiency of shale oil cores with cracks is 4.84%higher than that of shale oil cores without cracks.During pressurization imbibition,the imbibition efficiency of shale oil cores with cracks is higher than that of shale oil cores without cracks.The rock oil core is 11.15%higher.During the spontaneous imbibition process of shale,large pore throats(T₂>100ms)and medium pore throats(10ms<T₂<100ms)are produced less than tight sandstone,and the flow efficiency of fractured shale medium pore throats and large pore throats Larger than tight sandstone.The hydrophilicity of shale is enhanced after spontaneous infiltration of active water,and the infiltration efficiency is improved.Spontaneous imbibition can increase the imbibition efficiency of matrix shale,and pressure imbibition can increase the imbibition efficiency of fractured shale.Large pore throats(T₂>100ms)are produced to a greater extent during nitrogen displacement.Compared with tight sandstones with the same permeability,shale nitrogen displacement has lower displacement efficiency.The production of small pore throats(T₂<10ms)in the process of nitrogen displacement is less than that of tight sandstone.