Study On Imbibition Experiment And Numerical Simulation Of Yanchang Tight Oil Reservoir

Due to the " low permeability,low porosity,low pressure,high capillary pressure and high effective stress" of tight reservoir,namely,it is very difficult to develop tight reservoir,rapid production decline,stable production and enhanced oil recovery are major problems in tight oil reservoir development.Due to the multi-nanometer pore throat system in tight reservoir,the fluid flow space is a network of capillary tubes which are different in size and bend to each other,so it is difficult to develop.In this paper,taking the core of the extended tight reservoir as the sample,the pore structure of the core under the reservoir condition is analyzed by means of nuclear magnetic field,and the experimental results of the high temperature and high pressure imbibition instrument are combined,using COMSOL software to simulate imbibition process,the law and influence factors of imbition under reservoir condition are summarized.The main results are as follows:(1)Extending the mesopores and macropores of tight sandstone samples provides most of the pore volume,accounting for more than 60%,and is the main site of tight sandstone imbibition.The pore size of the samples measured in the experiment ranges from 20 nm to 40 nm.The mesopores and macropores contribute mainly to the pore volume and specific surface area of the compact sandstone.(2)Under the stratum condition,the oil mainly occupies the middle pore and the big pore,occupies less to the small pore,the oil occupies about 30% of the movable water in the pore.(3)The imbibition rate of the short core is higher than that of the long core.As the length of the core decreases,the matrix content in the core decreases,the fractures increase and the imbibition increases,in the short core,the more cracks,the stronger capillary force,the higher imbibition rate.(4)The influence of 4MPa pressure on imbibition of tight sandstone mainly lies in the influence of pore structure,the ratio of small pore is large,the imbibition recovery rate is lower,the large pore and middle pore is main,the imbition recovery rate is little.The temperature also has certain promotion function to the imbibition,the actual mechanism needs to further study.(5)The imbibition model established by COMSOL multi-physical field simulation software can fit the water saturation and oil saturation after imbibition reaction,and display the dynamic change of imbibition process intuitively,and draw the relevant image and curve.