液氮压裂辅助气体吞吐提高页岩油采收率实验OA

In order to improve matrix fluid flow capability of shale reservoir and solve the problem of low depletion recovery,a new method of liquid nitrogen fracturing assisted gas huff-and-puff to enhance oil recovery is proposed.This method is used to carry out N2 and CO2 injection cyclic huff-and-puff experiment on the cores after liquid nitro-gen fracturing,and to study the influence of different gas injection media,gas injection pressure and gas injection methods on shale oil recovery.NMR T2 spectrum test is combined to clarify the characteristics of micro-pore struc-ture changes after liquid nitrogen fracturing assisted gas huff-and-puff.The results show that liquid nitrogen can sharply reduce the surface temperature of rock from 76.2℃to-170℃within 5 minutes,instantly forming thermal stress of about 303 MPa,and compressing rock with induced fractures formed.With same gas injection pressure af-ter liquid nitrogen fracturing,cumulative recovery of 3 rounds of 3 injection modes including CO2 huff-and-puff,N2 huff-and-puff and N2 huff-and-puff followed by CO2 huff-and-puff are 57.34%,27.35%and 50.17%,respectively.The 3rd injection mode not only reduces CO2 demand but also gives full play to displacement advantages of the 2 kinds of gas injection media.Core porosity increases from 6.74%to 12.04%,permeability increases from 0.024×10-3 μm2 to 6.242×10-3 μm2,and average pore size increases from 4.94 nm to 47.79 nm.The research provides new idea and method for efficient development of shale oil and gas.