Experimental study on the mobility of Junggar Basin's Jimsar shale oil by CO₂ huff and puff under different temperatures and pressures

Micro- and nano-scale pore-throat fissure systems were mainly developed in the Jimsar shale oil reservoir of the Junggar Basin with the oil of viscous and difficult to be produced.CO₂ huff-and-puff is an important technology to enhance the oil recovery. To understand the mobility law of Jimsar shale oil reservoir under CO₂ huff and puff, 45 cores of the Lucaogou Formation in this area were studied in this study.The cores was classified into dolomitic sandstone, doloarenite and lithic sandstone. The overburden porosity of the reservoir is 2.0%-22.7%, and the average value is only 11.0%. The average overburden permeability is 0.01×10^-3 μm², and more than 90% of the samples have permeability lower than 0.1×10^-3 μm². According to physical property classification, 20 rock samples were further selected and 6 key parameters for low-field NMR measurement were optimized. By comparing the experimental data of shale oil mercury injection with those of low-field NMR, the linear relationship between T₂ value and pore radius of shale core was established in logarithmic coordinates.The pore radius distribution of shale was obtained quantitatively according to the T₂ spectrum. 9 kinds of CO₂ huff and puff experiments were carried out under different temperatures and pressures. The analyses of recovery rate, utilization degree and other indicators show that shale oil in small pores(r < 300 nm) is difficult to produce, and the utilization degree of shale oil in medium pores (300 nm < r < 1 000 nm) and large pores(r>1 000 nm) is relatively higher, and increases with the increase of temperature and pressure.