Experimental Study on the Feasibility of "Radial Jet Drilling + CO₂ Huff-n-Puff" for the Development of Shale Oil

To enhance shale oil recovery and facilitate sustainable resource exploitation, an innovative integration of CO₂ huff-n-puff and radial jet drilling (RJD) technologies is presented. Its feasibility is verified through core-scale experiments, and the influence of laws of parameters such as the number of huff-n-puff cycles, soaking time, injection pressure, and radial borehole length has been analyzed. The results demonstrate that the "RJD + CO₂ huff-n-puff" significantly improves injectivity in low-permeability shale reservoirs. Under experimental conditions, compared to the core without radial boreholes, the presence of radial boreholes significantly enhances the cumulative oil recovery (CRR) of shale oil, with a maximum improvement of nearly 100%. The CRR of cores shows a logarithmic increase with an increase in the number of huff-n-puff cycles. The first four cycles account for about 85% of the final recovery rate. Increasing the soaking time leads to a gradual rise in the CRR for all core samples. However, prolonged soaking time exhibits limited improvement in the CRR, which means that an optimal soaking time exists. CRR increases consistently with higher injection pressures. In particular, when the injection pressure of CO₂ approaches the miscible pressure, the oil recovery efficiency can be significantly enhanced. The CRR approximately increases linearly with an increase in the radial borehole length. The recommended parameters for the core size CO₂ huff-n-puff experiment are as follows: huff-n-puff cycles 4, soaking time 6 h, and injection pressure 20 MPa. These findings provide a strong theoretical and experimental foundation for applying the "RJD + CO₂ huff-n-puff" technique in low-permeability shale reservoir development.