New Method for Quantitative Prediction of Liquid Flowback Based on the Capillary Bundle Model.

Liquid invasion damage plays a main role in the formation damage of low-permeability sandstone reservoirs. The long-term retention of working fluid in the formation will cause serious water blocking damage. In order to research the quantitative prediction of liquid flowback in low-permeability sandstone reservoirs, a new method for quantitative prediction of liquid flowback based on the capillary bundle model was proposed, which took into account the boundary layer effect. Besides, taking the low-permeability sandstone samples of Penglaizhen formation in the Sichuan basin as an example, the quantitative prediction of liquid flowback was carried out. Finally, a series of experiments including gas displacement experiment and nuclear magnetic resonance experiment were conducted to examine the validation of the new method for quantitative prediction of liquid flowback. The study indicates that the results of quantitative prediction were in good agreement with the experimental results. Liquid flowback is closely related to pore structure, boundary layer effect, and displacement pressure in low-permeability sandstone reservoirs. For the sandstone sample with a permeability of 5.5 mD, most of the liquid could be displaced out at 1 MPa, and liquid saturation in the sandstone sample tends to be stable at 32%; for the sandstone sample with a permeability of 0.0349 mD, liquid flowback process is more durable, thereby the cumulative mass of liquid flowback and liquid saturation change gradually, and liquid saturation tends to be stable at 55%. This study not only provides an insight into the microscope mechanisms of liquid flowback but also predicts the cumulative mass of liquid flowback and liquid saturation accurately.