Review on Phase Behavior in Tight Porous Media and Microscopic Flow Mechanism of CO₂ Huff-n-Puff in Tight Oil Reservoirs

Table 4

Summary of microscopic flow mechanisms by other methods.

Methods	Reference	Main conclusions
Experiments
Outcrop plate model experiment	Zhou et al. [70]	To inject CO2 at pressure lower than miscible pressure, which is conducive to CO2 fingering into the reservoir and driving out more crude oil when the well is opened.
Direct visualization experiments with a microfluidic system	Nguyen et al. [71]	The solubility of CO2 is bigger than that of N2 so that CO2 forms more bubbles within the fracture. Bubbles gradually expand with the local mass transferring between gas and liquid and pressure reduction, and then displace the crude oil.
Core experiment	Alfarge et al. [72]	Increasing the exposure time and contact area between the injected CO2 and the target formation can achieve better performance of CO2 huff-n-puff.
Core experiment and numerical simulation	Li et al. [73]	Natural fracture spacing shows the greatest impact on the CO2 penetration depth.
Theory
Pre-Darcy model	Wang et al. [74]	The pre-Darcy flow models can reduce errors caused by the improvement of crude oil properties while simulating the nonlinear flow degree.
Mathematical model	Chen et al. [75]	Due to the boundary layer effect, the absolute permeability is no longer a fixed value.