This paper explores displacement mechanisms of the residual oil film in microchannels by analyzing the following items after wetting hysteresis occurs: resistance on the residual oil film by the rock wall, the interfacial tension between displacement fluid and residual oil film, and horizontal stress acting on residual oil film by displacement fluids. Based on the continuity equations, motion equations, and constitutive equations of viscoelastic fluid, the numerical simulation is used to calculate the distribution of horizontal stress acting on the residual oil film by displacement fluids with different rheological properties. The results of the study show that increasing the horizontal stress on the oil film fundamentally mobilized the oil film and made it movable. Under the condition that the flow rate of the displacement fluid was constant, the value and direction of the horizontal stress acting on the oil film by the viscoelastic fluid changed. The elasticity changed the law of stress on the residual oil film, which is more conducive to mobilizing the oil film.

Regarding the increasing production from unconventional reservoirs, especially shale reservoirs, it is essential to determine appropriate drilling fluid in drilling operations to have maximum efficiency. Selective performance of drilling fluids may increase the formation penetration rate and increase the drilling efficiency. This paper compares the three types of drilling fluids to compare their rheological properties and provide the best drilling fluid composition for shale stabilization. This paper can bring reliable experimental results for petroleum industries, especially drilling operations, to reduce the formation damage and shale instabilities in subsurface formations. To perform the tests under the same conditions, the formulation of all samples is the same in terms of both utilized polymers to determine the effect of other compositions in selected drilling fluids. For the silicate drilling fluid, since silicates perform well at higher pH (potential of hydrogen), the pH of the silicate drilling fluid is increased to 11 by the addition of sodium hydroxide (NaOH). The lowest decrease in fluid viscosity is related to silicate fluids, indicating the more excellent thermal stability of these types of drilling fluid than glycol and potassium chloride (KCl). Plastic viscosity (PV) is about 20 cP for silicate drilling fluids, while it has the minimum value for glycol drilling fluids after heating. It is about 7.5 cP. Apparent viscosity (AV) is about 23 cP for silicate drilling fluids, while it has the minimum value for glycol drilling fluids after heating. It is about 11 cP. The yield point (YP) before heating is almost the same for different fluids, but after heating the drilling fluids, the reflux point for silicate and glycol drilling fluids is significantly reduced. The yield point is about 6.5 Ib/100ft² for silicate drilling fluids, while it has the maximum value for glycol drilling fluids after heating. It is about 8 Ib/100ft².

This paper establishes a flow equation using non-Newtonian fluid mechanics and defines the deformation of residual oil using numerical computation in order to conduct a study on the flow law of residual oil in microchannels of rock during polymer flooding, the influence of flooding fluid elasticity on the deformation of residual oil, and flooding mechanism of viscoelastic displacing fluid. Computation shows that advancing contact angle increases and receding contact angle decreases as the viscosity ratio decreases. The higher elasticity of polymer solution with higher concentration or molecular weight leads to significantly more obvious deformation of residual oil and benefits migration and stripping of residual oil. The impact of the initial wetting angle of residual oil film on deformation is analyzed. A smaller initial wetting angle corresponds to a bigger change of advancing contact angle and smaller change of receding contact angle. A better understanding of the flooding process is gained via a study on residual oil deformation in polymer flooding. Consequently, oil flooding efficiency and oil recovery can be enhanced. This is the hydrodynamic mechanism of enhanced oil recovery (EOR) by polymer flooding.