The Theoretical Model of Capillary Pressure in Regular Polygonal Pores

The pore shape in real oil/gas reservoir is very complex, and capillary behaviors of polygonal pores can not be simulated by the Yang-Laplace equation. In order to study effects of wettability and geometrical shape of pore in the capillary behavior of regular polygonal pores, based on the theory of MS-P and the rule of two-phase displacement in polygonal pore, theoretical models of drainage and imbibition capillary pressure for equilateral triangular, square and pentagonal pores are derived under the homogeneous wettability. And capillary behaviors of pores with different wettability and shape factors was analyzed under the same conditions. The results show: percolation characteristics of drainage and imbibition are same in pore corner under the same wettability, while the significant difference in pore center. With the increase of contact angle, oil drainage resistance and water imbibition driving force decrease, while oil imbibition driving force and water forced imbibition resistance increase. Non-wetting phase can completely saturate pore under the breakthrough pressure for the specific wettability. Snap-off level decreases with the increase of contact angle in the homogeneous water-wet system, while the law of homogeneous oil-wet system is opposite. Shape factor has no obvious influence on breakthrough pressure of oil drainage. With the increase of shape factor, oil and water imbibition driving force, water forced imbibition resistance decrease, and nonwetting phase saturation when non-wetting phase invades into pore corner increases. The Snap-off phenomenon is the most obvious in the pentagonal pore. © 2021, Science Press. All right reserved.