A New Model for Determining the Effective Permeability of Tight Formation

Abstract

Unlike conventional reservoirs, tight reservoirs have complex pore structures and severe boundary-layer effect. The pore throat of tight reservoirs is in nanoscale and the boundary layer cannot be ignored because the boundary layer has an important effect to the fluid flow and its influence increases with the reduction in the pore throat radius. These are the main reasons for the ultra-low permeability and low oil recovery for these reservoirs. However, previous studies have paid limited attention to the influences of the boundary-layer effect and the pore size distribution. In this paper, a new model was built to determine the effective permeability for the tight gas and oil reservoirs by taking into account the boundary-layer effect and the pore distribution. The results from this new model show good agreement with the experiment data, and the main factors that impact the effective permeability were analyzed in the study. It is found that the fluid type, means and standard deviation of pore radius, and displacement pressure gradient are the main factors influencing effective permeability. The relationship of air permeability and liquid permeability is also analyzed for tight reservoirs.

Dynamic capillarity during displacement process in fractured tight reservoirs with multiple fluid viscosities

“…8,40 The thickness of the boundary layer is suggested to be associated with the pore radius of porous media, the displacement gradient, and the fluid viscosity. 41,42 In this work, the where h represents the boundary layer thickness, μm; r stands for the pore radius, μm; ∇p denotes the displacement pressure gradient, MPa/m; and represents the fluid viscosity, mPa·s. Such boundary layer narrows the effective fluid flow radius, which can be defined as:…”

A Fractal Permeability Model Coupling Boundary-Layer Effect for Tight Oil Reservoirs

“…According to the experiment in the reference, the thickness of boundarylayers is decided by fluid viscidity, pressure gradient, pore radius and fluid type. 11 Cao et al 9 proposed an empirical equation to calculate the thickness of boundary-layers:…”

“…9 As Eq. (4) shows, for the same fluid viscosity and pressure gradient, the ratio of boundary-layer thickness to pore radius h/r increases with the decreasing pore radius.…”

“…Among of them, several permeability models coupling boundary-layer effect were proposed, and most of them were based on the capillary tube model. 8,9 Experiments also were conducted to measure the thickness of boundarylayers and investigate the effect of boundary-layer on effective liquid permeability. 6,[11][12][13][14][15][16] The experiment results showed that the thickness of boundarylayer is related to pressure gradient, fluid viscosity, pore radius and fluid type.…”

“…6,[11][12][13][14][15][16] The experiment results showed that the thickness of boundarylayer is related to pressure gradient, fluid viscosity, pore radius and fluid type. 11 With nanoscale simulation using dissipative particle dynamics and experimental data published in literatures, Cao et al 9 proposed an empirical equation to calculate boundary-layer thickness, and assuming that pore size distribution can be represented with Gaussian function, the authors developed a permeability model for tight oil reservoirs coupling boundarylayer effect.…”