Experimental Study of Nonlinear Flow in Micropores Under Low Pressure Gradient

As throat radius decrease to micro-nanoscale, seepage in unconventional reservoirs such as ultra-low permeability and tight reservoirs differs from conventional ones. Flow experiment in micropores is a promising approach to study characteristics of microflow. In this paper, a visual experimental device was established. Water flow through micropores with radius of 1.38–10.03 \(\upmu \hbox {m}\) was investigated, under 0.033–16 MPa/m. The results showed that in microscale, water flow did not agree with Poiseuille equation. Flow rate was lower than theoretical value and showed nonlinear characteristics. In the near wall area, due to the attraction of solid wall, a stagnant fluid layer was formed. It occupied flow space and thus lowered flow rate. Its thickness declined with pressure gradient increasing, which led to nonlinear flow characteristics. When the pressure gradient was very high, the thickness stopped declining and kept constant. Afterward, the flow transited to linear. In pores with smaller radius, the steady stagnant layer was thinner, but took a larger proportion of the flow space. For tubes of \(r = 1.38, 4.81, 10.03\,\upmu \hbox {m}\), the thickness of steady stagnant layer was 0.11, 0.23, 0.27 \(\upmu \hbox {m}\), respectively.