Network modeling of liquid flow in Yanchang shale

Abstract

The pore geometry and slip conditions are two principal characteristics of liquid flow in shale noncircular nanopores. We have considered the pore shape and liquid slippage on the pore interior wall in pore-network models of the Yanchang shale in China. Multiple scanning electron microscopy (SEM) images of the Yanchang shale samples were analyzed to document and summarize various pore shapes and sizes. Fluid-flow behavior in noncircular pores significantly deviates from the flow behavior in circular pores used in many current models. In addition, liquid flow simulations in conventional reservoir systems assume a no-slip flow boundary condition, which is unacceptable in nanoscale pores associated with the Yanchang shale. We studied liquid permeability in the Yanchang shale by developing realistic pore-network models based on nitrogen sorption data and SEM image analysis. The input data to the developed pore-network models include pore-size distribution, total organic carbon, porosity, surface area, pore geometry, and liquid slip length. We found that the effective permeability based on the realistic multigeometry model is significantly higher than the predicted Darcy permeability. The apparent permeability discrepancy between Darcy’s law and the realistic slip-corrected multigeometry model is higher for shale samples with an increasing number of noncircular pores. We also found that neglecting the liquid slip and noncircularity of pores significantly underestimates apparent permeability in Yanchang shale samples.