A method for analyzing nanopore connectivity of shale using a fluid suction experiment

Abstract

A method for analyzing the pore connectivity of shale based on a suction experiment of tracer fluid is presented. Sodium chloraurate solution is absorbed into shale pores which have been previously evacuated, and then the solute in the pores is converted to gold by heating. After the suction experiment, the sample surface is polished and analyzed with scanning electron microscopy, in order to get the characteristics of connected pores at the nano-scale. The results of two core samples from the Wufeng-Longmaxi formations in the Sichuan Basin show the connected network in shale could be divided into three parts. The interior connectivity of pores in organic matter is related to the density of pores, and organic matter normally has low flow efficiency because of narrow throat radius. Fractures distributed at grain boundaries such as minerals, organic matter and clay sheets are advantageous pathways, and organic pores are connected by grain boundaries. The development of micro-cracks/fractures, which have high permeability, could significantly improve shale connectivity. Shale pore connectivity has great anisotropy, which means connectivity parallel to bedding is much better than that vertical to bedding.

Keywords

• fluid suction
• connectivity
• pore throat
• grain boundary fracture
• micro fracture
• anisotropy