BACKGROUNDStudies have shown that the nano-pores in shale are at the same magnitude as the gold particles that make up the conductive film, and thus the pore size of nano-pores is blocked and buried by gold particles. The planar morphological characteristics of nano-pores cannot be observed due to the 'secondary transformation' of pores. Moreover, limited by the resolution and depth of field of the instrument, the spatial ductility and other structural characteristics of nano-pores cannot be observed. Therefore, how to truly reveal the spatial structure characteristics of nano-pores and how to effectively avoid the 'secondary modification' of nano-pores in shale reservoirs by gold particles has always been a difficulty in microanalysis.

OBJECTIVESTo characterize the two/three dimensional structural characteristics of nano-pores in shale.

METHODSAtomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to observe the pore features.

RESULTSThe distribution of organic and inorganic pores in the black shale of the Longmaxi Formation in the Sichuan Basin has strong non-meanness, and the pore size and spatial ductility of the pores were significantly positively correlated. The organic pores were distributed in a honeycomb shape, with the pore size from 0.1 to 0.4μm. The pores show an obvious 'integrated' feature in the three-dimensional space and have good spatial connectivity. Inorganic pores mainly develop interlayer pores of clay minerals, and the pore size was mainly distributed between 16 and 57nm. In addition, there were a few irregular dissolution pores in mineral grains.

CONCLUSIONSThe non-meanness of pores in the 2D plane of shale leads to abrupt changes in the distribution of pores and throats, which affects the reservoir performance. The non-meanness of pores in shale in three-dimensional space leads to the great difference of permeability of shale reservoir in the longitudinal direction, which affects the physical characteristics of the reservoir.