BACKGROUNDShale pore structure is the key to determine reservoir storage and migration capacity. It is of great significance for improving the productivity assessment of continental shale gas in China, and fracturing technology.

OBJECTIVESTo investigate the pore structure and three dimensional distribution mode of the seventh member of Yanchang Formation shale and its controlling factors.

METHODSAr-ion milling SEM and synchrotron micro X-ray microscopy were used to characterize the pore structures.

RESULTSThe SEM results indicated that the interparticle pores (300-600nm) and micro-fractures were the main reservoir space of the seventh member of Yanchang Formation shale gas. Most of the micro-fractures were formed by the precipitation of clay minerals and presented as a flat shape, which likely caused collapse of borehole walls. Organic pores were less developed and mainly associated with organic clay minerals. The micro X-ray microscopy showed that the seventh member of Yanchang Formation shale had laminated structures at micro-scale with organic matter laminations of 10-20μm in thickness. The results indicated that the seventh member shale had strong plasticity, which was against horizontal fracturing.

CONCLUSIONSThe results can provide significant data support for developing a percolation model and improving fracturing technology of shale gas.