Modelling the water transport behavior in organic-rich nanoporous shale with generalized lattice Boltzmann method

摘要

The hydraulic fracturing fluid could easily infiltrate the ultra-tight shale matrix due to the large slip of the liquid flow, showing higher-than-expected fluid-loss in varieties of shale gas development cases. One possible reason is that the water transport behaviors through the pores with nanoscale significantly deviate from that occurring at larger scales. The classic Darcy law, being widely and successfully used in conventional porous media becomes insufficient for the nanoporous shale. In this study, a generalized lattice Boltzmann method with liquid slip effect incorporated is established to understand the transport behavior of hydraulic fracturing fluid in nanopores dominated shale matrix and to demonstrate a new insight into the transport behaviors. The results show that the flow capability of fracturing fluid in the shale matrix with strong hydrophobic organic nanopores is significantly improved due to the huge wall-fluid interaction. And this would considerably change the flow field (magnitudes and preferred pathway) with and without the micro-fractures, contributing a lot to the huge hydraulic fracturing fluid loss reported from the practical fields. The huge fluid-loss emphasizes the importance for liquid slip effect in organic nanopores of shale matrix. Especially, in the organic-rich shale gas reservoir, the fracturing fluid can be infiltrated into the ultra-tight shale formation easier than commonly expected during the hydraulic fracturing operation.