A novel hybrid thermodynamic model for pore size distribution characterisation for shale

Abstract

Scholars often see the gas adsorption technique as a straight-to-interpret technique and adopt the pore size distribution (PSD) given by the gas adsorption technique directly to interpret pore-structure-related issues. The oversimplification of interpreting shale PSD based on monogeometric thermodynamic models leads to apparent bias to the realistic pore network. This work aims at establishing a novel thermodynamic model for shale PSD interpretation. We simplified the pore space into two geometric types—cylinder-shaped and slit-shaped. Firstly, Low-temperature Nitrogen Adsorption data were analyzed utilizing two monogeometric models (cylindrical and slit) to generate PSDcyl. and PSDslit; Secondly, pore geometric segmentation was carried out using Watershed by flooding on typical SEM images to obtain the ratio of slit-shaped ∅s and cylinder-shaped pores ∅c. Combining the results of the two, we proposed a novel hybrid model. We performed pyrolysis, XRD, FE-SEM observation, quantitative comparison with the results obtained by the DFT model, and fractal analysis to discuss the validity of the obtained PSDHybrid. The results showed that: the hybrid model proposed in this work could better reflect the real geometry of pore space and provide a more realistic PSD; compared with thermodynamic monogeometric models, PSD obtained from the hybrid model are closer to that from the DFT model, with an improvement in the deviation from the DFT model from 5.06% to 68.88%. The proposed hybrid model has essential application prospects for better interpretation of shale pore space. It is also worth noting that we suggest applying the proposed hybrid model for PSD analysis in the range of 5–100 nm.