Experimental investigation of the flow properties of layered coal-rock analogues

Coals are heterogeneous and the zones of interest for gas production (high fracture density) are often friable. 3D printed (3DP) rocks can create a repeatable analogue by minimizing specimen variability. This study investigates a series of 3DP coal seam gas packages under various flow conditions to determine the impact of fracture network and interburden rock on the dynamics of permeability. The 3DP coal analogue is treated with sodium silicate and carbon dioxide to reduce porosity and permeability. Seven cylindrical specimens are analysed including: the intact 3DP coal analogue, the intact interburden analogue, the unidirectionally and multi-directionally fractured coal analogues, and packages of coal-interburden-coal with different fracture systems. These specimens are subjected to isotropic triaxial flow tests to compare the properties of natural and synthetic rocks. The experimental results revealed that the pore compressibility of 3DP rock treated with sodium silicate is in the same range as coal. 3DP specimens with multi-directional fractures exhibited lower fracture compressibility than ones with unidirectional fractures. The results suggested that the flow properties of a single coal layer might differ from that of a composite coal-interburden rock. The experimental outcomes indicate that 3D printing is a valuable tool to investigate coal behaviour under depletion conditions.(c) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the impact of fracture networks and interburden rock on the dynamics of permeability by analyzing a series of 3D printed coal seam gas samples under various flow conditions. The results show that the 3D printed rock samples treated with sodium silicate exhibit similar pore compressibility to coal, and specimens with multi-directional fractures have lower fracture compressibility compared to those with unidirectional fractures.