An insight into pore-network models of high-temperature heat-treated sandstones using computed tomography

Abstract

The pore network attributes help assess the fluid-flow behaviour in various reservoir rocks. As, in the cases of various unconventional energy exploration, the reservoir rocks are being exposed to different sets of temperatures that result in microstructural alteration in the pore and throat scale. Since the last decade, X-ray computed tomography (XCT) has been proved to be a useful tool in determining the micro-scale pore structures. However, such results are greatly influenced by the structure of the rocks, pore spaces, grain size, and nature of minerals. Here in this study, an attempt has been made to investigate the microstructural alteration and pore-network configuration of thermally-treated three Indian sandstones (Dholpur sandstone, Jodhpur sandstone and Gondwana sandstone) of varying mineralogy using the high-resolution micro-CT techniques. Microstructural modifications, the evolution of pores spaces, pore-size distribution, pore-network attributes such as nature of connectivity, pore radius, pore-volume, pore coordination number, throat radius and throat channel lengths of the three sandstones were investigated in a temperature range from 25 °C to 800 °C. The microstructural responses of these sandstones in terms of pore-space evolution and pore network models were found to be dependent on the presence of clay minerals. The overall trend of porosity for Dholpur and Gondwana sandstone was found to increase as a function of temperature. For Jodhpur sandstone, the maximum porosity was achieved at 600 °C and thereafter a decreasing trend up to 800 °C. Gondwana sandstone, most clay-rich, was found to be most vulnerable to elevated temperatures compared to the other two sandstones. The maximum average pore coordination number for Dholpur and Jodhpur sandstone was observed at 600 °C (7.097) and 800 °C (6.953), respectively.