# Damage Characteristics of Thermally Deteriorated Carbonate Rocks: A Review
## 5 Thermal Deterioration of Porous Network  
The physical properties of rocks greatly help to anticipate the behavior of carbonate rocks under different loading conditions. The anisotropic character of such rocks is attributed to their depositional environment, diagenesis conditions, past stress histories, pressure, temperature, and chemistry of pore fluids. The heterogeneity in the physical characteristics depends on the rock fabric and microstructures [103]. The microstructural patterns are generally defined by the texture (size, shape, and sorting), density, cementation between the particles, the orientation of particles, and cracks under regional or local stresses [104]. These microstructural variations immensely affect the porous network and transport properties of carbonate rocks. The porosity, permeability, and acoustic waves attenuation are the most widely studied physical parameters to evaluate the physical-mechanical behavior of carbonate rocks and other materials under undamaged or damaged conditions [7; 12; 13; 87; 104; 105; 106; 107; 108; 109; 110; 111].  
The porosity of the limestone and dolostone mainly consists of two-pore systems: primary pores and secondary pores. The natural fractures or breaks, cavities, organic growth, and dissolution of material in the cracks due to fluid transportation are the main factors that enhance the porosity to a large extent [104]. The size of the intergranular and intragranular pores falls within the range of 30 to 50 \(\upmu\)m, whereas secondary pores include micro-fissuring, vugs, the disappearance of cementation, and the opening of grain boundaries are typically in the range of 0.5 to 50 mm [112]. The aforementioned pore sizes were measured at ambient conditions. These opening sizes can be considerably larger than their documented values when rocks are subjected to high temperatures. The transport properties of carbonate rocks depend on pore geometry, connectivity, and tortuosity. The permeability is an important physical parameter that provides valuable information about the connectivity of primary or secondary pores. The high porosity of a rock is not referred to as its high permeability; rather, it is characterized by the connectivity of the pores [113]. Like porosity and acoustic waves, permeability is also sensitive to temperature. Several studies have been conducted to investigate the thermal weakening effect on the permeability of carbonate rocks. Table 5 describes the major development in the evaluation of transport properties of thermally exploited carbonate rocks.  
Acoustic wave transmission through limestone is mainly governed by grain contact and cementation. The strong bond or cementation between rock grains makes it stiff, which favors wave propagation. The microcracks, vugs porosity, and pore aspect ratio significantly affect the acoustic wave velocities [103]. The primary minerals in limestone and dolostone have specific values of elastic bulk modulus and the coefficient of thermal expansion. The temperature beyond the threshold limit of these properties significantly alters the physical-mechanical behavior of these rocks [114]. High temperature (\(>\)500 \({}^{\circ}\)C) enhances secondary porosity by developing micro-fissures, opening grain contact boundaries, removing cementation between grains, and accelerating chemical reactions that ultimately reduce physical characteristics and acoustic wave velocities to a minimum level [115; 116; 117; 118; 119].