Coupled Effects of Acid and Temperature on the Damage Characteristics of Sandstone

To better understand the acid-temperature coupling mechanism, it is critical to quantify the coupled effects of acid and temperature on the damage characteristics of sandstone. In this paper, macroscopic mechanical properties and microstructure changes of sandstone samples under different acid-temperature conditions are obtained by uniaxial compression experiments and nuclear magnetic resonance (NMR) measurements. Stress–strain curves and failure modes, changes in porosity, T 2 (transverse relaxation time) spectra and fractal characteristics under different acid-temperature conditions are analyzed. Damage mechanism of acid-temperature coupling is discussed and damage variables caused by acid and temperature are defined, respectively. The results show that the effects of acid and temperature on the failure modes of sandstone samples are different. Based on the T 2 spectral morphology of samples, the pores are classified into micro pores (< 0.1 μm), meso pores (0.1–1 μm) and macro pores (≥ 1 μm). With the increase of acidity, the sum of micro pores and meso pores gradually increase while macro pores gradually decrease. With increasing temperature, micro pores tend to decrease while meso pores and macro pores increase gradually. The fractal dimension of macro pores is largest, followed by the overall pore structure and meso pores. The damage variable caused by physical effect D p is greater than that caused by chemical effect D c . There is an exponential decreasing relationship between σ c , E and total damage variable D .