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, T2 (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 T2 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 Dp is greater than that caused by chemical effect Dc. There is an exponential decreasing relationship between σc, E and total damage variable D. Highlights: Quantification of coupled effects of acid-temperature on the damage characteristics of sandstone. Changes of microscopic characteristics on the effects of acid-temperature coupling. Definition of damage variables separately for the effects of acid and temperature. [ABSTRACT FROM AUTHOR]