Effect of acidification on the microstructure and physical properties of shale

As the main shale gas reservoir in Guizhou, it is proved that Longmaxi Formation has good shale gas accumulation conditions and resource development potential. In order to reveal the response law of acidification on the micropore structure and physical properties of Longmaxi Formation shale in Guizhou, the difference in physical properties of shale microstructures before and after acidification, such as pore volume, porosity, specific surface area and pore size distribution was quantitatively characterized by X-ray diffraction(XRD) analysis, mercury intrusion measurement, low-temperature nitrogen adsorption and nuclear magnetic resonance(NMR) experiment. The structural characteristics of the shale pores before and after acidification were analyzed. The results show that: Acidification increases the pore volume, porosity, specific surface area and pore size of shale. After the acidification, the hysteresis loop of the shale in dehydration curve and the low-temperature nitrogen absorption-desorption curve increase significantly, acidification increases the pore volume of the ink bottle hole; Due to the influence of acidification, the development direction of shale dominant pores is from meso-pores and mesopores around 110 nm to mesopores and most macro pores around 2 800 nm. The number of meso-pores decreases, the number of macro-pores increases, and the connectivity of shale pores is significantly better; Acidification has obvious chemical dissolution and etching effects on minerals and clay components in shale pore fractures, and has obvious effect on volumetric transformation of shale pore fractures, increasing permeability of shale reservoirs, thereby improving the migration and seepage ability of shale gas; The accompanying hydration under shale acidification plays an important role in the cracking, expansion and failure of the shale pores along the bedding plane, but the hydration mechanism under shale acidification needs further study.