酸化作用对页岩微观结构及其物性的影响

龙马溪组页岩作为贵州页岩气的主要储气层位，勘探及钻井均证实其具有良好的页岩气成藏条件和资源开发潜力。为揭示贵州龙马溪组页岩微观孔隙结构及其物性对酸化作用的响应规律，基于X射线衍射分析（XRD）、压汞、低温氮吸附及核磁共振（NMR）等实验手段，定量表征页岩酸化作用前后的孔隙体积、孔隙率、比表面积、孔径分布等页岩微观结构物性参数的差异性，分析酸化作用前后页岩孔裂隙的结构特征。研究表明:酸化作用增大了页岩的孔隙体积、孔隙率、比表面积和孔径，酸化作用后页岩进-退汞曲线及低温氮吸/脱附曲线的滞后环明显增大，酸化作用增大了墨水瓶孔的孔隙体积；受到酸化作用影响，页岩优势孔隙由介孔和110 nm左右大中孔向介孔与2 800 nm左右宏孔发展，介孔数量减少，宏孔数量增加，页岩孔隙的连通性明显变好；酸化对页岩孔裂隙中矿物质及黏土成分具有明显的化学溶解和刻蚀作用，对页岩孔裂隙体积的改造效果显著，增加了页岩储层的渗透性，进而提高了页岩气的运移与渗流能力；酸化作用下伴随的水化作用对页岩孔裂隙沿层理面起裂、扩展延伸起促进作用，但是页岩酸化作用下的水化作用机制尚需进一步研究。 

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.