EXPERIMENTAL STUDY OF ACIDIZATION IMPACT TO PORE TOPOLOGICAL STRUCTURE VARIATION OF NIUTITANG SHALE

The ultra-low permeability and porosity of shale reservoir dominants gas storage and transport capabilities. Recent research shows that the acid solution would dissolve some specified minerals in shale matrix,improve the porosity together with the permeability,therefore and enhance the gas flow. The hydrochloric acid,hydrofluoric acid and mixed acid are applied to immerse the shale matrix with the SEM together with MATLAB applied to identity the porosity variation. Also the SEM and XRD are combined to measure the element changes before and post the immersion. The reaction mechanism and degree between shale samples and different acid solutions are analyzed. The results and discussions show the initial porosity of the shale matrix is 10.68% while enhanced to 1.21,1.3,2.61 and 2.99 times of the initial value after immersion. After soaking for one hour,a quantity of quartz and clay are remained on the surface of shale matrix after hydrofluoric acid immersion; and the content of clay minerals decreases obviously and lots of quartz remain when treated with mixed acid,which indicates that the clay minerals are more likely to be dissolved. After 24 hours of acidification,the mixed acid reacts violently with quartz and clay minerals because of its strongest acid. The porosity network is well developed after acidification with mixed acid prompting the gas reservoir performance.