Experimental study of the sequential porosity evolution of sandstone under acid erosion

Abstract

To comprehensively understand the evolution of sandstone porosity during sandstone matrix acidizing is of significance to the petroleum exploration. In this study, a self-designed experimental apparatus was applied to simulate the sequential water-rock reactions of sandstone under acidic erosion. A combination of methods, including the ultrasonic velocity measurement, low-temperature nitrogen absorption tests and high pressure mercury injection (HPMI) measurements, scanning electron microscopy (SEM) imaging and computed tomography (CT) scanning were used to analyze the characteristics of porosity. The X-ray diffraction (XRD) and X-ray fluorescence (XRF) was applied to analyze the variations of minerals and elemental content in the sandstone specimens, an acidity meter and coupled plasma mass spectrometry (ICP-MS) was used to measure the chemical parameters change in the reacted solution. The results show that, the acidic erosion significantly increased the porosity abundance and decreased the minerals and elements content in the sandstone specimens, and improved the aqueous elemental Ca, Na, K and Mg concentrations in the reacted solution. These effects of acidic erosion decreased with increasing reacted distance. The porosity enhancement can be primarily attribute to the depletion of minerals in sandstone, and the reduction of acidic effect is not only due to the acid consuming, but also associated with the different sensitivity of minerals in response to H+. This study can provide some experimental references to sandstone matrix acidizing, and recommend a useful tool for further research works.