Abstract:

To elucidate the micro-scale modification mechanisms of shale reservoirs by methane in-situ explosive fracturing, the evolution characteristics of micro scale and nano scale pore structures in shale were investigated under synergistic effects of high temperature and dynamic impact. This study selected typical shale samples and comprehensively applied 3D contour measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) to study the macro-micro roughness characteristics, pore and crack structures and mineral composition changes with temperature of shale fragments after high temperature and dynamic impact. The results show that with the increase of temperature, the millimeter-scale roughness of shale section first decreases slightly and then rises sharply. The organic matter nano-pores in shale decrease, complex cracks appear in quartz, gas pores are produced in carbonate minerals, interlayer structures of clay minerals are destroyed, and the porosity of shale body gradually increases from 1.488% at room temperature to 1.997% at 700 ℃. The mineral composition of shale is significantly different at different high temperatures. XRD quantitative analysis shows that the mass ratio of quartz increases while that of dolomite and calcite decreases. This study proves that high-temperature combustion has a modification effect on shale roughness and pore-crack from the micro-nano scale.

Key words: high-temperature effect, dynamic impact, shale, micro-nano scale, pore structure, evolutionary characteristics, explosion fracturing, roughness