Terahertz for the detection of the oil bearing characteristics of shale

Abstract

Studying the trace organic matter (OM) in shale is of great significance to develop exploration plans for shale oil and gas exploration. Due to the low OM content, currently there are significant limitations in determining shale trace OM characteristics. This paper reports the analysis of the pyrolyzation products of shale using THz time-domain spectroscopy (THz-TDS) technology combined with pyrolyzation technology, based on the sensitivity of THz to organic and mineral differences. The THz parameters, including the time delay and amplitude of the THz peaks, were extracted to describe the pyrolyzation of shale. In the first-stage of pyrolyzation, the THz response does not change significantly in the range of < 300 °C. In the second stage of 300–700 °C, the THz parameters in the second stage decrease or increase sharply because the OM gradually decomposes. In the third stage, in the high temperature from 700 to 1000 °C, minerals such as calcite decompose. In addition, a turning point between organic matter decomposition and mineral reactions occurs at 700 °C, which helps to identify organic matter and minerals More importantly, the THz parameter can reflect a rate of change of up to 41%, which is far higher than the 4.1% rate of mass change during the pyrolyzation stage at 300–700 °C. Based on verification through thermal gravimetric analysis (TGA), mass spectroscopy (MS), X-ray diffraction (XRD), and scanning electron microscopy (SEM), we believe that the use of the THz combined with pyrolyzation technology method is practical for characterizing the organic matter in shale.