Evolution of the Anisotropic Thermophysical Performance for Low-Maturity Oil Shales at an Elevated Temperature and Its Implications for Restoring Oil Development

Thermophysical properties determine the thermally upgraded area of low-maturity oil shales, which is of significance for restoring oil recovery but needs more in-depth investigations. We introduced a laser-flash NETZSCH LFA-467 analyzer to measure the dynamic response of thermal diffusivity (D), thermal conductivity (K), and specific heat capacity (c) at an in situ elevated temperature as well as their anisotropy in the orthogonal direction relative to shale bedding. The D and K values decrease with a rising temperature, while c values remain almost unchanged at a high temperature. The total organic carbon (TOC) content significantly affects the D and K values, mainly in the anisotropy coefficient (a newly proposed parameter), but sparingly influences the c values. The anisotropy coefficient of samples with a high TOC content is similar to 2 times greater than that with a low TOC content. The greatest D value decay rate of a high TOC content sample reaches similar to 75%, while that for a low TOC content sample is similar to 43%, found in the bedding-perpendicular samples. Results also suggest that the anisotropy of the thermophysical property derives from the lamellar structure of shale rock; the space (like pore and/or fracture) therein is averse to the heat movement. For the hypothetical vertical well mode or horizontal well mode, the arrangement of reasonable space between wells of heat injection and restoring oil production is of significance under the heating-induced dynamic evolution of thermophysical parameters. Hopefully, this work is helpful in enhancing the knowledge on the heat flow behavior in low-maturity oil shale when thermal upgrading is implemented.