Thermal conductivity properties of rocks in the Chang 7 shale strata in the Ordos Basin and its implications for shale oil in situ development

In situ conversion is a key area of China’s continental shale oil research. The thermal properties of rocks in the seventh member of the Triassic Yanchang Formation (Chang 7) in the Ordos Basin, especially the high temperature thermal properties are still unknown, which seriously restricts the optimization and feasibility evaluation of in situ conversion. Some fresh samples were collected from the Chang 7 shale layer and tested with a quick thermal conductivity meter, differential scanning calorimetry and thermal expansion instrument to obtain the thermal diffusivity, specific heat capacity, thermal expansion coefficient, and thermal conductivity parameter of muddy siltstones, tuffs, mudstones and shale. The thermal diffusivity and thermal conductivity of rocks with different lithologies in the Chang 7 member are different, and decrease with the decrease of sandy content, namely argillaceous siltstones > tuffstones > mudstones > shale. The thermal diffusivity and thermal conductivity have anisotropy, and the horizontal direction is 1 to 3.5 times the vertical direction, and the difference increases as the temperature increases. With the increase of temperature, the thermal diffusivity of rock decreases, the specific heat capacity of rocks increases and the thermal conductivity first decreases and then increases. The anisotropy of shale thermal properties is the strongest, which is a manifestation of rock heterogeneity, and is related to microscopic strata. The sandstone anisotropy may be related to permeability in different directions of rock.