Abstract:

Rock thermal physical properties are key parameters in the fields of geothermal, engineering geology, and oil and gas geology. In order to have a clear understanding of the influence of factors such as pore fluid medium and saturation on the thermal conductivity of clastic rocks, in this study, typical clastic rock samples from the Cenozoic of  Qaidam basin were selected, and their thermal conductivities were measured by applying the unsteady state method. The thermal conductivity of clastic rocks decreases with the increase of porosity, and the decrease of thermal conductivity can be up to 37.6% in the samples of dense reservoirs with porosity lower than 5.0%. The thermal conductivity of  clastic rocks showes a significant positive correlation with the saturation degree, and the effect of water saturation on  transverse and longitudinal thermal conductivity is more significant than that of oil saturation. The ranges of thermal conductivity anisotropy coefficients of clastic rocks in dry state and in water-saturated state are 0.648-1.546 and 0.840-1.200, respectively, indicating that the saturation degree has an attenuating effect on the anisotropy of thermal conductivity. The greater effect of quartz content on the thermal conductivity of the rocks and the brittleness of the quartz-rich clastic rocks result in more developed microfractures in the rock samples, whereas microfractures in situ formation are usually saturated with pore fluids, it is hypothesized that the development of fractures negatively affects the actual stratigraphic thermal conductivity and its anisotropy in dry conditions, but under water-bearing conditions, groundwater convection along the microfractures significantly increases the thermal conductivity.

Key words: clastic rocks, thermal conductivity, porosity, fluid medium, anisotropy of thermal conductivity, rock thermal physical properties