EFFECT OF THERMAL-CONDUCTIVITY ANISOTROPY OF ROCKS ON THE SUBSURFACE TEMPERATURE-FIELD

The effect of thermal conductivity anisotropy on the heat flow is eval uated by solving numerically the heat conduction equation in 2-D model s of anisotropic structures. The most common case of sedimentary rock anisotropy with two principal conductivities, parallel and normal to t he bedding, is considered. For the effect due purely to anisotropy to be studied, both diagonal terms of the conductivity matrix of the anis otropic prism are put equal to the conductivity of the surrounding iso tropic half-space. The results are presented in the form of figures sh owing isolines of horizontal and vertical heat flow densities (HFD). T he greatest vertical HFD variations occur along the vertical sides of the prism and attain +/-7 per cent of the basal heat flow for the real istic conductivity model adopted. In addition, the vertical HFD within the prism was compared with the value calculated as if the data were measured in a vertical borehole. In this case, only the vertical tempe rature gradient is known. The difference between the two quantities re presents the contribution of the horizontal temperature gradient to th e vertical HFD. It attains 1-3 per cent of the HFD in models with an a spect (length-height) ratio of the prism of less than 2. An anisotropi c body acting also as a heat flow refractor was investigated with a mo del of horizontally deposited sedimentary rock, with a factor of aniso tropy of 1.5, surrounding a prism of the same rock with inclined layer s. Vertical HFD changes concentrate along the sides of the prism and v ary from -10 to +15 per cent of the HFD.