| Abstract |
The new methods and instruments developed for measurement of rock thermal properties (thermal conductivity, thermal diffusivity, volumetric heat capacity, and coefficient of linear thermal expansion) provided a sharp increase in the quality of experimental data for geothermal reservoirs. Optical scanning technology firstly provides numerous high-precision, nondestructive, non-contact measurements of thermal conductivity and diffusivity directly on full cores, core plugs and non-consolidated rock samples along with determination of thermal property tensor components and the recording of thermal property variations along cores. The instrument for simultaneous determination of thermal conductivity and diffusivity at formation temperature (up to 250 deg C), and 3-component pressure (pore, confining axial, and lateral pressures) allows the measurements at formation conditions to study thermal property variations during the heating of reservoirs and oil production in thermal enhanced oil recovery. The instrument for measurements of the coefficient of linear thermal expansion at temperatures up to 250 deg C within every temperature interval of 20 deg C provides measurements on core plugs accounting for rock anisotropy. Application of the new technique for studying more than 80,000 cores from different regions provided a representative thermal property database for rocks saturated by brine and steam accounting for rock anisotropy and inhomogeneity as well as formation pressure and temperature. New correlations between thermal and other physical properties were established. The new experimental data demonstrated that previous information on thermal reservoir properties often needs to be significantly corrected. The new instruments provide the detailed information on the spatial and temporal variations in the reservoir thermal properties and possibility to exclude the following unsolved problems in rock thermal property measurements: (1) disturbing influence of the thermal resistance of a sample-equipment contact on the measurement results particularly for porous and fractured rocks, (2) significant influence of rock inhomogeneity and anisotropy which could not be accounted most often earlier, (3) impossibility to measure thermal conductivity and thermal diffusivity tensor components simultaneously in most cases, (4) impossibility to provide the high-precision non-destructive measurements on full cores and core plugs without mechanical treatment of cores, (5) difficulties with the measurements of coefficient of linear thermal expansion at elevated temperatures (up to 250 deg C) with measurements within every narrow temperature intervals (15-25 deg C). Analysis demonstrated that existing theoretical models, especially applied in the commercial simulators for thermo-hydrodynamical modeling, can not provide the reliable thermal property data prediction from other reservoir properties. The new theoretical models of effective thermal conductivity of heterogeneous medium, based on the effective medium theory, were developed to improve the quality of the rock thermal conductivity prediction. |