THERMAL CONDUCTIVITY ESTIMATES OF A SANDSTONE AT VARIOUS SCALES OF SAMPLE SIZES: IMPACT ON THE CONCEPT OF ROCK HETEROGENEITY

Thermal conductivity is an important parameter in the oil and gas industry. Estimations of thermal conductivity has become challenging recently. This is mainly because of complications in the rock fabric. Previous studies have shown that fabric controls thermal characteristics. However, several factors remain unclear and one of which is the validity of thermal conductivity estimates for samples of various sizes. One sandstone sample from Bandar Iskandar, Perak was used for this study. The needle probe method was used to estimate thermal conductivities. Several lines on one face of the sample block were evaluated at various distances from the heat source. The sandstone appears homogeneous at the meso-scale and comprises quartz. In general, the t at equilibration increases with increasing distance from the heat source. The actual equilibration time appears shortest for the longest distance from the heat source and occurs around 1800s. Reducing the distance increases the time needed for equilibration. The equilibration time tends to differ between lines from t ranging from 2.5 to 3.5 for a distance of 0.1m from the heat source. This difference appears to be rather proportionately consistent between the lines for differing distances from the heat source. Therefore, it is proposed that a transformation factor be employed to provide a better estimation of the thermal conductivity of the rock for various sizes of samples. The study shows that a polynomial expression can be derived that provides a reasonably accurate transformation of estimated thermal conductivity values for the various distances evaluated. This undoubtedly has an impact on estimated thermal conductivity values for the entire rock for various sizes of samples used. This study also reemphasizes the need to exercise caution in utilizing the concept of homogeneity even at a meso- and possibly micro-scale of observation.