Experimental analysis on characteristics of micro-structure and mineralogy changes in thermal spallation drilling

Abstract

Thermal spallation drilling is a promising technology expected to exploit hydrocarbons in hard rocks. In this paper, thermal spallation experiments are conducted on six types of rocks. Comparisons are made in terms of mineral compositions and micro-structures. Spallation temperatures are obtained, and analytical results are compared with experimental data. Results show that spallation temperatures obtained by analytical method show good agreement with experimental data. Additionally, drilling performances can be continuous or intermittent for various types of rocks. Quartz expands in different rocks after thermal impact. Calcite increases and dolomite decreases due to thermal decomposition. Moreover, the induced thermal stresses in sandstone push against the micro-particle and melting may occur. For granite, micro-cracks and micro-particles exist after spallation. In contrast, there are no cracks in shale, but melt holes and micro-particles distributed randomly due to reaction. For limestone, there exist relatively large cracks, micro-cracks and micro-particles. For dolomite, no obvious micro-particles remain but only a few micro-cracks. The variations of elements correspond well with mineral changes. However, under the conditions of this paper, marble fails to break due to strong homogeneity. All results can provide guidance for the further study on the rock-breaking of thermal spallation drilling.