Combined Methods of Thermal Analysis for Characterization of Rocks Containing Hydrocarbon

摘要

Combined methods of thermal analysis TG/DTA/MS and TG/DSC in conjunction with Thermomechanical Analyzer (TMA) were used for characterization of thermal properties of hydrocarbon bearing shales. Results were obtained on three different samples: oil shale, high carbonate content shale, and a shale bearing natural gas. The analysis was performed in temperature range RT-950°C under helium atmosphere with heating rate 10°C/min. All samples were crushed but not powdered, and a weight of 100 mg was used. Combined TG/DTA/MS indicates that each sample shows three transitions: 1. A minimal mass loss between 100°C-300°C and during this period water (masses 18 and 17 used as water signatures) is being detected by the mass spectrometer. 2. The second mass loss is attributed to the decomposition of organic material between the temperatures of 350°C-500°C, and the mass spectrometer shows a hydrocarbon fragmentation trend with the dominant evolving ions with masses 41, 43, 55, 57, and 71. There is a small endothermic reaction that occurs during this decomposition. 3. At ～650°C the calcium carbonate begins to decompose, and lasts until ～900°C. The evolving gas measured during this period is carbon dioxide. Combined TG/DSC registered an endothermic reaction occurring during organic/kerogen decomposition and calcium carbonate decomposition. The carbonate rich sample shows similar trends but with a more prominent dehydration event occurring at ～110°C-140°C, the hydrocarbon within the sample shows a similar fragmentation trend but it accounted for only 4% in weight of the sample. The carbonate rich sample has a greater carbonate decomposition of ～22% (which equivocates to 50% of the rock being calcium carbonate). The information on physicochemical transitions of sample materials were correlated to dimensional changes measured by dilatometry (TMA) results and proved useful in understanding the nature of expansion and contraction of the shale with changing temperature.