Date of Graduation

1985

Document Type

Thesis

Abstract

The orientation of the optical axis, or the minimum reflectance of the reflectance indicatrix of vitrinite, can be used to indicate the direction of maximum stress, i.e., the resultant stress of vertical compaction and lateral stress, during coalification. Furthermore, the attitude of the minimum reflectance with reference to bedding plane is a good parameter for evaluating whether maximum thermal maturation is achieved prior to or after folding or other structural changes, and thus reflects the tectonic and coalification history of coal. The purpose of this study was to investigate the orientation of the reflectance indicatrix of vitrinite and relate it to the coalification history of coal seams. A technique was developed to measure and calculate the direction of the optical axis of vitrinite, and because of the biaxiality of anthracite, both uniaxial and biaxial indicatrix models were taken into consideration. A series of coal samples of different rank and from different geographic locations (anthracite from Pennsylvania, and bituminous coal from highly tectonically disturbed regions in the Canadian Rockies and from the Appalachian coal region) were collected and examined. The analysis results illustrate that in both the Canadian Rockies and Appalachian coal region, at least in the sampled areas, the optical axes exhibit a "fixed" angular relationship with stratification. These suggest that coalification was achieved prior to folding in those two studied areas. Furthermore, the large angle between the normal of the bedding and the minimum reflectance axis of the coals from the Canadian Rockies indicates that the lateral stress had played a more important role during coalification in this area than in the Appalachian coal region. Bituminous coal samples were subjected to uniaxial load deformation at elevated temperature and examined microscopically. The laboratory results indicate an optical axis rotation of up to 17 degrees when the coal samples were heated to 330(DEGREES)C, and under 150 lb load for 5 hours. This result provides evidence supporting the idea that the optical axis orientation is determined by the resultant stress of the vertical load stress and the lateral compressive stress during the stage of coalification. The reflectance indicatrix can be applied to (1) detect potential ground control problems in coal mines, and (2) help to distinguish good from bad oil sites in oil exploration.

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