Standardization of Petrographic Measurements

Science Center Objects

Advent of the ‘shale revolution’ since about 2005 has caused increased demand for reliable petrographic measurements of thermal maturity in shale via vitrinite reflectance, long considered the ‘gold standard’ approach. A standardized methodology for organic reflectance measurement in shale first became available in 2011 (ASTM D7708), based on prior work by task members. However, interlaboratory studies to test reproducibility in vitrinite reflectance measurements demonstrate significant work remains to be done in improving accuracy and precision. Work in this task also examines sample effects caused by preparation technique, e.g., mounting medium (thermoplastic vs. epoxy resin) or polishing method (broad ion beam milling vs. mechanical polish). Standardization efforts in this task were recognized by bestowment of the 2019 Organic Petrology Award from external organization International Committee for Coal and Organic Petrology (ICCP).

Objective:

Improve standardization and reliability of petrographic measurements of thermal maturity including organic reflectance and fluorescence.

Methodology:

Past efforts in this task have established criteria for the identification and distinction of vitrinite and solid bitumens and have codified a technique for their reflectance measurement when dispersed in sedimentary rocks. Testing and methodology improvement is accomplished through interlaboratory studies (ILS) on well-characterized shale samples of different thermal maturity, organic richness and organic matter type abundance. These collaborative studies help to determine best practices, establish repeatability and reproducibility statistics, and promulgate the most successful approaches. The interlaboratory study approach occurs via participation from members of the International Committee for Coal and Organic Petrology (ICCP), the Society for Organic Petrology (TSOP), and through cooperation with the American Society for Testing and Materials (ASTM). The Reston Organic Petrology Laboratory supports this research via project coordination, sample preparation, vitrinite reflectance, fluorescence, quantitative organic petrography assessment, and transmitted light petrography.