Elemental mapping and geochemical characterization of gas producing shales by laser induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIES) has been used for the analysis of hydrocarbon bearing shale samples. Shale samples taken from a Marcellus gas well at depths ranging from 7498 to 7551 ft (2285.4-2301.5 m) were analyzed by LIBS using an 81 x 81 grid pattern covering an 8 x 8 mm area. The data collected from these experiments were used to construct 2D elemental maps for each sample including the hydrocarbon forming elements C and H. Results show that the spatial elemental composition of the shale varies due to the matrix of the rock, and as a function of the sample depth. The accuracy of the analysis was confirmed by analyzing a shale sample of known elemental concentrations and obtaining a good agreement between analyzed and reference values. It has been shown that LIBS can be used to determine elemental composition variations in hydrocarbon bearing shales in a laboratory setting. Extending this capability into wellbores will enable producers to rapidly target resources with greater accuracy.