Elemental Analysis of Bitumen and Crude Oil Samples by Laser Induced Breakdown Spectroscopy

This project tests the feasibility of using Laser Induced Breakdown Spectroscopy (LIBS) to analyze the elemental composition of crude oil and bitumen by a comparatively new, non-destructive technique. LIBS analysis uses a focused laser pulse that ablates and excites atoms, forming a short-lived plasma. As the plasma cools, the electrons decay into lower-energy orbitals and release photons. The light is collected with an optic fiber, diffracted, and recorded on a CCD camera as a spectrum. The spectra contain peaks of essentially all elements in the periodic table and can be analyzed by correlating peak intensity to concentration or by using principal component analysis. Our study compares the reproducibility and accuracy of elemental analysis (particularly S, Ni and V) in He, air, and Ar environments. S, Ni and V directly impact the hydrocarbon value of crude oils, and therefore analytical capabilities are crucial.

Bitumen samples were analyzed using an Ocean Optics LIBS 2500 system with a Nd-YAG laser (1064 nm wavelength) in Ar, He, and air. Optimal operating conditions were Q-switch delay time of -3.0 ms and laser energy of 211 mJ. Sulfur peaks are present in He saturated environments; in Ar, S peaks interfere with a large Ar peak, and S peaks are absorbed in air. Analyzing in Ar has the expected effect of increasing peak/background; Ni and V peaks were present in Ar but absent or subdued in He and air.

LIBS analysis would allow crude oil samples to be immediately and accurately analyzed on site, giving operators timely and critical information, also eliminating unnecessary sample destruction. LIBS would also be invaluable in analyzing piston core extracts where typically sample size is too small for elemental analysis. Therefore, LIBS could further aid exploration in key areas where there is little to no available well data.