Behavior of Specialty Optical Fibers in Crude Oil Environment

To mimic extreme downhole application conditions, a series of optical fibers was aged in crude oil at a pressure of 2000 psi and temperatures of 100-300 °C. The fibers under investigation used various coatings, including dual and single acrylate, silicone/acrylate, carbon/acrylate, silsesquioxane-type hybrid, polyimide, carbon/polyimide, acrylate/PFA and polyimide/PFA. Interactions with crude oil led to swelling, delamination, and dissolution of some of the coatings, which ultimately resulted in reduction of mechanical strength of the fibers. For different coating types, the temperatures were determined above which a significant strength degradation was observed. Carbon/polyimide, acrylate/PFA, and polyimide/PFA coatings were found to be the most oil-resistant. The amount of hydrogen generated by crude oil was evaluated from the attenuation spectra collected from the immersed fibers. For this analysis, two fibers (one doped with germanium and the other with germanium and phosphorus) were utilized as sensors. Using this approach, it was possible to estimate the amount of hydrogen generated by crude oil at different temperatures.