Temperature And Pressure Insensitive Spectroscopic Method For Measuring (Ch4)-C-13 During Oil And Natural Gas Drilling Operations

A novel rugged two-section driving NIR TDLAS scheme was implemented to reduce temperature and pressure sensitivity of methane carbon isotope measurement during oil and natural gas drilling operations. Isotope spectra line groups with same lower energy levels were selected to derive the concentration of (CH4)-C-13 and (CH4)-C-12. Dynamic pressure linewidth broadening was introduced in the absorbance curve fitting. Various uncontrollable factors such as spectra shift, stretching, and baseline trending were incorporated in the comprehensive multi-peak fitting. The results showed that the sensitivity of isotope ratios to temperature and pressure variation was greatly suppressed. The delta(CH4)-C-13 uncertainty in the temperature test was 2.8 parts per thousand with fitted delta(CH4)-C-13-T slope of 0.021 parts per thousand/degrees C in 25 +/- 5 degrees C range. The delta(CH4)-C-13 uncertainty in the pressure test was 1.4 parts per thousand with fitted delta(CH4)-C-13-P slope of <0.001 parts per thousand/mbar from 400 to 1000 mbar. The limit standard deviation of long-term test was 0.15 parts per thousand (@135 s). The results indicate that our scheme is a promising solution for delta(CH4)-C-13 measurement during drilling operations due to the enhanced robustness.