Jinesh C. Jain

High throughput method for Sr extraction from variable matrix waters and 87Sr/86Sr isotope analysis by MC-ICP-MS

Natural isotope tracers, such as strontium (Sr), can facilitate the tracking of brine migration caused by CO2 injection in carbon storage sites and assist in identifying the origin of formation waters associated with oil and gas exploration. However, it might be necessary to analyze tens of samples with complex chemical compositions over a short period to identify subsurface reactions and respond to unexpected fluid movement in the host formation. These conditions require streamlined Sr separation chemistry for samples ranging from pristine groundwaters to those containing high total dissolved solids, followed by rapid measurement of isotope ratios with high analytical precision. Here we describe a method useful for the separation of Sr from energy related geofluids and the rapid measurements of Sr isotopic ratios by MC-ICP-MS. Existing vacuum-assisted Sr separation procedures were modified by using inexpensive disposable parts that also eliminate cross contamination. These improvements will allow an operator to independently prepare samples for Sr isotope analysis using fast, low cost separation procedures and commercially available components. We optimized the elution chemistry by adjusting acid normality and elution rates to provide better separation of Sr from problematic matrices (e.g. Rb, Ca, Ba, K) associated with oilfield brines and formation waters. The separation procedure is designed for high sample throughputs that are ready for immediate Sr isotope measurements by MC-ICP-MS. Precise Sr isotope results can be achieved by MC-ICP-MS with a throughput of 4 to 5 samples per hour. Fluids from a range of geologic environments analyzed by this method yielded results within the analytical uncertainty of 87Sr/86Sr ratios previously determined by standard column separation and TIMS. This method provides a fast and effective way to use isolate Sr in a variety of geologic fluids for isotopic analysis by MC-ICP-MS.

Determination of Rare Earth Elements in Geological Samples Using Laser-Induced Breakdown Spectroscopy (LIBS):

Laser-induced breakdown spectroscopy (LIBS) was used to detect rare earth elements (REEs) in natural geological samples. Low and high intensity emission lines of Ce, La, Nd, Y, Pr, Sm, Eu, Gd, and Dy were identified in the spectra recorded from the samples to claim the presence of these REEs. Multivariate analysis was executed by developing partial least squares regression (PLS-R) models for the quantification of Ce, La, and Nd. Analysis of unknown samples indicated that the prediction results of these samples were found comparable to those obtained by inductively coupled plasma mass spectrometry analysis. Data support that LIBS has potential to quantify REEs in geological minerals/ores.

In situ measurements of calcium carbonate dissolution under rising CO2 pressure using underwater laser-induced breakdown spectroscopy

In the present study, we applied underwater laser-induced breakdown spectroscopy (underwater LIBS) for rapid in situ measurements of calcium carbonate (CaCO3) dissolution as a function of CO2 pressure (pCO2). A pulsed Nd:YAG laser at 1064 nm was used to produce gaseous plasma in the fluid surrounding a pressed pellet of CaCO3 powder. The ensuing plasma emission was spectrally analyzed, and the intensity of the calcium emission line at 422.67 nm was used to monitor Ca2+ cation released to the water. Barium emission line at 455.40 nm was simultaneously recorded as an internal standard to calibrate calcium signal intensity. The study shows that relatively strong and well-resolved spectral lines of both Ca2+ and Ba2+ cations can be obtained in CO2-saturated water. More importantly, the results show that underwater LIBS is capable of performing quantitative analysis at elevated pCO2, with an estimated Ca2+ detection limit of about 9 ppm over 50–350 bar. In the solution with the initially added CaCO3 pellet, the concentration of Ca2+ increases by a factor of 2 as pCO2 increases from 50 to 150 bar and remains nearly constant when pCO2 is further increased up to 350 bar. Finally, our study provides evidence that underwater LIBS could be a useful tool to investigate/monitor carbonate dissolution (at low ppm levels) in various geochemical applications.

Influence of CO_2 pressure on the emission spectra and plasma parameters in underwater laser-induced breakdown spectroscopy

Optical emission spectroscopic studies have been carried out to investigate the pressure effect of CO2 on laser-produced underwater plasma. The plasma was generated by focusing 1064 nm, 6 ns pulses from a Nd:YAG laser in a CO2-bearing solution. The temporal evolution of the continuum emission, Sr and Ba lines, and plasma electron density and temperature was characterized under CO2 pressure ranging from 10 to 300 bars. The electron density measurements were made using the Stark broadening of the 455.40 nm Ba II line, while the temperature measurements have been performed by the Saha-Boltzmann method using the Sr I-II lines at 460.73 and 407.77 nm, respectively. It was found that CO2 pressure has little effect on the emission line intensity and signal-to-background ratio. The electron density and the temperature are found to be independent of the CO2 pressure at early times. When time becomes longer, the electron density exhibits an appreciable rise as the CO2 pressure increases, while the temperature is found to be unchanged.