Mercury Isotopes in Shale Gas From Wufeng-Longmaxi Shale Formation of Sichuan Basin, Southern China: A Preliminary Investigation

A series of investigations have been conducted concerning the study of traditional stable isotopes and rare gas stable isotopes in natural gas. However, little is known regarding non-traditional stable isotopes of mercury in natural gas, especially in the development and utilization of shale gas in recent years. In fact, the presence of mercury in natural gas (including shale gas) provides a basis for research on mercury isotopes. Mercury was extracted from shale gas at the Wufeng-Longmaxi Formation in the YS108 block of the Zhaotong National shale gas demonstration area in the Sichuan Basin by using an acid potassium permanganate solution, followed by the analysis of mercury content and stable isotope composition. The mercury content in the marine shale gas at the Wufeng-Longmaxi Formation ranged from 171 to 2,906 ng/m(3), with an average of 1,551.08 +/- 787.08 ng/m(3) (n = 37, 1 SD). The Delta Hg-199 values of mercury stable isotopes range from 02 parts per thousand to 0.39 parts per thousand, with an average of 22 parts per thousand +/- 0.08 parts per thousand (n = 37, 1 SD); the delta Hg-202 values range from -1.68 parts per thousand to -0.04 parts per thousand, with an average of -0.87 parts per thousand +/- 0.31 parts per thousand (n = 37, 1 SD), which are significantly different from the Delta Hg-199 and delta Hg-202 information of coalbed gas, but similar to the Delta Hg-199 and delta Hg-202 information of terrestrial oil-type gas and the Delta Hg-199 in the main hydrocarbon-forming organic matter of lower organisms such as algae (t-test, p > 0.05). This indicates that terrestrial target strata with abundant algae or strata with positive Delta Hg-199 are the target strata for the exploration of terrestrial oil and gas.

Automated summary

Little is known about the non-traditional stable isotopes of mercury in natural gas, especially in shale gas. This study extracted mercury from shale gas in the Sichuan Basin and analyzed its content and stable isotope composition. The results suggest that terrestrial target strata with abundant algae may be the target for terrestrial oil and gas exploration.