SPATIO-TEMPORAL VARIABILITY OF MERCURY CONTENT IN HYDROCARBON GAS DEPOSITS

Nikolai R. Mashyanov*, Vladimir V. Ryzhov, (Earth's Crust Institute, St. Petersburg State University, St. Petersburg, 199034, Russia); Nina A. Ozerova (Institute of Geology of Ore Deposits, Petrology, Mineralogy and Geochemistry, Russian Academy of Sciences, Moscow, 109017, Russia)

The fossil fuels combustion is a significant source of mercury input in the environment. Content of mercury in raw hydrocarbons is mainly determined by regional geologic position of deposits. Mercury concentration in hydrocarbon gases in Russia varies widely from values less than 0.01 to 1.1*104 ng/l (2 ng/l being the average).

The determination of Hg content and resources in hydrocarbon deposits, as a rule, has been executed on the basis of single measurements. The obtained data shows significant spatial-temporal variability of mercury content in hydrocarbon gases. Long-term variability of local and average Hg content in gas deposits can produce significant difference in mercury amount evaluation depending on the time of measurements. Maximal spatial difference (up to 2-3 orders) can exist in vertical direction in different productive horizons of the deposit, but Hg distribution can be heterogeneous within the limits of one productive bed, as well.

In the gas wells the consecutive concentration can fluctuate dozens of times during observation period of several years. Continuous time course measurements performed during a period of many days and fulfilled using Zeeman spectrometer RA-915 on two gas condensate deposits revealed a new phenomena - regular "short-term" variation of mercury content in hydrocarbon gases with periods from 0.3 to 25 hours, and amplitude between 10 and 80 % of Hg average concentration during the period the measurements have been carried out.

Spatio-temporal variability of mercury concentration in hydrocarbon gases is bound to be considered in determination of mercury resources in gas deposits and evaluation of Hg input in the environment due to Hg-containing hydrocarbon deposits exploitation.