Study On Mercury Isotopes Of Continental Oil/Gas Source Rocks

The fact that mercury is generally contained in terrestrial source rocks and oil and gas,as well as the tracer effect of the three-dimensional system of stable isotope of mercury,provide a scientific basis and theoretical support for mercury isotope as an indicator of oil source comparison.This paper studies the mercury content and mercury isotopic characteristics of terrestrial source rocks,reservoirs and non-source rocks,and compares the mercury isotopic characteristics of terrestrial source rocks with marine sediments,possible oil-forming organic matter,and oil and gas,obtained the following preliminary results:（1）The mercury content of terrestrial source rocks,reservoirs and non-source rocks are mostly distributed in a few ng/g,and there is no significant difference in mercury content values in terrestrial source rocks,reservoirs and non-source rocks.（2）The range ofΔ¹⁹⁹Hg of terrestrial source rocks is 0.02‰～0.20‰,and the average value is 0.10±0.04‰（1SD,n=13）,the range ofδ²⁰²Hg is-3.21～-0.20‰,and the average value is-1.85±0.83‰（1SD,n=13）.ReservoirΔ¹⁹⁹Hg range is 0.05‰～0.31‰,mean value is0.16±0.09‰,（1SD,n=8）,δ²⁰²Hg range is-3‰～-1.40‰,mean value is-2.33±0.53‰,（1SD,n=8）.The range ofΔ¹⁹⁹Hg of non-hydrocarbon source rocks is-0.06‰～-0.03‰,and the average value is-0.04±0.01‰（1SD,n=5）,the range ofδ²⁰²Hg is-2.44‰～0.66‰,and the average value is-0.98±1.1‰（1SD,n=5）.（3）Terrestrial source rocks and marine sediments have similar mercury isotope characteristics:mercury isotope non-mass fractionationΔ¹⁹⁹Hg is positive,and mercury isotope mass fractionationδ²⁰²Hg is negative.In essence,there is no difference between continental oil formation and marine oil formation.Both are formed in brackish water and saline water sedimentary environments,the main source of oil-forming organic matter is algae.（4）There is no significant difference between the mercury isotope information(whetherδ²⁰²Hg orΔ¹⁹⁹Hg)in oil and gas and terrestrial source rocks,and there are significant differences with theΔ¹⁹⁹Hg information of non-hydrocarbon source rocks,indicating thatΔ¹⁹⁹Hg information is in source rock deposition and hydrocarbon generation,there is inheritance in the process.It is preliminarily believed that only sedimentary rocks with positiveΔ¹⁹⁹Hg information may become effective source rocks.This result has guiding significance for the exploration of continental oilfields.（5）According to the mercury isotope characteristics of algae,terrestrial source rocks and oil and gas,a mercury isotope model for the continental oil-forming process has been preliminarily established:after a large number of algae die,they enter the sediments,and then form source rocks containing a large amount of algae organic matter,and then form the continental oil-forming process of continental oil and gas fields,always inheriting positive mercury isotope non-mass fractionation and negative mercury isotope mass fractionation information.