天然气中汞同位素特征及其作为气藏成因的一项鉴别指标研究

Mercury is widespread in natural gas and generally higher than that of two or more orders in atmosphere,and as an earlier established genetic indicator for gas reservoir, however, limited to the analytical technology, the research of mercury genetic indicator in nature gas for gas reservoir has remained in the mercury content and the progress is very slow since its emerges. In recent years, with the development of MC-ICP-MS analytical technology on mercury isotope, the established "3-D" system of mercury stable isotope and its special source tracer, it is necessary to study intensively and improve the mercury vapor genetic indicator for gas reservoir. In view of the above opinions, this work aims to: (1) understand the mass dependent fractionation(MDF) and mass independent fractionation(MIF) signal in natural gas and study it as a genetic indicator characteristics for gas reservoir to replenish and perfect the existing integrated genetic indicators for gas reservoir, and better service and guide the nature gas exploration work; (2) analyze mercury isotope signal in petroleum and the condensates to provide the basis for the further study of the mercury isotope fractionation mechanism in petroleum; (3) reveal the geochemical information in different genetic type of natural reservoir, such as the potential gas source rock, migration, mixing and lost history of nature gas using the MDF and MIF signal as far as possible for enriching nature gas genetic theory and further comprehensive research of mercury isotopic fractionation mechanism in nature gas.

天然气普遍含汞且较高，是较早建立的天然气成因鉴别指标之一，但限于分析测试技术至今还一直停留在汞蒸汽含量方面的研究，进展缓慢。随着近年来MC-ICP-MS对汞同位素的精准分析、汞稳定同位素三维体系的建立及其源解析和特殊的示踪作用等研究进展，有必要完善汞蒸汽这一成因鉴别指标。鉴此项目：（1）系统了解各类成因天然气中汞同位素的质量分馏和非质量分馏信息，研究其作为一项相对可靠的天然气成因鉴别指标的特征，补充和完善现有的天然气成因综合鉴别指标体系，更好地服务和指导天然气的勘探开发工作；（2）初步了解石油及其凝析物中汞同位素信息，为今后开展石油成藏过程中的汞同位素分馏机制提供基础；（3）尽可能利用汞同位素的质量和非质量分馏信息揭示蕴涵于各成因天然气中的有关潜在气源岩的性质、天然气的运移、混源以及气藏的运聚和散失史等地球化学信息，丰富天然气成因理论，也为进一步综合研究天然气中汞同位素分馏机制提供依据。

采用高锰酸钾和硫酸混合溶液三级串联吸收法系统采集和研究了辽河油田欢喜岭采油厂典型油型气、中原油田典型油型气和鹤壁六矿典型煤型气中的汞含量和汞同位素组成信息，研究了天然气中汞同位素组成信息作为一项油型气和煤型气成因鉴别指标的可靠性，并初步研究了油型气和煤型气中汞同位素组成分布的值域和阈值，为天然气的成因鉴别提供了可靠依据，取得了以下成果：.1) 油型气和煤型气中的汞含量几乎没有差异且范围较宽（16.58到100910.30 ng/m3），很难根据天然气中汞含量厘定天然气的成因，仅依靠这一指标甚至导致相反或错误的结论。油型气汞含量介于45.42 ng/m3~100910.30ng/m3之间，平均值20725.37 ng/m3；煤型气中汞含量介于16.58 ng/m3~95.16 ng/m3之间，平均值55.87 ng/m3；瓦斯发电站用气中汞含量分布范围是793.11ng/m3~2214.01ng/m3，平均值1374.39 ng/m3。.2) 采用三级串联的4%w/vKMnO4+10%v/vH2SO4混合溶液吸收天然气中的汞，吸收效果显著，其中一级吸收率89.54%，二级吸收效率8.34%，三级吸收效率2.13%，（n=55）。.3) 煤型气汞的质量分馏 (δ202Hg)比油型干气、湿气的质量分馏汞 (δ202Hg)更偏负、偏轻；煤型气中汞的非质量分馏信息（Δ199Hg）均为负值，而油型气中汞的非质量分馏信息（Δ199Hg）均为正值。油型气干气和纯煤层气气中汞的Δ199Hg/Δ201Hg≈1，说明油型干气和煤型气中汞的非质量分馏主要是由煤与油气形成前的Hg2+光化学还原导致。.4) 瓦斯电厂用气中汞同位素组成表现了明显的二元（煤与空气）混合特征：δ202Hg范围是-1.43‰～-0.33‰，平均值是-1.08‰±0.32‰（n=18，1SD），Δ199Hg范围是-0.02‰～0.27‰，平均值是0.12‰±0.09‰（n=18，1SD）。.5) 油型气和煤型气中汞同位素组成差异明显，初步认为可以作为一项鉴别油型气和煤型气成因的可靠指标：天然气中δ202Hg在-3.33‰～0.19‰之间，Δ199Hg范围在0.05‰～0.32‰之间,可以判定为油型干气；天然气中δ202Hg在-3.79‰～0.02‰之间，Δ199Hg在-0.04‰～0.27‰之间，可以判定为油型湿气；天