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天然气汞含量作为判识煤型气和油型气的一项重要指标已经被很多学者所接受,但在勘探实践中应用的并不多,究其原因是对该指标的认识还不够深入。探讨该指标的前提是搞清天然气中汞的形成机制,通过对美国和中国不同产煤区煤中汞含量和不同煤阶下煤的产气率进行统计分析,认为煤系有机质具备形成高含汞天然气的物质基础。但很多检测数据显示并不是所有的煤型气均具有较高的汞含量,有的甚至接近于0。为解释这一现象,开展了煤的吸汞和热释汞实验,发现煤在低温下不仅不能够释汞反而会从周围环境中吸收汞,只有当温度升高到一定程度煤中的汞才会在热力的作用下大量释放出来,因此说气源岩类型和地层温度共同决定了天然气汞含量的高低。全国八大盆地500多口气井的汞含量数据统计分析表明,当天然气汞含量大于30 000ng/m3时,可基本判断该天然气类型为煤型气。当天然气汞含量介于10 000～30 000ng/m3之间时,其为煤型气的几率较大,在结合其他地质资料的情况下也可比较容易得出合理的结论。但当天然气汞含量介于5 000～10 000ng/m3之间甚至更低时,天然气汞含量只能作为判识煤型气和油型气的辅助参数。
As an important index for judging coal gas and oil gas, natural gas mercury content has been accepted by many scholars, but its application in exploration is not much. The reason is that the understanding of this indicator is not deep enough. The premise of this indicator is to find out the formation mechanism of mercury in natural gas. Through the statistical analysis of the mercury content in coal in different coal producing areas in the United States and China and the coal production rate in different coal rank, it is considered that the organic matter in coal system has high content of The material basis of mercury gas. However, many test data show that not all coal-type gases have high mercury content, and some are even close to zero. In order to explain this phenomenon, experiments of mercury adsorption and pyrolysis of mercury in coal were carried out. It was found that coal not only can not release mercury but absorbs mercury from the surrounding environment at low temperature, only when the temperature rises to a certain extent Will be released in large quantities under the action of heat. Therefore, the type of gas source rock and formation temperature jointly determine the level of mercury in natural gas. The statistical analysis of mercury content in more than 500 gas wells in the eight major basins of the country shows that when the mercury content of natural gas is more than 30 000 ng / m3, the type of natural gas can be basically judged as coal-type gas. When the mercury content of natural gas is between 10 000 ~ 30 000 ng / m 3, it is more likely that it will be a coal-type gas, and reasonable conclusions can be drawn relatively easily when combined with other geological data. However, when the mercury content of natural gas is between 5 000 ~ 10 000 ng / m 3 or even lower, the mercury content of natural gas can only serve as an auxiliary parameter for judging the coal-based gas and oil-based gas.