我国煤层气组份、碳同位素类型及其成因和意义

本文研究了我国14个煤矿和3口中深井煤层气的组份、甲烷碳同位素组成,发现煤矿煤层气大部分有变干变轻的特征,而中深井煤层气则没有此现象。我国原生带煤层气和从褐煤热模拟成煤作用获得的煤层气亦没有变干变轻。因此认为煤矿煤层气变干变轻是由于受到次生改造的结果。     

中国生物气中烷烃组分的碳同位素特征及其鉴别标志

我国生物气中烷烃气的碳同位素组成特征是:随生物气中烷烃气分子的碳原子数的增加,δ~(13)C值分布区间,主频率段分布范围均随之缩小,δ~(13)C最轻的和最重的界限值也随之变重;生物气中乙烷的碳同位素和丙烷的碳同位素之间呈线性正相关关系;δ~(13)C_1,δ~(13)C_2和δ~(13)C_3值随重烃气(C_(2+3))含量的增加有变重趋势。文中首次研究了我国生物气的δ~(13)C_1-C_(2+3)(％),δ~(13)C_2-C_(2+3)(％)和δ~(13)C_2-δ~(13)C_3的关系及其相关性回归方程,并指出,δ~(13)C_1<—55‰和C_(2+3)<0.5％是鉴别我国生物气的良好指标,δ~(13)C_2-δ~(13)C_3<-10‰可作为鉴别生物气的一项新指标。     

COMPOSITION, CARBON ISOTOPE CHARACTERISTICS AND THE ORIGIN OF COAL-BED GASES IN CHINA AND THEIR IMPLICATIONS

The compositions and the carbon isotope characteristics of methanes of the coal-bed gases from 14 coal mines and 3 deep to medium boreholes are studied in this paper.It is found that the coal-bed gases from the coal mines are characterized by the drying or lightening phenomena, which are absent in coal-bed gases from the boreholes.The drying and lightening features were not observed in the coalbed gases derived from both the primary zones and the lignite pyrolysis simulation experiments.Therefore, it is considered that the drying and lightening of coal-bed gases in the coal mines result from the secondary destructive processes.The origins of dried or lightened coal-bed gases may be due to (ⅰ) desorption-diffusion, (ⅱ) the exchange equilibrium of carbon isotopes between CH_4 and CO_2, and (ⅲ) mixing of primary coal-bed gases with syncoalification or postcoalification of biogenetic gases, among which the desorption-diffusion origin is of primary importance.     

中国一些地区温泉中天然气的地球化学特征及碳、氦同位素组成

中国一些地区温泉气的主要组分是CO_2或N_2,烷烃气含量低或无,同时含极微量的氦。温泉气的δ~(13)C_1主频率峰在-20‰至-22‰,说明温泉气的甲烷主要是无机成因的。温泉气的δ~(13)C_(CO_2)主频率峰在-4‰至-8‰,反映温泉气的CO_2也主要是无机成因的。δ~(13)C_(CO_2)值与CO_2含量正相关,其回归方程为δ~(13)C_(CO_2)(‰)≈0.966lgCO_2-6.354,δ~(13)C_(CO_2)值与N_2含量负相关,其回归方程为δ~(13)C_(CO_2)(‰)≈-3.193-0.109 N_2。根据氦同位素组成特点,可划分出幔源温泉气和壳源温泉气,前者R/R_a>1,后者R/R_a<1。     

各类烷烃气的鉴别

本文利用天然气中烷烃气组分变化及其碳同位素系列演化特征、煤型气甲烷回归方程δ~(13)C1≈14.12logR_o-34.39,油型气甲烷回归方程δ~(13)C_1≈15.80logR_o-42.20,δ~(13)C_1-C1/C_(2+3)图版、δ_(13)C_1-R_o图版、δ~(13)C_1-δ~(13)C_2-δ~(13)C_3图版、煤型气δ~(13)C_(1-3)-R_o图版和轻烃C_7系统三角图版,鉴别有机烷烃气和无机烷烃气,并又对有机烷烃气中煤型烷烃气,油型烷烃气予以判别。     

Geochemical Characters, Carbon and Helium Isotopic Compositions of Natural Gas From Hot Springs of Some Areas in China

The main components of hot spring gases in some areas of China are CO2 or N2, and they have no or trace alkanes and very lower quantity of He . The δ13C1 values of hot spring gases mainly range from - 20‰to - 22‰ , which suggest the methane mainly be the inorganic origin in these gases. The δ13Cco2 values of hot spring gases are mainly from -4% to - 8%, so these carbon dioxides are also the inorganic origin. δ13Cco, values positively correlate with CO2 contents, their regression equation is δ13Cco2(‰)≈0. 966 log-CO2 - 6. 354; δ13Cco2 values negatively correlate with N2 contents, their regression equation is δ13Cco, (‰)≈ - 0.109N2 - 3.193. According to the helium isotopic compositions, we can distinguish mantle-derived hot spring gases from crustal hot spring gases, the former with R/Ra>1 and the latter with R/Ra<1.     

Characteristics of Carbon Isotopes of Alkane Components and Identification Marks of Biogenic Gases in China

The carbon isotope composition of alkane component in biogenic gases of China has the following characteristics:with the increase of carbon number of the alkane molecules in biogenic gases, (i) the distribution range of the δ13C values and their main frequency sections become narrower, and both the heaviest and the lightest δ13C boundary values shift to their heavier end; (ii) the δ13C values of ethane and propane in biogenic gases present a positive linear relationship and (iii) the values of δ13C1, δ13C2 and δ13C3 tend to become heavier with the increase of heavy alkane component (C2+3) in biogenic gases. The authors studied the relationship between the δ13C values and the amount of heavy alkane components in biogenic gases (δ13C1 -C2+3(%). δ13C2 -C2+3(%) ,δ13C3-C2+3(%) for the first time and set up the interrelated regression equations between δ13C and C2+3 content (C2+3%), and advance that δ13C1< -55‰ and C2+3<0. 5% are two fine marks for identification of biogenic gases of China. δ13C