川中高石梯—磨溪地区产层天然气地球化学特征

Geochemical Characteristics of Natural Gas Production Layers in Gaoshiti-Moxi Region,Central Sichuan,China

在四川盆地高石梯-磨溪地区的震旦系-侏罗系发现了多个具有商业开采价值的天然气藏,目前尚无针对该区各产层天然气地球化学特征的系统性研究。本次研究以天然气的实验分析数据为基础,基于油气地球化学理论,重点对比不同产层天然气组分及碳同位素的特征差异,探索各产层天然气标志特征。研究表明,各产层天然气组分以CH4为主,陆相产层天然气C2H6、重烃含量远高于海相产层,且不含H2S;各产层天然气中CO2含量总体上随埋深的加深而升高;陆相甲烷的碳同位素值小于-36‰,海相甲烷的碳同位素值大于-36‰,且各产层天然气在C1-CO2碳同位素交会图上显示出较大差别。根据天然气特征差异,建立了研究区各产层的天然气划分图版。

Large amount of natural gas has been discovered in Sinian-Jurassic Gaoshiti-Moxi area of Sichuan Basin, while there is no systematic analysis on the geochemical characters of the natural gas in each layer in this area. Based on the experimental data and petroleum geochemistry, this paper addresses the components and carbon isotopes of the natural gas in the study area. The results show that the mainly component is CH 4 in all layers. The contents of ethane and heavy hydrocarbons in the terrestrial layers are much more than those in the marine layers. There is no H 2S discovered in the terrestrial layers. The CO 2 contents increase as the increasing burial depth in all layers. For the carbon isotope of methane, those values in the terrestrial layers are lower than -36‰, while those in the marine layers are higher than -36‰. Moreover, the carbon isotopes of C 1-CO 2 in different layers show significant differences vertically. Consequently, according to the natural gas characters, the division charts for the geochemical characters of natural gas in each layer have been established in the study area.