辽西金羊盆地下侏罗统北票组页岩气地球化学特征及其成因

金岭寺-羊山盆地(金羊盆地)是中国北方侏罗系发育最完备的地区之一,盆地内充填的下侏罗统北票组为一套湖相泥岩,具有良好的油气潜力。在金羊盆地章吉营子凹陷西缘布置实施的4口地质调查井中,有3口井见油气显示。通过对SZK2及SZK3钻井岩心进行现场解析,北票组泥页岩在浅层测试到可观的页岩气含量,且随着深度的变化,总含气量及甲烷含量有所增加。另外,其总含气量与有机碳含量呈良好的正相关关系,是影响页岩含气量的关键因素。对比金羊盆地北票组泥页岩吸附气C同位素特征,其气体成因主要存在生物成因气和煤型气2种类型,表明下侏罗统北票组页岩气具有混合多成因的特征。通过X衍射分析综合评价,金羊盆地下侏罗统北票组泥页岩压裂条件好、天然气吸附能力强,具备一定的页岩气勘探前景,是有利的页岩气勘探开发新层系。

An analysis of the genesis and geochemical characteristics of shale gas in Lower Jurassic Beipiao Formation in Jinyang Basin

The Jinlingsi-Yangshan Basin (Jinyang Basin) is one of the basins with the most completely Jurassic strata in northern China. The Lower Jurassic Beipiao Formation in the basin is composed of a set of lacustrine mudstones, and has beneficial potential of oil and gas. There are four wells in the west of the Zhangjiyingzi depression of Jinyang Basin, of which oil and gas shows were found in three wells. Field desorption of drill core from the SZK2 and SZK3 wells shows that the shale gas content collected from the shallower strata of mud shale of Beipiao Formation is considerable with the increasing depth, the total gas content and methane content increase. In addition, the total gas content and organic carbon content show a good positive correlation, which is a key factor affecting the gas content of the shale. A comparison with characteristics of adsorbed gas carbon isotope of the shale shows that the gas mainly came from biogenic gas and coal gas, and the shale gas has the characteristics of hybrid origin. The X diffraction analysis of mud shale from Beipiao Formation indicates that the favorable conditions of fracturing and strong gas adsorption capacity result in the good prospect of shale gas exploration. Beipiao Formation is favorable for shale gas exploration.