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基于天然气组分以及组分同位素分析结果,结合凹陷烃源岩有机地球化学特征与地质背景,对廊固凹陷天然气的成因类型及其分布规律进行了研究。结果表明,廊固凹陷浅层(<1 900m)与中深层(>1 900m)天然气的地球化学特征存在很大的差异,具有不同的成因类型。浅层天然气藏以次生型生物改造气藏为主,是热成因气的湿气部分遭受细菌降解而产生的次生生物气与残留热成因气(主要为甲烷)混合而成。其主要特征为:气体干燥系数大于95%,但重烃气含量较高(ΣC_(2~+)>0.5%);甲烷稳定碳同位素组成较轻(δ~(13)C_1值分布在-60‰~-50‰之间);异构丁烷含量增加,丙烷含量明显减少;很多气样稳定碳同位素序列在丙烷处发生局部倒转。深层天然气主要为偏腐殖型热成因气,而且大多数天然气为干酪根初次裂解气。深层天然气以低—中等成熟度(RO值范围为0.5%~0.8%)为主,主要来自成熟度相当的沙三下亚段烃源岩;而曹家务、固安地区深度超过4 000m的4个气样以及别古庄地区奥陶系潜山气藏成熟度较大(RO值范围为1.1%~1.5%),来自深层的沙四段—孔店组烃源岩。廊固凹陷深层天然气的分布受控于烃源岩干酪根类型以及热成熟度,浅层天然气的分布则主要与沟通深部热成因油气的断裂活动强度有关。固安、柳泉、郎东等地区浅层是次生型生物改造气藏的主要分布区与有利勘探带,固安—旧州地区大兴断层深部的砾岩体以及别古庄地区的潜山是深层热成因天然气的有利勘探区带。
Based on the results of gas composition and isotopic analysis of components, combined with the organic geochemical characteristics and geologic background of source rocks in the depression, the genetic types and their distribution of natural gas in the Langgu Sag were studied. The results show that the geochemical characteristics of the natural gas in the shallow layers (<1900 m) and middle deep layers (> 1 900 m) in the Langgu Sag are quite different and have different types of genetic types. Shallow gas reservoirs are dominated by secondary bioremediation gas reservoirs, which are a mixture of secondary biogas generated by bacterial degradation and residual pyrogen gas (mainly methane) that is part of the thermodynamics gas. The main features are: the gas drying coefficient is more than 95%, but the content of heavy hydrocarbon gas is high (ΣC_ (2 +)> 0.5%); the stable carbon isotope composition of methane is relatively light (δ ~ (13) ‰ ~ -50 ‰); the content of isobutane increases and the content of propane decreases obviously; and the stable carbon isotope sequence of many gas samples is locally reversed at propane. The deep natural gas is predominately humic thermogenesis and most of the natural gas is the kerogen primary pyrolysis gas. The deep natural gas is dominated by low-moderate maturity (RO values range from 0.5% to 0.8%), mainly from the Matushuanku sub-stage source rocks with similar maturity. However, the deep natural gas with a depth of more than 4 000 m Gas samples and Ordovician buried hill gas reservoirs in Beguguzhuang area (RO range 1.1% -1.5%) come from deep source rocks of the Shasi Member-Kongdian Formation. The distribution of deep natural gas in the Langgu Sag is controlled by the kerogen type and thermal maturity of source rocks. The distribution of shallow gas is mainly related to the intensity of fault activity in communicating deep thermal geneses. Gu’an, Liuquan and Langdong are the main distribution areas and favorable prospecting belts of the secondary biogenic gas reservoirs, the conglomerate bodies deep in the Daxing fault in the Gu’an-Jiuzhou area and the buried hills in the Begu Zhuang area are A favorable exploration zone for deep thermogenic natural gas.