Tracing interaction between hydrocarbon and groundwater systems with isotope signatures preserved in the Anyue gas field, central Sichuan Basin, China
Tracing interaction between hydrocarbon and groundwater systems with isotope signatures preserved in the Anyue gas field, central Sichuan Basin, China
复制标题
利用中国四川盆地中部安岳气田保存的同位素特征追踪碳氢化合物与地下水系统之间的相互作用
DOI：
10.1016/j.gca.2020.01.039
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发表时间：
2020-04-01
影响因子：
5
通讯作者：
Zhou, Zheng
中科院分区：
文献类型：
--
作者：
Li, Yan;Qin, Shengfei;Zhou, Zheng
安岳气田是位于四川盆地中部的大型气田。虽然以前已经进行了许多研究，但这个领域的形成机制尚不清楚，目前还在争论中。为了更好地了解成藏历史、地下水在沉积盆地内的输导作用以及水气相互作用，对安越气田13个游离气样品进行了稳定气同位素和稀有气同位素的测定。此外，对9个地层水样和5个储层沥青样进行了稳定碳同位素分析。气体样品中的δ C-13（CH4）值在-35.0 ~ -32.6‰之间，显示了热成因的证据。三种不同类型样品（自由气、水溶气和储层沥青）的δ C-13值显示出一种不能用石油裂解后自由气聚集来解释的模式。表明安岳气田存在气-地下水相互作用。根据其地理位置和地层成因，游离气样品可分为两类。第1组和第2组样品的He-3/He-4比值（R/R-a）分别在0.0118 ~ 0.0132和0.0115 ~ 0.0256之间，表明He主要来源于地壳。Ne-26/Ne-22和Ne-21/Ne-22比值表明空气源和地壳源之间存在混合。第1组和第2组样品的Ar-40/Ar-36比值分别为1658 ~ 2109和2168 ~ 5973，显著高于空气值298.6。相比之下，较重的稀有气体（Kr和Xe）的同位素组成主要是类似空气的。组1样品中He-4和Ne-21*的相对富集可能与低温环境下轻惰性气体优先释放有关。第2组样品很好地符合溶解度控制的瑞利分馏模型，表明存在地下水中气体脱气的开放系统。天然气样品中过量的重惰性气体可归因于烃源岩在地质演化过程中沉积组分的加入。4考虑原位开采和外部通量的地下水年龄表明安岳气田有年轻地下水的加入。低气-地下水比和高CH4/Ar-36比表明，安越气田龙王庙现有气藏中只有一小部分天然气与相对年轻的地下水接触。根据所有样品的稀有气和稳定碳同位素结果，我们提出了安岳气田天然气保存和成藏历史中天然气与地下水相互作用的两阶段过程。(C) 2020 Elsevier Ltd.版权所有。
Anyue gas field is a large gas field located in the central Sichuan Basin, China. Although many studies have been carried out previously, the formation mechanism of this field is unclear and currently under debate. To better understand the accumulation history, the role that groundwater plays in transporting hydrocarbons within sedimentary basins and water-gas interactions, stable and noble gas isotopes were measured in thirteen free gas samples from the Anyue gas field. In addition, nine formation water samples and five reservoir bitumen samples were analyzed for stable carbon isotopes. delta C-13(CH4) values in the gas samples range from -35.0 to -32.6 parts per thousand, showing evidence of thermogenic origin. delta C-13 values among three different types of samples (free gases, water-dissolved gases and reservoir bitumen) show a pattern that cannot be explained by oil cracking followed by free gas accumulation. It suggests the occurrence of gas-groundwater interaction in the Anyue field. Free gas samples can be divided into 2 distinct groups by their geographical locations and stratigraphical source formations. He-3/He-4 ratios (R/R-a) in group 1 and group 2 samples range from 0.0118 to 0.0132 and 0.0115 to 0.0256, respectively, indicating He is mainly derived from the crust. Ne-26/Ne-22 and Ne-21/Ne-22 ratios suggest a mixing between the air and crust sources. Ar-40/Ar-36 ratios ranging from 1658 to 2109 and 2168 to 5973 in group 1 and group 2 samples, respectively, are significantly higher than the air value of 298.6. In comparison, heavier noble gas (Kr and Xe) isotopic compositions are predominantly air-like. The relative enrichment of He-4 and Ne-21* in group 1 samples can be possibly explained by preferential release of light noble gases in a low temperature environment. Samples in group 2 show a good fit to the solubility-controlled Rayleigh fractionation model, suggesting the presence of an open system degassing of gases from the groundwater. The excess heavy noble gases in natural gas samples can be attributed to the addition of sedimentary components from the source rocks during geological evolution. 4 He groundwater ages considering in-situ production and external flux indicate the addition of young groundwater into the Anyue gas field. Low gas-groundwater ratios and high CH4/Ar-36 ratios suggest that only a small portion of the gases in the current Longwangmiao reservoir of Anyue gas field has been in contact with the relatively young groundwater. Based on the noble gas and stable carbon isotope results in all samples, we propose a two-stage gas and groundwater interaction process during the gas preservation and accumulation history in the Anyue gas field in China. (C) 2020 Elsevier Ltd. All rights reserved.