渤中凹陷西南洼东营组烃源岩地球化学特征及环境指示意义

东营组烃源岩在渤中凹陷广泛分布，明确该套烃源岩特征及其形成的古环境对于推动渤中凹陷常规-非常规油气勘探具有重要意义。通过对渤中凹陷西南洼东营组烃源岩样品进行有机、无机地球化学实验，分析该套烃源岩品质、有机质来源和古沉积环境，并与凹陷内主力烃源岩沙河街组进行对比分析。结果显示：(1)东营组不同层段烃源岩特征差异显著，且与沙一二段烃源岩呈现明显不同。东二下段与东三段有机质丰度高，已达到成熟-高成熟阶段，东营组整体有机质类型均以Ⅱ型为主；(2)通过Pr/nC₁₇-Ph/nC₁₈等图版以及干酪根类型判断东营组有机质来源为混合型，与沙一二段的低等藻类输入明显不同；(3)综合Sr/Cu、Mn/Fe等16种元素含量或比值以及Pr/Ph、伽马蜡烷指数分析烃源岩形成时期的古环境，与沙一二段烃源岩干旱气候下强还原咸化湖盆的形成环境所不同，东营组整体形成于温湿气候下，伴随较强陆源输入，受控于弱氧化淡水环境；纵向上，从东三段-东一段古气候变化不大，水体盐度基本一致，但水深逐渐变浅，水体氧化条件呈现逐渐增强的趋势；(4)利用Co、La含量定量恢复东营组沉积时的古水深，...

Geochemical characteristics and environmental implications of source rocks of the Dongying Formation in southwest subsag of Bozhong Sag

Source rocks of the Dongying Formation are widely distributed in the Bozhong Sag. It is of great significance to clarify the characteristics and paleoenvironment of the source rocks to promote conventional and unconventional oil and gas exploration in the Bozhong Sag. In this study, organic and inorganic geochemical experiments were carried out on the source rock samples collected from the Dongying Formation in the Bozhong Sag, with aims to analyze the quality and paleoenvironment and compare it with the Shahejie Formation. The results show that: ①the characteristics of source rocks in different layers of the Dongying Formation are significantly different from those in Es_1-2.The abundance of organic matter in the lower and third members of the Dongying Formation (Ed₂L and Ed₃) is high and has reached the mature-high maturity stage. The organic matter of the Dongying Formation is mainly type Ⅱ. ②According to the Pr/nC₁₇-Ph/nC₁₈ charts, the source of organic matter in the Dongying Formation is mixed type, which is obviously different from the low algae of Es_1-2.③The paleoenvironment during the formation of source rocks was analyzed by combining the contents or ratios of 16 elements, such as Sr/Cu, Mn/Fe, Pr/Ph and the gammacerane index. Different from the strong reduction-salinized lacustrine basin in the arid climate of Es_1-2, the Dongying Formation was formed in a warm and humid climate, accompanied by strong terrigenous input, and controlled in a weakly oxidized freshwater environment. Longitudinally, the paleoclimate changes little from Ed₃ to Ed₁, and the water salinity is basically the same, but the water depth becomes shallower and the water oxidation conditions show a trend of increasing gradually.④Using Co and La contents to quantitatively restore the paleo-water depth during the deposition of the Dongying Formation, and suggests that Ed₃ (50.4 m)>Ed₂ (35.7 m)≈Es_1-2(33.2 m)≈Ed₁(31.7 m). The calculated results are consistent with the previous qualitative results of paleo-water depth.