四川盆地阆中地区灯影组储层沥青地球化学特征及其意义

震旦系灯影组是四川盆地海相深层天然气勘探的重点层系之一。近年来在高石梯—磨溪古隆起北斜坡阆中地区的天然气勘探中，灯影组四段储层内发现沥青呈广泛分布，但对其地球化学特征及相关油气成藏条件的研究较为薄弱。通过分析沥青的有机地球化学特征，揭示了阆中地区灯影组储层沥青的成因和来源，探讨了沥青对古油藏规模和相关油气成藏条件的指示意义。研究表明，阆中地区灯影组储层中的沥青为正常埋藏演化过程中热裂解作用成因，其质量含量、等效镜质体反射率和δ¹³C平均分别为1.36%、4.29%和-32.3 ‰。生物标志化合物和碳同位素组成特征的对比分析表明，震旦系灯影组沥青与下寒武统烃源岩具有较好的亲缘关系，沥青主要来自阆中地区西侧拉张槽内下寒武统烃源岩生成的原油并经裂解作用而形成，灯影组四段下伏的灯影组三段和陡山沱组泥质烃源岩可能也有一定贡献。阆中地区的古油藏规模约为32.3×10⁸t，裂解生气强度可达49.23×10⁸m³/km²，天然气的保存条件是控制阆中地区灯影组四段现今气藏规模的关键因素。

Geochemical characteristics of reservoir bitumen from Dengying Formation in Langzhong area of Sichuan Basin and its implication

The Sinian Dengying Formation is one of the important strata for natural gas exploration in deep marine carbonate sequence in Sichuan Basin. In recent years, during natural gas exploration in Langzhong area at the northern slope of the Gaoshiti-Moxi paleo-uplift, it is found that bitumen is widely distributed in Member 4 of Dengying Formation. However, there is less research of its geochemical characteristics and hydrocarbon accumulation conditions in this area. Based on analyzing the organic geochemical characteristics of bitumen, this paper reveals the origin and source of reservoir bitumen of Dengying Formation in Langzhong area, and further explores its implication on the scale of paleo-oil pools and hydrocarbon accumulation conditions. The results indicate that the reservoir bitumen of Member 4 of Dengying Formation is formed by thermal cracking in the process of normal burial and evolution, and its mass content, equivalent vitrinite reflectance, and δ¹³C values are 1.36%, 4.29%, and -32.3 ‰ on average, respectively. The comparative analysis of biomarkers and carbon isotopic compositions indicates a favorable affinity between the reservoir bitumens of Member 4 of Dengying Formation and Lower Cambrian source rocks. The bitumen is mainly formed through the cracking of crude oil generated by the Lower Cambrian source rocks in the intracratonic sag to the west of Langzhong area, or probably by the underlying argillaceous source rocks in Member 3 of Dengying Formation and Doushantuo Formation. The reserve in paleo-oil pools in Langzhong area is around 32.3×10⁸ t, and the oil-cracking gas generation intensity reaches 49.23×10⁸m³/km². The preservation conditions of natural gas is the key factor controlling the scale of existing gas pools in Langzhong area.