川西坳陷天井山古油藏油源判识及其与深层油气成藏关系厘定

Oil source correlation and its relationship with deeply buried hydrocarbon accumulations in Tianjingshan Paleouplift area,northern segment of Western Sichuan Depression

四川盆地西部坳陷北段天井山古隆起区具有丰富油气显示,古油藏油源示踪与成藏破坏过程厘定对川西坳陷北段深层油气成藏过程与机理研究具有重要意义。天井山古隆起构造解析明确寒武纪—奥陶纪之交的构造事件在川西坳陷北段有显著表现。天井山古隆起的形成是早古生代绵阳—长宁拉张槽形成后构造—沉积性质由拉张转向挤压的重要节点。川西坳陷北段油气地质条件分析表明,下寒武统麦地坪组—筇竹寺组是海相油气的最佳烃源岩。将灯影组储层沥青纳入川西坳陷北段古油藏研究范畴,完成完整的天井山古隆起区烃源岩—古油藏油源示踪。有机碳同位素与生物标志化合物指标指示,古油藏的主要母源是下寒武统富有机质黑色泥页岩,最终建立“天井山古隆起古油藏系统”概念。根据相应的生储盖组合划分、油源判别与构造期次梳理,再次证实川西坳陷北段复杂构造背景下深层海相油气多期多样成藏过程可分为“原生油藏—原生气藏”与“次生油藏—原生气藏”两类。

The Tianjingshan Paleouplift(TJS PU)area in the northern segment of Western Sichuan Depression(NSWSCD)has abundant oil and gas shows.The traceability of paleooil reservoirs and their destruction are of great significance to the study of the characteristics and mechanism of deep hydrocarbon accumulations.This study focuses on the tectonic evolution of Mianyang-Changning Intracratonic Sag(MY-CN IS)and TJS PU.The Cambrian-Ordovician tectonic movement was significant in the NSWSCD,as indicated by the formation of the TJS PU.From tension to compression tectonic-sedimentary evolution,the TJS PU is an important node in the Early Paleozoic.The analysis of deep marine hydrocarbon geological characteristics in the NSWSCD shows that the Lower Cambrian Maidiping-Qiongzhusi formations are the best source rock.Reservoir bitumen in the Dengying Fm is used as a template to identify organic geochemical parameters of paleooil reservoir systems with different layers and different phases in the TJS PU area.Organic carbon isotope and biomarker compounds indicate that the main source of paleo oil reservoirs is the Lower Cambrian organicrich black shale,and the concept of“Tianjingshan Paleouplift paleoreservoir system”is finally established.According to the corresponding classification of sourcereservoir-caprock combination,oil source identification and tectonic evolution period study,it is once again confirmed that the deep marine oil and gas multiphase and diverse accumulation process under the complex structural background of the northern segment of the Western Sichuan Depression can be divided into“primary oil reservoir-primary gas reservoir”and“secondary oil reservoir-primary gas reservoir”types.