Reservoir characteristics and multi-stage hydrocarbon accumulation of the Upper Triassic Yanchang Formation in the southwestern Ordos Basin, NW China
Reservoir characteristics and multi-stage hydrocarbon accumulation of the Upper Triassic Yanchang Formation in the southwestern Ordos Basin, NW China
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DOI：
10.1177/0144598719870257
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发表时间：
2020-03
影响因子：
2.7
通讯作者：
Siyi Fu;Zhiwei Liao;A. Chen;Hongde Chen
中科院分区：
文献类型：
--
作者：
Siyi Fu;Zhiwei Liao;A. Chen;Hongde Chen
上三叠统延长组长8、长6段是鄂尔多斯盆地的主要产油层段。最近，在延长组上部（例如，鄂尔多斯盆地西南部长3段也具有良好的油气勘探潜力。但对优质储层成因、油气运移和成藏模式的研究还很不够。本研究综合运用岩石学、矿物学和流体包裹体测试等方法，对储层特征进行评价，重建油气成藏过程中的油气运聚史。结果表明，延长组储层孔隙度低（8 - 14%），渗透率中等（0.5 - 5 mD），非均质性强，储层物性受次生孔隙控制。在本研究中确认了两种类型的溶解。地层下部次生孔隙的形成与有机酸活动有关，而上部的溶解作用主要受与不整合面伴生的大气淡水的影响。延长组经历了早白垩世早期、早白垩世晚期和晚白垩世中期三个阶段的油气充注。在盆地演化的基础上，建立了延长组油气运聚模式。认为油气在早期成藏，在二次运移过程中，油气通过构造裂缝和连续、幕式排烃引起的超压运移到延长组上部，在后期形成潜在的油气藏。
The Chang-8 and Chang-6 members of the Upper Triassic Yanchang Formation (lower part) are regarded as the main oil producing members of the Ordos Basin. Recently, new hydrocarbon discoveries have been made in the upper part of the Yanchang Formation (e.g., Chang-3) in the southwestern Ordos Basin, implying that this interval also has a good potential for hydrocarbon exploration. However, studies on the origin of the high-quality reservoir, hydrocarbon migration, and accumulation patterns remain insufficient. In this study, integrated petrological, mineralogical, and fluid inclusion tests are employed to evaluate reservoir characteristics, and reconstruct the history of hydrocarbon migration and accumulation during oil and gas reservoir formation. The results reveal that the Yanchang Formation is characterized by low porosity (8 − 14%), medium permeability (0.5 − 5 mD), and strong heterogeneity; the reservoir properties are controlled by secondary porosity. Two types of dissolution are recognized in the present study. Secondary pore formation in the lower part of the formation is related to organic acid activity, while dissolution in the upper part is mainly influenced by atmospheric fresh water associated with the unconformity surface. The Yanchang Formation underwent hydrocarbon charging in three phases: the early Early Cretaceous, late Early Cretaceous, and middle Late Cretaceous. A model for hydrocarbon migration and accumulation in the Yanchang reservoirs was established based on the basin evolution. We suggest that hydrocarbon accumulation occurred at the early stage, and that hydrocarbons migrated into the upper part of the Yanchang Formation by way of tectonic fractures and overpressure caused by continuous and episodic hydrocarbon expulsion during secondary migration, forming potential oil reservoirs during the later stage.