Natural CO₂ was discovered in Nantun Formation in the northern Wuerxun Sag. A better understanding of the main controlling factors of CO₂ distribution in this area is necessary. In this paper, a 3D geological model of Nantun Formation is established based on well-logging and seismic interpretation results, constrained by dual facies conditions. The 3D geological model includes structural, lithologic, physical property information and the spatial distribution of magmatic intrusions. This comprehensive model can display the stratigraphic framework, fault distribution and spatial characteristics of sandstone reservoirs and physical properties. Modelling results show that the sandstone reservoirs of Nantun Formation are of low permeability and low porosity, with N1 Member characterized by a higher sandstone content than N2 Member. The CO₂ is of inorganic origin degassed from intruded magma, and most CO₂ is stored at structural traps in the west of the Surennuoer strike-slip fault zone. There is a spatial relationship among the CO₂ distribution, Surennuoer strike-slip fault and magmatic intrusion bodies, indicating a genetic link. Therefore, we propose that the strike-slip fault and magmatic bodies are the main controlling factors of CO₂ distribution and that reservoir quality plays a secondary role. The CO₂ accumulation model is established showing the CO₂ degassed from magmatic intrusion body, migrated upward along deep faults and was stored in shallower structure traps. Generally, this modelling method is helpful to understand the controlling factors of CO₂ accumulation, which can be widely applicable in other areas with natural CO₂ occurrence.

乌尔逊凹陷北部南屯组发现天然CO ₂。更好地了解 CO ₂的主要控制因素在这方面的分布是必要的。本文基于测井和地震解释结果，在双重相条件约束下，建立了南屯组三维地质模型。3D地质模型包括构造、岩性、物性信息和岩浆侵入体的空间分布。该综合模型可以显示砂岩储层的地层格架、断层分布和空间特征及物性。模拟结果表明，南屯组砂岩储层渗透率低、孔隙度低，N1段砂岩含量高于N2段。CO ₂是从侵入岩浆中脱气的无机来源，大多数 CO ₂储藏于苏仁诺尔走滑断裂带西部的构造圈闭。CO ₂分布与苏伦诺尔走滑断层与岩浆侵入体之间存在空间关系，具有成因联系。因此，我们认为走滑断裂和岩浆体是CO ₂分布的主要控制因素，储层质量起次要作用。建立的CO ₂聚集模型显示了从岩浆侵入体中脱气的CO ₂沿深部断层向上运移并储存在较浅的构造圈闭中。一般来说，这种建模方法有助于了解 CO ₂的控制因素可广泛适用于其他天然CO ₂产区。