横山地区山2段物源沉积体系及其地质意义

Provenance Sedimentary System of the Shan2 Member in Hengshan and Its Geological Significance

针对鄂尔多斯盆地东南部横山地区山西组山2段沉积体系复杂及钻井含气性多变等问题,采用重矿物组合法、测井法、压汞法等多种方法,系统开展物源、沉积相、储层特征研究,揭示其地质意义。结果表明:山2段西部为辫状河三角洲前缘沉积,东部为曲流河三角洲前缘沉积体系侧翼分支河道沉积;西部砂岩以中—粗粒岩屑石英砂岩为主,孔隙类型多样,物性条件好;东部砂岩以中—细粒石英砂岩为主,仅发育残余粒间孔,物性整体较差;气藏富集与2种沉积体系控制下沉积储层发育特征密切相关,西部主河道及河道心滩广泛发育,天然气呈大面积富集成藏,东部分支河道局部河道砂体发育区有利于天然气藏富集。建议今后针对2种沉积体系采取不同的勘探部署方案。此次研究明确了横山地区2种沉积体系的成因与发育特征,进一步厘清了其控制下的储层特征及对天然气富集成藏的影响,研究成果对类似地区油气成藏的认识与勘探具有重要的借鉴意义。

In view of the complex sedimentary systems and the variable drilling gas content in the Shanxi Formation Shan2 Member of Hengshan in the southeastern Ordos Basin. Heavy mineral combination, logging, mercury intrusion and other means are used to systematically analyze the provenance, sedimentary facies and reservoir properties and reveal their geological significance. Result indicates that the western and eastern parts of the Shan2 Member are considered as braided river delta front deposition and lateral branching channel of meandering delta front deposition. The western sandstone is dominated by medium-coarse lithic quartz sandstone with diverse pore types and favorable physical reservoir properties. The eastern sandstone is dominated by medium-fine grained quartz sandstone with on- ly residual intergranular pores relatively poor physical reservoir properties. The gas enrichment is greatly dependent on the sedimentary reservoir properties under two sedimentary systems. Drainage line and channel bar are widely de- veloped in the west and natural gas is enriched in large area. The branch channel with well-developed channel sandbodies are favorable to natural gas enrichment. It is recommended to adopt different exploration and deployment programs for the two sedimentary systems in the future. This research clarifies the genesis and development of the two sedimentary systems in Hengshan. In addition, it also further determines the reservoir properties under the con- trol of the two sedimentary systems and its effect on natural gas accumulation. This research could provide certain reference for the understanding and exploration of hydrocarbon accumulation in similar areas.