Tight oil sandstones in Upper Triassic Yanchang Formation, Ordos Basin, N. China: Reservoir quality destruction in a closed diagenetic system
Tight oil sandstones in Upper Triassic Yanchang Formation, Ordos Basin, N. China: Reservoir quality destruction in a closed diagenetic system
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DOI：
10.1002/gj.3319
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发表时间：
2018-09
影响因子：
1.8
通讯作者：
Mingjie Liu;J. Gluyas;Weibin Wang;Zhen Liu;Junbang Liu;X. Tan;Wei Zeng;Ying Xiong
中科院分区：
文献类型：
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作者：
Mingjie Liu;J. Gluyas;Weibin Wang;Zhen Liu;Junbang Liu;X. Tan;Wei Zeng;Ying Xiong
鄂尔多斯盆地三叠系延长组研究表明，延长组是一个典型的油气储层。结果表明，致密砂岩储层（平均孔隙度为9.83%，平均渗透率为0.96 mD）的成岩作用和质量受封闭成岩系统控制。砂岩中观察到的碳酸盐胶结物来自于邻近泥岩中发生的有机质脱羧作用。这些反应提供了CO 32-，CO 32-与砂岩中颗粒溶解产生的阳离子发生反应。与碳酸盐胶结物有关的成岩地球化学系统的平均规模很小（<6 × 10−2 m3），包括砂岩及其邻近的泥岩。碳酸盐胶结物倾向于集中在边缘砂岩中，这表明CO 32 −进入砂岩的通量限制了碳酸盐沉淀的数量。此外，中心砂岩（距离砂泥岩界面的距离主要在1 m以上）中长石溶解量及其副产物的质量接近平衡，砂岩渗透率随长石溶解孔隙的增加而呈下降趋势。中心砂岩的孔隙空间将只是重新分布，原生粒间孔转化为长石溶孔和粘土矿物微孔。因此，砂岩储层的最佳部位往往是砂岩的中部。特别是，厚度超过2米的砂岩可能是潜在的油气藏，因为它们保留了最好的孔隙度（平均13.6%）和渗透率（平均1.8 mD）。研究结果为世界其他含油气盆地致密油砂体的勘探提供了重要指导。
An investigation of the Triassic Yanchang Formation, Ordos Basin, N. China, revealed that the diagenesis and quality of tight oil sandstone reservoirs (with an average porosity of 9.83% and an average permeability of 0.96 mD) were controlled by a closed diagenetic system. The carbonate cements observed in the sandstone were derived from decarboxylation of organic matter that occurred in the adjacent mudstones. These reactions supplied CO32−, which reacted with cations derived from grain dissolution in the sandstones. The average size of the diagenetic geochemical system with respect to carbonate cements was small (<6 × 10−2 m3), comprising sandstone and its adjacent mudstone(s). The carbonate cements tend to concentrate in the marginal sandstone, which is taken to indicate that the flux of CO32− into the sandstones limited the quantity of carbonate precipitated. In addition, the mass is near balance between the amount of feldspar dissolution and its by‐products in the central sandstone (distance to the sandstone/mudstone interface is mainly more than 1 m), where the permeability of sandstone will present a decreasing trend with the increase of feldspar dissolution pores. The pore space of central sandstone will be just redistributed, with primary intergranular pores converting to feldspar dissolution pores and clay mineral micropores. Thus, the best part of the sandstone reservoirs tends to be the central part of sandstone. In particular, sandstones that are more than 2 m thick could be the potential hydrocarbon reservoirs because they retain the best porosity (average of 13.6%) and permeability (average of 1.8 mD). The results of our study provide an important guide for the exploration of tight oil sandstones in other petroliferous basins over the world.