Abstract The volcanogenic tuff layers are widely developed in the organic-rich shale systems of unconventional oil and gas resources. The tuffaceous shale composed of terrigenous detrital components and water-laid tuff is characterized by the complex porous structure related to tuff and organic matter (OM), which hampers the prediction of surface wettability and in-situ oil movability for the tight reservoir. Moreover, the roles of two components in effecting the spontaneous imbibition (SI) behavior remain poorly known. In this current work samples were collected from the Upper Triassic Yanchang Formation of Ordos Basin to set up a novel SI scaling model of tuffaceous shales with the consideration of tuff-hosted and OM-covered pores. The contact angle experiments were conducted to test the wettability of the samples, and spontaneous imbibition (SI) experiments were performed to study the tight oil movability in tuffaceous reservoirs with n-decane. The contents of residual hydrocarbons in the tuffaceous shale were calculated via the Rock-Eval method. Incorporating the above parameters, we proposed a modified scaling model of the SI data considering two specific factors for the tuffaceous shale samples: Factor I of the tuff-hosted pores indicated by the tuff components and Factor II of the organic matter (OM)-covered pores indicated by the residual hydrocarbon contents. The results show that all the tested tuffaceous shale samples are oil-wetting. The imbibition slopes increase with the development degree of the tuff-hosted and OM-covered pores. Notably, zeolite-type minerals, the primary porous components in tuffaceous tight oil reservoirs, contribute the most to the tuff-hosted pores. The long-term interactions between the zeolite mineral surface and residual hydrocarbons notably enhanced the oil wettability of tuffaceous reservoirs and led to a high in-situ oil movability.

中文翻译：

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凝灰质页岩自吸行为的新比例模型：来自凝灰岩承载和有机质覆盖的孔隙系统的约束

摘要 非常规油气资源丰富的页岩系统中广泛发育火山凝灰岩层。由陆源碎屑和水凝凝灰岩组成的凝灰质页岩具有与凝灰岩和有机质（OM）相关的复杂多孔结构，阻碍了致密储层表面润湿性和原位油流动性的预测。此外，两个组件在影响自发渗吸 (SI) 行为中的作用仍然知之甚少。在目前的工作中，从鄂尔多斯盆地上三叠统延长组采集样品，建立了一种新的凝灰岩页岩 SI 比例模型，同时考虑了凝灰岩赋存和 OM 覆盖的孔隙。进行接触角实验以测试样品的润湿性，进行了自吸（SI）实验以研究凝灰质油藏中正癸烷致密油的可动性。凝灰质页岩残余烃含量采用 Rock-Eval 方法计算。结合上述参数，考虑到凝灰质页岩样品的两个特定因素，我们提出了 SI 数据的修正比例模型：凝灰岩组分指示的凝灰岩赋存孔隙的因子 I 和有机质 (OM) 覆盖的因子 II残余烃含量表示孔隙。结果表明，所有测试的凝灰质页岩样品都是油润湿的。渗吸斜率随着凝灰岩赋存和OM 覆盖孔隙的发育程度而增加。值得注意的是，沸石型矿物是凝灰质致密油藏中的主要多孔成分，对凝灰岩承载的孔隙贡献最大。沸石矿物表面与残余烃之间的长期相互作用显着增强了凝灰岩储层的油润湿性，并导致较高的原位油可动性。