Modelling diagenetic reactions and secondary porosity generation in sandstones controlled by the advection of low‐molecular‐weight organic acids,Basin Research

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Modelling diagenetic reactions and secondary porosity generation in sandstones controlled by the advection of low‐molecular‐weight organic acids
Basin Research ( IF 2.8 ) Pub Date : 2024-03-20 , DOI: 10.1111/bre.12860
Huan Li ₁ , Jay R. Black ₁ , Yiwei Hao ₂ , Peng Hao ₃ , Achyut Mishra ₁ , Ralf R. Haese ₁

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Higher secondary porosity was observed in the centre of a sandstone unit in the Eocene Shahejie Formation fan delta front sandstones from the Bozhong Depression, Bohai Bay Basin. This differs from past studies showing secondary porosity mainly in the marginal parts of sandstones adjacent to shales. This study utilized reactive transport models involving low‐molecular‐weight organic acids (LMWOA) to discuss potential processes resulting in the contrary distribution of secondary porosity. An interface model simulating LMWOA diffusion from adjacent shales to the sandstone resulted in secondary porosity in sandstones adjacent to shales. In contrast, an advection model simulating advective transport of LMWOA parallel to the sandstone bedding successfully generated higher secondary porosity in the central part. The central part of the sandstone exhibited better grain sorting (greater depositional porosity) and significantly less early carbonate cements compared to the marginal sandstone parts. Consequently, the central part had greater porosity prior to the dissolution through LMWOA. The initially higher porosity in the central part allowed for a higher advective flux of LMWOA‐rich water and associated lower pH, resulting in decreased oligoclase saturation, higher oligoclase dissolution rates and ultimately higher secondary porosity. This study indicates that grain sorting during sediment deposition, early carbonate cementation, LMWOA production in adjacent shales, and advection processes collectively control the diagenetic reactions and the distribution of secondary porosity in sandstones.

中文翻译：

模拟低分子量有机酸平流控制的砂岩成岩反应和次生孔隙生成

渤海湾盆地渤中坳陷始新统沙河街组扇三角洲前缘砂岩的砂岩单元中心存在较高的次生孔隙度。这与过去的研究不同，过去的研究表明次生孔隙主要出现在与页岩相邻的砂岩边缘部分。本研究利用涉及低分子量有机酸（LMWOA）的反应输运模型来讨论导致次生孔隙度相反分布的潜在过程。模拟 LMWOA 从邻近页岩扩散到砂岩的界面模型导致邻近页岩的砂岩中出现次生孔隙。相比之下，模拟平行于砂岩层理的LMWOA平流输送的平流模型成功地在中心部分产生了较高的次生孔隙度。与边缘砂岩部分相比，砂岩的中心部分表现出更好的颗粒排序（更大的沉积孔隙度）和明显更少的早期碳酸盐胶结物。因此，在通过 LMWOA 溶解之前，中心部分具有更大的孔隙率。中心部分最初较高的孔隙度允许富含LMWOA的水具有较高的平流通量和相关的较低pH值，导致寡长石饱和度降低、寡长石溶解速率较高以及最终较高的次生孔隙度。这项研究表明，沉积物沉积过程中的颗粒分选、早期碳酸盐胶结作用、邻近页岩中LMWOA的产生以及平流过程共同控制了砂岩中的成岩反应和次生孔隙度的分布。

更新日期：2024-03-20

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