S2_v1_0_20210422_11.xls from Full-scale pore size distribution features of uranium-bearing sandstone in the northwest of Xinjiang, China

As an important nuclear fuel, uranium in sandstone uranium deposits is mainly extracted by in situ leaching. The porosity of sandstone is one of the important indexes determining in situ leaching efficiency. Moreover, the microscopic pore size distribution (PSD) of the uranium-bearing layer has an important effect on porosity. It is necessary to feature the pore structure by various techniques because of the different pore types and sizes in the uranium layer. In this paper, combined with nitrogen gas adsorption, nuclear magnetic resonance techniques and scanning electron microscopy, the full-scale PSD features of uranium-bearing sandstone in the northwest of Xinjiang are effectively characterized. The results show that pores structure of uranium-bearing sandstone include dissolution pores (d ≤ 50 nm), intergranular pores (50 nm < d ≤ 200 µm) and microfractures. Intergranular pores of 60 nm and 1 µm are the significant contributors to pore volume. The effects of the pore volume of two-pore types (dissolution pores and intergranular pores) on the porosity of uranium-bearing sandstone are analysed. The results show that intergranular pores have the greater influence on the porosity and are positively correlated to the porosity. Dissolution pores have little effect on the porosity, but it is one of the key factors for improving uranium recovery. Moreover, the greater the difference of PSD between sandstones, the stronger the interlayer heterogeneity of uranium-bearing sandstone. This kind of interlayer heterogeneity leads to the change of permeability in the horizontal direction of strata. It provides a basis for a reasonable setting of well type and well spacing parameters.

作为重要的核燃料，砂岩型铀矿床中的铀主要通过原地浸出法（in situ leaching）进行开采。砂岩孔隙度是决定原地浸出效率的关键指标之一。此外，含铀层的微观孔径分布（pore size distribution, PSD）对孔隙度具有显著影响。由于含铀层内孔隙类型与尺寸各异，需通过多种技术手段对其孔隙结构进行表征。本文结合氮气吸附法、核磁共振（nuclear magnetic resonance）技术与扫描电子显微镜（scanning electron microscopy），有效表征了新疆西北部含铀砂岩的全尺度孔径分布特征。研究结果表明，含铀砂岩的孔隙结构可分为溶蚀孔隙（d ≤ 50 nm）、粒间孔隙（50 nm < d ≤ 200 µm）与微裂缝三类。孔径为60 nm与1 µm的粒间孔隙对孔隙体积的贡献最为显著。本文分析了两类孔隙（溶蚀孔隙与粒间孔隙）的孔隙体积对含铀砂岩孔隙度的影响。结果显示，粒间孔隙对孔隙度的影响更大，且与孔隙度呈正相关关系；溶蚀孔隙对孔隙度的影响较小，但却是提升铀回收率的关键因素之一。此外，不同砂岩间的孔径分布差异越大，含铀砂岩的层间非均质性越强。这类层间非均质性会导致地层水平方向的渗透率发生变化，该研究可为合理确定井型与井距参数提供依据。