纹层状页岩微观储层特征研究 ——以鄂尔多斯盆地西缘乌拉力克组为例【鄂尔多斯盆地乌拉力克组海相页岩气勘探专辑】
- 收稿日期:
2024-04-12
- 网络出版日期:
2024-08-27
摘要: 【目的】对鄂尔多斯盆地西缘中奥陶统乌拉力克组乌三段纹层状页岩的微观储层特征进行研究,深化认识纹层状页岩储层的有效性。【方法】通过岩性物理分离,综合X-射线衍射全岩矿物,扫描电镜和矿物扫描,有机地球化学,二氧化碳、氮气吸附及压汞测试等,对比分析纹层状页岩不同组构之间矿物学、有机地球化学及孔隙结构等特征的差异性。【结果】乌三段纹层状页岩由灰岩纹层、凝灰岩纹层及富硅质层频繁互层形成,灰岩纹层、凝灰岩纹层密度为60~180条/m,有机碳含量远低于富硅质层。纹层状页岩孔缝并存,其中富硅质层主要发育黏土矿物有关的粒间孔、粒内孔,有机孔发育很局限;灰岩纹层主要发育方解石、白云石粒内溶孔;凝灰岩纹层中主要为黄铁矿晶间孔、黏土矿物粒间和粒内孔及白云石粒内溶孔。灰岩纹层、凝灰岩纹层中碳酸盐矿物溶孔的形成与毗邻富硅质层中有机质演化产生的酸性流体溶蚀相关。沿着这些纹层边界近水平裂缝发育丰富,密度为63~130条/m,宽度为0.2~4.9 mm。灰岩纹层、凝灰岩纹层的微孔发育程度较富硅质层低,但大孔发育程度高。灰岩纹层中大孔的孔体积是毗邻富硅质层的2.5~4.3倍,大孔对总孔体积的贡献率约是毗邻富硅质层的1.9~2.1倍;凝灰岩纹层中大孔的孔体积是毗邻富硅质层的1.5~2.3倍。【结论】在纹层状页岩中,富硅质层中有机质生成油气,沿孔缝发生微运移,优先运移至相邻灰岩纹层、凝灰岩纹层中。灰岩和凝灰岩纹层大孔较多,游离气贡献多。乌拉力克组纹层状页岩游离气占比大,与灰岩和凝灰岩纹层发育丰富密切相关。
Microscopic Reservoir Characteristics of Laminated Shales: A Case Study of Wulalike Formation in the Western Margin of the Ordos Basin
- Received Date:
2024-04-12
- Available Online:
2024-08-27
Abstract: [Objective] Microscopic reservoir characteristics of laminated shales in the third member of the Middle Ordovician Wulalike Formation, western margin of the Ordos Basin have been studied to further understand the effectiveness of laminated shale reservoirs.[Methods] This study employs an integrated approach of X-ray diffraction (XRD), scanning electron microscopy (SEM) and mineral mapping, organic geochemical analysis, CO2 and N2 adsorption and mercury injection capillary pressure tests to comparatively analyze differences in mineralogy, organic geochemistry and pore structures between different textures within laminated shales obtained by mechanical separation.[Result] The laminated shales consist of limestone and tuff laminae and silica-rich beds. Limestone and tuff laminae with density of 60~180/m have lower contents of organic carbon than silica-rich beds. Laminated shales contain both pore and fractures. In silica-rich beds, clay minerals-related interparticle and intraparticle pores are abundant with rare organic pores. Calcite and dolomite intraparticle dissolved pores are dominant pore type in limestone laminae. Tuff laminae contain pyrite intercrystalline pores, clay-related interparticle and intraparticle pores, and dolomite intraparticle dissolved pores. Dissolved pores of carbonate minerals in limestone and tuff laminae are related to dissolution of acid fluids generated by organic matter thermal evolution in silica-rich beds. Near-horizontal fractures develop along boundaries between limestone and tuff laminae and silica-rich beds. Density of the near-horizontal fracture is 63~130 /m, and their width is 0.2~4.9 mm. Limestone and tuff laminae have less abundant micro-pores but more abundant macro-pores than silica-rich beds. The volume of macro-pores in limestone laminae is 2.5~4.3 times, and the contribution of macro-pores to total pore volume is 1.9~2.1 times as much as adjacent silica-rich beds. The volume of macro-pores in tuff laminae is 1.5-2.3 times as much as adjacent silica-rich beds. [Conclusion] In laminated shale reservoirs, oil and gas generated in silica-rich beds migrated along pores and fractures, and preferentially enriched in adjacent limestone and tuff laminae. Limestone and tuff laminae contain more abundant macropores and more free gas than silica-rich beds. The Wulalike Formation laminated shale reservoirs have high proportion of free gas, which are related to limestone and tuff laminae.
黄正良, 曹斌风, 刘洋, 罗晓容, 闫伟, 马占荣, 程明, 俞雨溪, 于洲. 纹层状页岩微观储层特征研究 ——以鄂尔多斯盆地西缘乌拉力克组为例【鄂尔多斯盆地乌拉力克组海相页岩气勘探专辑】[J]. 沉积学报. doi: 10.14027/j.issn.1000-0550.2024.085
Microscopic Reservoir Characteristics of Laminated Shales: A Case Study of Wulalike Formation in the Western Margin of the Ordos Basin[J]. Acta Sedimentologica Sinica. doi: 10.14027/j.issn.1000-0550.2024.085
Citation: |
Microscopic Reservoir Characteristics of Laminated Shales: A Case Study of Wulalike Formation in the Western Margin of the Ordos Basin[J]. Acta Sedimentologica Sinica. doi: 10.14027/j.issn.1000-0550.2024.085
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