海陆过渡相页岩气储层孔隙特征及主控因素分析——以鄂尔多斯盆地上古生界为例

Characteristics and main controlling factors of shale gas reservoirs in transitional facies:A case study of Upper Paleozoic in Ordos Basin

泥页岩中的微孔隙和微裂缝是页岩气的主要储集空间和渗流通道,孔隙和裂缝的发育程度关系到泥页岩中含气量的多少。为了更好地研究鄂尔多斯盆地上古生界泥页岩储层,将储集空间类型分为纳米级孔隙、微米级孔隙和微裂缝。运用扫描电镜、氩离子抛光与核磁共振测试技术,对纳米级孔隙、微米级孔隙和微裂缝发育特征分别进行定量表征,并结合有机碳含量、有机质显微组分及成熟度、X射线全岩衍射和黏土矿物等测试数据,对不同孔隙发育特征的主控因素进行分析。分析认为：（1）纳米级孔隙平均孔径分布在17.13~67.65 nm,平均面孔率分布于5.75%~9.37%;微米级孔隙孔径平均值分布范围3.17~5.61μm,平均面孔率分布范围10.2%~19.32%;微裂缝百分数在0.36%~0.72%。（2）有机碳含量、有机质成熟度和伊蒙混层含量对有机质纳米级孔隙发育有促进作用,方解石含量对其则具有抑制作用;石英含量和伊利石含量对泥页岩微米级孔隙发育具促进作用,碳酸盐含量和埋藏深度对泥页岩微米级孔隙具有抑制作用;石英含量、有机质成熟度和总有机碳含量对微裂缝发育有促进作用,碳酸盐含量对其则具有抑制作用。

Micro pores and micro fractures in shales are the main reservoir space and drainage channels for shale gas and the pore / fracture growth degree is related to gas content. To learn more about shale reservoirs of the Upper Paleozoic in the Ordos Basin,we classified the reservoir space into nanometer pores,micron pores and tiny cracks. Technologies such as scanning electron microscopy,argon ion polishing and nuclear magnetic resonance were applied to quantitatively characterize the development of different reservoir space. Combined with testing data such as TOC,organic composition and maturity,X-ray diffraction of whole rock and clay minerals,the controlling factors for different pore characteristics were analyzed. Two conclusions were made as follows.（ 1） The diameter of nanometer pores ranged from 17. 13 nm to 67. 65 nm on average,and the average plane porosity ranged from 5. 75% to 9. 37%. For micron pores,the average diameter was 3. 17- 5. 61 μm,and the average plane porosity was 10. 2%- 19. 32%. Tiny cracks accounted for 0. 36%- 0. 72%.（ 2） TOC,organic maturity and I / S content promoted the generation of nanometer pores,while calcite content inhibited it. For micron pores,quartz and illite contents were positively correlated with their development,while carbonate content and burial depth were negatively correlated. Quartz content,organic maturity and TOC promoted the development of tiny cracks,while carbonate content inhibited it.