Investigation on Pore Structures of Yanchang Formation Shale Using Micro X-ray Microscopy
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摘要: 页岩孔隙结构是决定储层储集与运移能力的关键,对完善我国陆相页岩气产能评估方法和压裂技术具有重要意义。本文选取鄂尔多斯盆地陆相延长组7段页岩,利用氩离子抛光-扫描电镜和微米X射线显微镜方法研究其孔隙结构特征与三维空间分布特征。扫描电镜结果表明,延长7段页岩中主要发育粒间孔(300~600nm)和微裂缝,是页岩气的主要储集空间。微裂缝多由黏土矿物沉淀形成,以平直状为主,易引发井壁坍塌等严重问题。有机孔发育较少,一般与有机黏土矿物共存,绝大部分有机质呈致密状。微米X射线显微镜测试进一步表明,长7段页岩在三维空间具有微米级纹层结构,其中有机质纹层厚10~20μm,揭示了延长组7段页岩层具有较强塑性,不利于水平压裂。该研究成果将为构建延长7段页岩气渗流模型、改进压裂技术提供重要数据支持。Abstract:
BACKGROUNDShale pore structure is the key to determine reservoir storage and migration capacity. It is of great significance for improving the productivity assessment of continental shale gas in China, and fracturing technology. OBJECTIVESTo investigate the pore structure and three dimensional distribution mode of the seventh member of Yanchang Formation shale and its controlling factors. METHODSAr-ion milling SEM and synchrotron micro X-ray microscopy were used to characterize the pore structures. RESULTSThe SEM results indicated that the interparticle pores (300-600nm) and micro-fractures were the main reservoir space of the seventh member of Yanchang Formation shale gas. Most of the micro-fractures were formed by the precipitation of clay minerals and presented as a flat shape, which likely caused collapse of borehole walls. Organic pores were less developed and mainly associated with organic clay minerals. The micro X-ray microscopy showed that the seventh member of Yanchang Formation shale had laminated structures at micro-scale with organic matter laminations of 10-20μm in thickness. The results indicated that the seventh member shale had strong plasticity, which was against horizontal fracturing. CONCLUSIONSThe results can provide significant data support for developing a percolation model and improving fracturing technology of shale gas. -
表 1 遥科1井延长7段页岩孔隙类型及其特征
Table 1. Pore types and characteristics of C7 Member shale from Yaoke-1 Well
孔隙类型 孔隙示意图 孔隙形态 孔径范围 分布特征 无机孔 粒间孔 三角形或狭缝形 30nm~1μm 发育在脆性矿物周缘及粉砂级黏土矿物碎屑之间,普遍发育,连通性较好 黏土矿物层间孔 平直狭缝状 长1~3μm,孔宽数十纳米 分布于黏土矿物层间,不甚发育 溶蚀孔 凹坑状 50~300nm 多见于石英、长石等矿物内部,彼此孤立 晶内孔、生物孔、晶间孔等 圆形、椭圆形或方形等 百纳米~数十微米 与矿物相关,如生物遗体被黄铁矿充填,彼此孤立; 或形成于矿物晶间 有机质与有机孔 致密有机质 连续且不规则状 N/A 有机质最主要的赋存方式,即粒间孔被有机质完全充填,且有机质内部无孔隙发育 集合体形式 N/A 与黄铁矿呈现出包裹关系,与微晶之间残余少许孔缝 有机质分散状,发育锯齿状孔隙 数百纳米至数微米 致密有机质与基质矿物接触面之间发育孔隙,较为普遍 有机孔 狭缝状、三角状 50~300nm 受控于黏土矿物层间孔结构,有机孔最主要的存在形式 凹坑状或椭圆状 30~200nm 受生烃作用控制,发育较少 微裂缝 狭缝状 长数微米,宽几百纳米 发育于脆性矿物的边缘或机械不稳定部位,较平直,延伸长 注:N/A表示not applicable(不适用)。 -
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