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下扬子地区二叠系发育一套海陆过渡相泥页岩,是目前页岩气勘探的重点层位之一。针对其微观孔隙体系及影响因素研究较少的现状,对皖南地区野外露头和岩心样品开展扫描电镜、氩离子抛光扫描电镜、压汞及氮气吸附实验分析。结果表明:二叠系页岩主要组分为有机质、石英、伊利石、方解石和黄铁矿,其中黄铁矿多呈草莓体形态与有机质共存,有机质则呈填隙状、薄膜状、条带状和壳体状分布在页岩中。二叠系页岩基本孔隙类型为无机矿物孔(晶间孔、粒间边缘孔、粒内孔和黏土矿物层间孔)、有机孔和微裂缝,其中有机孔和微裂缝是优势孔隙类型。不同有机质颗粒中孔隙发育情况差异很大,可能与有机质类型及显微组成有关;在构造应力作用下,有机质与黏土矿物充分混合产生縻棱化而形成与有机质相关的晶间孔和微裂缝。压汞法测试结果显示以微孔和过渡孔为主的页岩具有较高的孔隙度,孔隙连通性好、退汞效率高;而以大孔为主的页岩具有较低的孔隙度,孔隙连通性差、退汞效率低。中大孔的体积百分比随着石英含量的增加而增加;微孔和过渡孔的体积百分比随可溶有机质增加(S1)呈现降低的趋势;縻棱化有机质是页岩比表面积的主要贡献者;黏土矿物含量的增加可能会抑制页岩微孔隙的发育和比表面积的大小,与黏土矿物主要由伊利石和绿泥石组成有关。
The Lower Yangtze region Permian developed a set of marine-mudstone shale, which is one of the key layers of shale gas exploration. In view of the fact that there is little research on its microscopic pore system and its influencing factors, the field outcrops and core samples from Southern Anhui Province were analyzed by scanning electron microscopy, argon plasma scanning electron microscopy, mercury intrusion and nitrogen adsorption. The results show that the main components of Permian shale are organic matter, quartz, illite, calcite and pyrite. Pyrite mostly has the coexistence of strawberry body and organic matter, while the organic matter presents interstitial, thin film, Shaped and shell-like distribution in the shale. The basic types of pores in the Permian shales are inorganic mineral pores (intergranular pores, intergranular edge pores, intragranular pores and clay mineral interlayer pores), organic pores and micro-cracks, of which organic pores and micro-cracks are dominant pore types. The pore development of different organic matter particles is quite different, which may be related to the type and composition of organic matter. Under the tectonic stress, the organic matter and clay minerals are fully mixed to produce ridges and edges to form organic intergranular pores and micro-cracks. The results of mercury intrusion porosimetry show that the shale mainly composed of micropores and transitional pores has high porosity, good pore connectivity and high mercury removal efficiency, while the macropore-dominated shale has lower porosity, Pore connectivity is poor, mercury removal efficiency is low. The volume fraction of mesopore increases with the increase of quartz content. The volume fraction of micropores and transition pores decreases with the increase of soluble organic matter (S1). 縻 Prion organic matter is the main contributor to the specific surface area of shale. The increase in clay mineral content may inhibit the development of microporosity and the specific surface area of shale, which is related to the composition of clay minerals mainly composed of illite and chlorite.