下扬子地区二叠系海陆过渡相页岩孔隙体系特征

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。

Pore system characteristics of Permian transitional shale reservoirin the Lower Yangtze region,China

Permian shale,a set of transitional shale reservoir,is considered as an important shale gas exploration target in the Lower Yangtze region.For the reason of few researches on pore system characteristic and its controlling factors of the shale gas reservoir,SEM,FE-SEM,low-pressure N2 adsorption and mercury intrusion tests were carried out onthe Permian shales from the outcrop and HC well in the South Anhui.The results show the Permian shale mainly consist of organic matter,quartz,illite,calcite and pyrite,of which pyrite occurs as framboids coexisting with organic matter and the organic matter is distributed in shale in stripped,interstitial,thin film and shell shapes.The basic pore types are inorganic mineral pore(intercrystalline pore,intergranular edge pore,intergranular pore,and interlayer pore in clay minerals),organic pore and microfracture,of which organic pore and microfracture are the dominantpore types.In a shale,organic pores are not developed at all in some organic grains but are well developed in other organic grains,which may be related to the types and maceral compositions of kerogen.Under tectonic stress,shale rocks could develop mylonitization phenomenon exhibiting organic grains well blendwith clay minerals,and produce a mass of microfractures and nanopores between organic matter grains and clay minerals.Mercury intrusion tests show that shalemainly composed of micropore and transition pore has a high porosity,good pore connectivity and high efficiency of mercury withdraw,while the shale mainly dominated bymesopore and macropore has a low porosity,poor pore connectivity and low efficiency of mercury withdraw.The volume percentage of mesopore and marcopore is increasing with the increase of quartz,and that of micropore and transition pore has a decrease tendency along with the increase of soluble organic matter(S₁).Organic matter is the main contributor to specific surface area.However,clay minerals could significantly inhibit the numbers of microscopic pore and specific surface area due to the clay minerals being mainly dominated by illite and chlorite.