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作者简介:

滕建彬(1980—),男,山东青州人,高级工程师,在读博士研究生,从事油气储层综合评价研究。联系电话:15965292798,E-mail:tengjianbin.slyt@sinopec.com。

中图分类号:TE122.2+3

文献标识码:A

文章编号:1009-9603(2019)01-0080-08

DOI:10.13673/j.cnki.cn37-1359/te.2019.01.009

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目录contents

    摘要

    借助岩石学和地球化学分析手段,对济阳坳陷沙四段上亚段和沙三段下亚段页岩油储层进行原油赋存状态和物质组分分析。荧光特征分析结果表明:束缚型和游离型沥青分别选择性赋存于泥质纹层、碳酸盐纹层和裂缝内,泥质纹层作为生油的母质仓储,易于富集炭质沥青和沥青质沥青;碳酸盐纹层相对于泥质纹层具有更优越的储集空间,易于富集胶质沥青和油质沥青,更易流动的油质沥青则汇集到裂缝内。研究发现,方解石脉本质上是一种接近于完全充填的裂缝表现形式,总结出4个亮晶方解石脉体的识别标志,其中轴愈合线附近的方解石晶间孔和未愈合缝可以作为油质沥青的运移通道。页岩油储集空间的发育主要受控于岩石结构与构造及物质组分,矿物组分差异和有机质热演化是页岩油储集空间和含油性的2个主要影响因素。受此影响,泥页岩储集性表现为:①纹层状泥页岩储层具有高孔隙度;②碳酸盐含量高的泥页岩储层具有高孔隙度;③高有机质热演化程度的泥页岩储层具有高孔隙度。

    Abstract

    By means of petrology and geochemical analysis,the oil-bearing properties and material components of shale oil reservoirs in Upper Es 4 and Lower Es 3 Members in Jiyang Depression were analyzed. Fluorescence characteristics analysis results show that the resident and free asphaltene selectively occur in argillaceous laminates,gray carbonate laminates and fractures. Argillaceous lamina,as the parent material storage for oil-generated,is easy to enrich carbon asphaltene and bitu-miniferous asphaltene. Carbonate laminates have superior storage space compared with argillaceous laminates,which are suitable to accumulate gum asphaltene and crude oil asphaltene,and crude oil asphaltene can easily flow into microcracks. It is found that the calcite vein is essentially a kind of fully filled fracture. Four identification marks of recognition calcite vein are summarized,among which the calcite intercrystalline pore and the non healing crack near the shaft healing line can be regarded as the percolation path for the oil asphaltene. The spatial development and oil content of shale oil res- ervoir are mainly controlled by the rock texture,structure types and material components. Mineral composition differences and thermal evolution of organic matter are two main factors that influence shale oil storage space and oil content. As a re- sult,the storage of shale oil has following characteristics:shale with argillaceous laminates and gray carbonate laminates has high porosity,shale with high carbonate content has high porosity,and the higher thermal evolution degree of organic matter corresponds to the higher porosity.

  • 研究泥页岩储层物质组分与含油性的关系对准确评价页岩油勘探潜力具有重要的理论和现实意义[1-7]。济阳坳陷页岩油储层的物质组分主要为碳酸盐矿物、陆源碎屑矿物和泥质,少量黄铁矿、菱铁矿、有机质和生物碎屑等[8-9]。笔者研究发现,在页岩油的形成和储集过程中,不同类型沥青质在不同物质组分的泥页岩中表现出差异富集的特征。受此启发,利用荧光薄片检测和 X 衍射全岩矿物分析等微观分析技术,针对罗 69、利页 1、牛页 1 和樊页 1 井开展岩心物质组分和含油性关系研究,解析页岩油储层中的原油赋存状态,探讨物质组分对含油性的控制规律,以期为有利页岩油储层优选提供依据。

  • 1 地质背景

  • 在古生界基岩基底上,济阳坳陷自南向北发育东营、惠民、沾化和车镇 4 个凹陷。始新世早期,湖盆进入断拗阶段,构造运动相对稳定,湖盆持续下沉,在东营凹陷北断南超、北深南浅的箕状构造上,发育咸水-半咸水环境的沙四段上亚段以及淡水环境的沙三段下亚段和沙三段中亚段泥页岩,成为东营凹陷新近系目前所发现油气的烃源岩主体。东营凹陷沙四段上亚段岩性以灰色和深灰色泥页岩为主,凹陷中央沉积互层状泥质灰岩和灰质泥岩[10-13]。2007 年以来,为寻找油气资源接替阵地,分别在济阳坳陷的沾化凹陷钻探了罗69井,东营凹陷钻探了利页 1、牛页 1 和樊页 1 井,开启了济阳坳陷页岩油气勘探的新篇章。

  • 2 页岩油荧光特征与赋存状态

  • 2.1 荧光特征与含油性

  • 孙焕泉等针对页岩油储层的无机和有机储集空间开展了深入研究,但未观察到真实的页岩油赋存状态[14-17]。笔者利用荧光薄片分析原油在泥页岩中的赋存层系和分布规律,利用扫描电镜观察孔隙中的原油赋存状态,探讨有利于原油赋存的储集空间特点。

  • 荧光薄片观察到赋存于泥页岩中的烃类在紫外光激发下会发出不同的荧光,按照岩石荧光薄片鉴定标准[18],依据沥青组分与荧光颜色的关系、发光亮度和颜色确定烃类类型,将沥青组分分为油质沥青、胶质沥青、沥青质沥青和炭质沥青4类。

  • 根据研究区沥青组分与荧光的对应关系和4口探井泥页岩样品的荧光分析结果,将研究区泥页岩含油性划分为束缚型沥青和游离型沥青2大类型。

  • 2.1.1 束缚型沥青

  • 束缚型沥青包括发光极暗的炭质沥青和以发褐色荧光为主的沥青质沥青,还包括部分以橙色荧光为主的胶质沥青。垂直于岩石层理面,束缚型沥青呈现大面积浸染、顺层分散和局部集中 3 种分布形式(图1)。

  • 大面积浸染   沥青组分赋存于各类矿物的孔隙中,大面积浸染是罗69、利页1、牛页1和樊页1井沥青组分的主要分布形式。由于各类储集空间的发育受矿物组分粒径的影响,浸染于灰质、泥灰质、灰泥质和泥质晶间孔中的沥青组分发光颜色有所差异(图1a,1b)。裂缝与泥质基质孔隙在孔径上存在数量级上的差别,其含油性最好,油质沥青最为富集,大多发黄绿-绿蓝色荧光,基质呈褐色荧光不发光(图1c,1d)。方解石晶间孔所含烃类来自泥质纹层中干酪根的生烃充注,多倾向于胶质沥青和油质沥青,以淡黄橙色荧光为主(图1e)。泥质纹层主要富集炭质沥青和沥青质沥青,具有不发光-褐色荧光的特点,偶见淡绿蓝色荧光,普遍较暗,表明沥青含量较低。大面积浸染的沥青一般分布于泥质隐晶灰岩或隐晶灰质泥岩中,部分在块状泥岩中也常见。主要原因是这几类岩性原岩中沉积的有机质较均匀,矿物颗粒粒径相对均一,基质孔孔径大小分布较为集中,有机质呈薄层状、条带状均匀分布。

  • 图1 济阳坳陷罗69等4口取心井页岩油储层中的束缚型沥青和游离型沥青荧光特征

  • Fig.1 Fluorescence characteristics of resident and free asphaltene in shale oil formations of Well Luo69 and other 3 wells in Jiyang Depression

  • 顺层分散   束缚型沥青顺层分散于研究区泥页岩储层中,其含量一般小于 5%,以无结构藻类为主,属于Ⅰ型干酪根。荧光较强,以淡绿蓝色荧光为主(图1f),此类束缚型沥青主要顺层分布于纹层状—层状结构泥页岩中。

  • 局部集中   束缚型沥青局部富集,呈纹层状、条带状、长线状顺层分布,发中等褐色-橙色荧光 (图1g,1h),为胶质沥青发光特征。束缚型沥青以无结构藻类为主,属于Ⅰ型干酪根,受沉积影响主要分散于块状泥页岩中。

  • 研究区4口探井页岩油储层中的束缚型沥青的分布形式表现出显著的差异性(图1):罗 69井束缚型沥青的分布形式以大面积浸染和顺层分散为主。牛页 1 井束缚型沥青的分布形式主要为局部集中,少量为大面积浸染和顺层分散。樊页1井束缚型沥青的分布形式主要为大面积浸染和顺层分散,少量局部集中分布于碳酸盐纹层中。利页1井束缚型沥青主要大面积浸染于泥质纹层中。

  • 2.1.2 游离型沥青

  • 游离型沥青主要赋存于 2 类裂缝之中,一类是半充填-不完全充填型裂缝(图1c,1d),另一类是未充填型裂缝(图1g,1h)。

  • 如果泥页岩的含油性较好,未充填型裂缝中的沥青发中等亮绿色荧光和黄色荧光,属于游离的油质沥青。在 4 口探井泥页岩中均常见此类裂缝,其对油气储集和渗流均具有重要意义。半充填-不完全充填型裂缝中的充填物主要为方解石,少量白云石和黄铁矿,偶见重晶石及磷灰石等矿物。这种半充填-不完全充填型裂缝发中亮绿黄色、黄绿色荧光,有机质含量高,为油质沥青发光。脉体方解石一般发育微-中晶方解石,发中暗-暗黄绿色、绿色荧光,亦为油质沥青发光。纹层状微-显微晶白云石也有发育,但分布较为局限。白云石纹层一般发中亮、中等黄色、绿黄色荧光,有机质含量较高,为油质沥青。鉴于以上对束缚型和游离型沥青的荧光特征分析,泥质纹层可看做生油的母质仓储,碳酸盐纹层则是有利的储集空间,裂缝是主要的穿层和顺层长距离运移通道。有机质主要赋存于泥质纹层中,在热演化生烃过程中,排出的烃类首先浸染有机质本身,然后浸入泥质或与之相邻的碳酸盐纹层以及与之贯通的裂缝中。

  • 2.2 赋存状态

  • 济阳坳陷4口取心井页岩油储层中的游离型沥青以罗 69井和牛页 1井的最为典型,且利用扫描电镜已观察到泥页岩从地下采出卸掉岩压后,储层内部游离烃类溢出浸染黏土和方解石矿物的有力证据。

  • 罗 69 井新鲜页岩油储层样品的孔隙度为 8.3%,水平渗透率为 23.5 mD,发育裂缝,含油饱和度为 43.3%,含水饱和度为 5.7%,碳酸盐含量为 71.3%。方解石晶间孔缝发育,样品断面上原油呈油膜浸染状、液状,附着于页岩的各类矿物中(图2a—2d)。牛页 1 井新鲜页岩油储层样品孔隙度为 12.4%,水平渗透率为0.3 mD,含油饱和度为38.2%,含水饱和度为 34.9%,碳酸盐含量为 53%。由泥质和灰质互层组成,见层间裂缝、方解石晶间孔缝及黏土矿物粒间孔。扫描电镜分析结果显示,页岩的各类矿物晶间孔缝中具有丰富的液态烃类显示(图2e—2h)。原油呈浸染状,使得微晶石英表面表现为油润湿性,少量呈凝块状分布于层间缝中,1 μm 及以上孔径的孔隙和裂缝普遍具有储集原油的能力。

  • 图2 济阳坳陷罗69和牛页1井页岩油赋存状态扫描电镜照片

  • Fig.2 SEM photos of shale oil occurrence in Well Luo69 and Well Niuye1 in Jiyang Depression

  • 3 页岩油储层物质组分对含油性的控制规律

  • 碳酸盐矿物、泥质和陆源碎屑矿物具有不同的沉积排列方式,发育不同的岩石结构和构造类型,形成了纹层状、层状和块状泥页岩。利用岩石学和压汞孔隙分析等方法,对济阳坳陷沙四段上亚段和沙三段下亚段泥页岩储层进行矿物组分和孔径分析。研究区页岩油储集空间发育程度和含油性主要受控于物质组分,可进一步细分为岩石结构与构造及物质组分含量2个控制因素。

  • 3.1 岩石结构与构造

  • 分析研究区纹层状、层状和块状泥页岩储集空间和孔径分布统计结果(表1),发现不同岩相储集空间发育的优劣顺序。纹层状泥页岩由于泥质和灰质纹层的力学性质差异,易于发育裂缝,改善了页岩油储集空间的输导能力,加之方解石晶间孔缝和黏土矿物晶间孔,其孔渗性能优于层状和块状泥页岩储层。因此整体上,泥页岩储层的储集性由优到劣依次为:纹层状泥页岩、层状泥页岩和块状泥页岩。勘探实践中对纹层状和层状泥页岩的识别与界定十分重要,部分研究者将一切发育亮、暗纹层的岩石结构和构造作为纹层状和层状泥页岩的划分标准是有误的[10]。因为泥页岩中许多亮晶方解石纹层是以方解石脉体方式存在的,属于后期成岩的产物,不能作为岩石结构和构造的标志,为此笔者基于岩石薄片分析提出了4个简易识别标志以供参考。

  • 识别标志 1   识别标志 1 为聚片双晶发育特征的亮晶方解石纹层,晶体栉节状排列,沿上、下基底面生长,直至中轴愈合线,晶间孔缝中充满油质沥青(图3a,3b)。聚片双晶的方解石属于高矿化度流体充注于裂缝之中并发生化学结晶的产物,方解石晶间孔形态呈狭长缝状。而发育雾化边的微晶-细晶方解石保留了原始晶体的痕迹,是方解石重结晶的产物,晶形规则,方解石晶间孔发育。

  • 表1 不同岩石结构和构造页岩油储集空间类型和孔径分析数据

  • Table1 Analysis of pore space types and pore size distribution of shale oil formation with different rock texture and structure types

  • 图3 济阳坳陷牛页1等4口页岩油探井方解石脉体简易识别图版

  • Fig.3 Simple identification plate for calcite veins of Well Niuye1 and other 3 shale oil wells in Jiyang Depression

  • 识别标志2   识别标志2是统一消光的微晶-细晶方解石(图3c,3d),整体常常呈透镜状或纹层状产出(图3e,3f),单偏光下脉体中的方解石晶粒呈显微晶结构(图3c),正交偏光下则呈现为统一消光的特征(图3d)。

  • 识别标志 3   识别标志 3 是方解石脉常常具有多条共生的特点(图3a,3g)。泥页岩中裂缝的形成是方解石脉形成的前提,高矿化度地层水沉淀结晶是方解石脉形成的必要条件。受泥页岩岩石破裂强度的微观非均质影响,形成的裂缝具有形态和宽度方面的差异,方解石脉也表现为宽窄不一的透镜状和纹层状形态。由于方解石脉与裂缝发育的一致性,裂缝发育段也是方解石脉的集中发育段[6-7],受控于层理缝多条集中发育的特点,方解石脉亦呈多条共生的特点。

  • 识别标志 4   识别标志 4 是连晶结构的亮晶方解石(图3h),其与相邻的晶粒状方解石形成鲜明对比,是方解石脉体的典型标志之一。泥页岩中矿物组分的粒度决定了其难以发育较大的储集空间,阻碍了连晶方解石的形成,只有裂缝才能为连晶方解石的形成提供足够的生长空间。

  • 3.2 物质组分含量

  • 纹层状泥页岩中化学成因的晶粒方解石相比于丝片状的黏土矿物晶间孔,其孔径更大、晶型更规则、孔隙连通性也更好。因而纹层状泥质灰岩比灰质泥岩的储集空间更发育。氮气吸附和压汞实验结果表明,二者的优势孔径分布均呈双峰状,2个孔径分布集中区间相似,主要为 2~50 nm 和 90 nm~6.3 μm,纹层状泥质灰岩和灰质泥岩的 2 个孔径分布集中区间的相对百分比分别为 52% 和 48%,65% 和 35%,说明灰质组分含量增加对总孔隙度的贡献更大。

  • 相同岩石结构和构造泥页岩孔隙发育的微观控制因素主要是物质组分,为此着重探讨岩石矿物组分和有机质热演化对孔隙发育的影响。其中,岩石矿物组分对储集空间和含油性的控制作用分为矿物组分含量和矿物结晶程度2种主要方式。在有机质热演化过程中,存在2种影响孔隙发育的方式:一是直接产生有机质孔隙;二是在生烃过程中通过烃类释放改造原生储集空间,间接改善孔喉的大小和连通性,这种方式对孔隙发育的贡献尤为重要[16-17]

  • 3.2.1 矿物组分含量和矿物结晶程度

  • 研究区泥页岩中主要的无机矿物组分包括碳酸盐矿物、陆源碎屑石英和黏土矿物。根据高压压汞和核磁实验分析结果,发现黏土矿物含量高的泥页岩孔径主要为 2~90 nm,碳酸盐矿物含量高的泥页岩孔径主要为 90~1 000 nm。说明碳酸盐矿物含量对大孔径的贡献更大。矿物结晶程度改善孔隙最明显的现象表现在:方解石晶体的大小决定了孔隙的形状和孔径,马牙状和柱纤状方解石晶间孔的孔径明显优于微晶和泥晶方解石的晶间孔。虽然研究区泥页岩中白云石的绝对含量少,一般为 2%~10%,大多分散状分布,但研究发现白云石化的程度对储集空间的发育和物性的改善具有积极意义,同时具有重要的层序划分和成岩指示意义[19-22]

  • 牛页 1 井 3 355~3 390 m 取心段泥页岩的矿物组分含量分析结果(图4)表明:石英等陆源碎屑含量最高,其值为30%~55%,平均为40%,混杂于泥质纹层中。黏土矿物含量中等,为 8%~45%,平均为 13.3%;碳酸盐矿物含量中等,为 5%~70%,平均为 37%;对应孔隙度为 8%~13%,平均为 12%,该埋深段不是孔隙度最高的层段。随着埋深加大,超过 3 390 m,石英等陆源碎屑含量中等,为 10%~45%,平均为 22%;黏土矿物含量中等,为 5%~55%,平均为 23%;碳酸盐矿物含量变高,为 5%~80%,平均为 60%;对应孔隙度为8%~16%,平均为14.5%,是最高孔隙度发育段。测井核磁共振解释孔隙的孔径分布曲线主峰右移,孔径明显增大(图4)。因此,以方解石为主的碳酸盐矿物对泥页岩大孔径孔隙的贡献最大,是控制泥页岩储集性能的关键因素。在以方解石等碳酸盐矿物作为物质基础的前提下,研究区沙四段上亚段白云石化成岩程度对储集空间发育和物性改善也具有显著贡献[19]

  • 3.2.2 有机质热演化

  • 利用氯仿抽提法和小角中子散射法,测定泥页岩热模拟实验样品,对比介孔含量的变化,可以揭示有机质热演化对泥页岩孔隙和含油性的影响方式和程度[22]。小角中子散射分析结果表明:泥页岩介孔的发育具有规律性,随着镜质组反射率变大,细介孔的含量越来越少,中介孔和粗介孔的含量越来越多。随着有机质热演化程度的增加,细介孔向中介孔和粗介孔转化。以牛页 1 井为例,当埋深约为 3 380 m、镜质组反射率约为 0.65% 时,热演化增加的细介孔与中-粗介孔程度相当。超过该埋深和有机质热演化程度,细介孔大量转化为中-粗介孔。孔径分布的改变,指示了热演化过程中生烃作用对孔隙结构的改造。这一认识与 SUN 等热模拟实验的发现结果十分吻合[22]

  • 由于黏土矿物晶间孔的孔径主要为 2~50 nm,处于介孔孔径范围,介孔占总孔隙的 50% 左右,细介孔向中介孔和粗介孔的转化不仅对泥页岩孔隙度的增大具有明显贡献,而且提高了孔隙连通性和渗透率。长条状有机质大多顺层伴生在泥质纹层中,在有机质热演化过程中对黏土矿物微孔发育的影响最显著,这是造成细介孔向中介孔和粗介孔转变的主要原因,也是导致泥页岩物性改善的重要途径。

  • 图4 济阳坳陷牛页1井矿物组分含量及孔隙度、测井核磁共振孔径纵向分布规律

  • Fig.4 Longitudinal distributions of mineral and porosity and logging NMR aperture in Well Niuye1 in Jiyang Depression

  • 4 结论

  • 束缚型沥青的成分主要为浸染于黏土矿物中的沥青,属于Ⅰ和Ⅱ型干酪根发生降解后残留的生油母质及其吸附的烃类。伴随着生排烃的进程,油气中的轻质组分优先发生运移,少部分赋存在碳酸盐晶间孔和裂缝中。现今荧光显示好的泥页岩储层段仅代表有机质和残留烃含量高,是曾经生烃能力强的证据,但不一定代表是现今最有利的储集层段。

  • 裂缝演化到后期,表现为被方解石或重晶石半充填-完全充填,因此亮晶方解石脉体属于后期成岩的产物,是裂缝的填充物,不能作为岩石结构和构造标志。笔者提出了4个简易识别亮晶方解石脉体的标志:方解石聚片双晶发育、方解石统一消光、方解石脉多条共生、方解石具有连晶结构。

  • 束缚型和游离型沥青的荧光特征表明泥质纹层是生油的母质仓储,泥质纹层中的有机质及其热演化程度决定了生油量,表现为炭质和沥青质沥青荧光特征。碳酸盐纹层是与之相邻的最有利的储集空间,具有胶质沥青和油质沥青的荧光特征,裂缝则是最主要的跨泥页岩纹层和顺层长距离运移的通道,具有油质沥青的荧光特征。

  • 济阳坳陷沙四段上亚段和沙三段下亚段页岩油储集空间发育程度和含油性受岩石结构与构造、物质组分含量2个因素控制。纹层状、层状和块状3 类岩石结构和构造方面的差异本质上也是由碳酸盐矿物、泥质和陆源碎屑矿物的沉积叠置方式不同所致。

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