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页岩油是指赋存于有效生烃泥页岩层系中,已生成的未能完全排出而滞留或仅经过极短距离运移而就地聚集的原油,具有游离、吸附和溶解3种赋存状态(张金川等,2012;邹才能等,2013),其中游离油是目前工程技术条件下的主要潜在可采部分。依据赋存空间的不同,可将页岩油划分为基质型、夹层型和裂缝型3类(张金川等,2012)。近年来,受北美成功实现页岩油商业开发的启示(张林晔等,2014;黎茂稳等,2019),页岩油已成为中国石油勘探和地质研究的热点领域之一(马永生等,2022)。新疆吉木萨尔、胜利济阳、大庆古龙等国家陆相页岩油示范区正在建设推进中(赵文智等,2022),国家能源局发布数据显示2023年中国页岩油年产量已突破400万t,再创新高,展现出中国页岩油巨大的资源潜力。与美国海相页岩形成环境、页岩油富集条件不同,中国陆相页岩油储层普遍呈现出沉积环境多样、岩相非均质性强、成熟度差异大等特征(王民等,2014;黎茂稳等,2019,2020;金之钧等,2021a),给页岩油甜点优选和效益开采带来巨大挑战。总体来看,中国目前已经实现商业开采的页岩油类型主要为夹层型页岩油,而对资源体量更大的基质型页岩油尚未实现大规模开发(朱国文等,2023)。基质型页岩油储集空间以纯泥页岩纳米—微米孔隙和微裂缝为主,通常具有超低渗透率、高黏土和低碳酸盐矿物的特征,且较高的有机质含量对页岩油具有强吸附滞留作用,被认为是最难实现工业开采的页岩油类型(Jarvie,2012;Jin Zhijun et al.,2021b)。因此,阐明陆相基质型页岩油富集条件,建立页岩油富集模式,对实现此类页岩油大规模有效开发具有重要意义。
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松辽盆地上白垩统青山口组一段(青一段)暗色泥页岩厚度大、有机质丰度高、有机质类型好、热演化程度适中且普遍存在超压,是该区主要生烃层,也是页岩油勘探的首要目标,其中盆地北部的齐家和古龙凹陷是最具潜力的基质型页岩油勘探区(朱国文等,2023)。以往松辽盆地北部页岩油富集条件、富集因素等研究主要集中于古龙凹陷,如柳波(2018)、Liu Bo(2019)等将古龙凹陷青一段划分7类岩相,并认为其中的中有机质纹层状泥岩相是基质型页岩油的优势岩相;赵莹(2020)、朱国文(2023)等指出古龙凹陷页岩储集空间主要为密集分布的有机质生烃缝,页岩油具有较好的可动性;何文渊等(2021)认为游离烃、总有机碳、成熟度以及总孔隙度是页岩油富集高产的核心参数。但是类似研究较少涉及齐家凹陷。青一段沉积时期,松辽盆地北部主要存在两大沉积物源(张顺等,2011;朱国文等,2023),古龙凹陷主要受西部物源影响,而齐家凹陷更邻近北部物源,因此两个凹陷的青一段在岩性岩相和储集空间等方面存在一定差异。本文以齐家凹陷第一口青一段全取芯参数井松页油1井为研究对象,利用钻井、测录井、岩芯实验测试等资料和数据,综合分析齐家凹陷青一段泥页岩的岩性岩相特征,探讨基质型页岩油富集模式,以期为研究区页岩油后续勘探开发提供参考依据。
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1 地质概况
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松辽盆地位于中国东北部,是海西褶皱基底上叠加的中—新生代大型陆相含油气盆地,长约750 km,宽约350 km,呈北东向展布,面积约2.6×105 km2。松辽盆地构造上属于中—新生代断陷-坳陷叠合型盆地,垂向上具有“下断上坳”的双层结构,经历了白垩纪以来断陷盆地、坳陷盆地和构造反转3个演化时期(张兴洲等,2008)。钻井揭示,盆地内发育的地层自下而上主要有白垩系、古近系、新近系和第四系,沉积岩最大厚度超过10000 m(高有峰等,2009)。上白垩统青一段沉积期构造相对稳定,古地形平缓,发生了大规模的水进,沉积了分布广泛的厚层富有机质暗色泥页岩(图1)。齐家凹陷位于中央坳陷西北部,东侧紧邻大庆长垣,向南与古龙凹陷接壤,面积约2225 km2,是青一段页岩油勘探的有利区之一(朱国文等,2023)。松页油1井是部署在齐家凹陷南部针对青一段页岩油资源的一口直井参数井,完钻井深2547 m。该井完整揭穿了青一段并获取了全部岩芯,目的层青一段顶深2357 m,底深2448 m,厚度91 m。
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2 泥页岩地质特征
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2.1 泥页岩基本特征
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齐家凹陷松页油1井青一段岩性以泥页岩为主,占地层厚度比例约为95%,主要为泥岩、粉砂质泥岩、含介形虫粉砂质泥岩。其余岩性为泥质粉砂岩和粉砂岩,主要发育在青一段上部,此外局部夹有厚度极薄的介形虫层、泥灰岩和凝灰岩夹层,青一段主体沉积相类型为半深湖—深湖相。泥页岩颜色多为黑灰—灰黑色,精细观察岩芯发现存在3种沉积构造类型:层状构造、块状构造和纹层状构造(图2)。层状构造水平层理缝发育,密度可达1000~3000条/m(王玉华等,2020),部分可沿层面散裂为板片状;块状构造主要特征是岩石无颜色、粒度、矿物组成的明显变化,较致密,整体表现为均质;纹层状构造以泥岩中夹有数量不等的粉砂岩或泥质粉砂岩纹层为特征,砂质纹层厚度多数小于1 mm,反复间隔出现,往往具有韵律性变化,与相邻层在颜色、粒度、矿物组成方面差异较大。如果砂质纹层厚度与泥岩相当,可变化为互层状构造。3种类型中以层状构造最发育,占比约为50%,块状构造、纹层状构造分别约占27%和23%。
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在有机地球化学特征上,根据钻井现场岩芯地化录井数据,泥页岩TOC值介于0.9%~5.0%,集中分布在1.5%~3.5%之间,平均2.4%;S1值在1.0~19.4 mg/g之间,多数介于4~10 mg/g,平均6.5 mg/g。松页油1井青一段TOC和S1值随埋深增加都呈现先增大后减小的变化规律(图2)。据Xiao Fei et al.(2021b)研究,松页油1井青一段有机质主要为Ⅰ型和Ⅱ1型,干酪根显微组分以倾油腐泥组为主,是典型的以生油为主的泥页岩;Ro值介于1.21%~1.28%,平均值1.26%,表明烃源岩处于生油窗末期,已经生成的大量液态烃为页岩油富集奠定了良好的物质基础。
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在矿物组成上,青一段泥页岩优势矿物为石英、斜长石和黏土矿物,含有少量方解石、白云石、黄铁矿、钾长石、铁白云石和菱铁矿(图2)。黏土矿物含量为8%~45%,平均36%;石英含量为27%~42%,平均35%;长石含量为8%~51%,平均19%;方解石含量为1%~27%,平均6%,主要以胶结物形式充填于砂质碎屑颗粒间,局部层段方解石含量较高与介形虫沉积有关。基于矿物成分,Allix et al.(2011)划分泥页岩为5种类型:硅质泥岩、泥质泥岩、硅质泥灰岩、泥质泥灰岩和钙质或白云质泥岩,依据此标准,松页油1井青一段泥页岩均为硅质泥岩,即长英质泥岩。
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图1 松辽盆地北部青一段沉积相及地层柱状图(据Xiao Fei et al.,2021b;朱国文等,2023修改)
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Fig.1 Sedimentary facies distribution of the K2qn1 and stratigraphic column in the northern Songliao basin (modified from Xiao Fei et al., 2021b;Zhu Guowen et al., 2023)
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2.2 泥页岩储集特征
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泥页岩储层物性决定了页岩油的储集空间大小和自然渗流能力。中国齐家—古龙地区青一段泥页岩储层具有典型的低孔、低渗特征(邵红梅等,2021;孙龙德等,2021;蒙启安等,2022),与美国Marcellus、Barnett和Tuscaloosa等典型页岩油储层物性相比(Loucks et al.,2012;Milliken et al.,2013),青一段泥页岩物性普遍更好。松页油1井青一段二维核磁测井有效孔隙度平均值为5.63%,最大8.50%;渗透率平均值为0.046×10-3 μm2,最大值为0.535×10-3 μm2,具备有利的页岩油富集储层条件。
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松页油1井青一段岩芯宏观构造裂缝发育程度低,具有典型的纯页岩型页岩油储层特征。依据成因和几何形态将青一段泥页岩的储集空间分为孔隙和微裂缝两类。孔隙类型有粒(晶)间孔、粒(晶)内孔、有机质孔3种(图3)。粒(晶)间孔可以分为残余原生粒间孔、溶蚀粒间孔、晶间孔、黏土矿物间孔等。粒间孔多为长条状、多边状,常出现在石英、长石等脆性矿物周围,孔隙大小为50 nm~3 μm。在埋藏成岩阶段,大多数原生粒(晶)间孔在压实、胶结作用之下消失。后期酸性流体进入残余原生粒(晶)间孔溶蚀周边矿物,形成溶蚀粒间孔、黏土矿物间孔。晶间孔出现在黄铁矿集合体、金红石晶体间。粒(晶)内孔包括粒内溶孔、晶内孔以及黏土矿物集合体内孔,大小为10 nm~1.5 μm。粒内溶孔成因与粒间溶孔相似,主要见于长石、方解石等易溶矿物颗粒内部,一般与粒间溶孔同时或者之后形成。晶内溶蚀微孔少量见于金红石、白云石晶体内。有机质孔是块状有机质内或有机质生排烃后因体积减小形成的孔隙,可分为有机质边缘孔(缝)和有机质内孔。边缘孔(缝)为弯曲的长条状,是生排烃后与接触矿物边缘形成的微缝,最长为3 μm;内孔多为椭圆状、蜂窝状,孔隙相对较小,大小在500 nm以内。
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图2 齐家凹陷松页油1井青一段综合柱状图
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Fig.2 Comprehensive stratigraphic column of the K2qn1 in the SYY1 well, Qijia sag
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不同沉积构造泥页岩发育的主要储集空间类型存在差异,其影响因素被认为是矿物成分和有机质含量(Yang Jianguo et al.,2021b)。层状、纹层状泥岩相储集空间类型以黏土矿物、脆性矿物间孔等粒间孔为主,块状泥岩相主要是黏土矿物孔和大的溶蚀孔等粒内孔。有机质孔是页岩油气较为重要的储集空间类型(Milliken et al.,2013)。有机质按其是否含孔可分为含孔有机质和无孔有机质,数字岩芯测试结果显示,松页油1井青一段泥页岩的无孔有机质含量普遍更高,约占60%。
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3 泥页岩岩相特征
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3.1 岩相划分方法
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半深湖—深湖相沉积的泥页岩看似都为单一的暗色细粒颗粒,实际上不同泥页岩之间存在较大差异(Hammes et al.,2011)。松辽盆地青一段泥页岩的有机质丰度、矿物成分和沉积构造具有明显的关联性(柳波等,2021)。综合对比国内外学者的岩相划分方法,选择“有机碳含量—沉积构造—矿物成分”三因素方案(Lazar et al.,2015),基于青一段泥页岩TOC与原始氢指数、黏土矿物含量的相关关系(王飞宇等,2016;柳波等,2021),以TOC值1%和2%界定低、中、高的有机质含量,沉积构造按层状、块状和纹层状划分,矿物成分以Allix等提出的分类方法划分(Allix et al.,2010),将青一段泥页岩划分为5类岩相:高有机质层状长英质泥岩相、高有机质块状长英质泥岩相、中有机质层状长英质泥岩相、中有机质块状长英质泥岩相、中有机质纹层状长英质泥岩相(图4、图5)。
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图3 齐家凹陷松页油1井青一段典型储集空间类型
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Fig.3 The typical reservoir space types of the K2qn1 in the SYY1 well, Qijia sag
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图4 齐家凹陷松页油1井青一段泥页岩矿物成分三角图
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Fig.4 Ternary diagram showing mineral composition of the K2qn1 shale in the SYY1 well, Qijia sag
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3.2 泥页岩岩相特征
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高有机质层状长英质泥岩相一般为灰黑—黑色,质地坚韧不易破碎,层理缝发育,具有油脂光泽。矿物成分主要为石英、长石和黏土矿物,长英质矿物含量为46%~56%,平均52%,黏土矿物含量为38%~45%,平均40%,碳酸盐含量平均为4%。有机质含量高,TOC值一般在2%~3.5%,少数可达4%~5%。镜下观察碎屑粒级非常小,具有显微纹层。
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高有机质块状长英质泥岩相颜色一般为黑色,岩芯及镜下观察到其块状构造特征比较明显,碎屑分布均匀,层理不发育。矿物成分以长英质和黏土矿物为主,含量分别为55%、38%,碳酸盐含量为7%。有机质含量高,TOC值为2%~3%。碎屑粒级总体粗于高有机质层状长英质泥岩相,其沉积速率更快。
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中有机质层状长英质泥岩相宏观特征与高有机质层状长英质泥岩相相近,有时颜色稍浅,层理缝同样发育。长英质矿物含量为54%,黏土矿物含量为39%,碳酸盐含量3%。有机质含量中等偏高,TOC值多数在1.5%~2%。镜下观察碎屑粒级细小,有时可见颜色深浅间隔的细纹层,长英质矿物含量及粒级不均一,垂直纹层方向发生微小变化。
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中有机质块状长英质泥岩相颜色主要呈现深灰色—黑灰色,块状构造。长英质矿物含量在44%~54%之间,平均49.5%,黏土矿物含量介于36%~45%,平均41.4%,碳酸盐含量4%左右。有机质含量中等,TOC值在1%~2%之间。岩芯观察可见岩石较致密,矿物分布均匀,长英质矿物含量比高有机质长英质泥岩略有增加。
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图5 齐家凹陷松页油1井青一段泥页岩岩相划分标准图
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Fig.5 Classification criteria of lithofacies for the K2qn1 shale in the SYY1 well, Qijia sag
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中有机质纹层状长英质泥岩相主要是泥岩或粉砂质泥岩夹砂质细纹层而形成,颜色表现为黑灰色夹灰—深灰色纹层。长英质矿物含量高于其他岩相,为55%~83%,平均63.6%,黏土矿物含量偏低,介于15%~38%,平均22.9%,碳酸盐类含量3%左右,部分含介形虫者可达到27%。有机质含量中等,TOC值介于1%~2%。镜下可见浅色纹层。
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松页油1井青一段主要发育高有机质层状长英质泥岩相(占比40%),其次为中有机质纹层状长英质泥岩相(占比23%)、中有机质块状长英质泥岩相(占比18%),少量发育中有机质层状长英质泥岩相(占比10%)、高有机质块状长英质泥岩相(占比9%)。整体上看,高有机质泥岩相和层状泥岩相主要分布在青一段中下部,中有机质泥岩相、块状泥岩相和纹层状泥岩相多数位于青一段上部。岩相充填序列特征与泥页岩形成的沉积环境差异密切相关(Liu Bo et al.,2019),层状泥页岩相形成于湖侵下的静水强还原—还原沉积环境,多为高有机质泥页岩;块状泥岩相主要形成于沉积速率较快的静水还原环境,以中有机质泥页岩为主;纹层状泥岩相沉积环境水体变浅,水动力变强,均为中有机质泥页岩。
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4 基质型页岩油富集模式
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4.1 页岩油可动性分析
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在泥页岩层系中,原油的可流动性对于页岩油的评价具有至关重要的作用。可流动的原油是页岩油资源中具有工业价值潜力的部分。在传统认识中,相对于北美海相页岩油,中国陆相页岩油热演化程度总体偏低,原油密度和黏度高、气油比低,因此流动性较差(杨智等,2019;胡素云等,2020)。但是事实情况并非全部如此。
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松页油1井直井压裂测试青一段页岩油原油颜色为亮黄色,密度0.82~0.86 g/cm3,100℃下的黏度为4.9~18.9 mPa·s,为中等黏度轻质油。饱和烃和芳香烃的总含量平均为83%,表明烃源岩成熟度较高,生成的油气基本为轻质原油。从原油物性和族组成上看,齐家凹陷南部页岩油可流动性较好。
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泥页岩中存在一定的自由油流动阈值,可动油指数(OSI=S1×100/TOC)需要超过100 mg/g(Jarvie,2012)。北美鹰滩(Eagle Ford)页岩中,在OSI >100 mg/g富集区内,主要为工业油流井;OSI <100 mg/g范围内,主要为见页岩油显示井或者干井(Jarvie et al.,2017)。因此本文应用OSI值表征齐家凹陷南部页岩油可动性。前人研究表明,松辽盆地北部青山口组泥页岩轻烃损失可使实验测得的S1值偏低约75%左右(薛海涛等,2016),为确保OSI更接近真实值,避免岩芯易挥发轻烃损失导致S1值偏低,本文计算OSI使用的S1和TOC值均来自录井现场岩芯热解数据。松页油1井青一段OSI值介于116~449 mg/g,平均值312 mg/g,全部高于100 mg/g的富集区临界值(图6a),超过已规模开发的北美鹰滩页岩油(OSI值100~200 mg/g),表明齐家凹陷南部青一段页岩油可动潜力大。在纵向上,青一段OSI值总体表现为随深度增加而逐渐增大,青一段下部可动性更好(图6b)。
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TOC值在1%~2%之间的样品OSI值平均为308 mg/g,TOC>2%的样品OSI值平均为337 mg/g。TOC与OSI关系图显示,在TOC<3%时二者呈正相关关系,TOC>3%时OSI不再随TOC的增大而逐渐增加(图6c)。因此高有机质泥页岩的可动性总体略好于中有机质泥页岩,有机质含量在一定程度上控制了页岩油的可动性。
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4.2 页岩油富集的有利岩相
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青一段页岩油储层虽然总体致密,主要由细粒碎屑组成,但是矿物成分复杂、非均质性较强。不同深度的储集层形成条件存在差异,致使其有机碳含量、矿物组成或沉积构造有较大区别(沈骋等,2021),进而导致储层内页岩油的赋存特征存在差异。泥页岩岩石中有机质含量、矿物组成、沉积构造与储层内的油气含量及赋存状态关系密切(Wang Guochang et al.,2012),三者是页岩油储层岩相划分的基础,纵向上各种岩相组合控制了青一段泥页岩中可动页岩油的宏观分布。
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上文述及,青一段有机质丰度在一定程度上控制可动烃的富集。从矿物组成上看,一般认为泥页岩中黏土矿物含量越高,其吸附烃含量越高,可动油含量就越低;反之,如果长英质矿物含量越高,可动油就越富集(张君峰等,2020)。松页油1井青一段纯泥页岩黏土矿物含量总体相差较小,推测其不是控制可动油富集的主要因素,而长英质矿物含量非均质性较强(图2)。通过以上分析,可以初步确定高有机质含量和高长英质矿物含量对页岩油富集更为有利。因此,下文主要针对高有机质层状泥岩相和高有机质块状泥岩相进行对比分析,明确页岩油富集的最有利岩相。
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图6 齐家凹陷松页油1井青一段S1与TOC(a)、OSI与埋深(b)和OSI与TOC(c)相关关系图
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Fig.6 Crossplots of S1 vs. TOC (a) , OSI vs. buried depth (b) , and OSI vs. TOC (c) for the K2qn1 shale in the SYY1 well, Qijia sag
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页岩油储层的微观孔隙特征对泥页岩储集和渗流性能具有重要影响(Zhang Jizhen et al.,2017;曾维主等,2019)。层状泥页岩低温氮气吸附等温线滞留回环较小,属H3型(Thommes et al.,2015),孔隙以狭缝型为主,而块状泥页岩滞留回环相对较大,反映出球形介孔更为发育(图7)。高压压汞实验显示,当压力在0.1~0.5 MPa时,层状泥页岩样品开始进汞,之后随压力的增加汞饱和度平缓连续上升;压力为5~10 MPa时,块状泥页岩样品开始进汞,主进汞段平缓且长(图7)。表明层状泥页岩孔隙相对较大,孔径分布较连续,普遍发育50 μm以上的微缝,而块状泥页岩小于50 nm的介孔占比更高。此外,层状泥页岩中发育的层理缝一方面增大了储集空间,另一方面沟通了各类不同尺寸的孔隙,这对泥页岩储集性能的改善发挥了重要作用。X射线断层成像技术(X-CT)可以利用大量X射线衰减图像重构出孔喉三维结构特征(Sakdinawat et al.,2010),实现对孔隙空间分布及孔隙系统连通性的研究(郝乐伟等,2013)。从纳米CT三维图像发现,不同沉积构造类型的泥页岩之间孔隙结构差别较大(图8)。图像中不同的颜色代表互不连通的孔隙团,同种颜色的团块内部孔隙是连通的。块状泥页岩总孔隙体积明显低于层状泥页岩,而且孔隙连通性也较差。表明发育层状构造的泥岩比块状构造泥岩孔隙度更大、渗透性更好。青一段泥页岩地面水平渗透率比垂直渗透率高10~100倍(朱国文等,2023),层状页岩更是高达几百倍(柳波等,2021)。
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激光共聚焦扫描是致密储层含油性及孔隙分析的重要手段(鲁锋等,2023)。三维重建模型显示,泥页岩孔隙中含有大量页岩油,并充填整个孔隙空间,在粒间孔壁的表面同样吸附有大量的原油(图9a)。页岩油分布不均匀,主要以絮状、团块状、席状分布在矿物颗粒的粒间孔、粒内孔和有机质孔内,较大的粒间孔中含油多,晶间孔和有机质孔含油少。层状泥页岩中大部分轻质组分在层理缝之间的连通孔隙中集中连片分布,含油饱满(图9b),可动性较好。块状泥页岩的轻质组分在泥岩基质中呈星点状分布在颗粒的夹角处或溶蚀孔隙中(图9c),与层状泥页岩相比,其轻质组分赋存的孔径更小,连通性不好,重质组分所占比例略高于层状泥页岩(图9d)。
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综上分析认为,相对于其他岩相,高有机质层状长英质泥岩相有机质含量高,可动烃富集;储集空间以介孔为主,也发育一定数量的宏孔,同时存在大量的层理缝,具有孔-缝组合孔隙结构特征,孔隙连通性更好,是研究区控制页岩油富集的最有利岩相。与其上下紧密接触的物性致密、突破压力高的块状泥岩相为顶底板隔层,对页岩油油层起到封盖作用。
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图7 齐家凹陷松页油1井青一段不同构造类型泥页岩孔隙结构定量表征
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Fig.7 Quantitative characterization of pore structure of the K2qn1 shale with different structural types in the SYY1 well, Qijia sag
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图8 齐家凹陷松页油1井青一段不同构造类型泥页岩孔喉球棍模型及孔隙连通性模型
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Fig.8 Ball stick model of pore-throat and pore connectivity model of the K2qn1 shale with different structural types in the SYY1 well, Qijia sag
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(a)—层状泥页岩孔喉球棍模型;(b)—层状泥页岩孔隙连通性模型;(c)—块状泥页岩孔喉球棍模型;(d)—块状泥页岩孔隙连通性模型
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(a) —ball stick model of pore-throat of bedded shale; (b) —pore connectivity model of bedded shale; (c) —ball stick model of pore-throat of massive shale; (d) —pore connectivity model of massiveshale
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4.3 页岩油富集模式
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青山口组一段沉积时期,伴随着地壳的升降运动,松辽湖盆发生了1次大规模水侵(辛仁臣等,2004),形成了广泛分布的半深湖—深湖相沉积环境,沉积了上百米的厚层暗色泥页岩。温暖潮湿的气候条件下,以蓝细菌、疑源类等微生物为主、以真核藻类为辅的多元生物群落繁盛(王华健等,2023;Xiao Fei et al.,2024),水体富营养化触发高生产力(王岚等,2022),同时缺氧下的还原环境有利于泥页岩中有机质保存,奠定了青一段基质型页岩油大规模富集的物质基础。
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陆相湖盆在沉积旋回和物源输入的联合作用下,泥页岩有机质含量、沉积构造和矿物组成发生规律性变化,造成岩相类型的有序变化(柳波等,2021)。在温暖潮湿气候时期,物源供给充足,有机质来源丰富且保存较好,形成高有机质泥页岩。长期稳定的深水环境下,青一段沉积速率慢,受季节性及成岩作用等影响,泥页岩多表现为层状构造。而当气候转向干冷时期,物源输入减少,地层有机质含量降低,多形成块状和纹层状沉积。
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作为基质型页岩油富集的优势岩相,高有机质层状长英质泥岩相是青一段水侵湖进环境下的主体岩相。有机碳是生油的物质基础(蒙启安等,2022),发育层状构造的泥页岩常伴随着高TOC值(>2%),其表征含油量的游离烃S1、氯仿沥青“A”及表征可动性的OSI指数相对其他岩相更高,显示出更好的含油性和可动性。烃源岩热演化程度影响着滞留油气的流动性,成熟度越高,原油密度越小,黏度越低,地层压力系数越大(王玉华等,2020;何文渊等,2021),原油的流动性越强,有利于页岩油开发动用(胡素云等,2022)。松页油1井青一段Ro>1.2%,下部的层状泥页岩最高为1.28%,处于生油高峰期,游离烃S1含量最高可达19.4 mg/g,原油轻质组分与重质组分比例为1.0~1.2,气油比高,流动性较好。良好的成熟度、埋深及油气保存条件下,使青一段地层压力较高,实测下部页岩油油层甜点段地层压力系数为1.44,说明地层能量充足,油气富集。在核磁共振T1-T2谱图上,高有机质层状泥页岩其游离态油信号突出,揭示含油饱和度较高,达到30%~70%。
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图9 齐家凹陷松页油1井青一段层状泥页岩和块状泥页岩激光共聚焦原油及其轻重组分分布图
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Fig.9 Distribution of shale oil and its light and heavy components of the K2qn1 bedded and massive shales from laser confocal scanning in the SYY1 well, Qijia sag
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(a)—原油充填于粒间孔;(b)—原油集中连片分布;(c)—原油星点状分布;(d)—原油多孤立分布
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(a) —crude oil is filled in intergranular pores; (b) —crude oil is distributed continuously; (c) —crude oil is distributed in a star-point pattern; (d) —crude oil is mostly distributed in isolation
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高有机质层状长英质泥岩相的显著沉积特征是水平层理发育,背散射二维大面积成像显示层理缝密度最高可达3.5条/mm(图10a),扫描电镜矿物分析成像显示层状泥页岩矿物分布不均匀,粒径稍大的长英质矿物多数顺层理排列(图10b、c)。孔隙沿层理面集中分布,微米级宏孔较发育(图10d),宏孔比例可达20%~30%。在油气来源充足的情况下,储集空间越发育,页岩油就越富集。层状泥页岩密集分布的层理缝与孔隙连通形成孔-缝复合储集体,构成主要富油空间和渗流通道(朱国文等,2023),结合局部的构造缝,形成层理缝方向上的高孔渗带,极大提高了岩石渗流能力(孙龙德等,2021),是基质型页岩油长期稳产的保证。沉积环境控制下的各类泥页岩岩相,高有机质层状泥页岩可能更具备大规模页岩油富集成藏的潜力(图11)。
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实钻井表明,青一段优先勘探开发的基质型页岩油富集目标层段是高有机质层状泥页岩。松页油1井岩芯气显示比较活跃,高有机质层状泥页岩出筒时即使被泥浆包裹仍见大量气泡冒出,伴随气泡有油膜渗出,预示了丰富的轻烃含量和很好的可动性。以基质型页岩油为目标,在松页油1井高有机质层状泥页岩储层实施体积压裂后,试油获得工业油流;在直改平基础上实施的水平井段大规模压裂,敞口自喷求产获得14.37 m3/d高产工业油流(杨建国等,2021a)。后续试采9个月,产量及流压基本平稳,递减缓慢,地层能量保持较好。计算结果表明(肖飞等,2021a),齐家凹陷青一段基质型页岩油富集区面积为1957 km2,资源量为19.8×108 t。研究区基质型页岩油具有深入勘探的广阔前景和效益开发的巨大潜力。
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图10 齐家凹陷松页油1井青一段层状泥页岩微区层理缝、孔隙及矿物分布
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Fig.10 Micro-domain bedding fractures, pores and mineral distribution of the K2qn1 bedded shale in the SYY1 well, Qijia sag
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(a)、(d)—背散射二维大面积成像结果图;(b)、(c)—扫描电镜矿物分析成像图
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(a) , (d) —backscattering2D large area imaging results; (b) , (c) —scanning electron microscope image of mineral analysis
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图11 松辽盆地齐家凹陷南部青一段页岩油富集模式图
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Fig.11 Shale oil enrichment model of the K2qn1 in the southern Qijia sag, Songliao basin
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5 结论
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(1)松辽盆地齐家凹陷南部青一段发育半深湖—深湖相厚层暗色泥页岩,有机碳和游离烃含量高,有机质类型好,热演化已达到成熟阶段末期,矿物组成以长英质矿物为主,储集空间类型多样,具备页岩油富集的有利地质和储层条件。
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(2)青一段泥页岩可划分为高有机质层状长英质泥岩相、高有机质块状长英质泥岩相、中有机质层状长英质泥岩相、中有机质块状长英质泥岩相、中有机质纹层状长英质泥岩相五大类岩相,不同类型岩相的分布在物质条件上控制了页岩油的差异富集。高有机质层状长英质泥岩相是研究区控制页岩油富集的最有利岩相。
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(3)高有机质层状长英质泥岩相有机质含量高,生烃能力强,可动油占比较高,孔隙以狭缝型为主,连通性较好。由于层理缝的发育,连通微纳米孔隙形成了孔缝网络体系,改善了储集层储集性能。证实齐家凹陷深湖相纯泥页岩具有页岩油富集的有效储集空间,同时有物性致密的块状泥页岩作为顶底板隔层,且发育较高地层压力,基质型页岩油开发潜力大。
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致谢:东北石油大学柳波教授、王博洋副教授和白龙辉博士提供了实验帮助,审稿专家提出了宝贵的意见建议。在此一并致谢!
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摘要
松辽盆地齐家凹陷南部白垩系青山口组一段(青一段)发育半深湖—深湖相厚层暗色泥页岩,富含典型的纯页岩基质型页岩油。以松页油1井为例,利用钻井、测录井、岩芯实验测试等资料及数据,对青一段泥页岩地质特征、岩相类型和基质型页岩油富集模式进行了研究。结果表明,青一段泥页岩存在层状、块状和纹层状3种沉积构造类型,按照“有机碳含量—沉积构造—矿物成分”三因素分类方案,可以将泥页岩划分为高有机质层状长英质泥岩、高有机质块状长英质泥岩、中有机质层状长英质泥岩、中有机质块状长英质泥岩、中有机质纹层状长英质泥岩五大岩相。其中,高有机质层状长英质泥岩相是主体岩相,也是控制页岩油富集的最有利岩相。该岩相有机质含量高(TOC值一般为2.0%~ 3.5%),含油性好(S1最大值为19.4 mg/g),可动烃富集(可动油指数OSI平均值>300 mg/g);储集空间以介孔为主,也发育一定比例的宏孔,孔径分布较连续,主要为狭缝型孔隙,连通性较好。青一段泥页岩热演化程度较高(Ro平均值为1.26%),有机质已大量生烃,高有机质层状长英质泥岩相原油轻质组分占比达50%~55%,流动性较好;并且发育密集层理缝,连通微纳米孔隙形成了孔缝组合网络体系,改善了泥页岩储集性能,极大提高了岩石渗流能力。总体上看,齐家凹陷南部半深湖—深湖相高有机质层状长英质泥岩相具有相对较好的页岩油富集的物质条件和有效储集空间,同时以物性致密的块状泥页岩作为顶底板隔层,页岩油保存条件好,开发潜力巨大。
Abstract
Semi-deep to deep lacustrine shale strata within the first member of the Cretaceous Qingshankou Formation (K2qn1) in the southern Qijia sag of the Songliao basin are well-developed and represent a typical target for tight shale oil exploration. Using data from drilling, logging, and core tests, we conducted a comprehensive study of the geological characteristics, lithofacies type, and tight shale oil enrichment model of the K2qn1 using the SYY1 well as an example. Our results indicate the K2qn1 shale exhibits three kinds of sedimentary structures: Bedded, massive, and laminated. Based on total organic matter (TOC) content, sedimentary structure, and mineral composition, the K2qn1 shale in the SYY1 well can be divided into five lithofacies: Bedded siliceous mudstone with high TOC (>2.0%), massive siliceous mudstone with high TOC, bedded siliceous mudstone with moderate TOC (1.0%~2.0%), massive siliceous mudstone with moderate TOC, and laminated siliceous mudstone with moderate TOC. Among these, the bedded siliceous mudstone lithofacies with high TOC is the main lithofacies and the most favorable to control the enrichment of shale oil. It boasts high organic matter content (TOC values generally ranging from 2% to 3.5%), good free oil content (S1 values up to 19.4 mg/g), and abundant movable hydrocarbons (average OSI values exceeding 300 mg/g). Its reservoir space is mainly mesoporous, with a proportion of macropores also developed. Compared to other lithofacies, it exhibits a relatively continuous pore size distribution, dominated by slit pores, and good connectivity. The K2qn1 shale in the SYY1 well displays a high thermal evolution degree (average Ro value of 1.26%), indicating significant hydrocarbon generation from organic matter. In the bedded siliceous mudstone lithofacies with high TOC, light components constitute 50% to 55% of the shale oil, implying good oil mobility. In addition, this lithofacies is characterized by well-developed, dense bedding fractures. These fractures connect micro-nano pores, forming a pore-fracture network system that significantly enhances reservoir performance and rock permeability. Therefore, the bedded siliceous mudstone lithofacies with high TOC, developed in the semi-deep to deep lacustrine facies of the southern Qijia sag, presents a promising target for shale oil exploration. This lithofacies exhibits favorable material conditions and effective reservoir space for shale oil enrichment, while the surrounding tight massive shale acts as an effective seal, ensuring excellent preservation conditions.
Keywords
enrichment model ; shale lithofacies ; bedding fractures ; shale oil ; Qingshankou Formation ; Qijia sag ; Songliao basin