3D digital modelling and detailed anatomy of tight sandstone reservoir outcrop with oil-bearing heterogeneity: A case study of Angou outcrop of Triassic Yanchang Formation in Ordos Basin
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摘要: 由于缺少典型油砂露头，客观认识砂体内部受控于构型界面的储层含油非均质性受到制约，有效素材的缺乏一直阻碍着表征砂体内部含油非均质性及其与构型界面具体关系的认识。位于鄂尔多斯盆地东南部的安沟露头中致密砂岩含油非均质性表现明显，是储层含油非均质性和表征其与不同构型界面具体关系的有效素材。利用无人机多点位航拍对安沟油砂露头进行了三维数字露头建模，并对其三维数字模型进行了沉积−层序−成岩解剖，结果发现露头中原油充注仅分布于单层砂体内部，而砂体顶、底部并不含油。对实测剖面进行沉积相及层序地层分析，结果表明含油致密砂岩的沉积环境为曲流河水道，底面对应延长组7（长7）油层组和延长组6（长6）油层组界限的三级层序界面。砂体内含油非均质性与水道叠置、砂坝垂向加积和底形（交错层）构型界面关系密切。手持切割机对长7和长6油层组露头进行连续取样和岩石薄片镜下观察，研究发现单砂层顶、底和内部截然不同的结构、物性和成岩特征是造成安沟露头差异化含油的根本原因。安沟油砂露头的发现为客观认识砂体内部受控于构型界面的储层含油非均质性提供了难得的野外实例。该露头的详细解剖为致密砂岩储层含油非均质性明显受控于沉积作用和差异化的成岩作用提供了直接的地质证据。Abstract:
Objective Our understanding of architecture-controlled oil-bearing heterogeneity shown in tight sandstone reservoirs is hindered by scarcity of large-scale oil-bearing outcrops. Triassic lacustrine delta and fluvial succession exposed in a quarry near Angou village （Yanchang county, northern Shannxi province） is an analog for buried oil-bearing tight sandstones in the Ordos basin. Methods In this study, 3D digital outcrop modeling was carried out on the oil-bearing sandstone outcrop of Angou by using Unmanned Aerial Vehicle（UAV） multi-point aerial photography, and then the depositional sequence diagenetic anatomy and field anatomy were carried out on the 3D digital model of Angou oil-bearing sandstone outcrop. Based on field observations, drone-based measurement and digital outcrop modelling, continuous sampling using Husquvarna power cutter and petrographic and diagenesis analysis under section, a 2D architectural heterogeneity model incorporating spatial configuration of effective reservoir was created. Results The UAV 3D digital outcrop modeling and field dissection revealed that the oil charging was only distributed within the interior, but not at the top or bottom of sand body. The configuration and nature of bounding surface underlying this succession was reconstructed with reference to lateral tracing for distinctive markers and a detailed measured profile with facies and sequence stratigraphic analysis. The results show that the sedimentary environment of oil-bearing tight sandstone is curved river channel. In the quarry, fluvial sandstone succession is underlain by a regional surface interpreted as a third-order sequence boundaries on the basis of abrupt landward facies change and locally developed incised valleys <20 m deep. Architectural heterogeneity within the amalgamated sandbody is expressed by multiple fifth-order storey surfaces, sixth-order barform and seventh-order bedform. Continuous sampling and thin-section observation of outcrops show that the completely different structural properties and diagenetic characteristics of the top, bottom and interior of a single sand layer are the fundamental reasons for the different oil bearing in outcrops. The discovery of the Angou oil-bearing outcrop provides a rare field example for the objective understanding of the oil-bearing heterogeneity of the reservoir controlled by the configurational interface in the sand body. Conclusion In this study, the specific characteristics of oil-bearing heterogeneity in oil-bearing sandstone outcrop are described, the sedimentary background and possible levels of different configuration interfaces of extremely thick oil-bearing sandstone are revealed, and the causes of oil-bearing heterogeneity developing in sand bodies are qualitatively understood. [ Significance ] Of importance, the discovery and detailed anatomy of Angou outcrop provide direct geological evidence showing that sedimentation and diagenesis exert a strong control on the quality and heterogeneity of most tight clastic reservoirs. -
0. 引言
分离、鉴定原油和水中的酚类是进行酚类化合物地球化学研究的基础。许多学者利用碳C18固相萃取柱，可以确保将酚类化合物从原油中进行分离并鉴定(Li et al., 1992; 包建平和马安来, 1998; Peters et al., 2018)。烷基酚是一类由酚类烷基化后产生的化合物，亲水力强。对石油系统中咔唑和烷基酚的研究表明，它们在原油中的浓度和分布可能会与地下水接触发生油水分配作用而改变(Larter and Aplin, 1995; Li et al., 1995)。存在于储层孔隙中或与储层接触的地下水也可能选择性地从原油中去除水溶性物质。由于烷基酚具有高水溶性且分配系数低(分配系数定义为油中的溶解度C油/水中的溶解度C水，其中C油和C水是给定溶质在油和共存水中的平衡浓度)，它们的分配行为对地下油/水相互作用非常敏感，一些迹象表明，如果这些相互作用更好地量化，可能会为原油的二次运移提供更详细描述(Larter and Aplin, 1995；Taylor et al., 1997)。相关学者已在原油(Ioppolo et al., 1992；Taylor et al., 1997)、油田地层水和油田生产水中(Dale et al., 1997)测定了低分子(C0—C3)烷基酚(其中C0—C3表示连接到苯环上的碳原子数)的分布和浓度。水样中以苯酚(C0)和甲酚(C1)为主，进一步烷基化的C2(二甲基苯酚和乙基苯酚)和C3化合物的浓度相对较低。相反，与苯酚相比相关原油中C2—C3烷基酚的含量相对较高，苯酚和甲酚的油水分配系数低于C2—C3烷基苯酚。
用于确定油水分配系数的常规方法使用摇瓶法(Ioppolo-Armanios et al., 1995；Taylor et al., 1997)，但是不能立即将实验数据用于地下的真实条件。Taylor et al.(1997)在室温和80 ℃条件下，用分离漏斗进行原油/盐水(海水盐度的一半)的油水分配实验。通过将油中各组分的平衡浓度除以它们在水中的浓度来计算烷基酚的分配系数，结果表明，随着温度的升高，烷基酚的分配系数减小，并报道了20种C0—C3烷基酚的分配系数数据，揭示了烷基取代程度和位置对烷基酚的影响。较多烷基化的酚类和具有邻位取代的酚类比同分异构体或较少的烷基化同系物具有更高的分配系数。然而，以这种方式获得的分配系数数据可能与复杂的地下条件相关性不够紧密。为了了解地下条件下的分配行为，有必要在不同的温度下和适当盐度的水中进行分配系数测量。在本研究中，根据温度、盐水浓度和原油类型的变化，计算了自然浓度水平下的烷基酚分配系数；讨论了温度、盐水浓度和原油类型对烷基酚分配系数的影响。
1. 原油样品信息
绥中36-1油田位于辽东湾海域，辽东湾海域地处渤海海域的东北部，是渤海湾盆地的一个次级构造单元。全区由五个呈北东—南西向展布的次级构造单元组成，自西向东分别为辽西凹陷、辽西凸起、辽中凹陷、辽东凸起和辽东凹陷。绥中36-1油田位于辽西凸起的中间段，构造形态为北东走向的断裂背斜，东侧与辽中凹陷相邻，西侧为辽西凹陷(图 1)，是一个古潜山背斜油气藏(李德江等, 2007; 王祥等, 2011; Cheng et al., 2016; 胡洪瑾等，2019)。绥中36-1油田具有层状分布的油层，且储层分布较为稳定，自上而下钻遇的地层有：明化镇组(Nm)、馆陶组(Ng)、东营组(Ed)和沙河街组(Es)(图 1)。东营组分为三段，油田主要含油层段为东营组东二下段，埋深海拔为-1175 m~-1605 m。(殷秀兰等, 2006; 蔡盼盼, 2017; 张雪芳等, 2018; 薛永安等, 2021)。
图 1 辽东湾坳陷绥中36-1油田位置及地层信息图Figure 1. Location and stratigraphic information of the Suizhong 36-1 Oilfield in the Liaodong Bay depressionCheng et al.(2016)对绥中36-1油田中的部分原油研究发现，该地区原油大部分正构烷烃被降解程度高，部分藿烷被降解程度同样较高，甾烷、重排甾烷及三环萜烷类化合物的降解程度较低。文中三个绥中36-1油田东二段的原油样品均来自X区块，分别是X37、X45和X61(非烃组分的占比分别为37%、45%和61%)。三个原油样品经历过不同程度的生物降解作用(图 2)，正构烷烃及类异戊二烯烃基本上被降解消失，但仍然存在类异戊二烯烃的痕迹，藿烷轻微降解，大部分藿烷系列化合物的保存完整；三萜类化合物及甾烷系列化合物的保存完整。25-降藿烷是原油经过微生物作用使得其藿烷脱去甲基形成，通常出现在经历过严重降解程度的原油中(李素梅等，2008；王丹丹等，2017；冯伟平等，2020；方朋等，2021；李二庭等，2021；吕心婷等，2021)。在3个原油样品中均检测到25-降藿烷的存在，表明这3个原油的生物降解程度较为严重，X37原油的25-降藿烷的相对峰值最低。
图 2 绥中36-1油田X37、X45和X61原油质量色谱图Figure 2. Mass chromatograms of X37, X45 and X61 crude oil from the Suizhong 36-1 Oilfield2. 实验步骤
2.1 油水平衡实验和GC-MS条件
在实验中，分别设置了25 ℃、45 ℃、65 ℃三个温度值，探索原油中C0—C3烷基酚在不同温度下的分配差异；同时分别设置了4000 mg/L、6000 mg/L和8000 mg/L三种盐度的盐水，探索烷基酚不同盐水浓度下的分配差异；最后选取X37、X45和X61原油进行等条件的油水配比实验，分析不同非烃组分含量的原油对烷基酚分配的影响。实验步骤如下：
(1) 分别使用X37原油和盐水(4000 mg/L)各20 g放入100 mL顶空螺口瓶中，共配置三个相同油水质量比的混合溶液，将三个油水混合溶液放入超声波振荡器中分别以25 ℃、45 ℃、65 ℃超声振荡2小时，随后在同等温度条件下使用旋转机混合摇动3天，再放入同等温度条件下的恒温箱中，静置7天，使得原油和水充分混合达到平衡；
(2) 使用X37原油分别和4000 mg/L、6000 mg/L和8000 mg/L浓度的盐水进行混合，原油和盐水质量均为20 g，在温度为65 ℃条件下重复(1)中的混合平衡步骤；
(3) 分别使用X37、X45和X61三种原油与4000 mg/L的盐水进行等比例混合，在温度为65 ℃条件下重复(1)中的混合平衡步骤。
色谱条件：色谱仪为HP-7890B气相色谱仪；升温程序为35 ℃保持5 min，之后以2 ℃/min升至120 ℃，然后再以4 ℃/min升至310 ℃，310 ℃恒温13 min。质谱条件：质谱仪为HP-5977质谱仪；采用多离子方式检测。
2.2 原油中烷基酚的分离
实验中所用分离柱为安捷伦公司生产的3 mL C18固相萃取柱，内填有C18非极性吸附剂，实验用化学试剂为色谱级的正己烷和二氯甲烷(楼蔓藤和商振华，1998；赵美萍等，2003；李存法和何金环，2005)。分离实验是综合已有的研究方法并结合实际情况加以改进的，具体步骤如下：
(1) 除沥青质，称取原油样品100 mg，加入正己烷5 mL溶解，同时加入内标(苯酚-d6)1 μg，静止过夜以沉淀沥青质；利用脱脂棉过滤掉沥青质，并将滤液转移进行下一步；
(2) 固相萃取，使用3 mL正己烷润湿C18小柱，再将油样转移入C18小柱中，使用5 mL正己烷冲洗，此过程中饱和烃、芳香烃和其他一些非烃化合物(非烷基酚)被正己烷洗脱下来，再使用5 mL的二氯甲烷洗脱烷基酚类化合物，将滤液接入样品瓶中，使用氮吹仪浓缩至0.5 mL后转移至1.5 mL的GC-MS分析瓶中;
(3) 样品衍生化，加入100 μL的BSTFA(含1%TMCS)试剂，再将样品放入60 ℃恒温箱中静置2小时，使其充分反应。
2.3 水样中烷基酚的分离
文中参考Taylor et al.(1997)使用的方法并对该方法进行了改进，其具体步骤如下：
(1) 样品酸化，称取油水平衡实验的下层水样10 g并记录样品编号，加入20%磷酸将水PH调至2，随后加入内标(苯酚-d6)1 μg；
(2) 液液萃取，使用二氯甲烷∶乙酸乙酯=2∶1混合作为萃取溶剂，将水样转移到分液漏斗中，分三次加入萃取剂共15~20 mL，每次加入之后振荡分液漏斗并及时打开玻璃塞放气，经过三次萃取后水相中的烷基酚大部分被萃取到有机相中；
(3) 除水浓缩，将装有分离有机相溶液的烧瓶连接旋转蒸发器，使用47 ℃水温进行旋蒸至2 mL，加入约200 mg的无水硫酸镁试剂除去残留水，之后将浓缩液转移至5 mL样品瓶中，使用二氯甲烷冲洗三次烧瓶并将冲洗液转移至样品瓶，最后使用氮吹仪器进行浓缩，再将浓缩液转移至1.5 mL的GC-MS分析瓶中并加入BSTFA进行衍生化。
3. 实验结果
3.1 烷基酚的鉴定
因为酚是一种含羟基的极性化合物，如果这种带有极性官能团的化合物不经处理直接进入毛细色谱柱将会对色谱柱的柱效产生严重影响(Bowler et al., 1997; 史权等，1999)。因此在对酚类馏分进行GC-MS分析之前，对其进行衍生化操作。加入衍生化试剂BSTFA+1%TMCS后，酚类化合物发生硅烷化作用生成酚的硅烷化衍生物(图 3)，这种物质更稳定，有利于质谱分析(张渠等, 2009)。烷基酚经过硅烷化后可用m/z166、m/z180、m/z194和m/z208(图 4)检测C0—C3取代的硅烷化酚类系列；在硅烷化的烷基酚化合物的质谱图中的M+-15碎片离子丰度较高且常是基峰，所以用m/z151、m/z165、m/z179和m/z193也可以检测C0—C3取代的硅烷化酚类衍生物；烷基酚的质谱图中普遍出现m/z73优势峰，m/z73是由于硅烷基离子断开导致的。依据烷基酚的保留时间对原油样品中的烷基酚进行定性识别，原油中20种烷基酚的异构体名称、化学式及对应编号详情见表 1。
图 3 酚类化合物硅烷化的反应机理(张渠等, 2009)Figure 3. Reaction formula of alkylphenol and BSTFA (Zhang et al., 2009)
表 1 20种酚类化合物的峰号、分子式、分子量与中英文名称及简写Table 1. Information table of 20 phenolic compounds (peak number, molecular formula, molecular weight, Chinese and English names and abbreviations)峰号 分子式 分子量 中文名称 英文名称及简写 1 C6H6O 94 苯酚 Phenol(Ph) 2 C7H20O 108 2-甲基酚 2-Methylphenol/2-Cresol(2-MPh) 3 C7H20O 108 3-甲基酚 3-Methylphenol(3-MPh) 4 C7H20O 108 4-甲基酚 4-Methylphenol(4-MPh) 5 C8H34O 122 2-乙基酚 2-Ethylphenol(2-EPh) 6 C8H34O 122 2, 5-二甲基酚 2, 5-Dimethylpheno(2, 5-DMPh) 7 C8H34O 122 2, 4-二甲基酚 2, 4-Dimethylphenol(2, 4-DMPh) 8 C8H34O 122 3, 5-二甲基酚 3, 5-Dimethylphenol(3, 5-DMPh) 9 C8H34O 122 2, 6-二甲基酚 2, 6-Dimethylphenol(2, 6-DMPh) 10 C8H34O 122 4-乙基酚 4-Ethylphenol(4-EPh) 11 C9H48O 136 2-异丙基酚 2-Isopropylphenol(2-IPPh) 12 C8H34O 122 2, 3-二甲基酚 2, 3-Dimethylphenol(2, 3-DMPh) 13 C8H34O 122 3, 4-二甲基酚 3, 4-Dimethylphenol(3, 4-DMPh) 14 C9H48O 136 2-丙基酚 2-Propylphenol(2-PPh) 15 C9H48O 136 3-异丙基酚 3-Isopropylphenol(3-IPPh) 16 C9H48O 136 4-异丙基酚 4-Isopropylphenol(4-IPPh) 17+18 C9H48O 136 2, 4, 6-三甲基酚+
2, 3, 5-三甲基酚2, 4, 6-Trimethylphenol(2, 4, 6-TMPh)+
2, 3, 5-Trimethylphenol(2, 3, 5-TMPh)19 C9H48O 136 2, 3, 6-三甲基酚 2, 3, 6-Trimethylphenol(2, 3, 6-TMPh) 20 C9H48O 136 3, 4, 5-三甲基酚 3, 4, 5-Trimethylphenol(3, 4, 5-TMPh) 3.2 油水分配系数
烷基酚的油水分配系数指油水平衡后，烷基酚在原油中的浓度与水中的浓度之比，即公式(1)：
P=C油/C水 (1) 公式中P—油和水之间的分配系数；C油—水洗后原油中烷基酚组分浓度，kg/m3；C水—水中烷基酚组分浓度，kg/m3。
烷基酚的油水分配系数可以描述烷基酚在油水中的分布状况。对于不同油水分配系数的烷基酚异构体而言，其在同一条件下从油相中分配到水相中的能力是不同的。烷基酚的油水分配系数受到所处环境和原油流体组分的影响。烷基酚的油水分配系数在不同温度状态下的大小如图 5所示。苯酚的油水分配系数为2.4~3.2，C1烷基酚的油水分配系数为2.3~9.2，C2烷基酚的油水分配系数为11.6~46.8，C3烷基酚的油水分配系数为31.4~104.2。烷基酚的油水分配系数随着烷基酚的分子质量增加而增大，这一特征在不同温度状态下仍然保持。而同一烷基酚的油水分配系数随着温度的增加而减小，表明温度增大时有利于烷基酚从油相中分配到水相中。不同烷基酚异构体受温度的影响程度不同，苯酚和邻甲基酚在25 ℃和65 ℃时的油水分配系数变化不大，C2和C3烷基酚的油水分配系数变化较大。整体来看烷基酚在油水体系中的分配系数随着温度的增加而减小，并且相对低分子量的C0和C1烷基酚对温度的敏感程度弱于C2和C3，该实验结果与Bennett and Larter(1997)实验观察到的结果具有一致性。
图 5 X37原油在不同温度下的烷基酚油水分配系数大小(水的盐度为4000 mg/L)Figure 5. Oil-water partition coefficients of alkylphenols under different temperatures (The water salinity is 4000 mg/L)使用不同盐度的水与原油混合平衡后，烷基酚的油水分配系数的大小情况如图 6所示。三种盐度下原油中的烷基酚的分布特征与原始特征保持一致，没有见到烷基酚异构体之间的相对丰度变化。低油水分配系数的烷基酚异构体对盐度的敏感程度较低，油水分配系数值的变化十分接近，如苯酚和甲基酚。而高油水分配系数的烷基酚异构体，对盐度的敏感程度较高，随着盐度的增加，其油水分配系数的变化十分明显，如2, 6-二甲基酚和2, 4, 6-三甲基酚。观察实验结果可以得出，烷基酚在油水体系中的分配系数随着水相盐度的增加而升高；通过比对图 5与图 6发现，图 6的变化幅度更小，说明盐度的影响相对温度影响较弱。
图 6 X37原油在不同盐水浓度下的烷基酚油水分配系数大小(温度为65 ℃)Figure 6. Oil-water partition coefficients of alkylphenols under different salinities (The temperature is 65 ℃)X37原油非烃组分含量相对较低，仅为37%，X45原油和X61原油非烃组分含量相对较高，分别为45%和61%。X37原油、X45原油和X61原油在同一温度条件下与同一盐度的水混合平衡后，计算得到烷基酚在不同原油和水中的分配系数变化如图 7所示，三种原油C0—C1烷基酚的油水分配系数差异不如C2—C3显著，而且并未随着原油非烃组分升高而呈现出规律性的变化。
图 7 不同非烃含量的原油与水混合平衡后烷基酚的油水分配系数大小(温度为65 ℃，水的盐度为4000 mg/L)Figure 7. Oil-water partition coefficients of alkylphenols from crude oil with different contents of non-hydrocarbon (The temperature is 65 ℃, and the water salinity is 4000 mg/L)4. 讨论
随着温度的升高，烷基酚在油水中的分配表现为分配系数值的规律性降低。然而，这种现象在油与盐水的体系中并不普遍。例如，Carlisle and Kapoor(1982)和Knaepen et al.(1990)在储层压力和温度下研究了乙酸乙酯在油与盐水系统中的分配行为。两项研究均得出乙酸乙酯的分配系数随温度的增加而增加，表现出与烷基酚相反的趋势。Leo et al.(1971)研究了不同溶剂系统之间许多溶质的分配系数，并表明分配系数的变化与温度正相关或负相关，具体取决于所用的溶剂系统。因此，在实验室条件下进行的油水平衡实验测量所获得的分配系数数据来预测地下条件准确性可能还有待提高。
随着盐水浓度的增加，烷基酚的分配系数明显增加，表明在更高的盐水盐度下，烷基酚大多更倾向于留在油相中，这与温度升高的影响相反。许多盆地的温度和盐度都会随着深度增加而升高，但两者对分配系数的影响有着相反的作用，因此温度和盐度存在相互抵消的可能。原油与盐水系统中的乙酸乙酯也观察到了这种与盐度相关的行为(Carlisle and Kapoor, 1982; Knaepen et al., 1990)。Price(1976)研究了烃类在盐度不同、总氯化钠含量高达350000 mg/L的盐水中的水溶性变化，烃类的水溶性随着盐水盐度的增加而降低。烷基酚的分配行为可能也反映了水相的这种盐析效应(Bennett and Larter, 1997)。总之，结合已有的研究与实验结果表明原油与盐水体系中烷基酚的分配系数随着盐水盐度的增加而升高。
随着原油非烃组分的增加，烷基酚的分配系数并无明显相关性。苯酚、甲基酚的油水分配系数在原油非烃组分不同时相差较小。有一部分烷基酚油水分配系数与原油的非烃组分呈现出正相关性，但并不是所有烷基酚均有这种规律。Bennett and Larter(1997)实验室研究结果表明，烷基酚油水分配系数与原油中的非烃组分含量为正相关，并且相关性好。但此次实验并没有得到烷基酚的油水分配系数与非烃组分之间具有良好的正相关关系，这可能与原油流体的性质有关，因为X37和X45原油中的烷基酚的非烃组分的含量较为接近。
5. 结论
(1)温度、水相的盐度及原油中的非烃组分均会改变烷基酚的油水分配系数。烷基酚在油水体系中的分配系数随着温度的升高而减小，随着水相盐度的增加而增加，非烃组分的变化会影响烷基酚的油水分配系数，但在实验中未发现明显规律。
(2) 实验室条件下测量的分配系数数据虽然不能直接适用于预测地下条件下油和水之间烷基酚的分布，但可以提供一些原油性质相关的信息：温度对绥中36-1原油烷基酚分配系数的影响要大于盐水浓度，C2—C3烷基酚比低分子量的C0—C1烷基酚更容易受到温度变化的影响。
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图 1 鄂尔多斯盆地延河剖面位置和中生界油田分布简图
Figure 1. Simplified map of the location of Yanhe section and the distribution of Mesozoic Oil fields in Ordos Basin
图 2 安沟露头野外特征
a—三叠系延长组正层型（延河）剖面和安沟露头区位置图；b—安沟露头区三维点云模型及分区解剖方案（白色虚线为图3剖面实测路线）；c—B区露头致密砂岩中含油非均质性特征（箭头所指为结合型砂岩中灰白色不含油区域，其余棕色区域均普遍含油；白圈内为比例尺）
Figure 2. Field characteristics og Angou outcrop
(a) Location map of the stratotype (Yan river) section of Triassic Yanchang Formation and the Angou outcrop; (b) Low resolution point-cloud dataset showing the extent of three studied surfaces of the Angou outcrop (black dotted round rectangle) and location of measured section (white dotted line); (c) Close-up view of B-surface showing the heterogeneity of oil charging（The most brown areas are oil-bearing, whereas others are oil-free (white arrows)；proportional scale in the white circle)
图 3 安沟露头致密砂岩储层结构非均质性模型
a—B区露头三维点云模型面向105°方位的正射影像（红色条带为野外手持切割机连续取样位置）；b—结合型致密砂岩储层中不同级别构型界面和含油非均质性特征示意图（其中水道叠置和砂坝加积界面为写实，交错层等底形界面仅为示意，n代表古流向测量数值，玫瑰花图显示古流向）
Figure 3. Model for architectural heterogeneity in tight sandstone reservoir exposed in the Angou outcrop
(a) Digital orthophoto of 3D point-cloud model of B-surface facing 105-degree, area of continuous sampling using Husquvarna power cutter is denoted by red bands; (b) Diagram showing different-scale architectural boundaries and heterogeneity of oil charging in amalgamated tight sandstone reservoir (For simplicity, storey and barform surfaces are depicted explicitly, whereas bedform surfaces are shown schematically, n represents the measured number of paleo-flows, and the rose diagram shows the paleo-flows)
图 4 安沟露头C区实测地层剖面柱状图及典型岩相野外照片
n代表古流向测量数据a—实测剖面底部的深湖相长7张家滩页岩及上覆三角洲前缘亚相发育槽状交错层（白色箭头所指）和丘状交错层（黑色箭头所指）的灰白色巨厚层中粒石英岩屑砂岩；b—三角洲前缘亚相砂岩底部发育的重荷模（白色箭头所指）及内部发育的泄水构造（黑色箭头所指）；c—三角洲前缘亚相砂岩内部发育的包卷层理；d—三角州平原相粉砂质泥岩中直立的芦木化石；e—三角州平原亚相劣质煤层中大量保存的植物茎干（白色箭头所指）和叶片（黑色箭头所指）；f—三角洲前缘亚相砂岩内部发育的垂直虫孔；g—长6和长7地层界限上下不同方向的槽状交错层（箭头所指）；h—长6地层底部河流相砂岩底部发育的大型下切侵蚀面
Figure 4. Columnar diagram of measured stratigraphic section and field photographs of typical petrographic facies in Area C of Angou outcrop
(a) Profundal facies Zhangjiatan shale (lower-left corner) and trough (white arrows) and hummocky (black arrows) cross-stratifications and in overlying delta front facies sandstone; (b) Load casts (white arrows) and dewatering structures (black arrows) in delta front facies sandstone; (c) Convolute lamination in delta front facies sandstone; (d) Trunk of calamite fossil preserved in delta plain facies silty mudstone; (e) Stems and leaves of unidentified plant fossils in delta plain facies coal-bearing beds; (f) Rooting or unidentified burrowing (white arrows) in delta front facies sandstone; (g) Channelized incision surface developed on the top of delta front facies deposits of Chang 7 member, Overlying facies are coarser fluvial facies of Chang 6 member; (h) The stratigraphic boundary between Chang 6 and 7 members underlain and overlain by delta and fluvial facies sandstone with NEE- and SSW-oriented trough cross-stratifications (white arrows) n represents the number of measured paleo-flows
图 5 局部露头含油非均质性以及单层砂岩不同部位的物性与成岩特征
a—单层砂岩含油特征露头近照及连续取样记录，采样位置（红色箭头）；b—单层砂岩含油非均质性示意图及薄片样品位置；c—单层砂岩底部样品，发育有机质纹层的中粒长石砂岩，正交偏光；d—单层砂岩底部样品，发育假杂基（黑色箭头）、长石自生加大（灰色箭头）和黄铁矿胶结（白色箭头）的中粒长石砂岩，单偏光；e—单层砂岩中部样品，发育方解石和浊沸石连晶式胶结的细粒长石砂岩，正交偏光；f—单层砂岩顶部发育亮晶（白色箭头）和泥晶（黑色箭头）方解石基底式胶结的极细粒长石砂岩，正交偏光
Figure 5. Details of oil-bearing heterogeneity in local outcrops and physical properties and diagenetic characteristics in different parts of individual sandstone layer
(a) Close-up view of oil-bearing characteristic of each sandstone bed and record of continuous sampling for detailed observation, sampling location (red arrows); (b) Schematic diagram showing heterogeneity of oil charging in single bed of tight sandstone and positions of representative samples for thin-section; (c)The bottom sample of single-layer sandstone, medium grained arkose sandstone with organic lamination, cross-polarized light, sample B-1; (d) The bottom sample of single-layer sandstone is a mediumgrained arkose with pseudoheterobasic (black arrow), autogenetic extension of feldspar (gray arrow) and pyrite cement (white arrow), plane polarized light, sample B-2; (e)The central sample of single-layer sandstone developed fine grained arkose with calcite and turbidite intergranular cementation, cross-polarized light, sample B-3; (f)The top of the singlelayer sandstone is a very finegrained arkose with sparry (white arrow) and micrite (black arrow) calcite basement cement, cross-polarized light, sample B-4
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