塔中隆起中深5井与中深1井和烷基分布特征与油源启示

王道伟, 王铁冠, 李美俊, 宋到福, 师生宝



王道伟1,2,3*, 王铁冠2,3, 李美俊2,3, 宋到福2,3, 师生宝2,3

(1. 中海油能源发展股份有限公司 工程技术分公司, 天津 300452; 2.中国石油大学(北京) 油气资源与探测国家重点实验室, 北京 102249; 3. 中国石油大学(北京) 地球科学学院, 北京 102249)

0 引 言

图1 及其异构体的分子结构示意图

1 地质背景和样品

塔中隆起位于塔里木盆地中部, 是一个长期发育的继承性古隆起。随着油气勘探的深入, 先后发现了塔中Ⅰ号坡折带超亿吨级奥陶系生物礁型碳酸盐岩油气藏与塔中北斜坡下奥陶统岩溶风化壳型凝析气藏[11‒14]。在已确认塔里木盆地台盆区发育上奥陶统和寒武系-下奥陶统两套烃源层[15]的基础上, 对生物标志物和碳同位素的特征分析表明, 除了烃源较为明显单一的原油外, 塔中原油大部分为混源油[11]。

中深5井位于塔中隆起东部潜山区(图2), 试油过程中在下寒武统吾松格尔组(Є1w)6562~6671 m井段有油气显示, 产天然气776~10381 m3/d、原油7.2~ 23.86 m3/d。原油物理性质见表1,属于低凝、低黏度、低硫、含蜡轻质油, 原油族组成中饱和烃占90.6%,芳烃、非烃+沥青质含量分别为5.8%和3.6%。

图2 塔里木盆地构造分区与样品分布

表1 中深1井、中深1C井和中深5井原油物理性质

除中深5井以外, 还采集和分析了邻近的中深1井和中深1C井等原油样品, 以探讨该地区寒武系深层原油的油气来源。除此之外, 本文还涉及油气资源与探测国家重点实验室前期分析样品, 包括塔里木盆地台盆区典型代表寒武系和中上奥陶统的有效烃源岩及相关原油(表2)。

2 实验方法

按照常规分析方法进行原油族组分分离, 称取30~50 mg原油, 用正己烷沉淀过滤出沥青质, 再用正己烷、二氯甲烷+正己烷(2﹕1)在填有硅胶/氧化铝的层析柱上依次洗脱出饱和烃、芳烃馏分, 然后转入样品瓶中待进一步分析。饱和烃气相色谱分析采用岛津GC-2010型色谱仪, 配置HP-5MS色谱柱(30 m×0.25 mm×0.25 μm), 程序升温: 初温100 ℃, 保持1 min, 以4 ℃/min升至300 ℃,保持25 min。进样口温度保持300 ℃, 载气为He气(99.999%), 载气流速为1.0 mL/min。

芳烃色谱质谱分析在Agilent 6890 GC-5975i MS上进行, 配置HP-5MS弹性石英毛细柱(60 m× 0.25 mm × 0.25 μm), 程序升温: 从初温80 ℃保持1 min后, 以3 ℃/min的速率升至310 ℃, 保持16 min。进样口温度为300 ℃, 载气为He气(99.999%), 流速为1.0 mL/min, 不分流进样。质谱部分: EI电离源, 电离电压为70 eV, 获取数据方式为全扫描与选择离子同时进行, 质量扫描范围为50~600/。

表2 塔里木盆地沉积抽提物和原油中、苯并[a]蒽及其甲基取代物的相关参数

注: 1) TOC数据参考Li.[1]; 2)根据王飞宇等VRo=0.533VLRo+0.667换算关系式得到的镜质组反射率; 3)代表测定的平均值

3 结果与讨论

3.1 原油链烷烃组成

中深1井、中深1C井和中深5井原油的正烷烃发育较完整, 以低碳数为主, 均呈明显的前峰型单峰态分布(图3), 主峰碳数分别为C13或C15、C15、C14, 轻重比C21–/C22+值均大于3.8, 表明原油成熟度较高[16‒17]。但中深5井和中深1井原油饱和烃色谱基线基本平稳, 中深1C井色谱基线具有显著的“鼓包”(UCM峰), 且中-高碳数正烷烃损失较明显, 正烷烃系列的偏态分布更为突出, 部分原油可能已经裂解成气[18]。中深1井、中深5井原油的姥植比分别为0.87或0.98、1.05, 反映其烃源岩沉积水体为偏还原环境, 而中深1C井原油的Pr/Ph值为1.81, 表现出姥鲛烷优势, 表明其有机质的沉积环境可能偏氧化性[19]。

3.2 原油中甾萜类的分布特征

在众多生物标志物中, 甾烷类和萜烷类是应用最普遍的两类化合物, 可以反映烃源岩的有机质输入和沉积环境等特征, 适用于油-油和油源对比[20]。但在高成熟-过成熟的轻质油或凝析油中, 甾萜类等生物标志物浓度很低, 甚至低于色谱质谱(GC-MS)的检测限。中深5井和中深1井原油为高成熟原油, 而中深1C井原油已达过成熟[18], 从/191和/217质量色谱图(图4, 图5)上可以看出, 色谱质谱基线明显抬升, 信噪比很低, 萜烷和甾烷等生物标志物已基本完全裂解, 无法应用其进行准确的地球化学研究。

图3 中深5井、中深1井和中深1C井原油饱和烃气相色谱图

图4 塔里木盆地中深5井等井位原油中萜烷分布图(m/z 191)

图5 塔里木盆地中深5井等井位原油中甾烷分布图(m/z 217)

图7 塔里木盆地台盆区典型烃源岩抽提物中、苯并[a]蒽及其甲基取代系列的分布特征

图8 塔里木盆地台盆区代表原油中、苯并[a]蒽及其甲基取代系列的分布特征

中深5井、中深1井原油BaA/(BaA+Chy)值很低, 分别为0.04、0.11或0.05, 均小于0.20, 与其对应的甲基取代系列MBaA/2-Mchy值分别为0.12、0.14或0.13; 而中深1C井原油BaA/(BaA+Chy)值相对较高, 为0.48(>0.35), MBaA/2-MChy值为0.91(表2)。此外, 塔里木盆地其他来源于中上奥陶统的原油中, 成熟度从成熟到高成熟, 成熟度参数4-/1-MDBT值介于3.6~15.6之间, 但BaA/ (BaA+ Chy)与MBaA/2-Mchy值都很低, 而来源于寒武系烃源岩的原油中则较高(表2)。

图9是MBaA/2-MChy与BaA/(BaA+Chy)的相关图, 可以看出中深5井、中深1井原油与塔里木盆地台盆区上奥陶统烃源岩及相关原油聚在一起, BaA/(BaA+Chy)和MBaA/2-MChy值都很低(小于0.20), 而中深1C井原油与寒武系烃源岩及典型来自寒武系烃源岩的原油相似, BaA/(BaA+Chy)和MBaA/2-MChy值较高(大于0.20), 这与Li.[1]的研究结果一致。

3.4 全油及馏分稳定碳同位素特征

全油及其馏分碳同位素与其沉积有机质的碳同位素具有继承性, 一般相同来源原油因成熟度不同而产生的稳定碳同位素组成13C值的差异不超过2‰~3‰[27‒28]。因此, 碳同位素组成可以用于油-油、油-岩对比[29]。

图9 塔里木盆地台盆区下古生界烃源岩抽提物和原油中MBaA/2-Mchy与BaA/(BaA+Chy)的相关图

中深1井、中深5井全油及其馏分碳同位素组成均较轻, 分布范围介于–33.6‰~–30.6‰之间(表3),13C值均小于–30‰, 与上奥陶统烃源岩的13C值分布呈现良好的可比性(图10); 而中深1C井Є1x肖尔布拉克组凝析油及其馏分碳同位素组成比中深1井、中深5井原油明显偏重, 其13C值分布范围为–31.1‰~–27.6‰之间(表3), 与寒武系烃源岩的13C值分布具有可比性(图10)。

3.5 油源判识

此外, 甾烷、三环萜烷及三芳甾烷等生物标志物组成特征对比[30]表明, 中深1井阿瓦塔格组挥发油与中上奥陶统烃源岩及塔河原油具有良好的可比性; 而中深1C井肖尔布拉克组凝析油则与寒武系烃源岩及T904、塔东2、英南2井原油完全可以对比。生物标志物、单体碳及硫同位素等研究[18]也表明中深1井原油来源于中上奥陶统烃源岩, 而中深1C井原油来源于寒武系烃源岩。

,

图10 塔里木盆地台盆区下古生界烃源岩抽提物和原油及馏分碳同位素分布

表3 中深1井、中深1C井和中深5井原油和塔里木盆地代表烃源岩抽提物及馏分稳定碳同位素值

虽然中深1C井井底与中深1井水平距离仅为440 m[30], 但其来源于不同烃源岩, 主要是由于中下寒武系之间盐岩层的遮挡, 使得油气只发生侧向运移, 同时塔中Ⅰ号断裂以及与之相交的北东向走滑断层成为油气主要的运移通道, 从而使满加尔坳陷中上奥陶统烃源岩生成的油气运移到中深1井中寒武统聚集成藏, 而中深1C油气则由下部寒武系烃源岩垂向运移而来[18]。

4 结 论

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The distribution of chrysene and methylchrysenes in oils from wells ZS5 and ZS1in the Tazhong Uplift and its implications in oil-to-source correlation

WANG Dao-wei1,2,3*, WANG Tie-guan2,3, LI Mei-jun2,3, SONG Dao-fu2,3and SHI Sheng-bao2,3

1. EnerTech-Drilling and Production Company, CNOOC Energy Technology and Services Limited, Tianjin 300452, China;2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;3. College of Geosciences, China University of Petroleum, Beijing 102249, China

Oils from the Lower Cambrian Є1w Wusonggeer Formation dolomite reservoirs were found in Well ZS5 in the Tazhong Uplift of the Tarim Basin. The oils are characterized by low freezing point, low viscosity and low sulfur content. They belong to waxy light oils. This study analyzed the distribution patterns of chrysene, benzo[a]anthracene and alkyl-substituted series in crude oils from wells ZS5, ZS1 and ZS1C. The composition of chrysene, benzo[a]anthracene and carbon isotopic analyses were also made for the representative Cambrian and Upper Ordorvician source rocks from the cratonic region of the Tarim Basin. It is shown that oils from wells ZS5 and ZS1 are characterized by low abundances of benzo[a]anthracene and methylbenzo[a]anthracene relative to chrysene and methylchrysenes, and low13C values. The case is consistent with that of organic matter from the Upper Ordovician source rocks. In contrast, crude oils from Well ZS1C are characterized by relatively high abundances of benzo[a]anthracene and methylbenzo[a]anthracene, and high13C values, which can be correlated with those of organic matter from the Cambrian source rocks in the cratonic region of the Tarim Basin. For the lack of conventional steroids and terpenes in light oils or condensates with high maturity, chrysene and alkyl-substituted homologues can be used as effective molecular markers.

Well ZS5; chrysene; benzo[a]anthracene; methylchrysene; Tarim Basin

P593; P599

A

0379-1726(2016)05-0451-11

2015-03-10;

2015-06-10;

2016-04-26

国家自然科学基金(41272158); 油气资源与探测国家重点实验室导向性课题(PRP/indep-2-1402)

王道伟(1989–), 男, 硕士, 地质学专业, 油气藏成因机理与分布预测方向。

WANG Dao-wei, E-mail: wangdaoweino1@126.com; Tel: +86-10-89739011