王道偉, 王鐵冠, 李美俊, 宋到福, 師生寶

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王道偉1,2,3*, 王鐵冠2,3, 李美俊2,3, 宋到福2,3, 師生寶2,3

(1. 中海油能源發(fā)展股份有限公司 工程技術分公司, 天津 300452; 2.中國石油大學(北京) 油氣資源與探測國家重點實驗室, 北京 102249; 3. 中國石油大學(北京) 地球科學學院, 北京 102249)

0 引?言

圖1 及其異構體的分子結構示意圖

1 地質(zhì)背景和樣品

塔中隆起位于塔里木盆地中部, 是一個長期發(fā)育的繼承性古隆起。隨著油氣勘探的深入, 先后發(fā)現(xiàn)了塔中Ⅰ號坡折帶超億噸級奧陶系生物礁型碳酸鹽巖油氣藏與塔中北斜坡下奧陶統(tǒng)巖溶風化殼型凝析氣藏[11?14]。在已確認塔里木盆地臺盆區(qū)發(fā)育上奧陶統(tǒng)和寒武系-下奧陶統(tǒng)兩套烴源層[15]的基礎上, 對生物標志物和碳同位素的特征分析表明, 除了烴源較為明顯單一的原油外, 塔中原油大部分為混源油[11]。

中深5井位于塔中隆起東部潛山區(qū)(圖2), 試油過程中在下寒武統(tǒng)吾松格爾組(?1w)6562~6671 m井段有油氣顯示, 產(chǎn)天然氣776~10381 m3/d、原油7.2~ 23.86 m3/d。原油物理性質(zhì)見表1,屬于低凝、低黏度、低硫、含蠟輕質(zhì)油, 原油族組成中飽和烴占90.6%,芳烴、非烴+瀝青質(zhì)含量分別為5.8%和3.6%。

圖2 塔里木盆地構造分區(qū)與樣品分布

表1 中深1井、中深1C井和中深5井原油物理性質(zhì)

除中深5井以外, 還采集和分析了鄰近的中深1井和中深1C井等原油樣品, 以探討該地區(qū)寒武系深層原油的油氣來源。除此之外, 本文還涉及油氣資源與探測國家重點實驗室前期分析樣品, 包括塔里木盆地臺盆區(qū)典型代表寒武系和中上奧陶統(tǒng)的有效烴源巖及相關原油(表2)。

2 實驗方法

按照常規(guī)分析方法進行原油族組分分離, 稱取30~50 mg原油, 用正己烷沉淀過濾出瀝青質(zhì), 再用正己烷、二氯甲烷+正己烷(2﹕1)在填有硅膠/氧化鋁的層析柱上依次洗脫出飽和烴、芳烴餾分, 然后轉(zhuǎn)入樣品瓶中待進一步分析。飽和烴氣相色譜分析采用島津GC-2010型色譜儀, 配置HP-5MS色譜柱(30 m×0.25 mm×0.25 μm), 程序升溫: 初溫100 ℃, 保持1 min, 以4 ℃/min升至300 ℃,保持25 min。進樣口溫度保持300 ℃, 載氣為He氣(99.999%), 載氣流速為1.0 mL/min。

芳烴色譜質(zhì)譜分析在Agilent 6890 GC-5975i MS上進行, 配置HP-5MS彈性石英毛細柱(60 m× 0.25 mm × 0.25 μm), 程序升溫: 從初溫80 ℃保持1 min后, 以3 ℃/min的速率升至310 ℃, 保持16 min。進樣口溫度為300 ℃, 載氣為He氣(99.999%), 流速為1.0 mL/min, 不分流進樣。質(zhì)譜部分: EI電離源, 電離電壓為70 eV, 獲取數(shù)據(jù)方式為全掃描與選擇離子同時進行, 質(zhì)量掃描范圍為50~600/。

表2 塔里木盆地沉積抽提物和原油中、苯并[a]蒽及其甲基取代物的相關參數(shù)

注: 1) TOC數(shù)據(jù)參考Li.[1]; 2)根據(jù)王飛宇等VRo=0.533VLRo+0.667換算關系式得到的鏡質(zhì)組反射率; 3)代表測定的平均值

3 結果與討論

3.1 原油鏈烷烴組成

中深1井、中深1C井和中深5井原油的正烷烴發(fā)育較完整, 以低碳數(shù)為主, 均呈明顯的前峰型單峰態(tài)分布(圖3), 主峰碳數(shù)分別為C13或C15、C15、C14, 輕重比C21–/C22+值均大于3.8, 表明原油成熟度較高[16?17]。但中深5井和中深1井原油飽和烴色譜基線基本平穩(wěn), 中深1C井色譜基線具有顯著的“鼓包”(UCM峰), 且中-高碳數(shù)正烷烴損失較明顯, 正烷烴系列的偏態(tài)分布更為突出, 部分原油可能已經(jīng)裂解成氣[18]。中深1井、中深5井原油的姥植比分別為0.87或0.98、1.05, 反映其烴源巖沉積水體為偏還原環(huán)境, 而中深1C井原油的Pr/Ph值為1.81, 表現(xiàn)出姥鮫烷優(yōu)勢, 表明其有機質(zhì)的沉積環(huán)境可能偏氧化性[19]。

3.2 原油中甾萜類的分布特征

在眾多生物標志物中, 甾烷類和萜烷類是應用最普遍的兩類化合物, 可以反映烴源巖的有機質(zhì)輸入和沉積環(huán)境等特征, 適用于油-油和油源對比[20]。但在高成熟-過成熟的輕質(zhì)油或凝析油中, 甾萜類等生物標志物濃度很低, 甚至低于色譜質(zhì)譜(GC-MS)的檢測限。中深5井和中深1井原油為高成熟原油, 而中深1C井原油已達過成熟[18], 從/191和/217質(zhì)量色譜圖(圖4, 圖5)上可以看出, 色譜質(zhì)譜基線明顯抬升, 信噪比很低, 萜烷和甾烷等生物標志物已基本完全裂解, 無法應用其進行準確的地球化學研究。

圖3 中深5井、中深1井和中深1C井原油飽和烴氣相色譜圖

圖4 塔里木盆地中深5井等井位原油中萜烷分布圖(m/z 191)

圖5 塔里木盆地中深5井等井位原油中甾烷分布圖(m/z 217)

圖7 塔里木盆地臺盆區(qū)典型烴源巖抽提物中、苯并[a]蒽及其甲基取代系列的分布特征

圖8?塔里木盆地臺盆區(qū)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, 分別為0.04、0.11或0.05, 均小于0.20, 與其對應的甲基取代系列MBaA/2-Mchy值分別為0.12、0.14或0.13; 而中深1C井原油BaA/(BaA+Chy)值相對較高, 為0.48(>0.35), MBaA/2-MChy值為0.91(表2)。此外, 塔里木盆地其他來源于中上奧陶統(tǒng)的原油中, 成熟度從成熟到高成熟, 成熟度參數(shù)4-/1-MDBT值介于3.6~15.6之間, 但BaA/ (BaA+ Chy)與MBaA/2-Mchy值都很低, 而來源于寒武系烴源巖的原油中則較高(表2)。

圖9是MBaA/2-MChy與BaA/(BaA+Chy)的相關圖, 可以看出中深5井、中深1井原油與塔里木盆地臺盆區(qū)上奧陶統(tǒng)烴源巖及相關原油聚在一起, BaA/(BaA+Chy)和MBaA/2-MChy值都很低(小于0.20), 而中深1C井原油與寒武系烴源巖及典型來自寒武系烴源巖的原油相似, BaA/(BaA+Chy)和MBaA/2-MChy值較高(大于0.20), 這與Li.[1]的研究結果一致。

3.4 全油及餾分穩(wěn)定碳同位素特征

全油及其餾分碳同位素與其沉積有機質(zhì)的碳同位素具有繼承性, 一般相同來源原油因成熟度不同而產(chǎn)生的穩(wěn)定碳同位素組成13C值的差異不超過2‰~3‰[27?28]。因此, 碳同位素組成可以用于油-油、油-巖對比[29]。

圖9?塔里木盆地臺盆區(qū)下古生界烴源巖抽提物和原油中MBaA/2-Mchy與BaA/(BaA+Chy)的相關圖

中深1井、中深5井全油及其餾分碳同位素組成均較輕, 分布范圍介于–33.6‰~–30.6‰之間(表3),13C值均小于–30‰, 與上奧陶統(tǒng)烴源巖的13C值分布呈現(xiàn)良好的可比性(圖10); 而中深1C井?1x肖爾布拉克組凝析油及其餾分碳同位素組成比中深1井、中深5井原油明顯偏重, 其13C值分布范圍為–31.1‰~–27.6‰之間(表3), 與寒武系烴源巖的13C值分布具有可比性(圖10)。

3.5 油源判識

此外, 甾烷、三環(huán)萜烷及三芳甾烷等生物標志物組成特征對比[30]表明, 中深1井阿瓦塔格組揮發(fā)油與中上奧陶統(tǒng)烴源巖及塔河原油具有良好的可比性; 而中深1C井肖爾布拉克組凝析油則與寒武系烴源巖及T904、塔東2、英南2井原油完全可以對比。生物標志物、單體碳及硫同位素等研究[18]也表明中深1井原油來源于中上奧陶統(tǒng)烴源巖, 而中深1C井原油來源于寒武系烴源巖。

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圖10?塔里木盆地臺盆區(qū)下古生界烴源巖抽提物和原油及餾分碳同位素分布

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烴源巖抽提物及餾分穩(wěn)定碳同位素值

雖然中深1C井井底與中深1井水平距離僅為440 m[30], 但其來源于不同烴源巖, 主要是由于中下寒武系之間鹽巖層的遮擋, 使得油氣只發(fā)生側向運移, 同時塔中Ⅰ號斷裂以及與之相交的北東向走滑斷層成為油氣主要的運移通道, 從而使?jié)M加爾坳陷中上奧陶統(tǒng)烴源巖生成的油氣運移到中深1井中寒武統(tǒng)聚集成藏, 而中深1C油氣則由下部寒武系烴源巖垂向運移而來[18]。

4 結?論

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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 ?1w 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

國家自然科學基金(41272158); 油氣資源與探測國家重點實驗室導向性課題(PRP/indep-2-1402)

王道偉(1989–), 男, 碩士, 地質(zhì)學專業(yè), 油氣藏成因機理與分布預測方向。

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