Origin and source of natural gas in the Upper Paleozoic in Linxing area, Ordos Basin

  • Wei-qiang HU ,
  • Yang-bing LI ,
  • Xin CHEN ,
  • Li-tao MA ,
  • Cheng LIU ,
  • Ying HUANG ,
  • Fang QIAO ,
  • Duo WANG ,
  • Zai-zhen LIU
Expand
  • CNOOC EnerTech⁃Drilling & Production Co. , Tianjin 300452, China

Received date: 2019-07-22

  Revised date: 2019-08-29

  Online published: 2020-01-09

Supported by

the National Natural Science Foundation of China(41502132)

The Research Project of China National Offshore Oil Corporation(CNOOC-KJPTGCJS2016-01)

Highlights

Study of the origin and source of natural gas plays an important role in exploration and development, which can provide a theoretical basis for natural gas migration and accumulation. Based on the comprehensive analysis of the characteristics of the natural gas composition, carbon isotope, light hydrocarbons and source rocks in the Upper Paleozoic in Linxing area of Ordos Basin, the origin and source of Upper Paleozoic natural gas in this area are discussed. The study shows that methane is the main component of natural gas, with low contents of heavy hydrocarbons and non-hydrocarbons, mainly belonging to dry gas in the Upper Paleozoic in Linxing area. The values of δ13C1, δ13C2 and δ13C3 of natural gas are in the ranges from -45.6‰ to -32.9‰, -28.9‰ to -22.3‰ and -26.2‰ to -19.1‰, respectively. The carbon isotopic values of alkane gas show a general trend of positive carbon sequence. δ13C1 value is less than -30‰, with typical characteristics of organic origin. There is a certain similarity in the composition characteristics of light hydrocarbons. The C7 series shows an advantage of methyl hexane, while the C5-7 series mainly shows an advantage of isoalkane. The Upper Paleozoic natural gas in this area is mainly composed of mature coal-derived gas, containing a small amount of coal-derived gas and oil-type gas mixture; the natural gas reservoirs of Shihezi Formation are mainly transported by pressurized diffusion of hydrocarbon generation from Shanxi Formation source rock hydrocarbons to filling and accumulation in near-source reservoir or far-source reservoir. The natural gas reservoirs of Taiyuan Formation mainly come from the source rocks of Taiyuan Formation itself, and are generated and stored in the source rocks, in which it is self-generation and self-preservation.

Cite this article

Wei-qiang HU , Yang-bing LI , Xin CHEN , Li-tao MA , Cheng LIU , Ying HUANG , Fang QIAO , Duo WANG , Zai-zhen LIU . Origin and source of natural gas in the Upper Paleozoic in Linxing area, Ordos Basin[J]. Natural Gas Geoscience, 2020 , 31(1) : 26 -36 . DOI: 10.11764/j.issn.1672-1926.2019.08.009

0 引言

随着勘探开发技术的不断突破与发展,非常规油气已成为中国原油产量稳定和天然气产量飞速增长的接替能源[1,2,3,4,5]。从国家能源发展战略来看,进军非常规油气领域是“十三五”的一个重要发展战略。中石油、中石化和中海油均致力于快速发展非常规油气产业,先后建立了致密气、页岩气和煤层气国家示范工程项目。鄂尔多斯盆地是中国陆上第二大含油气盆地,总体为西翼陡窄,东翼宽缓的南北向不对称大型叠合克拉通盆地[6,7,8],蕴含非常丰富的非常规油气资源[9,10,11,12,13]。经过50余年的勘探开发研究,陆续在盆地内发现了苏里格、大牛地、榆林、子洲、米脂、神木、乌审旗及东胜等致密砂岩大气田,是我国目前发现千亿立方米级以上大气田最多的盆地,显示该区具有巨大的天然气勘探潜力[14,15,16,17]
临兴地区位于鄂尔多斯盆地东缘,油气资源丰富。该区钻井气测显示,从石千峰组5段(千5段)—太原组普遍含气,单井钻遇气层厚度主要分布于20~80 m之间,平均厚度为34.6 m;气层主要集中发育在千5段、上石盒子组(盒4段)—下石盒子组(盒8段)、太原组。通过压裂试验显示,部分勘探井获得工业气流或低产气流,表明研究区具有良好勘探前景[18,19,20]。由于临兴地区上古生界天然气勘探开发程度相对较低,对该区上古生界天然气成因及来源缺乏系统认识。特别是早白垩世,东中部紫金山岩体的侵入,形成紫金山隆起区[21,22],隆起区的形成对天然气运移成藏过程的控制作用尚不清楚,制约了研究和认识的深入。因此,有必要加强对临兴地区上古生界天然气成因及来源的分析研究,为该区上古生界天然气藏聚集成藏提供依据。

1 地质背景

鄂尔多斯盆地属于大型克拉通盆地,构造总体形态为东翼宽缓、西翼陡窄的南北向不对称矩形盆地,主要经历了4个沉积阶段:中晚元古代发育坳拉谷盆地阶段、古生代发育大型稳定克拉通盆地阶段、中生代发育前陆盆地阶段、新生代发育周缘断陷盆地阶段[9]。盆地划分为6个二级构造单元:天环坳陷、西缘冲断带、晋西挠褶带、伊陕斜坡、渭北隆起和伊盟隆起(图1)。
图1 研究区沉积构造综合示意

Fig.1 Comprehensive schematic diagram of sedimentary and structures in the study area

临兴地区主要位于鄂尔多斯盆地东缘的临县和兴县境内,主要位于晋西挠褶带,总体为简单的单斜构造,仅在局部有差异,整体呈东高西低之势[23,24,25]。根据野外露头对比观察和钻探测井等资料显示[26,27],研究区石炭系—二叠系自下而上发育有本溪组(C2 b)—太原组(P1 t)—山西组(P1 s)—石盒子组(P2 sh)—石千峰组(P3 sq)。其中,C2 b—P1 t—P1 s发育泥岩和煤为主,常作为气源岩;P2 sh—石千峰组5段主要发育砂泥岩互层。同时,石千峰组厚层泥岩可作为气藏的区域盖层,封堵天然气向上运移,并与下伏的储集层形成多套储盖组合关系。笔者在岩心观察的基础上,利用临兴地区20口井的气体组分、碳同位素、轻烃和30余口井的烃源岩有机碳、岩石热解、镜质体反射率等大量地球化学测试资料,对研究区上古生界天然气地球化学特征、成因类型、气源及烃源岩生烃潜力等进行综合分析研究,确定天然气成因及来源,为后续勘探领域的拓展提供方向性指导。

2 实验分析及方法

本文采集临兴地区20口井的20个气样进行天然气组分、碳同位素以及轻烃分析;30口井的200余样次的泥岩和煤进行岩石热解分析、有机碳含量测定、镜质体反射率测定,以上测试均由中海油能源发展股份有限公司工程技术分公司非常规实验中心完成。其中,天然气组分分析采用Agilent 7890B气相色谱仪,碳同位素分析采用Elementar isoprime vision同位素测定仪,轻烃采用Agilent 6890A气相色谱仪,岩石热解分析采用Rock-Eval 6热解分析仪,有机碳含量测定采用CS-744碳硫分析仪,镜质体反射率测定采用CRAIC 508PV镜质体反射率仪。天然气组分、碳同位素、轻烃测试结果见表1表2;泥岩和煤的岩石热解、有机碳测定、镜质体反射率测定统计结果详见表3
表1 鄂尔多斯盆地临兴地区上古生界天然气组分和碳同位素

Table 1 The natural gas composition and carbon isotope in Upper Paleozoic in Linxing area, Ordos Basin

井号 层位 组分含量/%

干燥

系数

δ13C/‰(VPDB) R O/%
CH4 C2H6 C3H8 iC4H10 nC4H10 CO2 N2 C1 C2 C3
X-1 P2 sq 99.32 0.21 0.00 0.00 0.00 0.40 0.00 0.998 / / / /
X-2 P2 sh 93.06 0.98 0.21 0.04 0.05 0.04 5.54 0.986 -37.7 -25.5 -23.5 0.58
X-3 P2 sh 97.96 1.56 0.28 0.05 0.05 0 0.11 0.981 -36 -26.1 -23.5 0.77
X-4 P2 sh 96.82 1.35 0.36 0.06 0.07 0.02 1.2 0.981 -37.3 -27.2 -24.8 0.62
X-5 P2 sh 97.14 1.17 0.2 0.04 0.03 0.03 1.32 0.985 -37.5 -27.1 -24.0 0.6
X-6 P2 sh 99.11 0.15 0 0 0 0.57 0 0.990 / / / 1.95
X-7 P2 sh 91.16 4.69 1.33 0.19 0.26 0.02 1.94 0.934 -34.8 -27.5 -25.3 0.94
X-8 P2 sh 93.93 2.73 0.76 0.13 0.19 0.04 1.76 0.961 -36.4 -26.6 -24.7 0.72
X-9 P2 sh 93.82 1.15 0.32 0.06 0.09 0.01 3.78 0.983 -36.5 -28.9 -26.0 0.71
X-10 P2 sh 98.92 0.84 0.13 0 0 0.11 0 0.990 -32.9 -23.9 -21.6 1.28
X-11 P2 sh 98 1.44 0.28 0.05 0.05 0.06 0.11 0.982 -37.2 -26.1 -24.1 0.63
X-12 P2 sh 94.56 3.6 0.9 0.14 0.15 0.08 0.49 0.952 -34.6 -25.9 -24.5 0.97
X-13 P1 s 90.74 5.2 1.68 0.23 0.32 0.05 1.45 0.924 -33.2 -28.1 -26.2 1.21
X-14 P1 t 96.04 0.75 0.08 0.02 0.02 2.1 0.97 0.991 -39.8 -24.1 -20.3 0.41
X-15 P1 t 92.68 6.31 0.28 0.13 0.12 0.15 0.45 0.931 -41.3 -22.3 / 0.32
X-16 P1 t 93.33 0.12 0 0 0 0.02 6.47 0.990 -40.4 -26.5 -19.1 0.38
X-17 P1 t 96.53 1.14 0.17 0.03 0.03 1.8 0.25 0.986 -41.1 -24.8 -22.8 0.33
X-18 P1 t 95.93 1.48 0.23 0.04 0.04 1.58 0.62 0.982 -39.6 -24.6 -22.7 0.43
X-19 P1 t 95.92 0.27 0 0 0 2.2 1.6 0.990 -40.3 / / 0.38
X-20 P1 t 93.37 0.17 0.00 0.00 0 5.50 0.96 0.990 -46.5 / / /

注:①天然气R O值计算公式来自于戴金星[28]:δ13C1=14.12LgR O-34.39

表2 鄂尔多斯盆地临兴地区上古生界天然气轻烃参数

Table 2 The light hydrocarbon parameters of natural gas in Upper Paleozoic in Linxing area, Ordos Basin

井号 层位 nC7/% MCH/% ∑DMCP/% C5-7正构烷烃/% C5-7异构烷烃/% C5-7环烷烷烃/%
X-2 P2 sh 12.4 65.8 21.9 18.5 55.4 26.1
X-4 P2 sh 24.5 58.2 17.3 30.9 56.5 12.6
X-5-1 P2 sh 14.9 66.7 18.5 15.3 47.0 37.7
X-5-2 P2 sh 14.5 65.7 19.8 25.6 52.0 22.4
X-8 P2 sh 26.8 53.5 19.7 30.6 46.5 22.9
X-9 P2 sh 26.6 52.7 20.8 14.4 26.8 58.8
X-7 P2 sh 29.1 57.0 13.9 35.9 43.9 20.2
X-13 P1 s 22.6 60.6 16.8 33.0 52.3 14.7
X-14-1 P1 t 14.4 63.7 21.9 13.2 34.2 52.5
X-14-2 P1 t 12.1 69.6 18.3 20.2 44.8 35.0
X-17 P1 t 15.2 67.8 17.0 18.2 39.7 42.1
表3 鄂尔多斯盆地临兴地区上古生界烃源岩地球化学参数

Table 3 The geochemical parameters of source rocks in Upper Paleozoic in Linxing area, Ordos Basin

类别 有机碳/% (S 1+S 2)/(mg/g) R O/% T max/℃
P1 s 58.50 ~ 74.00 63.82 5 51.57 ~ 167.84 102.91 ( 5 ) 0.98 ~ 1.13 1.07 ( 5 ) 458.0 ~ 463.0 461.0 ( 7 )
暗色泥岩 0.75 ~ 21.80 3.28 ( 49 ) 0.54 ~ 71.10 5.03 ( 37 ) 0.78 ~ 1.38 0.98 ( 31 ) 426.0 ~ 480.0 461.0 ( 35 )
P1 t 45.60 ~ 76.10 63.28 ( 16 ) 45.33 ~ 309.37 158.53 ( 13 ) 0.87 ~ 1.45 1.18 ( 9 ) 447.0 ~ 501.0 463.2 ( 23 )
暗色泥岩 0.82 ~ 19.20 4.16 ( 22 ) 0.53 ~ 8.81 2.80 ( 17 ) 0.81 ~ 1.42 1.07 ( 24 ) 442.0 ~ 510.0 470.3 ( 20 )
C2 b 39.60 ~ 84.60 64.03 ( 14 ) 38.67 ~ 250.00 118.18 ( 10 ) 0.93 ~ 1.48 1.21 ( 8 ) 454.0 ~ 517.0 485.3 ( 15 )
暗色泥岩 0.78 ~ 12.00 3.66 ( 30 ) 0.58 ~ 17.93 3.12 ( 25 ) 0.89 ~ 1.39 1.12 ( 29 ) 450.0 ~ 508.0 482.7 ( 30 )

注: 58.50 ~ 74.00 63.82 5=

3 天然气地球化学特征

3.1 组分特征

临兴地区上古生界天然气组分(表1)测试结果表明:CH4含量分布于90.74%~99.32%之间,平均值为95.42%; C2H6含量分布于0.12%~6.31%之间,平均值为1.77%;C3H8含量分布于0~1.68%之间,平均值为0.36%;干燥系数介于0.924~0.998之间,平均值为0.975,20个气样中仅有3个为湿气,其余气样均为干气。非烃气体主要是CO2和N2,其中,CO2含量分布于0~5.5%之间,平均值为0.74%;N2含量分布于0~6.47%之间,平均值为1.45%。

3.2 碳同位素特征

临兴地区上古生界天然气碳同位素测试结果(表1)表明:δ13C1值分布于 -46.5‰~ -32.9‰之间,平均值为 -38.0‰;δ13C2值分布于 -28.9‰~ -22.3‰之间,平均值为 -25.9‰;δ13C3值分布于 -26.2‰~ -19.1‰之间,平均值为 -23.5‰,总体呈现δ13C1值偏低,δ13C2和δ13C3值偏高的分布特点。研究区天然气碳同位素值总体表现出正碳序列变化(δ13C113C213C3) (表1图2),并且δ13C1值均小于 -30‰,具有典型的有机成因气特征。
图2 临兴地区上古生界天然气单体碳同位素分布特征

Fig.2 The characteristics of carbon isotopic distribution of natural gas monomers in Upper Paleozoic in Linxing area

3.3 轻烃特征

临兴地区上古生界天然气轻烃参数(表2)表明,C7系列中甲基环己烷指数(MCH)分布于52.7%~69.6%之间,均大于50%,平均值为61.9%;各种构型的二甲基环戊烷(ΣDMCP)分布于13.9%~21.9%之间,平均值为18.7%;正庚烷(nC7)分布于12.1%~29.1%之间,均小于35%,平均值为19.4%;C5-7系列中正构烷烃主要分布于13.2%~35.7%之间,平均值为23.2%;各种构型的C5-7异构烷烃主要分布于26.8%~56.5%之间,平均值为45.4%;C5-7环烷烷烃主要分布于12.6%~58.8%之间,平均值为31.3%。综合研究认为,研究区天然气轻烃组成相似,C7系列表现出甲基环己烷优势,C5-7系列主体表现出异构烷烃优势。

4 天然气成因分析

4.1 碳同位素判识成因

甲烷和乙烷碳同位素及其同系物碳同位素序列是判定天然气成因的重要指标,通常被用来判识天然气成因[28,29,30,31,32] 。有机成因气的烷烃气碳同位素组成具有正碳序列(δ13C113C213C313C4),甲烷碳同位素值一般小于 -30‰,而无机成因气则与之相反[33,34,35]。不同学者利用δ13C2判别煤成气和油型气划分界限不同,但整体差别不大。参考前人利用δ13C2对煤成气和油型气的划分,本文采用δ13C2值大于 -28‰和δ13C3值大于 -25‰,判识天然气为煤成气;δ13C2值介于 -30‰~ -28‰之间则判识为煤成气与油型气的混合气;δ13C2值小于 -30‰则判识为油型气。临兴地区天然气碳同位素值表现出正碳序列(δ13C113C213C3) (表1图 2),并且δ13C1值均小于 -30‰,属于有机成因;研究区天然气母质类型为腐殖型,以生气为主,与国外典型盆地Ⅲ型干酪根生成的天然气特征一致,与国内鄂尔多斯盆地大牛地地区煤成气特征基本一致(图3);δ13C2值分布于 -28.9‰~ -22.3‰之间,δ13C3值分布于 -26.2‰~ -19.1‰之间,16个样品中仅有2个样品δ13C2值小于 -28‰和δ13C3值小于 -25‰,样品点主要分布于煤成气区间内,属于煤成气,仅有少数样品点散落于混合气区间内,属于煤成气与油型气的混合气(图4,图5)。
图3 天然气δ13C1—δ13C2成因类型鉴别图版(图版来自于文献[43];大牛地数据来自于文献[33])

Fig. 3 The identification of genetic types of natural gas δ13C113C2(Plate from Ref.[43];Date of gases from Daniudi are from Ref.[33])

图4 天然气δ13C1—δ13C2成因类型鉴别图版(图版来自于文献[44])

Fig.4 The identification of genetic types of natural gas δ13C213C1 (Plate from Ref.[44])

图5 天然气δ13C1—δ13C2—δ13C3成因类型鉴别图版(图版来自文献[1])

Fig.5 The identification of genetic types of natural gas δ13C1 -δ13C2 -δ13C3 (Plate from Ref.[1])

4.2 轻烃判识成因

根据前人研究成果[36,37,38],轻烃中C7系列的各种结构的二甲基环戊烷(ΣDMCP)、正庚烷(nC7)和甲基环己烷(MCH)的相对含量,以及C5-7系列中环烷烃、正构烷烃和异构烷烃的相对含量来区分有机质类型。根据胡国艺等[39,40,41,42]的C7和C5-7轻烃系列判识标准:油型气的正庚烷(nC7)相对含量大于30%,甲基环己烷(MCH)相对含量小于70%;煤成气的正庚烷(nC7)相对含量小于35%,甲基环己烷(MCH)相对含量大于50%,C5-7正构烷烃相对含量小于30%。根据气样轻烃测试结果(表2)和轻烃分布三角图版(图6,图7)分析表明,研究区天然气轻烃C7系列中正庚烷(nC7)相对含量介于12.1%~29.1%之间,均小于35%;甲基环己烷(MCH)相对含量介于52.7%~69.6%之间,均大于50%,并且样品都落在煤成气区间范围内,属于煤成气。而C5-7系列中C5-7正构烷烃相对含量介于13.2%~35.7%之间,在11个轻烃样品中有7个样品的C5-7正构烷烃相对含量值小于30%,并且大部分样品点落在煤成气范围内,仅有少部分样品落在油型气区间内,即研究区上古生界天然气主要属于煤成气,含有少量油型混合气,这与前文碳同位素分析研究结果一致。
图6 天然气中C7轻烃系列分布三角图

Fig.6 The ternary diagram of C7 light hydrocarbon series distribution of natural gas

图7 天然气中C5-7轻烃系列分布三角图

Fig.7 The ternary diagram of C5-7 light hydrocarbon series distribution of natural gas

5 天然气来源分析

临兴地区上古生界源岩主要是煤,其次是暗色泥岩。其中,煤厚度主要介于12~22 m之间,均值为16 m;暗色泥岩厚度主要介于95~115 m之间,均值为103 m[45]。研究区煤和暗色泥岩测试结果(表3)表明,有机质丰度较高,属于中等—好烃源岩;有机质类型属于Ⅲ型,以生气为主;R O值主要介于0.8%~1.5%之间,处于成熟—高过成熟阶段,进入大量生气阶段。由于研究区东中部有紫金山岩体的侵入,导致紫金山周边地区的镜质体反射率值大于2.0%,甚至达到4.2%,处于过成熟阶段;生气强度主要介于(18~32)×108 m3/km2之间,为后期天然气的聚集成藏奠定了丰富的物质基础。
天然气δ13C1R O值具有良好的线性关系可作为气源对比有效手段。根据戴金星[28]建立的煤成气经验公式:δ13C1=14.12LgR O-34.39对研究区天然气成熟度进行计算。计算结果(表1)表明:研究区P1 t天然气R O值主要介于0.32%~0.43%之间,平均值为0.38%,明显低于实测的煤和暗色泥岩R O值;P2 sh天然气R O值主要介于0.58%~1.28%之间,平均值为0.82%,与实测的P1 t、P1 s烃源岩成熟度R O值相比偏低。由于研究区P1 t—P1 s属于海陆过渡相煤系地层,P1 s—P1 t主要处于微咸水—咸水沉积环境,水介质是影响天然气δ13C1的关键因素。水介质越咸,天然气的δ13C1值越低[33],导致计算的P1 s、P1 t天然气成熟度比实测R O值偏低。整体反映,P1 t天然气来自于自身的太原组烃源岩,P2 sh天然气除了来自P1 t烃源岩之外,主要来自于P1 s烃源岩。
MANGO[46,47,48]提出轻烃成因理论,对于同一种源岩生成的所有轻烃具有一样的K 1K 2值,该值只与油气的母质有关,与成熟度无关。
K 1=A 1/A 2
式中:A 1=2-甲基己烷+2,3-二甲基戊烷;A 2=3-甲基己烷+2,4-二甲基戊烷。
K 2=P 3/(P 2+N 2
式中: P 2= 2-甲基己烷+3-甲基己烷;P 3=2,2-二甲基戊烷+2,4-二甲基戊烷+2,3-二甲基戊烷+3,3-二甲基戊烷+3-乙基戊烷;N 2=1,顺-3-二甲基环戊烷+1,反-3-二甲基环戊烷+1,1-二甲基环戊烷。
临兴地区上古生界天然气的K 1值整体差异较小,主要分布于0.97~1.27之间,平均值为1.12(表3);K 2值主要分布于0.34~0.75之间,平均值为0.56(表4)。研究区上古生界天然气的K 1值、K 2值变化趋势(图8)基本一致,这说明其上古生界天然气来自于同一含油气系统。
表4 临兴地区上古生界天然气K 1值和K 2值分布

Table 4 The distribution of K 1 and K 2 values of natural gas in Upper Paleozoic in Linxing area

井号 层位 A 1/% A 2/% P 2/% P 3/% N 2/% K 1/% K 2/%
X-4 P2 h 2.22 2.08 2.99 2.53 1.06 1.06 0.63
X-5-1 P2 h 4.52 3.99 5.02 4.50 2.78 1.13 0.58
X-5-2 P2 h 2.19 1.87 2.42 2.84 1.55 1.17 0.71
X-8 P2 h 3.06 2.70 4.32 2.00 1.48 1.13 0.34
X-9 P2 h 9.97 7.83 14.04 10.02 4.95 1.27 0.53
X-7 P2 h 3.32 2.66 4.69 2.08 1.63 1.25 0.33
X-13 P1 s 1.88 1.68 2.64 1.64 1.15 1.12 0.43
X-14-1 P1 t 3.35 3.21 4.01 4.56 3.32 1.04 0.62
X-14-2 P1 t 2.07 2.03 2.72 3.04 2.30 1.02 0.61
X-17 P1 t 3.19 3.29 4.41 4.00 2.42 0.97 0.59
图8 临兴地区上古生界天然气K 1值和K 2值斜率分布

Fig.8 The distribution of the Slope of K 1 and K 2 values of natural gas in Upper Paleozoic in Linxing area

PRINZHOFER等[49,50]研究表明,天然气Ln(C1/C2)-(δ13C1-δ13C2)和δ13C1-(C2/C1)的分布规律可以综合反映天然气所经历的热演化和次生改造过程(主要是运移成藏过程)。天然气未经次生改造过程或次生改造过程较弱时,组分和碳同位素组成的差异主要受烃源岩成熟度控制,Ln(C1/C2)和δ13C1-δ13C2参数均随着烃源岩成熟度的增加而升高,δ13C1和C2/C1参数均随着烃源岩成熟度的增加而降低。天然气遭受扩散运移散失作用时,表现为Ln(C1/C2)降低,δ13C1-δ13C2差值则逐渐增大;δ13C1减小,C2/C1比值逐渐减小。临兴地区P1 t天然气的δ13C1-δ13C2差值与Ln(C1/C2)同步增大,δ13C1与C2/C1值同步减小,反映了P1 t天然气随成熟度的变化趋势;P2 sh气藏中天然气的δ13C1-δ13C2差值逐渐增大,Ln(C1/C2)则逐渐减小,δ13C1与C2/C1值同步增大,表明P2 sh天然气具有明显的扩散运移特征(图9图10)。综合分析认为,研究区P2 sh天然气藏主要是由P1 s烃源岩生烃增压扩散运移至近源或远源储层内充注成藏;P1 t天然气藏主要来自于P1 t自身的烃源岩,在源岩内自生自储成藏。
图9 临兴地区上古生界天然气Ln(C1/C2)—(δ13C1-δ13C2)关系

Fig.9 The relationship diagram of natural gas Ln(C1/C2)vs.(δ13C1⁃δ13C2)in Upper Paleozoic in Linxing area

图10 临兴地区上古生界天然气δ13C1—(C2/C1)

Fig.10 The relationship diagram of natural gas δ13C1vs.(C2/C1) in Upper Paleozoic in Linxing area

6 结论

(1)研究区上古生界天然气甲烷含量较高,重烃和非烃含量较低;干燥系数介于0.924~0.998之间,主要属于干气;碳同位素值总体表现出正碳序列变化趋势,并且δ13C1值均小于-30‰,具有典型的有机成因气特征;轻烃中C7系列表现出甲基环己烷优势,C5-7系列主要表现出异构烷烃优势。
(2)研究区上古生界天然气δ13C2值分布大部分都大于-28‰;甲基环己烷指数大于50%,正庚烷相对含量小于 35%,C5-7正构烷烃相对含量大部分均小于30%,主要属于煤成气,含有少量煤成气与油型气的混合气。
(3)研究区上古生界天然气主要处于成熟阶段,P1 t天然气随成熟度变化, 主要来自于P1 t自身的烃源岩,P2 sh天然气具有明显的扩散运移特征,除了来自P1 t烃源岩之外,主要来自于P1 s烃源岩。
1
戴金星,倪云燕,吴小奇.中国致密砂岩气及在勘探开发上的重要意义[J].石油勘探与开发,2012,39(3):257-264.

DAI J X, NI Y Y, WU X Q. Tight gas in China and its significance in exploration and exploitation[J]. Petroleum Exploration and Development,2012,39(3):257-264.

2
房忱琛,戴金星,吴伟,等.中国晚古生代煤系相关的气田及其在天然气工业上的重要意义[J].天然气地球科学,2016,27(6):960-973.

FANG C C, DAI J X, WU W, et al. The Late Paleozoic gas fields related to coal measure in China and their significances on natural gas industry[J]. Natural Gas Geoscience,2016,27(6):960-973.

3
刘鹏,王伟锋,孟蕾,等.鄂尔多斯盆地上古生界煤层气与致密气联合优选区评价[J].吉林大学学报:地球科学版,2016,46(3):692-701.

LIU P, WANG W F, MENG L, et al. Joint optimization of coal-bed methane and tight gas in the Upper Paleozoic of the Ordos Basin[J]. Journal of Jilin University: Earth Science Edition, 2016,46(3):692-701.

4
姚海鹏,李玲,周晓刚.鄂尔多斯盆地上古生界煤系非常规天然气赋存特征[J].煤炭科学技术,2017,45(4):102-109, 136.

YAO H P, LI L, ZHOU X G. Deposition features of unconventional natural gas in Upper Paleozoic coal measures of Ordos Basin[J]. Coal Science and Technology,2017,45(4):102-109, 136.

5
梁建设,朱学申,柳迎红,等.沁水盆地与鄂尔多斯盆地上古生界致密气成藏条件类比及勘探潜力[J].煤炭学报,2016,41(1):192-201.

LIANG J S, ZHU X S, LIU Y H, et al. Comparative study on accumulation condition of the tight gas in the Upper Paleozoic of the Qinshui Basin and Ordos Basin and its exploration potential[J]. Journal of China Coal Society,2016,41(1):192-201.

6
刘晓鹏,赵会涛,闫小雄,等.克拉通盆地致密气成藏地质特征与勘探目标优选——以鄂尔多斯盆地上古生界为例[J].天然气地球科学,2019,30(3):331-343.

LIU X P, ZHAO H T, YAN X X, et al. The geological characteristics of tight sandstone gas and exploration target evaluation in the craton basin: Case study of the Upper Paleozoic of Ordos Basin[J]. Natural Gas Geoscience,2019,30(3):331-343.

7
方国庆,刘德良.鄂尔多斯盆地中部东西向天然气聚集区带研究[J].石油实验地质,2000,22(2):146-151.

FANG G Q, LIU D L. Study of the west-east trend natural gas accumulation zone in the middle of the Ordos Basin,China[J]. Petroleum Geology & Experiment,2000,22(2):146-151.

8
赵林,夏新宇,戴金星,等.鄂尔多斯盆地上古生界天然气富集的主要控制因素[J].石油实验地质200022(2): 136-139.

ZHAO L XIA X Y DAI J X,et al. Major factors controlling the enrichment of the Upper Paleozoic natural gas in the Ordos Basin[J]. Petroleum Geology & Experiment,2000,22(2):136-139.

9
胡维强,赵靖舟,李军,等.鄂尔多斯盆地西南部上古生界烃源岩特征及其对天然气藏形成与分布的控制作用[J].天然气地球科学, 2015, 26(6): 1068-1075.

HU W Q, ZHAO J Z, LI J, et al. Hydrocarbon source rocks characteristics and its controls on formation and distribution of gas of Upper Paleozoic in southwest Ordos Basin[J]. Natural Gas Geoscience, 2015, 26(6): 1068-1075.

10
孔庆芬,张文正,李剑锋,等.鄂尔多斯盆地奥陶系盐下天然气地球化学特征及成因[J].天然气地球科学,2019,30(3):423-432.

KONG Q F, ZHANG W Z, LI J F, et al. Geochemical characteristics and genesis of Ordovician natural gas under gypsolyte in Ordos Basin[J]. Natural Gas Geoscience,2019,30(3):423-432.

11
姚泾利,胡新友,范立勇,等.鄂尔多斯盆地天然气地质条件资源潜力及勘探方向[J].天然气地球科学,2018,29(10):1465-1474.

YAO J L, HU X Y, FAN L Y, et al. The geological conditions, resource potential and exploration direction of natural gas in Ordos Basin[J]. Natural Gas Geoscience,2018,29(10):1465-1474.

12
孟尚志,张文忠,莫日和,等.柳林区块多煤层含气性差异与煤层气成藏模式[J].煤炭科学技术,2015,43(2): 49-57.

MENG S Z, ZHANG W Z, MO R H, et al. Difference characteristics in gas-bearing between multiple coal seams and coalbed methane accumulation models in Liulin Area[J]. Coal Science and Technology, 2015, 43(2): 49-57.

13
王明健,何登发,包洪平,等.鄂尔多斯盆地伊盟隆起上古生界天然气成藏条件[J].石油勘探与开发,2011,38(1): 30-39.

WANG M J, HE D F, BAO H P, et al. Upper Palaeozoic gas accumulations of the Yimeng uplift, Ordos Basin[J]. Petroleum Exploration and Development,2011,38(1):30-39.

14
倪春华,刘光祥,朱建辉,等.鄂尔多斯盆地杭锦旗地区上古生界天然气成因及来源[J].石油实验地质,2018,40(2):193-199.

NI C H, LIU G X, ZHU J H, et al. Origin and source of natural gas in the Upper Paleozoic in Hangjinqi area, Ordos Basin[J]. Petroleum Geology & Experiment, 2018,40(2):193-199.

15
李贤庆,冯松宝,李剑,等.鄂尔多斯盆地苏里格大气田天然气成藏地球化学研究[J].岩石学报,2012,28(3):836-846.

LI X Q, FENG S B, LI J, et al. Geochemistry of natural gas accumulation in Sulige large Gas Field in Ordos Basin[J]. Acta Petrologica Sinica,2012,28(3): 836-846.

16
彭威龙,胡国艺,黄士鹏,等.天然气地球化学特征及成因分析——以鄂尔多斯盆地东胜气田为例[J].中国矿业大学学报,2017,46(1):74-84.

PENG W L, HU G Y, HUANG S P, et al. Natural gas geochemical characteristics and genetic analysis: A case study of the Dongsheng Gas Field in the Ordos Basin of China[J]. Journal of China University of Mining & Technology,2017,46(1):74-84.

17
郝蜀民,李良,张威,等.鄂尔多斯盆地北缘石炭系—二叠系大型气田形成条件[J].石油与天然气地质,2016,37(2) :149-154.

HAO S M, LI L ZHANG W,et al. Forming conditions of large-scale gas fields in Permo-Carboniferous in the northern Ordos Basin[J]. Oil & Gas Geology,2016,37(2):149-154.

18
顾娇杨,张兵,郭明强.临兴区块深部煤层气富集规律与勘探开发前景[J].煤炭学报,2016,41(1):72-79.

GU J Y, ZHANG B, GUO M Q. Deep coalbed methane enrichment rules and its exploration and development prospect in Linxing block[J]. Journal of China Coal Society,2016,41(1):72-79.

19
郭本广,许浩,孟尚志,等.临兴地区非常规天然气合探共采地质条件分析[J].中国煤层气,2012,9(4):3-6.

GUO B G, XU H, MENG S Z, et al. Geology condition analysis for unconventional gas co-exploration and concurrent production in Linxing area[J]. China Coalbed Methane, 2012,9(4):3-6.

20
郑定业,姜福杰,刘铁树,等.鄂尔多斯盆地东缘临兴地区天然气成因类型及气源分析[J].地球科学与环境学报,2018,40(2):203-214.

ZHENG D Y, JIANG F J, LIU T S, et al. Genetic types and sources of natural gas in Linxing area, the eastern margin of Ordos Basin, China[J]. Journal of Earth Sciences and Environment, 2018,40(2):203-214.

21
葛岩,朱光辉,万欢,等.鄂尔多斯盆地东缘紫金山侵入构造对上古生界致密砂岩气藏形成和分布的影响[J].天然气地球科学,2018,29(4):491-499.

GE Y, ZHU G H, WAN H, et al. The influence of Zijinshan structural belt to the formation and distribution of tight sandstone gas reservoir in Upper Paleozoic, in the eastern Ordos Basin[J]. Natural Gas Geoscience,2018,29(4):491-499.

22
李阳,倪小明,王延斌,等.鄂尔多斯盆地临兴地区上古生界压力特征及成因机制[J].天然气地球科学201930(7):997-1005.

LI Y, NI X M, WANG Y B, et al.Pressure characteristics and genetic mechanism of Upper Paleozoic in Linxing area in Ordos Basin[J]. Natural Gas Geoscience, 2019,30(7):997-1005.

23
傅宁,杨树春,贺清,等.鄂尔多斯盆地东缘临兴—神府区块致密砂岩气高效成藏条件[J].石油学报,2016,37(增1):111-120.

FU N, YANG S C, HE Q, et al. High-efficiency reservoir formation conditions of tight sandstone gas in Linxing-Shenfu blocks on the east margin of Ordos Basin[J]. Acta Petrolei Sinica,2016,37(S1):111-120.

24
谢英刚,孟尚志,万欢,等.临兴地区煤系地层多类型天然气储层地质条件分析[J].煤炭科学技术,2015,43(9): 71-75, 143.

XIE Y G, MENG S Z, WAN H, et al. Analysis on geological conditions of multi type natural gas reservoir in coal measure strata of Linxing area[J]. Coal Science and Technology,2015,43(9):71-75, 143.

25
谢英刚,孟尚志,高丽军,等.临兴地区深部煤层气及致密砂岩气资源潜力评价[J].煤炭科学技术,2015,43(2):21-24, 28.

XIE Y G, MENG S Z, GAO L J, et al. Assessments on potential resources of deep coalbed methane and compact sandstone gas in Linxing area[J]. Coal Science and Technology, 2015,43(2): 21-24, 28.

26
赵俊斌,唐书恒,孙振飞,等.鄂尔多斯盆地东缘兴县地区山西组高分辨率层序地层与聚煤规律[J].中国煤炭地质,2015,27(4):1-7.

ZHAO J B, TANG S H, SUN Z F, et al. Shanxi Formation high-resolution sequence stratigraphy and coal accumulation pattern in Xingxian area, Ordos Basin eastern margin[J]. Coal Geology of China, 2015,27(4):1-7.

27
沈玉林,秦勇,申建,等.鄂尔多斯盆地东缘上古生界煤系叠置含气系统发育的沉积控制机理[J].天然气工业2017,37(11):29-35.

SHEN Y L, QIN Y, SHEN J, et al. Sedimentary control mechanism of the superimposed gas bearing system development in the Upper Paleozoic coal measures along the eastern margin of the Ordos Basin[J]. Natural Gas Industry, 2017,37(11):29-35.

28
戴金星. 天然气碳氢同位素特征和各类天然气鉴别[J].天然气地球科学,1993,4(2/3):1-40.

DAI J X. Hydrocarbon isotope characteristics and identification of various types of natural gas[J]. Natural Gas Geoscience,1993,4(2/3):1-40.

29
李剑,刘朝露,李志生,等.天然气组分及其碳同位素扩散分馏作用模拟实验研究[J].天然气地球科学,2003,14(6):463-468.

LI J, LIU C L, LI Z S, et al. Experiment investigation on the carbon isotope and composition fractionation of methane during gas migration by diffusion[J]. Natural Gas Geoscience,2003,14(6):463-468.

30
HUANG S P, FANG X, LIU D, et al.Natural gas genesis and sources in the Zizhou Gas Field, Ordos Basin, China[J]. International Journal of Coal Geology,2015,152:132-143.

31
陈敬轶,贾会冲,李永杰,等.鄂尔多斯盆地伊盟隆起上古生界天然气成因及气源[J].石油与天然气地质,2016,37(2):205-209.

CHEN J Y, JIA H C, LI Y J, et al. Origin and source of natural gas in the Upper Paleozoic of the Yimeng uplift,Ordos Basin[J]. Oil & Gas Geology,2016,37(2):205-209.

32
戴金星,夏新宇,秦胜飞,等.中国有机烷烃气碳同位素系列倒转的成因[J].石油与天然气地质,2003,24(1):1-6, 11.

DAI J X, XIA X Y, QIN S F, et al. Causation of partly reversed orders of δ13C in biogenic alkane gas in China[J]. Oil and Gas Geology, 2003,24(1):1-6, 11.

33
WU X Q, LIU Q Y, ZHU J H, et al. Geochemical characteristics of tight gas and gas-source correlation in the Daniudi gas field, the Ordos Basin, China[J]. Marine and Petroleum Geology,2017,79:412-425.

34
ZHAO J Z, ZHANG W Z, LI J, et al. Genesis of tight sand gas in the Ordos Basin, China[J]. Organic Geochemistry,2014,74:76-84.

35
LIU Q Y, JIN Z J, MENG Q Q, et al. Genetic types of natural gas and filling patterns in Daniudi Gas Gield, Ordos Basin, China[J]. Journal of Asian Earth Sciences,2015,107:1-11.

36
韩文学,麻伟娇,侯连华,等.天然气轻烃指标的地质意义——以鄂尔多斯盆地神木气田与塔西南坳陷山前带天然气藏为例[J].石油与天然气地质,2017,38(5):869-877.

HAN W X, MA W J, HOU L H, et al. Geological significance of light hydrocarbon index of natural gas: Taking Shenmu Gas Field and piedmont zone of the southwest Tarim Basin as examples[J]. Oil & Gas Geology, 2017,38(5):869-877.

37
戴金星.利用轻烃鉴别煤成气和油型气[J].石油勘探与开发,1993,20(5):26-32.

DAI J X. Identification of coal formed gas and oil type gas by light hydrocarbons[J]. Petroleum Exploration and Development,1993,20(5):26-32.

38
王玮,沈忠民,裴森奇,等.致密砂岩气藏油气轻烃特征及其地质意义——以四川盆地西北部须家河组气藏为例[J].石油实验地质,2018,40(6):818-827.

WANG W, SHEN Z M, PEI S Q, et al. Light hydrocarbon characteristics of petroleum in a tight sandstone gas reservoir and its geological significance: A case study of the Upper Triassic Xujiahe Formation gas reservoir in the northwestern Sichuan Basin[J]. Petroleum Geology & Experiment,2018,40(6):818-827.

39
胡国艺,李剑,李谨,等.判识天然气成因的轻烃指标探讨[J].中国科学(D辑), 2007,37(增刊Ⅱ):111-117.

HU G Y, LI J, LI J, et al. Study on the origin identification of natural gas by the parameters of light hydrocarbon[J]. Science in China: Series D,2007,37( SupplementⅡ):111-117.

40
胡国艺,李谨,李志生,等.煤成气轻烃组分和碳同位素分布特征与天然气勘探[J].石油学报,2010,31(1):42-47.

HU G Y, LI J, Li Z S, et al. Composition and carbon isotopic distribution characteristics of light hydrocarbon in coal-derived gas and natural gas exploration[J]. Acta Petrolei Sinica. 2010,31(1):42-47.

41
胡国艺,汪为胜,廖凤蓉.煤成气轻烃地球化学特征及其影响因素:以四川盆地须家河组为例[J].岩石学报,2012,28(3):905-916.

HU G Y, WANG W S, LIAO F R. Geochemical characteristics and its influencing factors of light hydrocarbon in coal derived gas: A case study of Sichuan Basin[J]. Acta Petrologica Sinica,2012,28(3):905-916.

42
HU G Y, LI J, SHAN X Q, et al. The origin of natural gas and the hydrocarbon charging history of the Yulin Gas Field in the Ordos Basin, China[J]. International Journal of Coal Geology,2010,81:381-391.

43
MELODYE A R, GEORGE E C, CHUNG H M. Modeling thermogenic gas generation using carbon isotope ratios of natural gas hydrocarbons[J]. Chemical Geology,1995,126(3-4): 219-232.

44
孙平安,王绪龙,唐勇,等. 准噶尔盆地浅层天然气多种成因地球化学研究[J].地球化学,2012,41(2):109-121.

SUN P A, WANG X L, TANG Y, et al. Geochemical constraints on the multiple origins of shallow-buried natural gases in the Junggar Basin [J]. Geochimica, 2012,41(2):109-121.

45
胡维强,刘玉明,李洋冰,等.鄂尔多斯盆地临兴地区上古生界烃源岩特征及其生排烃史研究[J].长江大学学报:自然科学版,2018,15(19):1-5.

HU W Q, LIU Y M, LI Y B, et al. The characteristics and generation-expulsion history of hydrocarbon source rocks of the Upper Paleozoic in Linxing Area of Ordos Basin[J].Journal of Yangtze University: Natural Science Edition, 2018,15(19):1-5.

46
MANGO F D. The origin of light cycloalkanes in petroleum[J]. Geochimica et Cosmochimica Acta,1990,54(1): 23-27.

47
MANGO F D. An invariance in the isoheptanes of petroleum[J]. Science,1987,237(4814):514-517.

48
MANGO F D. The origin of light hydrocarbons in petroleum: A kinetic test of the steady-state catalytic hypothesis[J]. Geochimica et Cosmochimica Acta,1990,54(5):1315-1323.

49
PRINZHOFER A, HUC A Y. Genetic and post-genetic molecular and isotopic fractionations in natural gases[J]. Chemical Geology, 1995,126: 281-290.

50
PRINZHOFER A, PERNATON E. Isotopically light methane in natural gas: Bacterial imprint or diffusive fractionation[J]. Chemical Geology,1997,142: 193-200.

Outlines

/