Molecular Size and Structure Characteristics of Tight Oil of Lucaogou Formation in Jimusar Depression
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摘要: 致密油分子尺寸及流动性的研究对致密油藏评价及开发具有重要意义.为明确吉木萨尔凹陷芦草沟组致密油的分子尺寸及其对原油流动的影响，综合核磁共振、红外光谱、元素分析和相对分子质量测定等结果，计算了典型井致密油不同馏分段的分子结构参数，采用Chemoffice软件模拟了相应的分子结构.结果显示致密油组分主要集中在350~500℃馏分段，平均分子中含有多环环烷烃和多环芳烃结构，平均分子尺度为1.232~4.026 nm，表明原油分子在纳米孔喉中占有率较高，影响孔喉流动下限.Abstract: The study of the size and fluidity of tight oil is of great significance for the evaluation and development of tight reservoirs. In order to determine the molecular size and its influence on mobility of tight oil of Lucaogou Formation in Jimusar depression, the average structure parameters of different fractions of Ji 174 tight oil were calculated on the basis of 1H-NMR, IR, elemental analysis and molecular weight measurement. According to the parameters, the molecular structures of several fractions from Ji 174 tight oil were simulated by using the Chemoffice software. The results show that the components of the tight oil are mainly concentrated in the fraction from 350 to 500℃, and there are polycyclic naphthene and polycyclic aromatic structures in the average molecules with the sizes of 1.232-4.026 nm. It is the large molecular scale that leads to high shares of oil molecules in nano-pore-throat and affects the pore throat flow limit of the reservoir.
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Key words:
- Jimusar depression /
- Lucaogou Formation /
- tight oil /
- molecular dimension /
- molecular structure /
- petroleum geology
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图 3 各馏分段平均分子结构
Fig. 3. The average molecular structure of each fraction of oil samples
图 5 边界层厚度随孔隙半径的变化关系
Fig. 5. The relationship curve of boundary layer thickness with pore size
表 1 原油平均结构参数
Table 1. The average structure parameters of crude oil
符号 参数意义 符号 参数意义 H/C 氢碳原子比 CN 分子中环烷碳数 Mn 相对分子质量 CP 分子中烷基碳数 C(%) 碳的百分含量 CS 分子中环烷碳数与烷基碳数和 H(%) 氢的百分含量 RA 分子中芳香环数 S(%) 硫的百分含量 RN 分子中环烷环数 N(%) 氮的百分含量 RT 分子中总环数 O(%) 氧的百分含量 fA 芳碳率 HA 与芳香碳直接相连的氢原子数 fN 环烷碳率 Hα 与芳香环的α碳相连的氢原子数 fP 烷基碳率 Hβ 芳香环的β碳及β以远的CH2、CH基上的氢原子数 σ 芳香环系周边氢取代率 Hγ 芳香环的γ碳及γ以远的CH3基上的氢原子数 HAU/CA 芳香环系缩合度参数 CT 分子中总碳数 NCH2/NCH3 分子中亚甲基与甲基数之比 HT 分子中总氢数 NCH3 分子中甲基数 CA 分子中芳香碳数 L 平均链长参数 
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表 2 原油馏分样品元素分析与相对分子质量测定结果
Table 2. Results of elemental analysis and relative molecular mass determination of oil fraction samples
项目 馏分段 IBP~200 ℃ 200~350 ℃ 350~500 ℃ ＞500 ℃ 馏分质量占比(%) 7.11 12.23 43.26 24.84 碳(%) 85.05 86.05 86.91 87.54 氢(%) 14.95 13.95 11.92 10.23 硫(%) 0 0 0.176 0.26 氮(%) 0 0 0.994 1.98 相对分子质量 130 240 748 1 080 平均分子式 C9.20H19.28 C17.20H33.21 C54.13H88.45S0.04N0.53 C78.72H109.61S0.09N1.53
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表 3 各种类型H的定义及化学位移
Table 3. The definition and chemical shift regions of different types of hydrogens
符号 归属 化学位移δ(10-6) HA 与芳香碳直接相连的氢原子数 6.0~9.0 Hα 与芳香环的α碳相连的氢原子数 2.0~4.0 Hβ 芳香环的β位以及β位以远的CH2、CH基上的氢原子数 1.0~2.0 Hγ 芳香环的γ位及γ位以远的CH3基上的氢原子数 0.5~1.0
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表 4 B-L法计算分子结构参数
Table 4. The average structure parameters of oil fraction samples
参数 馏分段 IBP~200 ℃ 200~350 ℃ 350~500 ℃ ＞500 ℃ HT 20 35 88 110 HA 0 0 2.021 1 2.720 5 Hα 0 1.293 0 6.117 1 8.589 8 Hβ 8.200 2 19.787 8 53.292 0 67.872 5 Hγ 10.428 0 11.408 0 26.569 6 30.817 0 fA 0 0 0.205 7 0.318 6 CA 0 0 11.139 3 25.080 6 CS 9.206 0 17.195 6 42.989 4 53.639 7 HAU/CA 0 0.679 6 0.456 0 0.279 7 Cα 0 0 3.058 5 4.294 9 CI 0 0 6.059 6 18.065 1 CF 6 6 13.096 9 25.639 6 RA 0 0 2.379 7 7.026 8 RT 0.565 7 1.588 5 5.332 1 12.376 5 RN 0.565 7 1.588 5 2.952 3 5.349 6 CN 0 4.765 5 8.856 9 16.048 8 CP 9.206 0 12.430 0 34.132 4 37.590 9 fN 0 0.277 1 0.163 6 0.203 8
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表 5 分子模拟结果
Table 5. Molecular simulation results of oil fraction samples
参数 馏分段 IBP~200 ℃ 200~350 ℃ 350~500 ℃ ＞500 ℃ 平均分子式 C9H20 C17H34 C55H90 C79H110N 分子直径(nm) 1.232 1.675 2.295~3.619 2.498~4.026 分子体积(nm3) 0.169 0.239 0.864~0.896 1.014~1.109
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