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Natural Gas Geoscience ›› 2021, Vol. 32 ›› Issue (12): 1810-1821.doi: 10.11764/j.issn.1672-1926.2021.10.002

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Microscopic characteristics and controlling factors of Chang 7 Member shale oil reservoir in northern Shaanxi area， Ordos Basin

Wenzhong MA1,2(),Yonghong WANG1,2,San ZHANG1,2,Shengbin FENG1,2,Bingying HAO1,2,Xiaoli CUI1,2   

  1. 1.Research Institute of Exploration and Development，PetroChina Changqing Oilfield Company，Xi’an 710018，China
    2.National Engineering Laboratory for Exploration and Development of Low Permeability Oil and Gas Fields，Xi’an 710018，China
  • Received:2021-07-21 Revised:2021-10-16 Online:2021-12-10 Published:2021-12-27
  • Supported by:
    The Major Science and Technology Projects of China National Petroleum Corporation(2016E-0501)

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Abstract:

Rich shale oil resources are developed in the Chang 7 Member of the Mesozoic Triassic Yanchang Formation in northern Shaanxi area， Ordos Basin. This paper mainly uses core， thin section， well logging and other data， focusing on high-precision pore analysis techniques such as scanning electron microscopy， micro-CT， two-dimensional FIB-SEM testing， etc. to finely portray the micro-features and to discuss its main controlling factors. The pores of the Chang 7 shale oil reservoir in the study area are mainly micro-pores with a radius of 2.0-50 μm and a throat radius of 0.3-13 μm. Numerous clustered pore-throat units are formed by micro-nano-level and micro-level throat connecting micro-level pores. The porosity is distributed between 3.0% and 13.0%， and the average porosity is 7.0%. The permeability is between 0.02×10-3 μm2 and 0.30×10-3 μm2， the average permeability is 0.15×10-3 μm2. The mercury injection curve is characterized by low displacement pressure， high mercury removal efficiency， and high proportion of thick throat. The Chang 7 Member shale oil reservoir in the study area has fine grain size and high content of plastic components. The main factors that cause its pores to decrease are the strong early compaction and the strong cementation of clay minerals and carbonates. The dissolution and the protective effect of the chlorite film have a certain pore-enhancing effect. The potential for Type I exploration and development of Chang 7 Member shale in northern Shaanxi area is huge. Compared with Qingcheng area， the class Ⅰ multi-stage superimposed sandstone reservoir of shale oil has great exploration and development potential in northern Shaanxi area.

Key words: Shale oil, Pore throat structure, Micro-nanopore, Northern Shaanxi area, Controlling factors

CLC Number: 

  • TE122.2

Fig.1

The tectonic unit of the Ordos Basin and location of the study area"

Fig.2

Triangular diagram of the rock types of Chang 7 Member reservoir in northern Shaanxi area"

Fig. 3

The mineral composition of the Chang 7 Member of the Ordos Basin"

Table 1

Comparison table of interstitial composition of Chang 7 Member reservoir in northern Shaanxi area"

区块层位水云母 /%绿泥石 /%铁方解石 /%铁白云石 /%高岭石 /%硅质 /%长石质 /%浊沸石 /%其他 /%合计 /%
姬塬长71亚段6.040.973.072.0001.200.0800.9014.27
长72亚段8.530.743.591.9901.240.0801.1817.34
长73亚段7.510.954.524.1000.550.0002.8220.47
新安边长71亚段3.452.265.771.2101.140.050.541.7615.65
长72亚段3.494.215.420.0900.760.070.060.9515.04
长73亚段4.622.356.670.0101.140.0900.8515.74

吴起—

安塞

长71亚段3.152.464.331.0601.160.100.580.9313.77
长72亚段3.932.986.030.8700.720.110.161.6616.46
长73亚段3.212.084.250.1401.180.090.303.6214.87
庆城长7段9.330.471.642.300.111.010.0700.2015.13

Table 2

Comparison of grain size composition of Chang 7 Member reservoir in northern Shaanxi area"

地区层位粒级分布/%粒度Φ值样品数
粗砂中砂细砂粉砂泥
吴起—安塞长73亚段03.985.27.13.83.07153
新安边长72亚段08.482.55.83.42.8174
姬塬长71亚段01.283.88.46.63.29106
全盆地长7段02.680.79.57.23.06730
志靖—安塞长61亚段012.379.35.72.72.6389
姬塬长81亚段0.215.972.85.162.54109

Fig.4

Diagenesis and characteristics of the Chang 7 Member in northern Shaanxi area"

Fig. 5

Pore types of Chang 7 Member reservoir in northern Shaanxi area"

Table 3

Statistics of pore types of Chang 7 Member reservoir in northern Shaanxi area"

区块层位粒间孔/%长石溶孔 /%岩屑溶孔 /%粒间溶孔 /%沸石溶孔 /%晶间孔 /%微裂隙 /%面孔率 /%样品数
姬塬长71亚段0.910.970.130.1100.040.022.1872
长72亚段0.840.730.100.0400.030.041.7637
长73亚段0.331.010.040.0300.0201.4329
新安边长71亚段0.860.580.040.100.030.050.061.73129
长72亚段1.170.880.080.0100.050.072.26339
长73亚段0.350.760.040.0900.020.081.3465
吴起—安塞长71亚段1.260.750.060.150.010.060.022.29112
长72亚段0.810.640.030.130.020.020.071.71104
长73亚段0.700.860.070.080.060.020.021.82133

Fig. 6

Three-dimensional pore throat system under micro-CT of Chang 7 Member shale oil reservoir in northern Shaanxi area"

Fig.7

Reservoir capillary pressure curve of Chang 7 Member in northern Shaanxi area"

Table 4

Statistics of pore throat structure parameters of the reservoirs of Type I shale oil in the Chang 7 Member in northern Shaanxi area"

沉积

类型

地区层位排驱压力 /MPa中值压力 /MPa中值半径 /μm最大进汞量 /%退汞效率 /%分选系数样品数
水下分流河道吴起—安塞长71亚段2.4413.690.0676.4629.381.6613
长73亚段2.279.100.9079.4926.731.5218
新安边亚段长71亚段1.9011.300.0877.3024.171.6715
长72亚段2.168.330.1078.0428.901.5842
重力流姬塬长71亚段2.639.380.0982.9327.771.2021
庆城长71亚段2.8910.310.0778.5025.701.2234
长72亚段3.3510.200.0778.4025.301.1858

Fig.8

The frequency distribution of the physical properties of the Chang 7 Member shale oil reservoir in northern Shaanxi area"

Fig.9

Comparison of horizontal and vertical permeability of Chang 7 Member shale oil reservoir in northern Shaanxi area"

Fig.10

The burial history of Chang 7 Member shale oil reservoir in northern Shaanxi area"

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