Natural Gas Geoscience ›› 2021, Vol. 32 ›› Issue (12): 1874-1879.doi: 10.11764/j.issn.1672-1926.2021.10.015

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Preliminary study on imbibition and oil displacement of Chang 7 shale oil in Ordos Basin

Zhiyu WU1,2(),Zhanwu GAO1,2,Shuwei MA2,3(),Jiyong ZHAO1,2,Jianchao SHI2,3,Zhen LI2,3   

  1. 1.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
    3.Research Institute of Exploration and Development,PetroChina Changqing Oilfield Company,Xi’an 710018,China
  • Received:2021-05-31 Revised:2021-10-21 Online:2021-12-10 Published:2021-12-27
  • Contact: Shuwei MA E-mail:wzy_cq@petrochina.com.cn;masw_cq@petrochina.com.cn
  • Supported by:
    The China National Science & Technology Major Project(2017ZX05069)

Abstract:

Chang 7 Member shale oil reservoir in Ordos Basin, China is continental and shows characteristics of low porosity and permeability with poor reservoir connectivity. Oil displacement efficiency of this type is low, because water breaks through underground during water flooding. Shale oil in the basin has been developed by large-scale fracturing to increase water-oil contact thus to improve oil recovery rate. Oil recovered by water imbibition was proved to be effective, and both development practices and indoor experiments showed that shale oil recovered by water imbibition accounts for 15%-40% of the total, providing a new method for oil displacement in shale oil reservoir. In this study, open-boundary core system was used to quantitatively study the impacts of pore radius, interfacial tension and permeability on oil recovery by water imbibition underground. Indoor experiments showed that shale oil produced from pores with radius less than 10μm accounts for 56%-80% of the total; shale oil recovered by water imbibition peaks when interfacial tension is 1.18 mN/m; core permeability is positively correlated with imbibition recovery when interfacial tension is less than 2 mN/m, while the two are not significantly correlated when interfacial tension is higher than 4mN/m.

Key words: Ordos Basin, Chang 7 Member, Shale oil, Imbibition and displacement

CLC Number: 

  • TE312

Fig.1

Scatter plots of water saturation of the 34 wells in the study area and their salinity"

Table 1

Volumetric concentration of the surfactant and the corresponding interfacial tension"

TOF-1表面活性剂浓度/%与模拟油界面张力/(mN/m)
50.290
0.51.183
0.053.750
0.00510.436

Table 2

Basic data of the core used in the experiment"

岩心编号长度/cm直径/cm孔隙度/%渗透率/(10-3 μm2
木21-22.3602.5089.810.159
里21-22.3062.5088.490.139
安25-20.0812.5108.890.081

Fig.2

Experimental flow chart of imbibition and displacement"

Fig.3

Imbibition T2 relaxation time spectra of core Mu 21-2 under 5% drainage aid solution"

Table 3

Relative recovery degree of core imbibition with different pore radius"

岩心

编号

孔隙度

/%

渗透率

/(10-3 μm2

不同孔隙半径采出程度/%
小于10 μm10~20 μm大于20 μm
平均值9.060.1372.0516.0211.92
木21-29.810.15974.8412.5812.53
里21-28.490.13980.9414.554.52
安25-28.890.08160.3720.9318.71

Fig.4

Recovery degree of core imbibition with different pore radius"

Table 4

The degree of imbibition recovery under different interfacial tension"

助排剂浓度/%界面张力/(mN/m)渗吸采出程度/%
木21-2里21-2安25-2
50.29027.16926.37625.747
0.51.18332.32027.48327.473
0.053.75024.66226.43021.641
0.00510.43622.49518.34920.730

Fig.5

Imbibition recovery efficiency of different cores varies with interfacial tensions"

Fig.6

Relationship between gas-measured permeability and movable oil saturation, imbibition saturation and displace-ment saturation of Chang 7 Member shale oil reservoir"

Table 5

Movable oil saturation under different permeability intervals of Chang Member 7 shale oil reservoir in Heshui area"

渗透率区间

/(10-3 μm2

总可动油饱和度/%渗吸可动油饱和度/%驱替可动油饱和度/%
<0.01524.18.3515.75
0.015~0.10035.289.4325.85
0.100~0.20033.675.2928.39

Fig.7

Distribution of imbibition and displacement production during dynamic imbibition"

Table 6

Contribution of imbibition to recovery during displacement"

岩心

编号

渗透率 /(10-3 μm2驱替速度 /(mL/min)焖井 时间/h总采收率 /%渗吸对采收 率的贡献/%
木21-110.200.104870.7523.03
木22-110.180.054869.0120.04
木22-120.180.014849.6414.70
木21-120.200.106067.8033.35
木21-120.200.107270.6932.87
木27-120.980.104872.1131.83
里23-120.0970.14861.12540.89
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