Lithologic Reservoirs ›› 2026, Vol. 38 ›› Issue (4): 170-179.doi: 10.12108/yxyqc.20260415

• PETROLEUM ENGINEERING AND OIL & GAS FIELD DEVELOPMENT • Previous Articles     Next Articles

Occurrence state and evolution of remaining oil after water flooding characterized by high-precision CT scanning: A case study from Cretaceous Sa-Pu reservoir, eastern Daqing placanticline, Songliao Basin

LI Zhaoyong1(), LUO Diao1(), CHI Bo1, LIU Shuang2, ZHAO Jiuyu1   

  1. 1 Exploration and Development Research Institute, PetroChina Daqing Oilfield Co., Ltd., Daqing 163712, Heilongjiang, China
    2 No. 6 Oil Production Plant, PetroChina Daqing Oilfield Co., Ltd., Daqing 163712, Heilongjiang, China
  • Received:2025-11-03 Revised:2025-12-14 Online:2026-07-01 Published:2026-07-06
  • Contact: LUO Diao E-mail:lizhaoyong@petrochina.com.cn;luodiao@petrochina.com.cn

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Abstract:

Focusing on Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, the occurrence state and evolution of microscopic remaining oil under different permeability conditions were systematically investigated by integrating high-resolution computed tomography （CT） scanning with water flooding experiments. Numerical simulations of relative permeability and wettability were conducted to formulate strategies for enhanced oil recovery. The results show that: （1） Cretaceous Sa-Pu reservoir in eastern Daqing placanticline is characterized by an average pore-throat radius of 6.1-8.0 μm, pore-throat ratioof 2.1-2.4, and connected porosity exceeding 95%. The pore throat structure of high permeability reservoirs (> 150.0 mD) is relatively homogeneity and well connected, while low-permeability reservoirs (< 50.0 mD) with strong heterogeneity, a disparity that fundamentally go-verns oil-water two-phase flow behavior and remaining oil spatial distribution. （2） The water flooding experiment and CT scanning results of core samples in the study area show that: microscopic remaining oil was identified as four types of occurrence state, such as network-like, pore-clustered, oil-film, and isolated-droplet forms. During water flooding, the remaining oil morphology evolves primarily from network-like to pore-clustered. In the early stage of displacement, well-connected network-like oil is dominated, and the recovery factor increases rapidly. As displacement progresses, in the middle and later stages, remaining oil becomes predominantly trapped in pore throats as pore clusters, resulting in a significant decline in oil displacement efficiency and a rapid rise in water-cut. Reservoir permeability is a key factor in controlling the evolution of the remaining oil morphology. High permeability reservoirs have longer low water-cut periods and higher ultimate recovery factor due to the more developed initial network-like oil. (3) Numerical simulations reveal Sa-Pu reservoir’s strong oil-wet nature, demonstrating that wettability reversal technology significantly enhances oil-phase mobility, with an average reduction in trapped oil saturation of 8.9%. (4) Differentiated development strategies based on permeability grading are proposed in the study area. Well pattern optimization is recommended at the high water-cut stage for high-permeability reservoirs, followed by wettability reversal and chemical flooding at the extra-high water-cut stage. Wettability reversal is implemented during the medium water-cut stage for medium-permeability reservoirs, and wettability reversal combined with chemical flooding are implemented during medium-to-low water-cut stages for low-permeability reservoirs.

Key words: CT scanning, remaining oil occurrence state, water flooding experiment, enhanced oil recovery, wettability, development strategy, Sa-Pu reservoir, Cretaceous, Daqing placanticline

CLC Number: 

  • TE311

Table 1

Porosity and permeability characteristics of core samples from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

样品
编号		 孔隙度/
%		 渗透率/
mD		 样品
编号		 孔隙度/
%		 渗透率/
mD
1# 24.4 246.5 4# 22.1 87.0
2# 21.6 183.0 5# 20.4 73.3
3# 23.4 108.0 6# 21.8 43.7

Fig. 1

Schematic diagram of experiment setup （a） and workflow （b） of displacement coupled with CT scanning"

Fig. 2

Comparison between calculated and measured porosity （a）, permeability (b) under different scanning resolutions for core samples from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

Fig. 3

Digital rock and pore network models of sample 2# from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

Fig. 4

Simulated capillary pressure curves and pore-throat radius distributions for core experiments of Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

Table 2

Microscopic pore structure characteristics of cores from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

样品
编号		 平均孔喉
半径/μm		 最大连通孔
喉半径/μm		 中值孔喉
半径/μm		 孔
喉
比		 配
位
数		 分选
系数		 迂
曲
度		 孤立孔
占比/%
1# 7.9 10.8 7.2 2.24 2 1.44 2.63 1.89
2# 7.4 9.7 6.1 2.28 2 1.42 2.71 1.88
3# 7.1 10.0 6.4 2.36 2 1.44 2.42 1.67
4# 6.6 8.5 5.8 2.37 2 1.40 2.68 1.06
5# 8.0 11.2 6.1 2.28 2 1.41 2.84 2.59
6# 6.1 8.4 4.7 2.14 2 1.46 3.30 3.16

Fig. 5

Three-dimension distribution of oil-water phases during water flooding experiments for sample 2# from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

Fig. 6

Two-dimension distribution of oil-water phases during water flooding experiments for sample 2# from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

Fig. 7

Oil droplet radius distributions at different displacement stages during water flooding experiments for core samples from Cretaceous Sa-Pu reservoir in eastern Daqing placanticline, Songliao Basin"

Table 3

Microscopic remaining oil occurrence states during water flooding experiments of Cretaceous Sa-Pu reservoir, eastern Daqing placanticline, Songliao Basin"

微观剩余油类型 微观模型 形状因子G 接触面积比Ror
网络状 G < 0.01 0 < Ror < 1.00
多孔状 0.01 < G < 0.10 0 < Ror < 1.00
油膜状 0.10 < G < 0.30 0.45 < Ror < 0.60
孤滴状 G > 0.30
0.10 < G < 0.30		 0 < Ror < 1.00
Ror < 0.45或Ror > 0.60

Fig. 8

Microscopic remaining oil distribution at different water flooding stages during water flooding experiments for core samples from Cretaceous Sa-Pu reservoir, eastern Daqing placanticline, Songliao Basin"

Fig. 9

Numerical simulation of water flooding performance of Cretaceous Sa-Pu reservoir， eastern Daqing placanticline, Songliao Basin"

Fig. 10

Numerical simulation of interfacial wettability evolution during water flooding of Cretaceous Sa-Pu reservoir， eastern Daqing placanticline, Songliao Basin"

Fig. 11

Comparison of oil-water relative permeability under different wettability conditions simulated by Shan-Chen model of Cretaceous Sa-Pu reservoir, eastern Daqing placanticline, Songliao Basin"

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