Mechanisms of Imbibition and Displacement in Horizontal Well Volume Fracturing for Shale Oil Recovery in Chang 7 Member, Qingcheng Oilfield

doi:10.7657/XJPG20250311

Abstract

Abstract:

Shale oil is primarily developed through horizontal well volume fracturing, where substantial fluid is injected into and produced from the matrix. However, the contributions of imbibition and displacement remain controversial. To clarify their mechanisms and contributions in shale oil reservoirs, the shale core samples from the Chang 7 member of the Qingcheng oilfield were used for analysis. The imbibition + displacement and displacement experiments under formation pressure, as well as imbibition experiments under varying pressures, were performed to obtain the nuclear magnetic resonance (NMR) T₂ spectra at different stages, and the impact of well soaking on production were analyzed. Furthermore, by integrating fractal theory and oil-water two-phase flow theory, a mathematical model of flow mechanics which considered displacement pressure and capillary pressure was established, and a chart illustrating imbibition and displacement under different pressure differences was plotted. The results show that displacement primarily mobilizes oil in medium-to-large pores, while imbibition recovers oil from pores and throats of all sizes. Compared to pure water flooding, post-imbibition water flooding demonstrates superior oil displacement efficiency, because imbibition can not only mobilizes oil directly but also facilitates subsequent water flooding performance.

Key words: Qingcheng oilfield, Yanchang formation, Chang 7 member, shale oil reservoir, horizontal well, volume fracturing, imbibition mechanism, displacement mechanism

CLC Number:

TE312

QU Xuefeng, CHANG Rui, HE You’an, LEI Qihong, HUANG Tianjing, WANG Gaoqiang, GUAN Yun, LI Zhen. Mechanisms of Imbibition and Displacement in Horizontal Well Volume Fracturing for Shale Oil Recovery in Chang 7 Member, Qingcheng Oilfield[J]. Xinjiang Petroleum Geology, 2025, 46(3): 344-352.

Figures/Tables 10

Table 1.

Fig. 1.

Table 2.

Fig. 2.

Table 3.

Fig. 3.

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Table 4.

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岩样编号	渗透率/ mD	孔隙度/ %	注入压力/ MPa	围压/ MPa	实验类型
L388-1	0.096	7.151	17	25	渗吸+驱替
X286-8	0.103	6.816	16	25	驱替
L388-2	0.111	8.766	19	25	渗吸+驱替
B117-3	0.112	7.676	16	25	驱替

岩样编号	渗透率/mD	孔隙度/%	注入压力/MPa
L388-3	0.122	10.377	0
L388-1	0.096	7.151	1
L388-2	0.111	8.766	3
L388-5	0.127	7.430	6

岩样编号	实验类型	含油饱和度/%	渗吸采出程度/%	渗吸后水驱采出程度/%	采收率/ %	各级孔喉中剩余油饱和度/%
岩样编号	实验类型	含油饱和度/%	渗吸采出程度/%	渗吸后水驱采出程度/%	采收率/ %	小孔	中孔	大孔
L388-1	渗吸+驱替	63.19	5.74	29.37	33.14	24.69	5.16	0.59
L388-2	渗吸+驱替	62.57	3.70	28.20	31.90	4.66	1.33	0.12
X286-8	驱替	65.96			20.73	29.03	4.79	0.69
B117-3	驱替	56.52			22.94	12.53	3.05	0.34

岩样编号	压力梯度/（MPa·cm^-1）	渗吸为主的孔喉半径/μm	渗吸和驱替为主的孔喉半径/μm	驱替为主的孔喉半径/μm	渗吸为主的孔喉体积占比/%	渗吸和驱替为主的孔喉体积占比/%	驱替为主的孔喉体积占比/%
C₁	0.3	0.730~5.650	5.650~15.730		92.00	8.00
C₂	0.3	0.001~0.260	4.250~15.270		75.79	24.21
C₃	0.3		4.230~19.650		75.71	24.29
C₁	1.0		0.730~5.650	5.650~15.730		86.72	13.28
C₂	1.0	0.001~0.070	4.250~5.480	5.480~15.250	53.33	17.64	29.03
C₃	1.0	0.003~0.100	4.230~5.460	5.460~19.650	52.96	11.82	35.22
C₁	2.0		0.730~1.570	1.570~15.730		59.75	47.54
C₂	2.0		0.001~0.070	4.250~15.250		53.33	46.67
C₃	2.0		0.003~0.100	4.230~19.650		52.90	47.04