Reservoir Characteristics and Sensitivity Controlling Factors of Yan’an Formation in Yanwu Oilfield, Ordos Basin

doi:10.7657/XJPG20250305

Abstract

Abstract:

To mitigate reservoir sensitivity damage and enhance oil recovery, the reservoir characteristics and sensitivity controlling factors of the 7th and 8th members of the Lower Jurassic Yan’an formation (Yan 7 and Yan 8 members) in the Yanwu oilfield, Ordos Basin were investigated. Using the data of petrophysical properties, cast thin sections, scanning electron microscopy (SEM), and mercury intrusion, and through various reservoir sensitivity experiments, the reservoir characteristics were identified, the reservoir sensitivities were evaluated, and the factors controlling reservoir sensitivities were analyzed. The results show that the Yan 7 and Yan 8 reservoirs are primarily composed of medium-grained feldspathic lithic quartz sandstones and medium- to fine-grained lithic quartz sandstones, respectively. The Yan 7 and Yan 8 reservoirs exhibit average porosities of 15.3% and 13.7%, average permeabilities of 498.9 mD and 343.0 mD, average plane porosities of 9.5% and 8.7%, and average pore diameters of 83.1 μm and 51.8 μm, respectively. The two reservoirs show weak-moderate velocity sensitivity, weak salinity sensitivity, weak-moderate acid sensitivity, strong alkali sensitivity, and negligible-to-weak stress sensitivity. The water sensitivities of the two reservoirs differs significantly: the Yan 7 reservoir shows a weak-moderate water sensitivity, while the Yan 8 reservoir has a moderate-strong water sensitivity. The sensitivities of the two reservoirs are primarily influenced by mineral composition, physical properties, and pore-throat structure, among which mineral composition plays a dominant role. The water sensitivity is closely related to the content and occurrence of illite; the acid sensitivity is influenced by the presence of chlorite and ferroan dolomite; and the strong alkali sensitivity results from high feldspar and quartz content. During reservoir stimulation, the pH values of injected fluids should be strictly controlled to minimize the reservoir damage induced by sensitivity.

Key words: Ordos Basin, Yanwu oilfield, Yan’an formation, reservoir characteristic, sensitivity evaluation, controlling factor

CLC Number:

TE122.2

YANG Long, ZHU Yushuang, KANG Yongmei, LIU Yiting, BAO Chenlong, HE Hui. Reservoir Characteristics and Sensitivity Controlling Factors of Yan’an Formation in Yanwu Oilfield, Ordos Basin[J]. Xinjiang Petroleum Geology, 2025, 46(3): 288-295.

Figures/Tables 9

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Table 1.

Table 2.

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储集层	样品编号	空气渗透率/mD	孔隙度/ %	均值/ %	初始渗透率/mD	变异系数	歪度	分选系数	平均喉道半径/μm	中值半径/μm	排驱压力/MPa	最大进汞饱和度/%	退汞效率/%
延7	M1	54.61	15.12	9.84	12.74	20.93	0.18	2.71	1.39	0.45	0.072	89.43	24.37
	M3	46.16	14.44	9.40	10.80	22.89	0.57	3.06	1.18	0.81	0.052	92.15	23.44
	M6	46.38	13.68	9.26	9.67	20.12	0.24	2.74	2.35	0.64	0.052	91.58	20.13
延8	M2	39.37	14.05	10.91	5.18	26.42	0.14	3.19	1.18	0.16	0.052	94.78	36.88
	M4	36.44	13.19	9.79	10.43	18.20	0.17	2.35	1.18	0.50	0.078	91.08	23.61
	M5	39.44	15.31	9.43	3.69	19.63	0.24	2.63	1.79	0.70	0.057	93.13	20.31

储集层	样品编号	速敏实验结果			水敏实验结果			酸敏实验结果			碱敏实验结果
储集层	样品编号	临界流速/ （mL·min^-1）	速敏指数	速敏程度评价	水敏后渗透率/mD	水敏指数	水敏程度评价	酸化后渗透率/mD	酸敏指数	酸敏程度评价	碱化后渗透率/mD	碱敏指数	碱敏程度评价
延7	M1	0.92	0.28	弱	11.09	0.13	弱	8.67	0.32	中等	1.41	0.89	强
	M6	0.31	0.17	弱	8.27	0.23	弱	7.96	0.26	弱	1.98	0.75	强
	M3	0.24	0.34	中等偏弱	5.42	0.44	中等	7.76	0.20	弱	2.54	0.74	强
延8	M2	0.12	0.32	中等偏弱	2.65	0.49	中等	3.96	0.24	弱	0.74	0.86	强
	M4	0.30	0.13	弱	6.14	0.41	中等	7.88	0.25	弱	1.76	0.96	强
	M5	0.07	0.24	弱	0.98	0.73	强	2.43	0.34	中等	0.73	0.80	强