低渗透-致密储层分类评价方法——以鄂尔多斯盆地三叠系延长组下组合为例

doi:10.11743/ogg20250520

Abstract

Abstract:

The classification and evaluation of low-permeability tight reservoirs remain a pressing challenge in hydrocarbon exploration and exploitation. Traditional approaches are either tailored to conventional reservoirs or oversimplify the categorization of low-permeability tight reservoirs， limiting their practical applicability. Although some recently developed evaluation methods have shown promising results， their broad adoption is hindered by difficulties in parameter acquisition and high implementation costs. In this study， we examine the general reservoir characteristics in the study area using casting thin section observations， scanning electron microscopy （SEM）， and high-pressure mercury injection （HPMI）. Based on these results， combined with extensive data processing and multiple clustering algorithms， we propose a K-means clustering-based classification and evaluation method for low-permeability tight reservoirs. Furthermore， we mathematically define the classification boundaries using porosity-permeability cross plots. The proposed classification and evaluation system offers several advantages. By adopting an algorithm-driven approach， it overcomes the limitations of traditional experience-based criteria， thus providing more scientifically robust classification results. Although the proposed method integrates eight key parameters that capture reservoir physical properties and pore structure characteristics （i.e.， porosity， permeability， sorting coefficient， median pressure， median pore radius， displacement pressure， maximum mercury saturation， and mercury withdrawal efficiency）， the final classification and evaluation results rely solely on porosity and permeability， which are both the most indicative of reservoir quality and the most accessible. Therefore， this method addresses the limitations of traditional ones， including difficulty in acquiring evaluation parameters and challenges associated with widespread application. Employing mathematically defined classification boundaries， it avoids the oversimplified “one-size-fits-all” cut-offs inherent to traditional classifications. The method has been applied to the classification and play fairway prediction of low-permeability tight reservoirs in the Chang 7-9 oil groups in the lower Yanchang Formation， Dingbian-Fuxian area， Ordos Basin， providing a reliable basis for sweet spot evaluation in this area.

Key words: classification, evaluation, cluster analysis, low permeability, tightness, reservoir, Yanchang Formation, Ordos Basin

CLC Number:

TE122.2

Weimin SHEN, Jingzhou ZHAO, Meili ZHAO. Methods for classification and evaluation of low-permeability tight reservoirs： A case study of the lower Yanchang Formation， Ordos Basin[J]. Oil & Gas Geology, 2025, 46(5): 1717-1730.

Figures/Tables 22

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References 31

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压汞曲线类型	特征值	歪度	分选系数	变异系数	中值压力/MPa	中值半径/μm	排驱压力/MPa	最大S_Hg/%	退汞效率/%
Ⅰ类	最大值	0.5	2.6	0.3	23.8	1.5	7.6	92.2	55.2
	最小值	-3.5	0.7	0.1	0.2	0	0.1	61.0	9.6
	平均值	-0.4	1.3	0.1	10.7	0.1	2.8	80.3	27.0
Ⅱ类	最大值	-0.3	1.8	0.1	49.0	0.1	10.2	74.2	52.1
	最小值	-4.1	0.6	0	13.9	0	0.8	50.3	12.4
	平均值	-1.5	1.1	0.1	30.6	0	4.3	61.5	26.4
Ⅲ类	最大值	-0.6	1.7	0.1	0	0	12.7	49.5	39.3
	最小值	-5.7	0.5	0	0	0	0.9	27.3	3.7
	平均值	-2.6	0.9	0.1	0	0	6.6	38.1	26.9
Ⅳ类	最大值	0.7	1.5	0.1	0	0	26.2	44.5	68.7
	最小值	-4.3	0.2	0	0	0	1.2	11.5	36.9
	平均值	-2.7	0.7	0.1	0	0	11.6	21.5	45.1

流动单元类型	FZI	FZI样本个数	孔隙度/%	渗透率/（10^-3 μm²）
Ⅰ类	< 0.2	61	（3.60 ~ 15.00）/10.58	（0.001 ~ 0.082）/0.044
Ⅱ类	0.2 ~ 0.6	335	（2.70 ~ 16.10）/8.53	（0.006 ~ 1.540）/0.147
Ⅲ类	0.6 ~ 1.1	137	（2.20 ~ 13.80）/7.07	（0.008 ~ 2.761）/0.463
Ⅳ类	1.1 ~ 1.9	64	（1.70 ~ 12.50）/5.35	（0.010 ~ 6.578）/0.573
Ⅴ类	≥ 1.9	36	（0.60 ~ 11.40）/3.89	（0.009 ~ 50.569）/3.394

参数类型	孔隙度/%	渗透率/（10^-3 μm²）	分选系数	中值压力/MPa	中值半径/μm	排驱压力/MPa	最大S_Hg/%	退汞效率/%
孔隙度	1.00	1.54	2.0	2.0	2.0	2.0	2.0	2.0
渗透率	0.65	1.00	1.3	1.3	1.3	1.3	1.3	1.3
分选系数	0.50	0.77	1.0	1.0	1.0	1.0	1.0	1.0
中值压力	0.50	0.77	1.0	1.0	1.0	1.0	1.0	1.0
中值半径	0.50	0.77	1.0	1.0	1.0	1.0	1.0	1.0
排驱压力	0.50	0.77	1.0	1.0	1.0	1.0	1.0	1.0
最大S_Hg	0.50	0.77	1.0	1.0	1.0	1.0	1.0	1.0
退汞效率	0.50	0.77	1.0	1.0	1.0	1.0	1.0	1.0

储层类型	特征值	孔隙度/%	渗透率/（10^-3 μm²）	分选系数	中值压力/MPa	中值半径/μm	排驱压力/MPa	最大S_Hg/%	退汞效率/%
Ⅰ类	最大值	16.10	6.58	2.97	10.88	0.76	2.67	90.46	56.63
	最小值	10.90	0.30	0.08	1.02	0.07	0.11	72.26	18.86
	平均值	13.60	1.56	1.22	4.31	0.34	0.58	81.81	38.26
Ⅱ类	最大值	15.00	10.97	3.17	39.84	0.92	7.65	97.70	52.84
	最小值	6.40	0.06	0.05	0	0	0.11	42.59	0.10
	平均值	11.20	0.61	1.31	10.39	0.15	2.16	78.92	31.05
Ⅲ类	最大值	11.90	1.39	6.48	136.61	0.98	24.11	99.05	55.22
	最小值	3.00	0.01	0.05	0	0	0.12	14.96	3.66
	平均值	8.00	0.16	1.09	19.15	0.06	4.37	70.92	26.20
Ⅳ类	最大值	7.20	0.45	4.73	127.64	0.16	39.84	95.87	68.71
	最小值	2.10	0	0.08	0	0	0.51	11.52	3.66
	平均值	4.64	0.06	1.03	20.32	0.02	7.04	51.77	27.59

参数类型	分类编号
参数类型	1	2	3	4
孔隙度	6.328	4.652	2.881	1.375
渗透率	6.332	4.099	2.483	1.470
中值半径	21.904	7.830	0.769	-3.269
排驱压力/MPa	0.426	0.510	0.659	0.783
最大S_Hg	0.162	0.227	0.269	0.243
退汞效率	0.445	0.375	0.322	0.356
（常量）	-68.364	-44.636	-28.309	-18.535

Methods for classification and evaluation of low-permeability tight reservoirs： A case study of the lower Yanchang Formation， Ordos Basin

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参数类型	主成分编号
参数类型	1	2	3	4	5
分选系数	0.811	0.521	—	—	—
最大S_Hg	0.806	0.521	—	—	—
排驱压力	-0.751	—	—	—	—
中值半径	0.740	—	—	—	—
歪度	0.672	—	—	—	—
孔隙度	0.584	-0.523	—	—	—
变异系数	0.557	—	—	—	—
中值压力	—	—	0.727	—	—
退汞效率	—	—	—	0.961	—
渗透率	—	—	-0.548	—	0.75

参数类型	分类编号
参数类型	1	2	3	4
孔隙度	6.319	4.634	2.874	1.370
渗透率	6.071	3.848	2.269	1.243
分选系数	5.238	5.040	4.294	4.554
中值压力	-0.077	-0.084	-0.063	-0.064
中值半径	25.844	11.375	3.997	0.229
排驱压力	0.841	0.925	0.999	1.139
最大S_Hg	0.172	0.241	0.277	0.250
退汞效率	0.512	0.440	0.377	0.415
（常量）	-73.636	-49.589	-31.853	-22.505

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