Three-dimensional modeling of multiscale fractures in Chang 7 shale oil reservoir in Qingcheng oilfield, Ordos Basin

doi:10.13745/j.esf.sf.2024.6.29

Abstract

Abstract:

Shale oil reservoirs generally develop multiscale natural fractures which are the main reservoir storage spaces and seepage channels. The development of multiscale natural fractures restricts efficient reservoir exploration and development. In this article, taking Chang 7 shale oil reservoir in Qingcheng oilfield, Ordos Basin as an example, combined with field surface outcrop, core, thin section, well log, and seismic data, the characteristics of multiscale fracture development are clarified on the basis of fracture classification; a multiscale fracture modeling method is developed. A three-dimensional discrete network model of multiscale fractures in well X in typical drilling area is established. Based on ant-tracking seismic attributes after stacking, the distribution characteristics of macroscale fractures are clarified, and a geological model of macroscale fractures is established using deterministic methods. Through geomechanical analysis, combined with fracture interpretation results from conventional well logging, intensity constraint models for mesosccale/small-scale fracture developments are established. Using the intensity constratint models, combined with relavant fracture parameters, geological models of mesoscale and small-scale fractures are established, respectively, using random modeling technique. Finally, fracture network models of all scales are fused to form a multiscale fracture network model, and an equivalent fracture attribute model is established. It was found that macroscale fractures of Chang 7₁ in area X are developed in the northeast while mesoscale and small-scale fractures are developed mostly in the west, southwest, and northeast of the study area. The established multiscale fracture model is consistent with the pattern of fracture development in single well and actual production performance data, thereby providing a geological basis for increasing shale oil and gas storage and production in well X drilling area in Qingcheng oilfield.

Key words: shale oil reservoir, multi-scale fracture, developmental characteristics, 3D discrete network model, Qingcheng oilfield, Ordos Basin

CLC Number:

LIU Yanxiang, LÜ Wenya, ZENG Lianbo, LI Ruiqi, DONG Shaoqun, WANG Zhaosheng, LI Yanlu, WANG Leifei, JI Chunqiu. Three-dimensional modeling of multiscale fractures in Chang 7 shale oil reservoir in Qingcheng oilfield, Ordos Basin[J]. Earth Science Frontiers, 2024, 31(5): 103-116.

Figures/Tables 11

Fig.1 Structural setting (a, modified from [38]) and sedimentary facies map (modified from [45]) of the study area

Fig.2 Stratigraphic column diagram of the study area

Fig.3 Characteristics of macroscale fracture development in Chang 71 reservoir

Fig.4 Rose chart of mesoscale and small-scale fractures in Chang 71 reservoir

Fig.5 Characteristics of mesoscale/small-scale fracture development in Chang 71 reservoir

Fig.6 Flowchart of multiscale fracture modeling for shale oil reservoirs

Fig.7 Intensity constraint model for fracture development

Table 1 Modeling parameters for mesoscale/small-scale fractures in the study area

裂缝类型	裂缝走向/(°)	走向占比/%	裂缝倾角/(°)	裂缝长度/m		裂缝开度/μm
中尺度裂缝	235	20	80	均值	17.9	均值	142
	105	52	80	最大值	50.5	最大值	204
	150	12	80	最小值	10.1	最小值	70
	195	16	80	方差	64.1	方差	1 937
小尺度裂缝	235	20	80	均值	4.4	均值	81
	105	44	80	最大值	9.9	最大值	114
	150	19	80	最小值	1.1	最小值	42
	195	17	80	方差	4.4	方差	451

Fig.8 3D geological model of multiscale fractures in Chang 71

Fig.9 Multiscale fracture equivalent attribute model

Fig.10 Crossplot showing the relationship between the average fracture equivalent permeability value and the average daily liquid production in the early development stage of well Chang 71

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