Formation Mechanism and Controlling Factors of Natural Fractures in Xujiahe Formation, Puguang Area

doi:10.7657/XJPG20260205

Abstract

Abstract:

The formation test and production test in the Xujiahe formation in the Puguang area of the Sichuan Basin are closely related to the development of natural fractures. Based on field geological outcrop, core and imaging logging data, the types and parameters of natural fractures in the Xujiahe formation in the Puguang area are statistically analyzed. Combining with regional tectonic evolution, the formation mechanism and controlling factors of the natural fractures are evaluated. The results show that the natural fractures in the Xujiahe formation are highly efficient. Two groups of effective fractures in NW-SE and NE-SW trending are developed in the formation. The NW-SE fractures are predominant, and dominated by low-angle oblique fractures with the aperture of 10-20 μm and the permeability of 10-50 mD, acting as important flow pathways in the reservoir. The natural fractures in the Xujiahe formation formed in three periods: (1) the late Yanshanian, when conjugate shear fractures were formed in nearly N-S and NW-SE trending under the action of NW-SE compression and then highly filled; (2) the early Himalayan, when a series of NE-SW natural fractures were formed under the NW-SE compression, and these fractures are effective; and (3) the late Himalayan, when conjugate shear fractures in NE-SW and nearly N-S trending were formed due to the intense NE-SW compression, associated with NW-SE structural fractures locally. The natural fractures in the Xujiahe formation are controlled by structure, lithology, sedimentary microfacies, and rock mechanical layer thickness, among which structure is the dominant factor.

Key words: Sichuan Basin, Puguang area, Triassic, Xujiahe formation, natural fracture, formation mechanism, controlling factor

CLC Number:

TE121.2

ZU Kewei. Formation Mechanism and Controlling Factors of Natural Fractures in Xujiahe Formation, Puguang Area[J]. Xinjiang Petroleum Geology, 2026, 47(2): 163-171.

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裂缝类型	裂缝倾向/（°）	裂缝走向/（°）	裂缝倾角/（°）	天然裂缝成因类型	主应力方位/（°）	裂缝形成时期
①	161	71	76	区域共轭剪切裂缝	214	喜马拉雅运动晚期
①	86	356	78	区域共轭剪切裂缝	214	喜马拉雅运动晚期
②	45 190~235	100~145	19~55	局部构造裂缝	190~235	喜马拉雅运动晚期
③	125 316~329	215~239	28~46	局部构造裂缝	305~329	喜马拉雅运动早期

岩性	成像测井累计厚度/m	裂缝数量/ 条	裂缝发育密度/ （条·m^-1）
泥岩	450.45	42	0.093
中砂岩	358.95	100	0.279
细砂岩	132.71	46	0.347
粉砂岩	143.89	51	0.354

沉积亚相	沉积微相	成像测井累计厚度/m	裂缝数量/ 条	裂缝发育密度/ （条·m^-1）
三角洲平原	沼泽	39.54	4	0.101
	分支河道	170.57	40	0.235
	分支间湾	111.59	9	0.081
三角洲前缘	水下分流河道	545.44	155	0.285
	水下分流间湾	165.23	15	0.090
	河口坝	43.09	7	0.162