Structural Differences and Impacts on Hydrocarbon Accumulation in Hangzhou Slope of Xihu Sag

doi:10.19657/j.geoscience.1000-8527.2020.094

Abstract

Abstract:

The Hangzhou slope is a frontier for oil and gas exploration in the Xihu sag. Structural characteristics are the basis for petroleum geological study. Based on the structures of the Hangzhou slope, the evolution of main controlling faults and their controls on hydrocarbon migration, we analyze the structural differences of slopes and their effects on hydrocarbon accumulation. The results show that the Hangzhou slope is divided into three parts: the northern, middle, and southern part. The strike direction of the faults in the middle section is NNE, and individual faults are small but numerous. There are E-dipping normal faults and W-dipping reverse faults. The Yingcuixuan main fault may have been active during the sedimentation of the Pinghu Formation, and the middle part of the Hangzhou slope had the strongest fault activity with maximum drop of 800 m, during the sedimentation of the lower part of the Pinghu Formation. The fault strike change, the sandstone content, and the lithological inversion around the main fault suggest that the sandbody is not well developed in the Yingcuixuan main fault’s upthrow wall in the middle part of the Hangzhou slope, whose sealing is better than that in the northern part. During the key accumulation periods (ca. 23 Ma and 12 Ma), the middle section of the Hangzhou slope was on the favorable oil and gas migration pathway. The middle part of Yingcuixuan main fault is inactive after 15 Ma, which enriches the oil and gas in the downthrow wall.

Key words: structural difference, fault evolution, hydrocarbon migration, Hangzhou slope, Xihu sag

CLC Number:

P548
TE122.2

CUI Min, XU Jianyong, GUO Gang, XIE Xiaojun, QI Peng, XIAO Xi, WANG Xin. Structural Differences and Impacts on Hydrocarbon Accumulation in Hangzhou Slope of Xihu Sag[J]. Geoscience, 2021, 35(04): 1106-1113.

Figures/Tables 11

Fig.1 Tectonic setting and structural framework of the Xihu sag[1,2]

Table 1 Stratigraphic column and tectonic evolution of the Xihu sag [1-2,6]

Fig.2 Major fault distribution of Pinghu Formation (a) and Huagang Formation (b) in the Hangzhou slope(location shown in Fig.1)

Fig.3 Structure and stratigraphic thickness map of the northern part of the Hangzhou slope (location shown in Fig.2)

Table 2 Fault characteristics and stratigraphic distribution of each section of the Hangzhou slope

断层和地层特征		北段	中段	南段
断层展布	主断裂走向	北北东	近南北	北北东
	次级断层走向	北东	北北东	北东
	次级断层数目	少	多	多
	次级断层延伸长度	长,最大25 km	短	短
	次级断层倾向	东	东和西	东
断层活动性	主断层活动性	多数20 Ma后不活动	15 Ma后不活动
断层活动性	次级断层活动性	多数平湖组中段后不活动	多数平湖组上段后不活动
地层展布	1 200~2 400 m地层厚度等值线间距	10 km左右地形较平缓	5 km左右地形陡	10 km左右地形较平缓
地层展布	2 400~3 600 m地层厚度等值线间距	15 km左右地形平缓	5 km左右地形陡	10 km左右地形较平缓

Fig.4 Structure and stratigraphic thickness map of the middle part of the Hangzhou slope (location shown in Fig.2)

Fig.5 Fault distance in different parts of the Pinghu Formation on the Yingcuixuan main fault of the Hangzhou slope

Fig.6 Fault drop in different parts of the Pinghu Formation on the Yingcuixuan main fault

Fig.7 Prediction of sandstone content in the northern and middle parts of the Yingcuixuan main fault in the Hangzhou slope

Fig.8 Lithologic juxtaposition of Pinghu Formation in the northern and middle parts of the Yingcuixuan main fault

Fig.9 Distribution of the latest active age of the Yingcuixuan main fault (location shown in Fig.2) and hydrocarbon expulsion rate in the Hangzhou slope

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