E-mail:Slli@cugb.edu.cn Li Shengli (197 1 1), male, associate professor, mainly engaged in oil and gas exploration and development research.
1. School of Energy, China Geo University, Beijing 100083.
2. Guangzhou Marine Geological Survey, Guangzhou 5 10760.
Abstract: There are obvious BSR (submarine-like reflection) distribution areas in the deep water area of the continental slope of Qiongdongnan Basin, and most of them are distributed in the strata since the late Miocene. Because BSR is an important geophysical reference sign to identify the existence of natural gas hydrate, and structural change is one of the important factors affecting its distribution, the relationship between Neogene structural subsidence history and BSR is discussed by analyzing the simulation data of single well basin at 424 virtual points in Qiongdongnan deepwater area, calculating the total settlement and load settlement, and then calculating the structural settlement and settlement rate in each geological period. The research shows that since the late Miocene, affected by the strike-slip of the Red River and the eruption of regional mantle-derived basic magma, it has experienced three stages of tectonic subsidence acceleration, especially the Pleistocene (since 65438+5.3 Ma). In space, the tectonic subsidence rate increases from the periphery to the central zone, and the change of the tectonic subsidence rate in the central rift zone is faster than that in the southern uplift zone, while the regional tectonic subsidence between the central rift zone and the southern uplift zone has maintained a rapid subsidence state, which provides favorable conditions for the preservation of natural gas hydrate. The BSR in the study area is mainly distributed in the area where the secondary structural units of depression and uplift are connected, and the tectonic subsidence rate is high, with an amplitude of 70 ~ 1 10 m/ma, which changes rapidly, which is beneficial to the formation and distribution of BSR.
Key words: deep water area of Qiongdongnan basin; BSR distribution; Tectonic subsidence rate; Quantitative simulation
Influence of Neogene Tectonic Subsidence Characteristics on BSR Distribution in QiongDong Nan Basin
Li Shengli 1, Sha Zhibin 2, Yu Xinghe 1, Cong Xiaorong 1, Jiang Longyan 1, Fang Jingnan 1, Wang Jianzhong.
1. School of Energy, China Geo University, Beijing 100083.
2. Guangzhou Marine Geological Survey, Guangzhou 5 10760, China.
Abstract: BSR found in the strata in the deep water area of Qiong Basin from late Miocene to the present is one of the important signs to identify natural gas hydrate, and it is often influenced by tectonic movement. According to the data analysis of 424 pseudo-well points, the relationship between BSR distribution and structural settlement is pointed out. The research shows that under the influence of the three-strike sliding movement of the Red River and the regional mantle-derived basic magmatic activity, there are three different tectonic subsidence acceleration periods in the deep water area of Qiong Basin, which are bounded by 5.3 Ma and 65438±0.8Ma. The third stage (1.8 Ma up to now) is the fastest stage of tectonic activity. From the edge of the basin to the center, the tectonic subsidence rate is getting faster and faster, and the change of the central fault block is faster than that of the southern uplift belt. The area between the central block and the southern uplift zone, which is favorable for the preservation of natural gas hydrate, maintains a relatively high subsidence rate, and BSR is mainly distributed in the marginal zone between secondary structural units, with high tectonic subsidence rate and rapid change. The area with high tectonic subsidence rate is 70m/Ma to 1 10 m/Ma.
Key words: Qiongdongnan deepwater area; BSR distribution; Tectonic subsidence rate
Preface of 0
The continental slope in the northern South China Sea is rich in natural gas hydrate resources.
In addition, the distribution of BSR also has certain requirements for the range of tectonic subsidence rate [23]. According to the research in this area, there can be a wide range of tectonic subsidence rate, but the main tectonic subsidence rate is in the range of 70 ~ 1 10 m/ma (Table 2). Too low tectonic subsidence rate can not provide enough accommodation space, while too high subsidence rate will lead to gas escape, which is not conducive to the formation of BSR corresponding to natural gas hydrate.
Table 2 Corresponding relationship between structural settlement parameters and BSR in deep water area
4 conclusion
1) since the late Miocene, there have been three rapid subsidence in the deep water area in the southeast of Qionghai: the first time was the late Miocene (1 1.6 ~ 5.3 Ma), and the second time was the Pliocene-Holocene (5.3 ~ 1.8 Ma). The third period of settlement (1.8 Ma till now) is different in time and space.
2) Different tectonic units have different tectonic subsidence laws. With the migration of subsidence center, the area between the central rift zone and the southern uplift has maintained a high tectonic subsidence rate. Among them, since the Pleistocene (since 1.8 Ma), the tectonic subsidence in most areas of the study area has accelerated, which provides favorable conditions for the preservation of natural gas hydrates.
3) Since the late Miocene, the strike-slip fault of the Red River is the main reason for the change of tectonic subsidence. The acceleration of tectonic subsidence since 65438±0.8Ma may be related to magmatic activity.
4) The structural subsidence in the middle and marginal areas of secondary structural units changes rapidly. Due to the rapid change of subsidence rate and the development of faults, it can provide a good migration channel, and the rapid change of tectonic subsidence rate is beneficial to the formation of BSR. The higher settlement rate of the structure is beneficial to provide enough accommodation space.
Acknowledgement: Liang Jinqiang and Wang Hongbin of Guangzhou Marine Geological Survey provided relevant information and help for this basic research. Thank you!
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