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前陆冲断带下盘的掩伏构造假象分析与校正——以准噶尔盆地东部“火北掩伏带”为例
黄芸,梁舒艺,高新峰,高明,伏小鹏
1.中国石油新疆油田公司勘探开发研究院 2.中国石油大学(华东)地球科学与技术学院
Analysis and calibration of false buried structures at the footwall of foreland thrust belt: A case study on "Huobei buried structure" in the eastern Junggar Basin
Huang Yun, Liang Shuyi, Gao Xinfeng, Gao Ming & Fu Xiaopeng
(1. Research Institute of Exploration & Development, PetroChina Xinjiang Oilfield Company, Karamay, Xinjiang 834000, China; 2. School of Geoscience, China University of Petroleum - East China, Qingdao, Shandong 266580, China)

Abstract

The foreland thrust belts between orogenic zones and basins and the buried structures at their footwalls are important oil & gas exploration fields. The studies on structural illusions and complex structures in time domain usually focus on the structural illusions that the images of the underlying structures are pulled up or down by the violent change of stratum thickness or special landforms (e.g. high-speed salt dome and submarine canyons). However, the effects of the thickness change and pinchout of volcanic rock matrix on the imaging of footwall structures and the "false fault and false structure" identification methods are rarely researched. In this paper, the buried anticline at the footwall of Carboniferous Kelameili foreland thrust belt to the north of Huoshaoshan Oilfield in the northeastern Junggar Basin (hereinafter "Huobei buried structure" for short) was taken as an example. Firstly, the verification process before and after the drilling of Well HB2 was described. Then, based on the comprehensive analysis of forward modeling, pre-stack depth migration section and diplog, the cause for "false anticline and false fault" at the footwall of Kelameili foreland thrust belt in time domain was discussed. And the following research results were obtained. First, the lateral change of formation velocity can lead to distorted structural forms of the underlying strata in the velocity anomaly zones, and consequently false structure and deviated structural high emerge. Second, Huobei buried structure and Well H14 north fault are the structural illusions which are resulted from the high-velocity layer of Carboniferous volcanics at the hanging wall of thrust fault and the abrupt change of lateral thickness. Third, the pre-stack depth migration technology (PSDM) is the best tool for solving the problem of structure illusion in time-domain section. If PSDM cannot work, the structural map can be obtained by establishing a correct 3D velocity field and conducting variable velocity time–depth conversion. In conclusion, whether the complex structural belt of overthrust nappe fault is true or not can be discriminated by establishing the typical structural pattern and seismic structure interpretation model of complex structure area and applying forward modeling, combined with diplog results. In addition, the discussion on the seismic interpr