川西龙门山复杂构造区精细模型构建和正演

Fine Model Construction and Forward Modeling of Complex Structural Areas in Longmen Mountain, Western Sichuan

摘要: 川西龙门山前带从推覆体下盘至前陆带，构造成排成带发育，勘探有利区进一步往西北拓展。目前红星1井首次钻穿推覆构造带，栖霞组获得高产工业气流，打开了龙门山山前带的勘探局面。但研究区为典型地震勘探双复杂地区，地震资料信噪比低，成像效果差，逆掩推覆体下盘构造落实程度低，严重影响圈闭落实。基于模型的观测关键参数测试分析能在较短时间以极低成本直观反应不同采集参数最终偏移成像结果，有效指导川西北部龙门山前带观测方案设计与优化，提高地震采集质量，降低勘探风险。基于模型分析的关键部分是建模和正演，因此，依据深度剖面和近地表调查成果构建了川西北部龙门山地区逆掩推覆体构造2D高仿真地质模型，实现了基于双复杂构造的精细建模。并通过二维波动方程正演得到了模拟单炮记录，通过与野外采集单炮对比，吻合度较高，为下一步观测参数测试分析打下了基础。

Abstract: Longmen Mountain Foothill in western Sichuan is developed in a row of structures from the lower wall of the thrust block to the foreland zone, and the favorable exploration area is further expanding to the northwest. At present, the Hongxing 1 well has drilled through the thrust belt for the first time, and the Qixia Formation has obtained high-yield industrial gas flow, opening up the exploration situation in the front of the Longmen Mountain. However, the research area is a typical seismic exploration complex area, with low signal-to-noise ratio and poor imaging effect of seismic data. The degree of implementation of the lower wall structure of the overthrust nappe is low, which seriously affects the implementation of traps. Model based observation key parameter testing and analysis can intuitively reflect the final migration imaging results of different acquisition parameters in a very low cost and in a short period of time, effectively guiding the design and optimization of observation schemes in the front of Longmen Mountain in northwest Sichuan, improving the quality of seismic acquisition, and reducing exploration risks. The key parts of model analysis are modeling and forward modeling. Therefore, based on depth profiles and near surface survey results, a 2D high simulation geological model of the overthrust nappe structure in the Longmenshan area of northwest Sichuan was constructed, achieving elaborate modeling based on dual complex construction. And simulated single shot records were obtained through two-dimensional wave equation forward modeling. Compared with field collected single shot records, the agreement was high, laying a foundation for the next step of observation parameter testing and analysis.