地震正演技术在涠西探区地层超覆型隐蔽圈闭识别中的应用

涠西探区经历了始新世流沙港组时期的湖泊沉积和渐新世涠洲组时期的三角洲沉积。在涠洲组沉积时期，由于涠西南低凸起隆升，在D次洼附近形成了西低东高的洼-隆格局，为地层超覆型隐蔽圈闭的发育提供了有利场所。为了精准刻画涠洲组下部发育的地层超覆型隐蔽圈闭，利用正演模型技术对调谐厚度、速度、地震分辨率对地层超覆点识别时的影响进行了分析。正演模拟分析认为地层厚度大于调谐厚度λ/4时，砂岩才能形成独立的反射轴；地层实际超覆点与地震超覆点之间的误差与砂岩和下伏地层的速度差大小有关，速度差越大，误差越大；地震资料的主频对地震反射尖灭点与地层实际尖灭点的误差有一定影响，主频越高，误差越小。根据涠西探区实际地震资料设计出地层超覆模型，通过正演模拟结果拟合尖灭点误差与夹角的变化规律，发现呈降幂函数关系；根据此函数关系修正实际地层超覆尖灭位置，提高了预测精度，降低了勘探风险。

Application of Seismic Forward Modeling Technology in Identification of Stratigraphic Overlap Subtle Traps in Weixi Exploration Area

Weixi exploration area has experienced lacustrine deposits during Liushagang Formation of Eocene and delta deposits during Weizhou Formation of Oligocene. During the deposition of Weizhou Formation, due to the uplift of Weixinan Low Uplift, a depression-uplift pattern of low west and high east was formed near D sub-depression, which provided a favorable place for development of stratigraphic overlap subtle traps. In order to accurately describe stratigraphic overlap subtle traps developed in the lower part of Weizhou Formation, the influence of tuning thickness, velocity and seismic resolution on the identification of stratigraphic overlap points is analyzed by forward modeling technology. The forward simulation analysis shows that only when the formation thickness is greater than the tuning thickness λ/4, the sandstone can form an independent reflection axis; the error between the actual overlap point of the formation and the seismic overlap point is related to the velocity difference between the sandstone and the underlying strata, and the larger the velocity difference, the greater the error; the dominant frequency of seismic data has a certain influence on the error between the seismic reflection pinch out point and the actual pinch out point of the formation, and the higher the dominant frequency, the smaller the error. According to the actual seismic data of Weixi exploration area, a stratigraphic overlap model is designed, and the variation law of pinch out point error and included angle is fitted by forward simulation results, and it is found that there is a power-down function relationship; according to this function relationship, the actual position of overburden pinch out is corrected to improve the prediction accuracy and reduce the exploration risk.