渤海旅大X构造区古近系近源扇体保真成像技术应用

Application of fidelity imaging to the Paleogene near-source fans,Lvda X structural area in the Bohai Sea

渤海旅大X构造区古近系东营组—沙河街组发育多个近源扇体,不同的扇体地震反射特征差异较大,岩性圈闭刻画困难。同时该构造位于辽东凸起边界断层根部,处于凹陷向凸起的过渡区,地层发生突变,横向速度变化剧烈,精细落实速度模型难度较大,影响了陡坡带边界断层及近源扇体的保真成像。为此,通过以下针对性的处理手段实现了高精度成像:①采取“分区、分域、分步,先强后弱、循序渐进”的精细去噪手段,并在涌浪干扰和分频折射线性干扰压制过程重视低频端有效信号与低频干扰的有效分离;②对鬼波和多次波压制除了常规质控外,细化了利用频谱的质控方法;③采取了分步补偿的方法,对干扰波压制、鬼波压制、多次波压制处理后,利用单炮、叠加重新统计振幅衰减因子,实现对中深层有效反射信号的合理补偿;④针对陡坡带断层的准确成像,在基于层位和地质模型获得的长波长速度模型基础上进行精细速度建模,落实边界断层位置,针对古近系低信噪比区,采取小尺度网格层析结合局部速度扫描以进一步落实速度细节。结论认为:该项基于地震数据和地质模式约束下的高精度叠前深度偏移速度建模技术,有效解决了陡坡带边界断层精细成像及近源扇体的保真成像难题,中深层地震反射特征清楚,目的层分辨率得到有效提高,断层成像明显改善。

There extended numerous near-source fans in the Paleogene Dongying Formation–Shahejie Formation,Lvda X structural area in the Bohai Sea.And the fans vary greatly in seismic reflection characteristics,making it difficult to depict lithologic traps.Meanwhile,located at the root of boundary faults in the Liaodong uplift,the structure stands in the transition zone from depression to uplift.Here,strata change sharply with intense variation in lateral velocity,bringing about some challenges to accurate velocity modeling,which may affect the fidelity imaging of the boundary faults in both steep slope zone and near-source fans.So,high-precision imaging was established through some procedures as follows.First,fine denoising was made progressively in a descending order of noise intensity by zones,domains,and steps,and an effective separation between low-frequency valid signal and low-frequency disturbance was appreciated in the suppression process of swell interference and frequency-division refraction linear interference.Second,for the suppression of ghost and multiples,a quality control method in addition to typical control was optimized dependent on frequency spectrum.Third,after the suppression of interference,ghost and multiples by adopting the distributed compensation,the amplitude attenuation factor was re-determined by single shot and superposition to realize the reasonable signal compensation of valid reflection to middle to deep layers.At last,for reasons of exact imaging on faults in the steep slope zone,the fine velocity modeling was performed on the basis of the long-wavelength velocity model derived from horizon and geological models to figure out the location of boundary faults.For the Paleogene with low signal-to-noise ratio,small-scale grid tomography was linked to local velocity scanning for further velocity ascertainment.It is concluded that,constrained by seismic data and geological models,this high-precision prestack depth migration velocity modeling can ensure the fine imaging of the boundary faults in the steep slope zone and the fidelity imaging in the near-source fans,resulting in clear seismic reflection characteristics in middle to deep layers,advanced resolution in target layers and significant improvement in fault imaging.