川中深层—超深层多次波识别和压制技术——以高石梯—磨溪连片三维区为例

Deep & ultra-deep multiple suppression in Central Sichuan:an example of Gaoshiti-Moxi

川中地区前震旦系勘探程度不高,远远满足不了深层地质研究的需求。现今主要依据地震资料研究前震旦系,但由于地层年代久、地层压力大、波阻抗差异小,导致地震波能量衰减大、有效信号能量弱,中、浅层存在的强反射界面容易掩盖深层有效的弱反射能量,大大降低了深层地震资料的信噪比,影响地震成像的真实性和可靠性,从而造成构造或地层假象,误导地质解释。为此,在详细分析川中深层地震资料特点的基础上,分析了深层的地震反射特征,认为深层寒武系和震旦系地震资料存在强多次波,超深层前震旦系的连续层状反射结构主要源于中、浅层强反射层产生的多次波,致使深层和超深层信噪比很低。基于多次波的认识和压制难点,确定了叠前和叠后联合、组合压制多次波的思路,应用层控速度分析、高分辨率抛物线Radon变换、优势炮检距叠加和叠后F-X域滤波压制残余多次波等关键技术压制多次波。高石梯—磨溪三维地震资料处理结果表明,提高了深层地震数据和测井合成记录相关性,超深层低角度席状多次波强反射能量得到有效压制,地层结构特征更为清楚,地震成像质量显著改善。

The Pre-Sinian in Central Sichuan is under-explored up to now, which is far from meeting the needs of deep geological research. At present, the research on Pre-Sinian is mainly based on seismic data. However, seismic energy attenuation is quite fast and signal energy is rather weak due to ancient strata, high formation pressure, and small impedance difference. Besides, some strong reflections at middle and shallow layers cover up weak deep signals, which greatly reduce the signal-to-noise ratio (SNR) of deep and ultra-deep seismic data. All these will result in structure or formation illusions and mislead the geological interpretation. For this reason, deep seismic reflection characteristics are analyzed on the basis of deep seismic data in Central Sichuan. It is believed that strong multiples exists in Cambrian and Sinian, and multiples at ultradeep Pre-Sinian are originated from shallow strong reflections, which leads very low SNR in deep and ultra-deep seismic data. To remove this kind of multiples, a strategy of multiple suppression combining prestack and poststack is proposed. The key techniques include strata-bound velocity analysis, high-resolution parabolic Radon transform, optimized offset stack, and poststack F-X domain filter to suppress residual multiple. On seismic processing results of Gaoshiti-Moxi 3D, seismic data has a better correlation with logging data;ultra-deep low-angle sheet multiples are effectively eliminated;seismic imaging quality is significantly improved;and characteristics of ultra-deep stratigraphic structures are clearer.