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The genesis of internal multiples is complicated and identification is difficult as their velocities are similar to the velocity of primaries, so their residual time is short. The existing conventional methods for identifying multiples are mainly used on a single-common mid-point (CMP) or single line, so the result is indistinct and inaccurate. The concept of velocity spread is proposed, whereby multiples are identified by obtaining the lateral spread of energy clusters on the velocity spectrum. The proposed method uses image segmentation to binarise the velocity spectrum, obtain the spread of velocity, and identify and predict multiples on the plane via attribute spread slicing. In a 3D seismic of Sichuan, the multiples predicted are in good agreement with the known wells. The case shows that velocity spread analysis can quantitatively identify and predict multiples interference, and is complementary to the existing multiples identification method. It can be used to monitor the multiples suppression effect in seismic processing and analyse the interference of multiples in interpretation. In addition, the method has good practicability for evaluating the reliability of reservoir prediction results and reduces the risk of well location deployment during exploration. [ABSTRACT FROM AUTHOR]

Abstract Aimed at the serious mismatch between the synthetic seismogram and the real data of the Sinian Dengying Formation and the Lower Cambrian Qiongzhusi Formation in the GS1 well area, Sichuan Basin, four aspects of internal multiples identification and suppression were studied. Firstly, a forward modeling method of internal multiple based on reflectivity method was developed. Through eight means such as post-stack and pre-stack forward modeling of internal multiple, and combined with VSP data, it was demonstrated that well-seismic mismatching in this area is mainly caused by the internal multiples. Secondly, the simulation results of internal multiple forward modeling using the stripping method combined with the internal multiple periodicity analysis showed that four groups of overburden layers with velocity inversion were the main sources of the internal multiples. Thirdly, by identifying internal multiples accurately and using suppression technology based on pattern recognition, an effective and replicable suppression scheme suitable for these formations was established, overcoming the difficulty of the small speed difference between internal multiple and primary reflection wave which makes the current methods ineffective. Fourthly, an evaluation index of internal multiple intensity was proposed, and the internal multiple intensity distribution diagram of the fourth member of Dengying Formation (Deng-4 Member) in Gaoshiti-Moxi area was compiled. This scheme greatly improved the well-seismic match, and the strata sedimentary features are clearer on the new seismic profiles with higher lateral resolution, with which smaller faults and geological anomalies can be identified and a series of the bead reflections in the Dengying Formation are first discovered. The coincidence rate of reservoir prediction based on seismic waveform classification was increased from 60% to 90%, and that of hydrocarbon detection based on dual phase medium theory was increased from 70% to 100%. [ABSTRACT FROM AUTHOR]