Elastic impedance(EI) inversion has been widely used in industry to estimate kinds of elastic parameters to distinguish lithology or even fluid.However,it is found that conventional three-term elastic impedance formula is unstable even with slight random noise in seismic data,due to the ill-conditioned coefficient matrix of elastic parameters.We presented two-term Fatti elastic impedance inversion method,which is more robust and accurate than conventional three-term elastic impedance inversion.In our method,density is ignored to increase the robustness of inversion matrix.Besides,P-impedance and S-impedance,which are less sensitive to random noise,are inverted instead of VP and VS in conventional three-term elastic impedance.To make the inversion more stable,we defined the range of K value as a constraint.Synthetic tests claim that this method can obtain promising results with low SNR(signal noise ratio) seismic data.With the application of the method in a 2D line data,we achieved λρ,μρ and VP/VS sections,which matched the drilled well perfectly,indicating the potential of the method in reservoir prediction.
Jin ZhangHuaishan LiuSiyou TongLei XingXiangpeng ChenChaoguang Su
Seismic while drilling(SWD) is an emerging borehole seismic imaging technique that uses the downhole drill-bit vibrations as seismic source.Without interrupting drilling,SWD technique can make near-real-time images of the rock formations ahead of the bit and optimize drilling operation,with reduction of costs and the risk of drilling.However,the signal to noise ratio(SNR) of surface SWD-data is severely low for the surface acquisition of SWD data.Here,we propose a new method to retrieve the drill-bit signal from the surface data recorded by an array of broadband seismometers.Taking advantages of wavefield analysis,different types of noises are identified and removed from the surface SWD-data,resulting in the significant improvement of SNR.We also optimally synthesize seismic response of the bit source,using a statistical cross-coherence analysis to further improve the SNR and retrieve both the drill-bit direct arrivals and reflections which are then used to establish a reverse vertical seismic profile(RVSP) data set for the continuous drilling depth.The subsurface images derived from these data compare well with the corresponding images of the three-dimension surface seismic survey cross the well.
A new prestack AVA simultaneous inversion using particle swarm optimization algorithm is proposed, which can obtain the elastic parameters such as P-wave and S-wave impedance from P-wave reflection data simultaneously. Compared with the conventional AVA inversion based on generalized linear technique, this method does not depend on the initial model and can reach the global minimum. In order to increase the stability of the inversion, low-frequency trends of P-wave and S-wave impedances are built into the inversion. This method has been successfully applied to synthetic and field data. The estimated P-wave and S-wave impedances can be combined to derive other elastic parameters, which are sensitive for lithology identification and fluid prediction.
Jin ZhangPeng ShenWeina ZhaoXubing GuoXing WangSong ChenXiugang Xu
The Mesozoic-Paleozoic marine residual basin in the South Yellow Sea(SYS) is a significant deep potential hydrocarbon reservoir. However, the imaging of the deep prospecting target is quite challenging due to the specific seismic-geological conditions. In the Central and Wunansha Uplifts, the penetration of the seismic wavefield is limited by the shallow high-velocity layers(HVLs) and the weak reflections in the deep carbonate rocks. With the conventional marine seismic acquisition technique, the deep weak reflection is difficult to image and identify. In this paper, we could confirm through numerical simulation that the combination of multi-level air-gun array and extended cable used in the seismic acquisition is crucial for improving the imaging quality. Based on the velocity model derived from the geological interpretation, we performed two-dimensional finite difference forward modeling. The numerical simulation results show that the use of the multi-level air-gun array can enhance low-frequency energy and that the wide-angle reflection received at far offsets of the extended cable has a higher signal-to-noise ratio(SNR) and higher energy. Therefore, we have demonstrated that the unconventional wide-angle seismic acquisition technique mentioned above could overcome the difficulty in imaging the deep weak reflectors of the SYS, and it may be useful for the design of practical seismic acquisition schemes in this region.
