1. State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China;
2. CNPC Key Laboratory of Geophysical Prospecting, China University of Petroleum(Beijing), Beijing 102249, China
Abstract：Conventional amplitude versus offset (AVO) achieves lithology identification and fluid prediction usually on normal moveout correction (NMO) gathers after true amplitude recovery.As amplitude and velocity vary with frequency,frequency-dependent AVO based on velocity versus frequency is developed for reservoir prediction.In fact,factors like stratum absorption and attenuation as well as NMO stretching can also lead to amplitude variation with frequency.Several factors related to frequency-dependent AVO,including velocity change with frequency,stratum absorption and attenuation,and NMO stretching,are discussed in this paper.Considering velocity variation versus frequency,this paper analyses frequency effects on velocity aimed at three common types of reservoirs based on White model,and furthermore studies dispersion influences on AVO curves of different types of reservoirs.For the stratum absorption and attenuation,the absorption and attenuation effects on amplitude,dominant frequency and bandwidth of AVO curves are quantitatively calculated based on a horizontal layered attenuation model,and their effect on different frequency components is also analyzed.NMO stretching effects on amplitude,dominant frequency and bandwidth are also analyzed.Through calculation and analysis,following conclusions are obtained:①In the seismic frequency range,stratum absorption and attenuation and NMO stretching are the main causes of frequency variation among many factors affecting frequency-dependent AVO curve; ②None absorption compensation for field seismic data,or inaccurate compensation and conventional NMO also lead to amplitude variation with frequency.Under these circumstances,frequency variation effect observed may not truly reflect reservoir conditions,thus the effects of the above factors need to be eliminated so that frequency variation effect can truly reflect the properties of reservoir itself.
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