Branch,CNOOC,Tianjin 300452,China On issues of formation quality factor Q inversion
Yun Meihou1,2, Dang Pengfei1, Li Weina1, Zhao Qiu-fang1,2, Nie Yan1
1. Institute of Resources & Environment, Henan Polytechnic University, Jiaozuo, Henan 454000, China;
2. Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region, Jiaozuo, Henan 454000, China
Abstract:Aiming at five existing problems in formation quality factor Q inversion or Q estimation,our research results show that the rationality of model structure,thickness and parameters selection is the key to the forward modeling analysis of attenuation.Meanwhile,we discuss in the paper the difference between Q inversion and impedance inversion,and point out the theoretical limitation of consecutive Q inversion.Further we analyze the discrepancies between prestack Q inversion and AVO inversion,and point out the intrinsic essence that seismic amplitude decreases with offset increase for formation absorption,which is called "QVO effect".That is,the ray average quality factors increases with offset increase.In effect the detectability of attenuation response caused by single thin gas reservoir is unreliable,and accurate quality factor Q inversion or estimation based this attenuation response leads to Q inversion uncertainty.Finally,the sensitivity strength of velocity and quality factor to gas saturation in reservoir does not mean the real effectiveness for gas reservoir detection.Only both velocity and quality factor cause seismic response variation which might indicate oil or gas reservoirs.Compared with the velocity,the attenuation response caused by the decrease of quality factor for a single thin gas reservoir is not very obvious.It has a great risk to detect oil gas reservoirs based on the quality factor Q inversion results.
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