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For a typical marine shale reservoir in the Jiaoshiba area,Sichuan Basin of China,P-impedance is sensitive for identifying lithology but not suitable for indicating good shale reservoirs.In comparison,density is an important quantity,which is sensitive for identifying the organic-rich mud shale from non-organic-rich mud shale.Due to the poor data quality and incidence angle range,density cannot be easily inverted by directly solving the ill-posed pre-stack seismic inversion in this area.Meanwhile,the traditional density regularizations implemented by directly using the more robust P-impedance inversion tend to be inaccurate for recovering density for this shale reservoir.In this paper,we combine the P-impedance and the minus uranium to construct the pseudo-P-impedance (PIp) at well locations.The PIp is observed to be sensitive for identifying organic-rich mud shale and has a good correlation with density in this area.We employ the PIp-density relation into the pre-stack inversion framework to estimate density.Three types of regularization are tested on both numerical and field data:These are no regularization,traditional regularization and the proposed approach.It is observed that the proposed method is better for recovering the density of organic-rich mud shale in the Jiaoshiba area.