Prediction of free hydrocarbon content in continental shale oil based on shear-wave anisotropic seismic inversion

Accurately evaluating the movability of shale oil is essential for efficient exploration and development of continental shale oil reservoirs. The free hydrocarbon content (S₁), a key pyrolysis parameter, is a crucial indicator for evaluating the movability of continental shale oil. However, quantitative seismic prediction of S₁ poses challenges and typically relies on indirect estimation through total organic carbon (TOC) content. Well log data show that the Qingshankou Formation shales in the Gulong Sag of the Songliao Basin exhibit pronounced seismic anisotropy, and the effective anisotropy parameter \sigma exhibits a strong correlation with S₁. To address these challenges, a seismic prediction method for free hydrocarbon content in shale oil reservoirs is proposed, based on pre-stack anisotropic inversion of shear waves. This method derives the anisotropy parameter \sigma by directly inverting vertical shear impedance, anisotropic shear modulus, and vertical shear velocity, and then quantitatively estimates S₁ using established rock physics relationships. Applied to continental shale oil reservoirs in the Gulong Sag, the method yields predictions that closely match drilling data and geological interpretations, providing a robust basis for seismic identification of shale oil movability sweet spots.