Abstract:

In recent years, the development of shale oil and gas shows that shale heterogeneity and lateral orientation have relatively great impacts on single well shale gas production, recovery factor and the economy of shale gas exploitation, and natural micro-fracture is the main factor resulting in shale heterogeneity.Accordingly, to carry out research on the natural micro-fractures and prediction of sweet spots within shale has become an inevitable choice for successful emplacement of high-yielding wells and improving economic benefits of shale gas exploitation.Based on the high resolution 3C/3D seismic data in Marcellus shale play within Appalachian Basin, North America, natural micro-fracture zone of Marcellus shale was predicted by means of fast and slow converted shear wave(PSV-1/PSV-2)integrated interpretation, then the open/closed fractures and gas-bearing property of extensional micro-fractures were separately identified and detected by utilizing combined attribute parameters like joint inversion density, velocity ratio of compressional and converted wave(v_P/v_S)extracted from joint inversion of compressional wave and converted shear wave(PP-PS).In addition, drilling data were used to verify the sweet spots predicted by geophysical method in Marcellus shale.Joint inversion technique(PP-PS) has outstanding advantages in natural extensional micro-fractures identification and gas-bearing detection, which can effectively reduce the drilling risk.

Key words: converted shear wave, joint inversion, micro-fracture detection, gas-bearing detection, Marcellus shale