Abstract:

Organicrich terrestrial shales developed in the Paleogene Shahejie Formation in the Jiyang depression, Bohai Bay Basin, China. Seismic prediction of shale oil sweet spots and its influencing factor analysis shall promote studies on shale oil seismic response in the Jiyang depression. Based on seismic, drilling, logging and geochemistry data, we investigated the geophysical response characteristics of shale oil sweet spots using multiattribute regression method, and performed the influencing factor analysis. The results revealed the parameters for shale oil geological and engineering sweet spots in the lower interval of the 3rd Shahejie Formation in the BNHC seismic area, Bonan subsag, Jiyang depression. Organic richness and shale porosity were in the ranges of 3%6% and 5.0%12.5%, respectively, with Ro value between 0.81% and 0.94%. Furthermore, widespread overpressure developed in the Shahejie Formation shale reservoir with pressure coefficient between 1.3 and 1.8. And shale brittle index was more than 40% in the Shahejie Formation. Factors affecting geophysical response characteristics of shale oil geological and engineering sweet spots included rock physics parameters, poststack seismic Pimpedance and Simpedance inversion data volumes, GR response volume, amplitude, etc. These factors affect the prediction of “sweet spots” to varying degrees. Our comprehensive study results suggest that a “continuous sweet spots” seismic response mode was developed in the Shahejie Formation, and poststack acoustic inversion volume is considered to be the most important factor affecting seismic prediction of shale oil sweet spots in the Shahejie Formation.

Key words: Jiyang depression, shale oil, Shahejie Formation, seismic prediction of“sweet spots”, influencing factors