Integrating multigeophysical data to improve structural imaging in the Dayangshu Basin

Abstract

We have used the integrated interpretation of gravity, magnetotelluric (MT) data, and seismic data to improve the structural imaging of the Dayangshu Basin. The Dayangshu Basin is mainly composed of clastic and volcanic rocks. The logging data in the basin show different degrees of direct hydrocarbon indication, suggesting that the Dayangshu Basin has good potential for exploration. However, the widely distributed volcanic rocks attenuate seismic waves and lead to poor seismic imaging. Thus, the seismic signal is weak in the Ganhe Formation (K1g) and reliable seismic images cannot be obtained below that formation. MT data can accurately obtain images of deep structures because the resistivity of volcanic rocks is significantly higher than that of sedimentary rocks. Therefore, to obtain a more reliable geologic model, we combine the traditional 3D MT inversion result with logging and seismic data to establish an initial model. The 3D MT fuzzy constrained inversion (FCI) produces a more reliable geophysical model and geologically meaningful results. The resistivity model inverted from FCI shows that volcanic rocks are widely distributed in the Ganhe Formation, and the resistivity value of the lower section of the Longjiang Formation is greater than that of the upper section of the Longjiang Formation. Finally, the 3D gravity inversion with structural constraints from 3D MT FCI method was performed to improve the model resolution in depth and to highlight the density variations within the Jiufengshan Formation, which can further optimize the geologic model. We have determined how the effective integration of gravity, MT, and seismic data can improve the structural imaging of the Dayangshu Basin.