Seismic prediction of horizontal principal stresses based on pore pressures and horizontal strains

The accurate prediction of geostresses is key to the planning and optimization of fracturing trajectories in the progress in shale oil reservoir development. In this paper, we use the interbedded sandstone and mudstone layers of the Triassic Yanchang Formation (TYF) in the Ordos Basin as a case study, to investigate seismic prediction methods for pore pressures and horizontal principal stress (HPS), two main aspects in seismic geostress prediction. First, we adjust the Eaton formulae by introducing how mud content affects the elastic characteristics. This adjustment overcomes the limitation that no distinction can be made between sandstone and mudstone, and thus improves the prediction accuracy of pore pressures in interbedded sandstone and mudstone layers. Then, we develop a formulae for calculating HPS by taking account of the lateral variation of strains based on the elastic mechanical model. The new formulae effectively calculates horizontal strains and improves the accuracy of the prediction of HPS. This approach leads to favorable results in the prediction of geostress for interbedded sandstone and mudstone layers in the TYF. The errors between predicted and measured maximum and minimum HPS values are reduced from 8.46% and 9.39% to 3.92% and 4.85%, respectively.