Influence of the density fitting considering depth and acoustic deviator on the formation pressure prediction precision

With the continuous development of deepwater drilling technologies, the drilling of narrow-density window tends to happen more frequently, and correspondingly the pressure prediction precision of deepwater formation is required more strictly. The density fitting of deepwater formation is the indispensable foundation for predicting the overlying rock pressure and analyzing formation pressure. Based on existing single model, however, the overlying rock pressure of deepwater formation cannot be predicted accurately. In this paper, referring to the pore pressure prediction process of the Eaton method of index number, combined with the non-linear fitting, the effect of acoustic deviator on the density was introduced into the Power-Law model to analyze the non-linear relationship between acoustic deviator and density. Then, a kind of corrected density fitting model was put forward. This model theoretically takes comprehensive consideration of the normal formation compaction and the abnormal density reflected by the change of acoustic velocity, so it can reflect the actual situations more accurately. In addition, it solves the difficulty that one single model cannot provide accurate density fitting of deepwater formation, and the prediction error of the fracturing pressure is reduced from 6.36% to 2.73%.