Genetic Analysis of Overpressure While Drilling Based on Isotope Logging Technology

The high pore pressure coefficient of the target layer in the Yingqiong Basin, combined with complex overpressure causes and a narrow drilling safety window, highlights the urgent need for new overpressure analysis technology to improve the accuracy of formation pressure monitoring during drilling and ensure operational safety. In this study, methane isotope logging data are incorporated into the drilling pressure monitoring process. By analyzing the load/unload curve and methane carbon isotope curve characteristics, the causes of formation overpressure can be determined in real time. When overpressure is encountered in the unloading formation, if the methane carbon isotope value increases uniformly or changes slightly with the increase of depth, it indicates that the formation pressure mainly comes from inside the formation, and the overpressure encountered in the drilling process is near-source or self-source. Conversely, if methane carbon isotope values change significantly with increasing depth, it suggests that something else is causing the overpressure. Using methane isotope logging data, the causes of formation overpressure are determined to be fluid expansion and pressure conduction, respectively. These understandings are consistent with the results of comprehensive data analysis after drilling. The methane carbon isotope technology has the advantage of being in real time, the judgment logic of this method is direct and reliable, and it is of great significance to improve the accuracy of formation pressure monitoring while drilling.