Research and Application of Middle to Deep Formation Pressure Prediction and Monitoring Technology in Fukang Sag, Junggar Basin

The Geological structure is complex in Fukang sag of Junggar Basin, with multiple sets of large-scale reservoirs developed, and the formation pressure varies greatly horizontally and vertically, which seriously affects the engineering safety. Before drilling, the causes of abnormal high pressure in the Fukang Sag were comprehensively analyzed by the combining analysis method of logging curves, Bowers loading and unloading curve method and pressure calculation inverse method, and the overpressure cause correction coefficient Rn was introduced to improve Eaton method to predict the formation pressure distribution characteristics. During drilling, a pressure calculation model of modified drillability Dr index method is established to monitor the change of actual drilling pressure. The results show that the overpressure from Badaowan to Jiucaiyuanzi formation in the Fukang sag is mainly caused by undercompaction and tectonic compression, while Upper Wuerhe, Lucaogou formation and Carboniferous System are mainly caused by hydrocarbon charge. The pressure relative error of the improved Eaton method is less than 5%. Compared with the traditional Dc index method, the accuracy of monitoring pressure while drilling is improved by 25% using a Dr index method, and the risk of a single well is prompted more than 10 times. In this study, a set of middle to deep formation pressure prediction and monitoring technology system was formed, which is of great significance to analyze the distribution law of abnormal high pressure in Fukang sag and reduce the complexity of drilling engineering.