Calculation method and application of formation fracture pressure in Baiyun deepwater area

Formation fracture pressure can be used not only for drilling design, but also for calculation of important parameters such as hydrocarbon sealing height of caprock and ancient pressure coefficient of fluid diapir area. In this study, the logging data of 38 exploration wells in Baiyun deep-water area are analyzed and sorted, the variation trend of mudstone density with buried depth is constructed, the variation trend of normal compacted mudstone density with buried depth is defined as "Three-stage" (< 800, 800-1200, > 2 200 m), and the dynamic formula of static rock pressure and Poisson's ratio with depth is fitted.The Eaton method is adopted to establish the chart of formation fracture pressure under different water depths, and the results are in good agreement with the leakage pressure obtained by actual drilling.Using the compiled fracture pressure-depth chart, the calculation method of the maximum hydrocarbon sealing height of the trap caprock in shallow buried area is clarified, and it is confirmed that the thin caprock in deep and ultra-deep water areas still has the hydrocarbon sealing ability. Combined with the study of oil and gas accumulation periods, it is clear that the maximum Paleopressure coefficient in the bottom splitting area around B2 well near the center of Baiyun sag is 1.69～1.713.Through comprehensive analysis, it is speculated that when the pore pressure in the study area reaches about 90% of the fracture pressure of the overlying mudstone, the overpressure system will produce cracks, the mudstone caprock will be damaged and oil and gas leakage will occur.