Bottom Hole Pressure Calculation of Fractured Carbonate Formation

Carbonate formation is widely distributed in China, mainly showing the sensitivity of the target formation and the development of fracture and cavity types and narrow pressure window. Drilling complicated conditions such as formation leakage or bottom hole pressure less than formation pressure due to gas entering wellbore occur from time to time. To solve these problems, calculating the bottom hole pressure accurately and conducting managed pressure drilling (MPD) for fractured carbonate formation are necessary. In this study, the single-phase hydraulic model based on H-B rheological model is calculated. According to the characteristics of fractured carbonate formation, the drilling fluid leakage model is obtained. By coupling the leakage model with the single-phase wellbore hydraulic model, the bottom hole pressure calculation method is suitable for fractured carbonate formation, which can provide reference for managed pressure control drilling technology. Such a technology is verified by Bozhong X well through the above calculation method of bottom hole pressure. The model is used to simulate the leakage behavior of transverse and longitudinal fractures. Moreover, the variation characteristics of the leakage rate and cumulative leakage amount of the drilling fluid in the fracture are investigated. By comparing the loss control with conventional drilling and MPD, the advantages of controlled pressure drilling operation in the loss control are described.