Optimization of pumping rate for well control during managed pressure drilling

Key words:  managed pressure drilling  well control  wellhead back pressure  circulating out of gas  well control safety  pumping rate optimization

Abstract:

Well control via managed pressure drilling (MPD) is a new and effective method to deal with gas kicks and overflow problems, which includes two stages:initial control response and circulating out of gases. According to the gas-liquid-solid multiphase flow theory, a MPD well control model based on rapidly applying wellhead back pressure method was established, and a finite difference method was used to iteratively solve the model. The effects of pumping rate on the maximum wellhead back pressure, maximum casing shoe pressure and maximum standpipe pressure were analyzed using the model, and an optimized design method for the pumping rate as the objective function for well control safety was proposed. The simulation results show that, in the stage of gas circulating out, the standpipe pressure remains unchanged with its maximum value, and the peak value of the wellhead back pressure appears before the gas front migrates to the wellhead, while the maximum value of the casing shoe pressure appears when the gas front migrates to the casing shoe. The reasonability of using the consistence of outlet flow and inlet flow to indicate the stoppage of bottom hole influx can be verified using the model. The calculated pressure values using the model agree well with the experimental results.