Real-time formation pressure inversion method based on back-pressure excitation response
Petroleum exploration technologies are constantly evloving towards deep and complex formations.In response to the gas kick that is prone to occur during the drilling process of deep and complex oil and gas reservoirs,the key for well control is to accu-rately and quickly invert the formation pressure at the time of gas kick,allow the bottom hole pressure to quickly return to the safety window,and suppress the influx of gas from the formation to the wellbore.In traditional drilling processes,most of the formation pressure inversion during gas kick relies on the well shut-in pressure recovery curve,but it is highly time-consuming and less timely to obtain formation pressure during well shut-in.For this reason,a method is proposed to invert formation pressure under back-pres-sure stimulation without well shut-in.Firstly,a simplified two-phase flow model was established to simulate the gas-liquid two-phase flow behavior in the annulus.The comparison with the OLGA multiphase flow simulator shows that the simplified two-phase flow model has high computational accuracy and can be used to provide real-time annulus data required for formation pressure inversion al-gorithms.Secondly,considering the relationship between the volume of each component during gas kick,a formation pressure inver-sion formula was derived by use of the reservoir model.This method requires applying back-pressure at the wellhead to stimulate the changes in gas kick response parameters(bottom hole pressure and outlet flow rate).The formation pressure is reversed using the ground measurement data obtained from the managed pressure drilling system after back-pressure stimulation and the annular data calculated by the simplified two-phase flow model.The results of simulation experiment show that the back-pressure excitation meth-od provides higher inversion accuracy when compared with the recursive least squares algorithm.Finally,taking into consideration errors in drilling fluid density and outlet flow rate,a robustness analysis was conducted on the back-pressure excitation algorithm.The experimental results show that despite of the errors in drilling fluid density and outlet flow rate,the back-pressure excitation al-gorithm still presents accurate inversion results and good robustness.
gas kickformation pressure inversionreservoir modelmanaged pressure drillingtwo-phase flow model
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