Method and system for managed pressure drilling

Abstract

A method for use with a managed pressure drilling (MPD) system, the system including a drill string having a drill bit, an annulus defined outside of the drill string, a mud pump for pumping mud down through the drill string and back up through the annulus, a control choke in an extraction path coupled to the annulus, a back pressure pump also coupled to the extraction path, and a programmable logic controller (PLC) for controlling the control choke, the method including: a) performing measurements to determine a dataset including, for each of a plurality of time steps k: a value of fluid flow rate through the drill bit q[k], a value of fluid flow rate through the control choke q[k], a value of fluid flow rate from the back pressure pump q[k] and a value of fluid pressure at the control choke p[k]; b) executing an inversion algorithm on the PLC to obtain a value for the bulk modulus of a fluid within the annulus, the inversion algorithm taking the dataset as an input, wherein the inversion algorithm accounts for a measurement bias bin one or more of said measurements; c) updating one or more control parameters of the PLC based on the value for the bulk modulus; and d) manipulating the control choke using the PLC to attain a desired pressure in the system.