Abstract

Well construction is a complex job in which annular pressures must be kept inside the operational window (limited by fracture and pore pressure). Monitoring bottomhole pressure to avoid fluctuations out of operational window limits is an extremely important job, in order to guarantee safe conditions during drilling job.

Several operational parameters have a direct impact on bottomhole pressure such as flow rate, rate of penetration, drilling fluid properties, etc. This way, due to the several parameters to be handled, bottomhole pressure control is a complex task and is (nowadays) a manual and very subjective job. Thus, control and automation of drilling operations is a required activity for future challenge of petroleum engineering.

This job presents the results of the implementation of a phenomenological model aiming the development of a classic PI (proportional - Integral) controller for bottomhole pressure during a drilling job. Some strategies were investigated by handling flow rate and a choke opening. An experimental unit was built to study pressure control, when the system is disturbed by an ROP steps or choke openings. Results show a non linear behavior, what requires the system investigation in different operational conditions in order to make a classic PI controller reliable. This fundamental study represents an important step in the understanding the requirements for the implementation of the drilling automation process.

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