Limiting Factors for the Ability to Achieve Accurate Pressure Control in Long Wells

Abstract

Extended-Reach Drilling (ERD) with narrow pressure margin or uncertain geo-pressure is a challenge with respect to accurate pressure control. The back-pressure Managed Pressure Drilling (MPD) method has been widely used in drilling operations with the aim of controlling annulus pressure within safe bounds, and may also be applicable for ERD wells. However, the ability to control the pressure accurately is limited by several factors. Some of which are related to back-pressure MPD operations in general and some of which are more specific to ERD wells. In this paper, a study is presented on how pressure control is affected and sometimes limited by the actual data availability and quality, equipment, hydraulic models, control algorithms, and downhole conditions during an MPD operation in an ERD well. By using a transient well flow model, the theoretically obtainable MPD performance can be simulated. The benefit by utilizing real-time downhole pressure measurements transmitted by a wired drill pipe is demonstrated by simulations. It is shown quantitatively how variations in delay of measurement and bandwidth will influence the ability to control downhole pressure accurately in an ERD well. Benefit by this approach is a more accurate prediction of what is obtainable with MPD and how various factors may influence the ability to control downhole pressure.

Identification and Optimal Control for Surge and Swab Pressure Reduction While Performing Offshore Drilling Operations

“…As described in Gravdal et al (2018), the system under consideration is limited in the sense of sensor measurements, time-delay, and under constant change due to geo-physical effects in the wellbore. We consider an ideal setting where measurements are not time-delayed and are aware that this effect may give a considerable performance decrease in the system identification and control of the pressure and flow in the wellbore.…”

“…Automatic pressure control is a measure of stabilizing the transient pressure in the wellbore. Implemented in the process control of the drillingrig, the conventional Proportional-Integral-Derivative (PID) controller is used to control the subsea or topside choke valve, creating a back-pressure in the well to effectively control the bottom hole pressure (BHP) (Gravdal et al, 2018). However, as pointed out in Gravdal et al (2018), changing conditions in the wellbore due to well geometry, open-hole sections, formation and fluid properties, along with changing temperature profile along the well can limit the PID controller in terms of required re-tuning during the operations.…”

“…Implemented in the process control of the drillingrig, the conventional Proportional-Integral-Derivative (PID) controller is used to control the subsea or topside choke valve, creating a back-pressure in the well to effectively control the bottom hole pressure (BHP) (Gravdal et al, 2018). However, as pointed out in Gravdal et al (2018), changing conditions in the wellbore due to well geometry, open-hole sections, formation and fluid properties, along with changing temperature profile along the well can limit the PID controller in terms of required re-tuning during the operations. These quantities are in many cases dependent on the movement of the DS, and it is emphasized that the control law should oppose limitations on the mechanical side of the drilling operation (Cayeux et al, 2014).…”