Gerhard Nygaard

Adaptive observer for kick detection and switched control for bottomhole pressure regulation and kick attenuation during managed pressure drilling

Control of the annulus pressure during drilling of oil and gas wells can be a challenging task, due to the complex dynamics of the multiphase flow. Since well kicks and fluid losses are potentially dangerous, it is important to improve the performance and the capabilities of estimation and control and to initiate an automatic well control system. Novel adaptive observers for estimation the flow rates through the well are developed for kick and loss detection, and asymptotic convergence properties are established. A switched control algorithm for feedback control of the choke and the back-pressure pump is proposed for pressure control and kick attenuation and asymptotic convergence is achieved. A new observer is developed to estimate the reservoir pore pressure for improved kick management. Simulation results obtained with a high fidelity drilling simulator are presented to demonstrate the effectiveness of the proposed observer and control scheme. The results show that the proposed observers effectively detect kicks in the early phase and that the automatic control scheme improves the kick handling.

Evaluating control designs for co-ordinating pump rates and choke valve during managed pressure drilling operations

When drilling into a petroleum reservoir it is critical to maintain a required downhole pressure to avoid well bore fracture or influx of petroleum fluids. Drilling into mature and often depleted petroleum fields may be difficult due to tight pressure margins.

Automatic control of managed pressure drilling

Managed pressure drilling (MPD) has emerged as a powerful technology for safe and efficient drilling of hydrocarbon wells. However, it poses interesting control challenges that must be addressed before the anticipated impact. These challenges stem from the strongly multivariable nature of the problem, the presence of critical constraints, and the inherent uncertainty in both models and measurements. In this work we give a brief overview of managed pressure drilling, and make the case that model predictive control is a natural approach to controlling MPD. We demonstrate the proposed approach on an example of model predictive control application to dual-gradient drilling, a particular variant of MPD.

USING NMPC BASED ON A LOW-ORDER MODEL FOR CONTROLLING PRESSURE DURING OIL WELL DRILLING

Abstract During petroleum well drilling operations, the pressure gradient in the well has to be maintained within the pressure restrictions of the formation. The well pressure can be controlled by restricting the drilling fluid flow through a choke valve at the top of the well. This paper proposes a closed-loop control algorithm using a finite horizon nonlinear model predictive control scheme based on a low order well model for this problem. The algorithm is tested on a rigorous high order model.

Modelling two-phase flow for control design in oil well drilling

Today, marginal oil wells are being drilled and the operating margins for the bottom-hole well pressures during drilling are becoming narrower. This requires an improved control of the pressure balance between the reservoir pore pressure and the well bottom-hole pressure. In oil well drilling applications, the pressure is typically controlled manually by adjusting the choke valve. This paper proposes a simple feedback PI-control scheme with feed-forward compensation of the known disturbances. A low-dimensional dynamic state model for two-phase flow has been developed to be able to tune the control parameters. The proposed method is presented and evaluated using a detailed oil well drilling simulator. The results show that the proposed control design keeps the bottom-hole pressure within the operating margins

Deep Water Drilling: Full Pressure Profile Control in Open Hole Section Utilizing Model Predictive Control

Managed pressure drilling has been introduced to reduce pressure related incidents related to targeting narrow pressure margins prospects or deep water prospects. The full pressure profile method, which will be presented in detail in this paper, classifies as a managed pressure drilling method, and is an extension of the well known constant bottom hole method. A case study on a deep water drilling system is presented to demonstrate how model predictive control can simultaneously control the height of the mud column and the flow rate to control the bottom hole pressure while trying to maintain an optimal casing shoe pressure. A model predictive controller is implemented to fully automate the pressure and flow dynamics. Computer simulations are presented to illustrate the potential of the chosen control strategy. Advantages and limitations associated with the full pressure profile control method is analyzed and discussed.

Utilizing Instrumented Stand Pipe for Monitoring Drilling Fluid Dynamics for Improving Automated Drilling Operations

Abstract This paper introduces a method to enable automatic updates of the density, compressibility and frictional effects of the drilling fluid during a drilling operation. By placing pressure sensors along the circulation path from the mud pump to the connection to the drillstring, the fluid dynamics can be examined more thoroughly at various flow rates and pressures. This will help filling the gap of reliable data on drilling fluid properties, which is of great importance in automated drilling operations.