Adaptive PI Control of Bottom Hole Pressure during Oil Well Drilling

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Real time kick estimation and monitoring in managed pressure drilling system

The influx of reservoir fluid (kick) has a significant impact on drilling operations. Unmitigated kick can lead to a blowout causing financial losses and impacting human lives on the rig. Kick is an unmeasured disturbance in the system, and so detection, estimation, and mitigation are essential for the safety and efficiency of the drilling operation. Our main objective is to develop a real time warning system for a managed pressure drilling (MPD) system. In the first part of the research, an unscented Kalman filter (UKF) based estimator was implemented to simultaneously estimate the bit flow-rate, and kick. The estimated kick is further used to predict the impact of the kick. Optimal control theory is used to calculate the time to mitigate the kick in the best case scenario. An alarm system is developed based on total predicted influx and pressure rise in the system and compared with actual well operation control matrix. Thus, the proposed method can estimate, monitor, and manage kick in real time, enhancing the safety and efficiency of the MPD operation. So, a robust warning framework for the operators based on real life operational conditions is created in the second part of the research. Proposed frameworks are successfully validated by applying to several case studies

Drillstring Washout Diagnosis Using Friction Estimation and Statistical Change Detection

In oil and gas drilling, corrosion or tensile stress can give small holes in the drillstring, which can cause leakage and prevent sufficient flow of drilling fluid. If such \emph{washout} remains undetected and develops, the consequence can be a complete twist-off of the drillstring. Aiming at early washout diagnosis, this paper employs an adaptive observer to estimate friction parameters in the nonlinear process. Non-Gaussian noise is a nuisance in the parameter estimates, and dedicated generalized likelihood tests are developed to make efficient washout detection with the multivariate $t$-distribution encountered in data. Change detection methods are developed using logged sensor data from a horizontal 1400 m managed pressure drilling test rig. Detection scheme design is conducted using probabilities for false alarm and detection to determine thresholds in hypothesis tests. A multivariate approach is demonstrated to have superior diagnostic properties and is able to diagnose a washout at very low levels. The paper demonstrates the feasibility of fault diagnosis technology in oil and gas drilling

Evaluation of the “Command Take-Over Procedure” in automated well control

The growing need for new technology in the pursuit of oil is creating new challenges related to well control. Drilling in HPHT (High Pressure High Temperature) reservoirs, arctic areas, and depleted zones might imply that the drilling window between the pore pressure and the fracturing pressure is narrow. This presents challenges in terms of gas influx. As of today kick handling is a manual procedure with the driller in charge. Automation of well control procedures can be the solution to several problems related to kick detection and kick handling. This thesis introduces theory about conventional well control as well as control theory and automated well control. A part of the work was experimental, and was performed at a simplified rig model at the two-phase laboratory at the University of Stavanger. The results are presented in chapter 6. The main focus in the experimental part is on the Command Take-over procedure. Several experiments were performed leading to the main experiment. The main principle of this procedure is that the drilling operation is run in MPD (Managed Pressure Drilling) mode with a PI-controller (Proportional Integral controller) on the MPD valve. When a gas kick occurs, the WCV (Well Control Valve) mode is activated with a PI-controller on the WCV. Further the BOP (Blow Out Preventer) is closed and the kick is circulated out of the well through the WCV. After the circulation, the operation is back to MPD mode, and the operation continues as planned. The results show that the Command Take-Over Procedure is feasible on actual drilling rigs. It is further possible to assume that the procedure is safer, because the procedure is automated, without the dependence of human judgement and ability to make good decisions in well control incidents. However, it is important to have a drilling crew available on the rig in case of mechanical failure. The procedure is also more efficient and time saving since the pump are constantly running during the procedure, and there might not be a need for a new mud with higher density to regain well control after a gas kick