Pressure maintenance within safe bounds and minimization of influx of fluids from the formation to the well during a kick are basic concerns of well control. Managed Pressure Drilling (MPD) offers improved capabilities over conventional well control methods to address these concerns. In this work we develop a methodology that capitalizes on the improved access to down-hole measurements offered by wired drill pipe telemetry, to maintain pressure within desired bounds during kick management. The objective of this methodology is to improve MPD by reducing non productive time, reducing formation damage and optimizing operational limits for the annular back pressure choke manifold. The proposed methodology estimates formation pore pressure automatically based on real-time measurements when a gas kick is taken during MPD. The methodology relies on the characteristics of the pressure build-up curve. Implementation of the methodology presumes the availability of standard MPD equipment for automatic annular back pressure control. A representative North-Sea well is used as test case geometry and an advanced hydraulics model is used as a virtual well in computer simulations that provide the basis for the presented results. The proposed methodology is demonstrated to both maintain pressure within desirable bounds and reduce formation fluid influx during a kick and thereby prevent the risk of hole stability problems and the cost associated with non-productive time. Introduction Managed Pressure Drilling is seen as a promising technology in order to meet the challenges of drilling wells with narrow margin between pore pressure and fracture pressure. This is often the case in depleted reservoirs or deep-water wells. MPD is a general description of methods for wellbore pressure management and includes techniques and equipment developed to limit kicks, lost circulation and differential sticking. The overall objective of Managed Pressure Drilling is to reduce the number of casing strings required to safely reach the target depth. The definition from IADC (2008) states that "Managed Pressure Drilling (MPD) means an adaptive drilling process used to control precisely the annular pressure profile throughout the wellbore. The objectives are to ascertain the downhole pressure environment limits and to manage the annular hydraulic pressure profile accordingly. MPD is intended to avoid continuous influx of formation fluids to the surface. Any flow incidental to the operation will be safely contained using an appropriate process." So far, main focus within the industry has been on development of automated chokes and on their control algorithm (Roes et al. 2006 and Godhavn et al. 2009), improved flow meters for influx and loss detection (Santos et al. 2005), and on alternative MPD concepts to actively control the pressure profile (Hinton 2009 and Fossli et al. 2008). The introduction of new telemetry systems for real-time downhole measurements (Hernandez et al. 2008), continuous circulation devices (Jenner et al. 2005) and innovative downhole tools (Bansal et al. 2007) are valuable contributions to the MPD tool box. However, the issue of developing an appropriate process to contain any flow incidental to the operation has not yet been addressed thoroughly. Specifically, although MPD does not encourage influx into the wellbore, there is usually a higher chance of receiving formation fluids (a kick) in MPD compared to conventional drilling. This is because the wellbore pressure profile is usually close to pore pressure somewhere in the open hole section. When a kick is detected, the well must be controlled properly in order to stop the influx, circulate out the formation fluid and continue the drilling operation. To control the well during these steps it is advantageous to get an accurate estimation of the pore pressure at the influx zone as quickly as possible.

Recent developments in drilling technology, such as increased sensory information, enhanced data processing and transmitting capacity and capability, and developments in computer controlled machinery, together with adaptation of already available process technology and know-how, are opening up new possibilities for drilling operations. Application of these combined technologies, together with advanced computer modeling, enables enhanced monitoring and increased optimization and control of drilling operations. This paper presents such an integrated system for monitoring and control of the drilling process, currently in the test phase. A key element in the methodology used here is that the models for fluid flow and drilling mechanics are continuously updated in real-time according to the measured data using Kalman filtering techniques. By comparing the calibrated models to real-time data, unwanted occurrences can be detected quickly, and mitigating actions may be taken, either through system control or through manual intervention. Using the calibrated models, safe limits for the drilling operation are computed and enforced, and procedures are optimized. The modules developed cover tripping and reaming, pump start up, friction tests, stick-slip prevention, bit load optimization and monitoring. The methodology may be applied to drilling operations where the drilling equipment is computer controlled. Surface and preferably downhole data must be available in real time. Rigorous testing with drilling data from offshore drilling operations has been performed, and several full-scale tests have been run on a test rig. The ability to maintain the drilling operation within critical limits has been demonstrated. The methodology may contribute to increased safety and reduced down time during drilling operations. Introduction A large part (25%, [1]) of the overall cost associated with drilling operations is a result of non-productive time due to unplanned well incidents. The main problems during drilling are related to events such as kick, stuck pipe, wellbore collapse, lost circulation and equipment failures, see [2]. Proper use of real time data has the potential to reduce the down time caused by these events significantly. Availability of real time drilling data is increasing, both from surface instruments and downhole gauges. Open standards for real time data access are being developed. Computer controlled drilling machinery like pumps, draw-work and top drive are available. High band-width communication between the rig sites and the office like fiber optic, high band width VHF and satellite are used. All these combined developments enable enhanced monitoring through data processing, and optimization and control of drilling operations through computer modelling and drilling machinery automation. For many years IRIS has developed advanced computer models for the oil industry. Among these are multiphase well flow models and torque and drag models. Testing and verification is done through studies with comparison to field data. Additional sub models have been incorporated to handle special effects and give the models special features. During the last few years the models have been developed in order to run real time and use available measurements of operational data such as flow rate, inlet temperature, surface torque and hook load. In order to run real time and to be a corner stone in a control system for the drilling operation, the models need to be fast and robust. Drilltronics - A Software System for Monitoring and Control IRIS (former RF-Rogaland Research) and National Oilwell Varco (NOV) have developed a new drilling, monitoring, control and prediction system called Drilltronics [3]. The main feature of the system is to combine existing hardware and software for monitoring and controlling the drilling process (system environment) with advanced mathematical models for the drilling process. In the implementation of the system we have used existing and upgraded system environment from NOV.

In this paper we present new methods for coordinated control of pump rates and choke valve for compensating pressure fluctuations during surge and swab operations. In hydrocarbon well drilling, automatic control of the choke valve improves the control of the bottom-hole pressure. This has made it possible to drill wells where it previously was not possible to reach total depth, due to narrow pressure margins in the reservoir. This concept is developed further in this paper, to also include automatic control of pump rates, coordinated with the choke valve control. In configurations where the choke valve is fitted with a flow rate controllable annulus back-pressure pump, the situation calls for structured methods for automatic and coordinated control of the main mud pump, the back-pressure pump and the annulus return choke valve. In this paper, well known methods for multivariable control are applied to the drilling process. These methods are based on identification of coupling and interaction between system input (controllable variables), e.g. pump rates and choke valve settings, and output (measured or estimated variables), e.g. pressure at given depths. It is shown how the well pressure profile can be kept within tight margins, subject to disturbances such as drillstring movement in surge and swab operations. Automatic coordinated control is shown through numerical simulations on a detailed, space-discretized well model. Comparisons are made with the case of complete manual control and the intermediate case where only the annulus return choke line pump is automated, using a simple linear controller. The results with automatic coordinated control of pump rates and choke valve are very promising - the performance of such a solution, measured by variance in pressure fluctuations, is improved - compared to both the case of manual control and the case of only automated choke line pump control. Introduction During surge and swab operations the downhole pressure will be affected by volume changes in the well caused by insertion or extraction of the drillstring, in addition to friction effects between the drillstring and the fluid in the annulus. Multiple control variables are adjusted in order to maintain underbalanced conditions along the well section exposed to the reservoir. The most important control variables are drillstring fluid pump volume rate, qp, drilling fluid density, rho, the annulus back pressure pump, qc, and choke valve opening area, Ac. Multiple measurements are available for evaluating whether the required downhole pressure conditions are maintained. Typical measurements available are flow rates, pump pressure, choke valve differential pressure and downhole pressure. To avoid pressure fluctuations during the drilling operations, multivariable process control can be required. In Balchen 1 there are descriptions of several approaches for controlling such a multivariable process. Control methods such as decoupling, feed-forward, modal control, LQG-control and robust control could be used. In addition the available models of the drilling process should be utilized to improve the control system.

Summary To manage the annular pressure profile during managed-pressure drilling (MPD) operations, simulations performed with advanced computer models are needed. To obtain a high degree of accuracy in these simulations, it is crucial that all parameters describing the system are as correct as possible. A new methodology for real-time updating of key parameters in a well-flow model by taking into account real-time measurements, including measuring uncertainty, is presented. Key model parameters are tuned using a recently developed estimation technique based on the traditional Kalman filter. The presented methodology leads to a more-accurate prediction of well-flow scenarios. Although the present study is motivated by applications in MPD, the idea of tuning model parameters should be of great importance in a wide area of applications. The performance of the filter is studied, using both synthetic data and real measurements from a North Sea high-pressure/high-temperature (HP/HT) drilling operation. Benefits by this approach are seen in more-accurate downhole-pressure predictions, which are of major importance for safety and economic reasons during MPD operations.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn order to manage the annular pressure profile during Managed Pressure Drilling (MPD) operations, simulations performed with advanced computer models are needed. To obtain a high degree of accuracy in these simulations it is crucial that all parameters describing the system are as correct as possible. A new methodology for real time updating of key parameters in a well flow model by taking into account real time measurements, including measuring uncertainty, is presented. Key model parameters are tuned using a recently developed estimation technique based on the traditional Kalman Filter.The presented methodology leads to a more accurate prediction of well flow scenarios. Although the present study is motivated by applications in MPD, the idea of tuning model parameters should be of great importance in a wide area of applications.The performance of the filter is studied, both using synthetic data and real measurements from a North Sea High-Pressure-High-Temperature (HPHT) drilling operation. Benefits by this approach are seen by more accurate downhole pressure predictions which are of major importance for safety and economic reasons during MPD operations.