The most important contributer to Improved Oil Recovery (IOR) on mature fields is drilling of infill wells. Managed Pressure Drilling (MPD) and Continuous Circulation System (CCS) techniques can be used for improved control of bottomhole pressure when drilling wells in depleted fields with narrow pressure windows, but rig heave is a challenge when drilling from floating drilling units. Rig heave, caused by sea waves, induces pressure oscillations downhole that may exceed the operational pressure window. These oscillations are called "surge & swab" and occur both during tripping in and out of hole as well as during drill pipe connections, when the topside heave compensation system used during drilling is disabled because the drill pipe is put in slips. Downhole choking was introduced as a method to reduce downhole pressure oscillations induced by the rig heave and the concept was tested in laboratory scale and using computer simulations (
This paper gives an overview of the surge & swab simulator, describing its capabilities and limitations. Data from drilling of a North Sea well is then used to validate the simulations made using the software. The well, used as example in this paper, was drilled conventionally from a floating rig. The downhole pressure variations recorded during three different drill pipe connections are compared with simulated downhole pressure. The simulations are based on the recorded rig heave as well as the actual drilling fluid, well design and drill pipe data. Results show that there is a good correlation between simulated and actual measured downhole pressure. The surge & swab simulation software is then used to simulate the same drilling pipe connections using three different techniques and combinations of techniques utilized for improved downhole pressure control: (1) Managed Pressure Drilling (MPD) (2) Managed Pressure Drilling combined with Continuous Circulation System (CCS) and (3) MPD combined with CCS and a downhole choke. Results show that rig heave-induced downhole pressure variations are reduced to a level which is considered acceptable for drilling a well with narrow pressure window for the last two cases, while utilization of backpressure MPD alone is not sufficient. The combination of MPD and CCS reduced surge & swab for two out of three connections. For the third and deepest connection, the surge & swab increased. The largest reduction in significant downhole pressure variations (43-68 % vs. conventional drilling for the three connections) occurs when MPD and CCS are combined with downhole choking.
Future work will consist of further developing the surge & swab simulator so that it will be possible to utilize it in well planning and as real-time decision support during drilling operations. The simulator will also be developed to include possibility of simulating various well completion operations such as running casings and liners. A prototype of the downhole choke is currently being tested at the mud loop of the Ullrigg test rig facility in Stavanger, Norway, and the next development phase consists of designing and building a complete downhole tool for testing in a well.
Heave induces pressure oscillations when drilling offshore from floating rigs. A time-domain model is proposed to analyze and predict such pressure oscillations. The model considers the coupled dynamics of the mud and the drillstring, Herschel-Bulkley-type rheology, and realistic geometries. A computationally efficient method to evaluate friction as a nonlinear function of the mud-flow rate and drillstring velocity is discussed. In a simulation study, we illustrate several nonlinear phenomena that have important practical implications but were not included in previous, simpler models. In particular, muds with a yield point can increase the pressure amplitudes significantly, and severe downhole-pressure oscillations are not detectable from topside measurements in many cases.
The focus of this paper is to illustrate how a first-principles model of the well hydraulics can be utilised to assess the magnitude of heave-induced pressure oscillations while drilling offshore from floating rigs. Such pressure oscillations are important to consider, as they can violate tight pressure margins. Based on numerical simulations, we identify situations in which significant downhole pressure oscillations must be expected. We discuss parameters that affect the pressure amplitudes, and illustrate how the simulator is set up to predict the to-be expected pressure oscillations. Such predictions are essential for making an educated decision on whether drilling is possible under given wave conditions and drilling parameters, both when planning a well and in real-time while drilling. We also illustrate how uncertain downhole parameters affect the pressure oscillations, and propose ways to handle the uncertainty in the predictions. Finally, practical issues such as the estimation of downhole pressure oscillations from on-site measurements, calibration of model parameters, ways to reduce the pressure oscillations via the choke, and the limitations thereof, are discussed.
The focus of this paper is on the benefits of model-based control for performance of pressure control and how to enhance robustness against changes in system dynamics by use of adaptive control in managed pressure drilling (MPD) operations. In this work, we present the advantages and disadvantages with adaptive model based control for MPD operations, by implementation of a choke pressure controller. The paper will show that model-based control enables pressure control down to fully closed choke and trapping pressure without a backpressure pump. Moreover, by adding adaption to the model-based controller it is made robust to changing well parameters, recovering control performance. This is part of a pre-study and preparation for flow loop testing in Abu Dhabi Winter 2016, where performance and robustness of the controller is tested for gas influx and a variety of standpipe pump rates and pressure ranges. The purpose of the flow loop testing is to verify that the controller gives satisfactory performance and is the final test stage before the technology is ready for field use.
Aarsnes, Ulf Jakob F. (Norwegian University of Science and Technology) | Di Meglio, Florent (MINES ParisTech) | Graham, Robert (Well Advanced Solutions) | Aamo, Ole Morten (Norwegian University of Science and Technology)
This paper proposes an extension to an existing operating-envelope technique used for underbalanced drilling (UBD) to enhance control of bottomhole pressure and inflow parameters. With the use of an implementation of the drift-flux model (DFM) with boundary conditions typically encountered in underbalanced operations (UBO), a steady-state analysis of the system is performed. Through this analysis, four distinct operating regimes are identified, and the behavior in each of them is investigated through steady-state calculations and transient simulations. In particular, the analysis reveals that a section of the operating envelope previously believed to be unstable/transient is, in fact, stable/steady when a fixed choke opening is used as an independent variable in place of a fixed wellhead pressure (WHP). This results in the steady-state operating envelope being extended, and gives an increased understanding of the well behavior encountered in UBO toward enabling the introduction of automated control. Finally, we investigate the mechanism behind severe slugging in UBO and argue that the cause is different from that of the slugging encountered in production and multiphase transport.
Aarsnes, Ulf Jakob Flø (Norwegian University of Science and Technology) | Gleditsch, Martin Standal (National Oilwell Varco) | Aamo, Ole Morten (Norwegian University of Science and Technology) | Pavlov, Alexey (Statoil Research Center)
The problem of heave-induced-pressure fluctuation during drilling is considered. The surge/swab pressures created by the vertical motion of the pipe can excite resonances that may amplify the magnitude of pressure oscillations by a factor of 10. The locations of the resonant frequencies depend on the topside-choke opening and can hence be avoided. By use of a model of the full coupled dynamics, it is shown that the elastic pipe and the mud-in-pipe can also exhibit resonant behavior significantly affecting the downhole pressure. Techniques to avoid resonances are discussed.
Automation has the potential to improve efficiency, precision, and safety of pressure and flow control during underbalanced drilling (UBD). In addition, advanced control theory can be used to extract more information from existing measurements to increase knowledge of the downhole conditions during operation.
An essential part of an advanced (model based) pressure control system is the hydraulic model. Even with high-bandwidth distributed downhole measurements, a calibrated hydraulic model is required to ensure robustness, e.g. to sensor loss, and obtain real time estimates of unmeasured quantities and reservoir characteristics.
In UBD operations, in contrast to Managed-Pressure-Drilling (MPD) operations, the flow in the annulus is inherently a multiphase gas liquid flow, which severely complicates the modelling. Much effort has been put into developing multiphase flow models, however, to date; most of these are too complex, and not suited for real-time applications. Consequently, the main gap with respect to automation of UBD is the lack of a fit-for-purpose model able to reproduce the main characteristics of the multiphase flow in the annulus, while being sufficiently robust and suitable for real-time applications.
In this work, we present recent advances on the development of a simplified fit-for-purpose model of the distributed gas-liquid dynamics, suited for advanced control of UBD operations. Using an automated calibration procedure, the model is shown to retain a
We present recent advances on the development of a simplified fit-for-purpose model of the distributed gas-liquid dynamics, suited for advanced control of UBD operations. We briefly describe the main modeling assumptions. Then, we present an automated calibration procedure that enables the model to retain accuracy despite its relative simplicity and the results are illustrated with a realistic case study. The simplification of the model enables real time coupling of the model with measurements. This is used to produce estimates of unmeasured quantities, such as gas distribution, and to perform reservoir characterization.
Godhavn, SPE, Statoil ASA, Norwegian University of Science and Technology Summary The two-phase dynamics of gas percolating up a vertical well filled with water is described by two ordinary-differential equations and algebraic relations. We model the gas as bubbles distributed with a distribution function along the well. The model is based on first principles and accommodates tracking of the front of the gas. An unscented Kalman filter (UKF) is used together with the model and wired-drillpipe (WDP) pressure measurements to estimate the liquid-holdup profile as the gas is circulated out of the well. The performance of the model and the method of estimation are compared with results from a state-of-the-art simulator. Introduction After the Macondo incident, the report to the US President (Graham et al. 2011) highlighted the need for automatic systems aiding the drilling crew in making the right decisions during critical events before possible blowouts. In this paper, we address the modeling of a gas kick in a vertical well and estimation of the liquid-holdup profile during circulation.
Kaasa, Glenn-Ole (Statoil) | Stamnes, Øyvind N. (Norwegian University of Science and Technology) | Aamo, Ole Morten (Norwegian University of Science and Technology) | Imsland, Lars S. (Norwegian University of Science and Technology)