An adaptive observer for hyperbolic systems with application to UnderBalanced Drilling

International audienceWe present an adaptive observer design for a first-order hyperbolic system of Partial Differential Equations with uncertain boundary parameters. The design relies on boundary measurements only, and is based on a backstepping approach. Using a Gradient Descent technique, we prove exponential convergence of the distributed system and estimation of the parameter. This method is applied to the estimation of uncertain parameters during the process of oil well drilling

Improved bottomhole pressure control for underbalanced drilling operations

Maintaining underbalanced conditions from the beginning to the end of the drilling process is necessary to guarantee the success of jointed-pipe underbalanced drilling (UBD) operations by avoiding formation damage and potential hazardous drilling problems such as lost circulation and differential sticking. However, maintaining these conditions is an unmet challenge that continues motivating not only research but also technological developments. This research proposes an UBD flow control procedure, which represents an economical method for maintaining continuous underbalanced conditions and, therefore, to increase well productivity by preventing formation damage. It is applicable to wells that can flow without artificial lift and within appropriate safety limits. This flow control procedure is based on the results of a new comprehensive, mechanistic steady state model and on the results of a mechanistic time dependent model, which numerically combines the accurate comprehensive, mechanistic, steady-state model, the conservation equations approximated by finite differences, and a well deliverability model. The new steady state model is validated with both field data and full-scale experimental data. Both steady state and time dependent models implemented in a FORTRAN computer program, were used to simulate drilling and pipe connection operations under reservoir flowing conditions. Actual reservoir and well geometries data from two different fields, in which the UBD technique is being employed, were used as input data to simulate simultaneous adjustments of controllable parameters such as nitrogen and drilling fluid injection flow rates and choke pressure to maintain the bottomhole pressure at a desired value. This value is selected to allow flow from the reservoir to substitute for reduction or cessation of nitrogen injection during drilling and for interruption of nitrogen and drilling fluid circulation during a pipe connection. Finally, a specialized procedure for UBD operations is proposed to maximize the use of natural energy available from the reservoir through the proper manipulation of such controllable parameters based on the results of the computer simulations

Inclusion of temperature in the AUSMV scheme with simulation examples from Underbalanced and Mud Cap Drilling

Master's thesis in Petroleum engineeringTransient flow modelling is actively used to understand dynamic flow scenarios. In this thesis a modification and improvement has been performed for a transient flow model called AUSMV (Advective upstream splitting method). To get a understanding behind some of the simulation scenarios, a brief literary study has been performed on the dual gradient drilling concept and the dynamics behind underbalanced drilling The dual gradient drilling concept is built on the manipulation of pressure using two different fluid densities. The hydrostatic pressure curve produced using dual gradient makes it easier to handle low margins between pore and fracture pressure. Drilling can be performed faster, cheaper and give better completion solutions. The downside with the dual gradient concept is the need for rig modification, re-training of personnel and new well control procedures. The AUSMV scheme can be used to solve the transient drift flux model. This transient drift flux model uses a set of conservations and closure laws. The conservations of liquid and gas mass and the conservation of momentum. To close the system, four closure laws are added. Two of these closure laws are for the liquid and gas densities. These two closure laws were changed with new models which incorporate temperature effects. An existing Matlab code of the AUSMV scheme was used as basis for the modifications and simulations. Two different drilling cases were simulated. The first one was a underbalanced drilling scenario with three different configurations. The main purpose of this simulation was to include and test the temperature dependent density and viscosity models for liquid and gas. The simulation results were compared against results produced from the original code. First the density models were implemented and tested. Then the viscosity was modified to include temperature. Simulation showed that the largest effect of including temperature, was related to the density models and their impact on the hydrostatic pressure which was reduced. The second simulation was a controlled mudcap drilling scenario. The objective for this simulation was to control the mud level using a suction pump. A suction pump removed mud from the middle of the well during simulation and the hydrostatic column dropped along with the bottom hole pressure. A steady state was reached when the injection rate of mass was equal to the suction rate. By adjusting the mass rates, the mud column could be adjusted and the hydrostatic bottom hole pressure controlled. Several modification had to be done to the model in order to make this simulation possible. First a sink term had to be implemented in the liquid mass conservation equation. In addition, the floating mud level in the well causes challenges for the outlet boundary condition treatment and several approaches for handling this was investigated. Finally the effect of numerical diffusion on the mud level interface was demonstrated and by refining the grid, a more accurate description of the mud interface was obtained. However this type of refinement had a computational time cost

Cuttings transport and hydraulics optimisation for underbalanced drilling (UBD) operations in concentric and eccentric, directional and extended reach wells.

Underbalanced drilling facilitates the effective control of wellbore pressures - amongst several other important advantages - when compared to conventional drilling technology. However, this involves the flow of multiphase fluids, which introduces additional complexities due to highly transient flow patterns, unpredictable wellbore hydraulics and increased tendency for the settling of drilled cuttings in the wellbore. An accurate prediction of fluid dynamics and cutting transport efficiency is required to achieve an effective pressure-management hole-cleaning operation. In this research, a theoretical, numerical and experimental study was performed to analyse and investigate cutting transport dynamics and wellbore hydraulics. The analytical study involved the development of several mechanistic models, which are valid for both single phase and two-phase flows in the concentric and eccentric annuli, both with and without inner pipe rotation. The study derives and presents Reynolds number and effective viscosity equations valid for annuli flow of both Newtonian and non-Newtonian Power law, Bingham plastic and Yield power law fluids. The study also used the solution of the continuity equation of motion for axial steady-state flows to formulate new Laminar and turbulent friction geometry parameter and friction factor equations, which take into account the combined effect of the fluid rheology, fluid circulation rate, pipe eccentricity and inner pipe rotation speed for the evaluation of the flow dynamics and pressure losses in the annuli. In addition, the study developed new flow gas-liquid pattern-dependent multi-layered models for the different cuttings transport mechanisms, valid for both horizontal and inclined annuli flows. Numerical computational fluid dynamics simulations were performed to discretise and solve the governing equations for fluid flow, using a finite volume mathematical approach to obtain velocity, viscosity and pressure fields for different input conditions. Furthermore, an experimental study was carried out to evaluate the interplay between the two-phase gas-liquid flow patterns and the major drilling parameters, and to investigate the influence on the cuttings and fluid flow dynamics in a horizontal and inclined drilling wellbore. Results showed that the effect of the drillpipe rotation on cuttings transport in the annuli is highly dependent on the fluid rheological properties, the drillpipe eccentricity, the wellbore inclination and fluid flow pattern. The annuli pressure gradient was found to be dependent on the fluid flow pattern and the prevailing cutting transport mechanism. The minimum requirements to clean an eccentric annulus is higher than that required for the concentric annulus. Furthermore, the local mixture properties and gas-liquid flow pattern of the fluid is strongly influenced by the inclination angle of the wellbore, which consequently influences annuli pressure losses and cutting transport dynamics. Although drillpipe rotation can improve cuttings transport through the annuli, the influence of drillpipe rotation on the cutting's movement in the two-phase gas-liquid drilling fluid is much less than that of the single-phase drilling fluid. Overall, a good match was found when the mathematical models were compared to the experimental data. The output of this research is very useful for implementing an efficient cutting transport operation, hydraulic program optimisation and effective wellbore control, particularly for managed pressure drilling operations

Predicción del flujo multifásico en tuberías: artículo de revisión

In this work a review about the most relevant methods found in the literature to model the multiphase flow in pipelines is presented -- It includes the traditional simplified and mechanistic models, moreover, principles of the drift flux model and the two fluid model are explained -- Even though, it is possible to find several models in the literature, no one is able to reproduce all flow conditions presented in the oil industry -- Therefore, some issues reported by different authors related to model validation are here also discussedEn este trabajo se presenta una revisión de los métodos más relevantes en la industria del petróleo para modelar el flujo multifásico en tuberías -- Se incluyen desde los modelos simplificados hasta los modelos mecanicistas además de explicar los principios de los modelos drift flux y two fluid -- Existe una gran cantidad de modelos en la literatura para simular el flujo multifásico en tuberías, empero, ningún modelo es capaz de reproducir todas las condiciones de flujo multifásico presentes en la industria del petróleo -- Finalmente, se mencionan algunos temas en los que se requiere más investigación que lleven a simulaciones con resultados más cercanos a los datos de pozos reale

Dynamic Simulation of Dual Gradient Drilling Operation using the Finite Element Method

The deepwater and ultra-deepwater drilling industry has created several techniques to overcome the Well-Control challenge in these scenarios. Dual Gradient Drilling is one of those techniques. Created in the mid-90’s the technique is relatively new and it is not fully integrated at the market yet. The main concept it is to use a lighter fluid on top of a heavier fluid inside the wellbore and marine riser, which allows the engineer a better control of bottomhole pressure. This work is focused on understand the fluid dynamics of a Dual Gradient Drilling operation. It uses the conservation equation along with the previous proposed density and rheological model to investigate how mud weight, thermal properties and well configuration affect the pressure and temperature profile. The system of equation is discretized using Finite Element Methods and the code implemented in Matlab®. The results demonstrated the importance of an accurate density model and its consideration during the development of the well plan. A sensitivity analysis shows the effects of the Overall Heat Transfer Coefficient over the temperature profile, proving that it is the major parameter controlling the heat exchange in the drilling process

Modeling and control of managed pressure drilling operations

The upstream oil and gas industry has witnessed a marked increase in the number of wells drilled in areas with elevated subsurface formation pressures and narrow drilling margins. Managed Pressure Drilling (MPD) techniques have been developed to deal with the challenge of narrow margin wells, offering great promise for improved rig safety and reduced non-productive time. Automation of MPD operations can ensure improved control over wellbore pressure profiles, and there are several commercial solutions currently available. However, these automation efforts seldom take into account the uncertainty and complex dynamics inherent in subsurface environments, and usually assume ideally functioning sensors and actuators, which is rarely the case in real-world drilling operations. This dissertation describes a set of tools and methods that can form the basis for an automation framework for MPD systems, with specific focus on the surface back-pressure technique of MPD. Model-based control algorithms with robust reference tracking, as well as methods for detecting system faults and handling modeling uncertainty, are integrated with a novel multi-phase hydraulics model. The control system and event detection modules are designed using physics-based representations of the drilling processes, as well as models relating uncertain variables in a probabilistic fashion. Validation on high-fidelity simulation models is conducted in order to ascertain the effectiveness of the developed methods.Mechanical Engineerin

Development of an optimised integrated underbalanced drilling strategy for cuttings transport in gas-liquid flow through wellbore annuli.

Although understanding the relationship between gas-liquid two-phase fluid flows and the effects of the major drilling variables is critical to optimising underbalanced drilling (UBD) operations, to date, this has been an area of limited research and knowledge. This study contributes to the limited knowledge base by: 1) determining the key operational drilling parameters which shape the gas-liquid two-phase multiphase flow behaviour characteristics during UBD operations, 2) evaluating the most critical operational issues that have impacted the implementation of global UBD programmes, and 3) investigating the Newtonian and non-Newtonian gas-liquid two-phase flow patterns which affect the wellbore hydraulics and cuttings transport efficiency during UBD operations. Thus, this study developed a rigorous integrated strategy for maximising the efficiency of UBD for the transport of cuttings in gas-liquid two-phase flow through wellbore annuli. An experimental approach was applied to analyse and evaluate the relationship between the gas-liquid two-phase flow patterns and the major operational drilling parameters (gas and liquid flowrates, fluid rheology, inner pipe rotation, pipe inclination angle, pipe eccentricity and solid particle size and density) and to investigate their influence and interaction on the fluid flow dynamics and solids transport mechanisms in horizontal and inclined annuli. Experimental results revealed that drilling fluid flowrate along with fluid flow pattern are the most prominent parameters that strongly influence the cuttings transport efficiency within wellbore annuli. Annuli cleaning requirements for a concentric annulus was found to be lower than that required for an eccentric annulus for both Newtonian and non-Newtonian fluids. Pipe inclination angle was shown to affect hole cleaning, with the degree of its effect being significantly influenced by the drilling fluid properties, prevailing gas-liquid fluid flow pattern and cuttings transport mechanism. Moreover, inner pipe rotation was observed to improve cuttings transport in both horizontal and inclined eccentric annuli to varying extents. Experimental evidence was supplemented with a theoretical approach. Flow pattern dependent multi-layered mathematical models applicable for any level of pipe eccentricity were used for the different cuttings transport mechanisms existing in the different fluid flow patterns (dispersed bubble, bubble, and slug), offering a unique method to evaluate cuttings transport efficiency and wellbore hydraulics performance for UBD operations. A favourable comparison was observed between the experimental data and proposed flow pattern dependent multi-layered mathematical models with an error margin of ±15%. This research has generated new knowledge and created value through mapping the factors influencing particle transport and by evaluating the fluid-particle dynamics (fluid forces, gas-liquid fluid flow patterns and particle transport mechanisms) for flow in wellbore annuli. It has further identified and evaluated the effect of gas-liquid two-phase fluid flow patterns on fluid-particle transport dynamics which results in areas of preferential flows and stagnation zones. It also proposed a systematic solution to the governing equations for the simultaneous flow of gas-liquid two-phase fluids and solid particles in wellbore annuli. Overall, the mapping of the major operational drilling parameters and their influence and interdependencies on wellbore dynamics and cuttings transport efficiency in the context of gas-liquid fluid systems, provides a tool for the prediction of cuttings transport mechanism, determination of the stationary bed height, and calculation of the annuli pressure losses. Therefore, wellbore pressure evaluation and management and hole cleaning requirements for UBD operations can be addressed