A general dynamic model for any flow-related operation during well construction and interventions has been developed. The model is a basis for a new generation support tools and technologies needed in today's environment with advanced well designs, challenging drilling conditions and need for fast and reliable real-time decision support. The solution method uses a "divide and conquer" scheme, which computes the flow in each well segment separately, and then solves for the appropriate flow in the junctions. This simplifies greatly simulating complex flow networks, such as multilateral wells and jet subs. The flexibility allows incorporating additional pumps in the flow loop, as in Dual Gradient Systems. The model includes dynamic 2-D temperature calculations, covering the radial area affecting the well and assuming radial symmetry in the vicinity of the well. Other features: Flexible boundary conditions (which includes drilling, tripping) Non-Newtonian frictional pressure loss Transient well-reservoir interaction Slip between phases Advanced PVT relationship The reason for this new approach was to respond constructively to today's challenges (complex and difficult drilling conditions, need for reliable real time decision support). Our approach has been more flexibility, improved accuracy, reduced numerical diffusion and increased computational speed. The paper will present the basic model assumptions; the model architecture, and solution methods. Integration of the model into a real time system with links to real time databases and advanced visualization tools is currently ongoing. Thus the model may follow the whole work process through planning, training, execution, and post analysis. Examples of applications of the model so far will be presented, as well as visions for future applications. Introduction Alongside the advances in instrumentation and the more intelligent tools being developed today, there is a need for advanced numerical simulators that can bring all the technologies together to do intelligent drilling that will increase safety, reduce the costs, and make previously "impossible" fields "possible". The challenge in making the simulators lies in making the simulator kernel able to include all the important physical parameters; the important events; compute correct results; and fast enough to meet real time requirements. Examples of some of the recent improvements of the "events" that simulators are able to dynamically simulate are: control during underground blowout1; and hydrate formation2. In order to do this, the kernel needs to be able to change boundary conditions and connectivity during a single simulation. The simulator kernel presented here fulfills the needs of the present and many of the future challenges, as shown in the examples. The next chapters briefly explain the models used in the simulator, and the numerical methods used. The flexibility of the simulator is illustrated through a few examples, and the results of its use in real situation are presented.

The rheological properties of drilling fluids are usually approximated to be independent of pressure and temperature. In many cases this is a good approximation. For shallow wells the temperature changes are not so large, and hence the rheological variations with temperature are small. Also, many wells have a large gap between pore pressure and fracture pressure, so errors in the estimation of the dynamic circulation pressure have no consequences for well integrity or kick probability. However, for wells with small margins between pore and fracture pressure, careful evaluations and analysis of the effects of temperature and pressure on wellbore hydraulics and kick probability is needed. This was a lesson from the serious well-control problems in many North Sea wells in general, and in the Saga 2/4-14 well in Norway in particular. Today wells of this type are planned and drilled around the world, for example in the North Sea, South-East Asia and also in South America. In this paper the effects of pressure and temperature are discussed and described for typical HPHT wells. Laboratory measurements show that rheology is very pressure and temperature dependent. The practical implications of these observations are illustrated through a series of calculations with an advanced pressure and temperature simulator. Introduction The rheological properties of a drilling mud at HPHT conditions are in some cases measured prior to the drilling of a HPHT section. Still, a more general knowledge of the pressure and temperature dependence of HPHT muds can be very useful when HPHT data are not available, e.g. at an early stage of planning. In the latter case the effects of HPHT dependent rheology can be studied through correlation based models. Several studies of the HPF rheology of water based and oil based drilling fluids have been presented in earlier papers, e.g. in Refs. [2–5]. Some of these, Refs. [3–5], include mathematical expressions that are to some extent theoretically motivated, and reproduce observed pressure and temperature dependence of one or more rheological parameters like e.g. viscosity, plastic viscosity or yield stress. The mathematical expressions include a multiplicative factor than can be written on the form where A, B, and C are independent of pressure (p) and temperature (T), but depend on the composition of the drilling fluid. The three constants are also different for different rheological parameters since pressure and temperature dependence of shear stress can be very different at low and high shear rates. The cited references present fits of the two parameters of the Casson and Bingham plastic models, to their p, T models. It could be attempting to determine p, T behaviour of the parameters of the more accurate three parameter models like the Hurschel-Bulkley or Robertson-Stiff models. The problem is that the parameters of the three parameter models depend on pressure and temperature in a less regular way than the parameters of two parameter models (see Figures in [4]). One reason for this is that the different parameters of three parameter models are correlated, such that it is not possible to extract the precise pressure and temperature dependence of each parameter due to measurement uncertainties. For the present work a slightly different procedure has been selected. Shear stress has been multiplied by a factor that depends on pressure, temperature, and shear rate. P. 297^

The RF kick simulator is a tool for well control engineering, study and training. The simulator accounts for all important physical effects related to a kick, and models kicks in both water based mud and oil based mud. In order to test the performance of the model, real gas kicks in both water based and oil based mud have been simulated. Surface and downhole data from full scale gas kick experiments have been used to verify the simulator. The data used are downhole annulus pressure data, surface pressures, mud flow rate out, pit gain and gas transport data. The measured gas influx rate into the well versus time has been used as input data to the gas kick simulations. The conclusion of the comparisons is that the RF kick model reproduces real kick data with acceptable accuracy. This confirms the capability of the RF kick simulator to model gas kicks. The simulator can therefore be used with confidence for the design of well control procedures and the evaluation of kick situations.

The present work discusses some improvements that have been introduced in a dynamic model, which was developed for simulating the two-phase flow transient phenomena associated with underbalanced drilling operations. The model enhancements are basically obtained by implementing mechanistic closure relationships and more accurate numerical schemes. This process of improvement is validated through comparison to full-scale experimental data in transient scenarios, showing that the gains in terms of increasing the model accuracy are significant. Introduction Flow modelling has become more and more important in the whole planning process of an UBD operation. Steady-state models have been used for years for designing the operational window. The only drawback here is that steady-state models are not able to reproduce accurately the transient behaviour that occurs during e.g. unloading, connections, and other inevitable transient situations that occur while performing the operation. On the other hand, dynamic models have this capability. Proper modelling can ensure that the operation can be designed in an optimum manner, and predict the drawdown for various conditions. It is of direct importance to maintain the underbalanced conditions throughout the whole operation to avoid formation damage. Previous experiences indicate that even temporarily overbalanced conditions can reduce the formation productivity. In that sense, both steady-state and dynamic modelling can be of great importance and, in this respect; reliable models are necessary. The present work is concerned with improvements in transient modelling of underbalanced operations. The accuracy of the model, which is an approximation of the reality, depends heavily on using proper closure laws (mechanistic model) for flow pattern description, pressure losses and gas slippage. Another source of error is the basic numerical scheme that solves the fundamental flow equations. The process of improvement involves a new mechanistic approach that has been implemented in a transient model. The simulation results are compared with full-scale data in both steady-state and transient conditions, with the main focus on performing connections. The enhanced model not only matchs up very well with the experimental data but also shows a significant improvement compared to older models, particularly, with regards to describing gas dominated systems properly. The paper also focuses on how numerical schemes can be improved with regards to numerical diffusion. Schemes of high accuracy are required for giving a correct description of the maximum flowrates occurring at the separator (e.g. during the liquid unloading). This is of great importance for sizing properly the surface equipment, particularly the separator. Results are presented showing how a numerical scheme with reduced false diffusion differs from a conventional one that greatly underestimates the maximum flowrates. Constructing a Flow Model In general, multi-phase flow can be described by the fundamental two-fluid model1. It consists of separate conservation equations for each of the phases with respect to mass, momentum and energy. A simpler model can be obtained by adding the momentum conservations equations into a mixture momentum equation. This model is named drift flux. In addition, if the temperature modeling is not of large importance, it is also possible to neglect the energy equations and assume a fixed temperature gradient. Based on this assumption, a simplified version of the drift flux model is presented below.

fax 01-972-952-9435.In order to realize the full potential of Drilltronics, surface and downhole drilling data must be available in real time. The drilling equipment will need to be computer controlled with an interface that supports automatic responses to the model's analysis.