Abnormal surface torque and hook load values are symptoms of downhole drilling condition deterioration which can result in unexpected situations. Usually, friction tests are performed at regular intervals and rig personnel uses these measurements to monitor trend variations in order to detect possible risk of poor hole cleaning or increased borehole tortuousity. The quality of the detection can vary greatly in function of the work load and experience of the drilling staff. The availability of real-time measurements through data servers make it possible to automate and systemize the monitoring process and therefore trigger alarms before drilling problems really occurs. This paper presents a computer system used to systematically analyse real-time data in order to monitor downhole conditions. Such a system can utilize much more data than just the above mentioned friction tests, because mechanical, hydraulic and temperature models can calculate predicted hook load and surface torque in any drilling conditions. The numerical models are automatically calibrated (adjustment of drill-pipe linear weight, factors for mechanical and hydraulic friction and heat generation). The evolution of proper calibration factors is used to detect poor downhole conditions. Automatically generated messages are sent to key personnel who can evaluate the potential problems and take necessary actions. To validate this new methodology, the system has been run on recorded data from three wells on an oil field in the North Sea. A data filtering technique has been developed and applied to solve problems with noisy and erratic real-time signals. With correct input parameters, the system has clearly indicated unexpected measurements several hours before a pack-off problem occurred and therefore proven that the methodology could help in detecting the worsening of downhole drilling conditions. Availability of large amount of real-time data at the rig site or in onshore drilling centres does not necessarily facilitate the recognition of drilling problems. However, online interpretation systems, as the one described above, can systematically analyze the logged data to detect as early as possible the deterioration of hole conditions during drilling operations and corrective actions can be taken before any major problem has really occurred. Introduction Deterioration of downhole conditions during drilling operations can be detected using the hook load and surface torque measurements. Typically, poor hole cleaning, wellbore tortuousity (due to micro-doglegs or larger directional deviation from the planned well path), wellbore instability, formation extrusion, under-gauge hole or junk in hole will have impact on the measured surface torque and hook load. On one hand, poor hole cleaning can result in stuck pipe or indirectly to formation fracturing (due to the increase of downhole pressure in the annulus). On the other hand, increased torque/drag values can hinder reaching the final depth of the well, cause drill-string failure, or prevent from running in the casing/liner string or the tubing string. Therefore it is desirable to monitor those parameters to get an early warning of possible hole condition deterioration.

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.

Summary A new system for real-time optimization and automated control of the drilling process has been tested successfully on the Statfjord C platform in the Norwegian sector of the North Sea. The demonstrated system uses continuously calibrated dynamic process models combined with real-time drilling-data input to calculate available parameter windows, and forward-model simulations are applied to provide optimized operational parameter sequences. The calculation results are applied directly in machine control. The system further applies automated testing combined with continuous diagnostics to provide process advisory. In the field test, pipe-movement control automation, pump-rate control automation, and automated wellbore-condition diagnostics were demonstrated, proving fail-safe application of process safeguard enforcement and optimization of operational procedures. Results from active and passive testing indicated that the new methodology has the ability to improve drilling-process reliability, safely increase drilling efficiency, and reduce the risk of human error. The authors provide a thorough description of the preparations and testing and present an evaluation of the test results, with reference to success criteria that were developed in cooperation with the field operator and drilling contractors involved in the test. Implications for the work organization are also discussed, particularly in relation to control of data input, decision making, and responsibility. The demonstrated technology applies direct integration of current know-how and best practices into the drilling-control system, and available real-time information is applied directly in controlling the drilling process.

During a drilling operation, a real-time analysis of surface and downhole measurements can give indications of poor hole cleaning. However, it is not always intuitive to understand how and where the cuttings are settling in the borehole because the transportation of cuttings and the formation of cuttings beds are largely influenced by the series of actions performed during the operation. With a transient cuttings-transport model, it is possible to get a continuously updated prognosis of the distribution of cuttings in suspension and in beds along the annulus. This information can be of prime importance for making decisions to deal with and prevent poor hole-cleaning conditions.A transient cuttings-transport model has been obtained by integrating closure laws for cuttings transport into a transient drilling model that accounts for both fluid transport and drillstring mechanics.This paper presents how this model was used to monitor two different drilling operations in the North Sea: one using conventional drilling and one using managed-pressure drilling (MPD). Some unknown parameters within the model (e.g., the size of the cuttings particles) were calibrated to obtain a better match with the top-side measurements (cuttings-flow rate, active pit reduction as a result of cuttings removal). With the calibrated model, the prediction of cuttings-bed locations was confirmed by actual drilling incidents such as packoffs and overpulls while tripping out of hole.On the basis of the calibrated transient cuttings-transport model, it is thereby possible to evaluate the adjustments of the drilling parameters that are necessary to stop and possibly remove the cuttings beds, thus giving the drilling team the opportunity to take remedial and preventive actions on the basis of quantitative evaluations, rather than solely on the intuition and experience of the decision makers. IntroductionDuring drilling operations, ensuring proper hole-cleaning conditions is extremely important. Otherwise, serious drilling problems can occur such as stuck-pipe incidents or packoff situations, which can lead to the fracturing of the formation and resulting mud losses. The end result of poor cuttings transport is an increase in nonproductive time. To predict how cuttings are transported, there has been performed a vast amount of experimental work and different attempts on developing appropriate cuttings-transport models. An overview of some of the work that has been performed is given by Pilehvari et al. (1999). It has turned out to be quite complex to describe the cuttings-transport process because transport is influenced by many different parameters such as wellbore geometry, inclination, fluid density, rheology, rate of penetration (ROP), drillstring rotation, flow patterns, flow rate, and cuttings size. One could divide the modeling approach into two

Drilling fluids perform a number of important functions during a drilling operation, including that of lifting drilled cuttings to the surface and balancing formation pressures. Drilling fluids are usually designed to be structured fluids exhibiting shear thinning and yield stress behavior, and most drilling fluids also exhibit thixotropy. Accurate modeling of drilling fluid rheology is necessary for predicting friction pressure losses in the wellbore while circulating, the pump pressure needed to resume circulation after a static period, and how the fluid rheology evolves with time while in static or near-static conditions. Although modeling the flow of thixotropic fluids in realistic geometries is still a formidable future challenge to be solved, considerable insights can still be gained by studying the viscometric flows of such fluids. We report a detailed rheological characterization of a water-based drilling fluid and an invert emulsion oilbased drilling fluid. The micro structure responsible for thixotropy is different in these fluids which results in different thixotropic responses. Measurements are primarily focused at transient responses to step changes in shear rate, but cover also steady state flow curves and stress overshoots during start-up of flow. We analyze the shear rate step change measurements using a structural kinetics thixotropy model.