This paper describes a new method for estimation of well bore position accuracies, when using gyroscopic tools. The developed method represents a solution to the industry's need for a general and flexible error model which is applicable for all gyroscopic surveying tools and services. The general gyro error model consists of a new set of error terms and a mathematical description of how the different error sources contribute to position uncertainties dependent on sensor configurations and operational modes. The model is suitable for appropriate modelling of most gyro surveying services. The error propagation mechanisms are chosen to be identical to those in the ISCWSA's MWD error model (SPE 67616), which has become an industry standard during the last five years. Thus future standardisation and software implementation are simplified. The description of the model and the attached numerical examples should be sufficient to implement the model. The paper is a product of a collaborative work in ISCWSA (Industry Steering Committee on Wellbore Surveying Accuracy). Introduction Work in recent years by a group of industry experts, members of the ISCWSA, culminated in the publication of an error model for magnetic Measurement While Drilling (MWD) survey tools1 which has become widely accepted and used within the oil industry. The work described here was born out of a desire to extend that model to encompass the full range of surveying techniques available to the industry, and, specifically, to include gyro survey tools. The formative work, which has led to this paper, took place within the meetings of the ISCWSA, with subsequent detailed development being undertaken by a Gyro Working Group within that committee. Gyro tools are widely used for completion surveys and to control the drilling of well bores in regions of high magnetic interference, where the magnetic tools become less reliable. Recent advances in gyro technology have led to the application of gyro survey tools during drilling operations; the MWD gyro. This paper contains a description of a gyro survey tool error model, generated to provide:estimation of well bore position accuraciesa standardised and generalised model for the oil industrya model that is easy to implement in well planning and survey management software The model described here has been generated in response to a demand for a single model which is adaptable to the broad range of gyro based systems and services available to the oil industry, both now and in the foreseeable future. The formulation, as described, has sufficient flexibility to model the growth of survey errors in such systems, taking into account the types of sensor used, the sensor configuration and any operational procedures which will influence the performance of the system. The model also attempts to provide a fair representation of the physical processes which influence the propagation of errors, whilst avoiding unnecessary mathematical complexity. A balance between these two objectives has been sought in the selection of an acceptable format for the model. There follows a description of the model for the derivation of inclination and azimuth errors in both stationary and continuous modes of survey operation. This description includes the definition of terms, a statement of the assumptions made in the preparation of the model and details of the gyro and accelerometer error terms that have been included. A subsequent section illustrates the application of the model to some example survey tools. A simplified derivation of the error model coefficients and software implementation details are given in the Appendices.

A very challenging HPHT well has been drilled utilizing an advanced ECD Management System including real time simulations, early diagnosis of upcoming problems, and real time simulations using state-of-the art models. The System uses all available real time drilling data (surface and downhole) in combination with real time modeling to monitor and optimize the drilling process. This information is used to visualize the wellbore in 3D in real time. It has been implemented in Total E&P Norge TASC (Total Activities Support and Collaboration) Center in Norway. The system is composed of the following elements, some of which are unique and ground-breaking:• An advanced and fast Integrated Drilling Simulator which is capable of modeling the different drilling sub-processes dynamically, with interaction between these sub-processes in real time.• Automatic quality check and corrections of drilling data; making it suitable for processing by computer models • Real time supervision methodology for the drilling process using time based drilling data as well as drilling models / the integrated drilling simulator.• Methodology for diagnosis of the drilling state and conditions. This is obtained from comparing model predictions with measured data.• Advisory technology for more optimal drilling. • A Virtual Wellbore, with advanced 2D and 3D visualization of the downhole process.• Data flow and computer infrastructure.Among the challenges during planning and drilling of this well have been:• Very small window between pore and fracture pressure. RT ECD simulations were performed with an advanced hydraulic and thermal wellbore model. • Increased probability for instabilities in the tight window. Was mitigated by RT stability modeling during drilling.• Pore pressure predictions which were updated during drilling.Experiences from the drilling as well as use of the ECD Management System will be summarized and presented. The usefulness of supervision and diagnosis functionalities is illustrated.

This paper describes a new method for the estimation of wellbore position accuracies when using gyroscopic tools. The developed method represents a solution to the industry's need for a general and flexible error model which is applicable for all gyroscopic surveying tools and services.The general gyro error model consists of a new set of error terms and a mathematical description of how the different error sources contribute to position uncertainties dependent on sensor configurations and operational modes. The model is suitable for appropriate modeling of most gyro surveying services.The description of the model and the attached numerical examples are demonstrated to be sufficient to implement the model. The model has now been implemented in a number of commercial well planning and survey-management software packages.The paper is a product of a collaborative work within the SPE Wellbore Positioning Technical Section (SPE WPTS), formerly the Industry Steering Committee on Wellbore Surveying Accuracy (ISCWSA).

A very challenging HPHT well has been drilled utilizing an advanced ECD & Temperature, Well Stability and Geo Pressure Management System including real time simulations, early diagnosis of upcoming problems and real time simulations using stateof-the art models. The System uses all available real time drilling data (surface and downhole) in combination with real time modelling to monitor and optimize the drilling process. This information is used to visualize the wellbore as well as simulation results in 3D in real time. It has been implemented in Total E&P Norge TASC (Total Activities Support and Collaboration) Center in Norway. Among the System elements are:• An advanced and fast Integrated Drilling Simulator which is capable to model the different drilling sub-processes dynamically, and also the interaction between these sub-processes in real time. The Integrated Drilling Simulator is used for automatic forward-looking during drilling, and can be used for what-if evaluations as well.• Data flow and computer infrastructure Among the challenges during planning and drilling of this well have been • Very small window between pore and fracture pressure. RT ECD simulations was performed with an advanced hydraulic and thermal wellbore model • Increased probability for instabilities in the tight window. Was mitigated by RT stability modeling during drilling • Uncertainties in pore pressure predictions. Was mitigated by updating predictions during drilling.Experiences from the drilling as well as use of the decision support System will be summarized and presented.

The surveyed position accuracy degrades when one approaches the magnetic and geographical poles. Both magnetic and gyroscopic tools are affected. We have analyzed the accuracy of several magnetic and gyroscopic services in a number of representative synthetic wellbores. Locations representative for the North Sea and the Barents Sea are chosen. The results show that an increase in horizontal target dimension by a factor of 2 is necessary when moving from 60°N to 75°N, to maintain the same hitting probability.Examples of areas which may be affected by these findings, are: target design, well planning, surveying programs and practices, anti-collision criteria, and the ability to drill relief wells.