Nonlinear Estimation with Applications to Drilling

An essential part of an automated MPD control system is the hydraulic model, which in many cases is the limiting factor for achievable accuracy of the system. A lot of effort has therefore been put into developing advanced hydraulic models that capture all aspects of the drilling fluid hydraulics. However, a main drawback is the resulting complexity of these models, which require expert knowledge to set up and calibrate, making it a high-end solution. In practice, much of the complexity does not contribute to improve the overall accuracy of the pressure estimate, simply because conditions in the well changes during MPD operations, and there are not enough measurements to keep all of the parameters in an advanced model calibrated. We will demonstrate that a simplified hydraulic model based on basic fluid dynamics is able to capture the dominating hydraulics of an MPD system. Furthermore, we will demonstrate that by applying algorithms for online parameter estimation, similar to those used in advanced control systems in the automotive and aerospace industry, the model can be calibrated automatically using existing measurements to achieve a level of accuracy comparable to that of an advanced hydraulic model. The results are demonstrated using field data from MPD operations in the North Sea, as well as dedicated experiments carried out in a full-scale drilling rig in Stavanger.