A generalized quasi-static model of drill string system

• An inversion quasi-static model of drill string system is proposed.
• A generalized model of including forward and inversion calculations is deduced.
• The application of the generalized model shows its availability, simplicity and high-efficiency.

Accurate prediction of the drilling status needs an effective inversion calculation of the relevant parameters of the drill string system. In the previous studies, the inversion calculation was done by a trial and error method of low efficiency. To overcome this shortcoming, an automatic generalized quasi-static model of high efficiency of the drill string system is proposed in this paper. Firstly, the general form of the quasi-static model of drill string system (forward model) is given. However, practice has proven that the calculated results from the forward model are usually not consistent with the measured results of the drill string system. Then, the relevant deviations in the forward calculation are analyzed, and an inversion model is proposed to revise the model parameters. Different forms of the inversion models in the drilling design and actual drilling stages are given. Thirdly, the forward model and inversion model are further combined into a unity, namely generalized model. The generalized model is not only an advanced model depicting the drill string system, but also a powerful tool applied to practice. At last, the application of the generalized model to a real field is discussed.