As the drilling sections become deeper and longer, transferring more weight downhole to improve ROP is the primary concern to the operator. Drillstring buckling is a primary concern when using very aggressive drilling parameters. Buckling is a phenomenon where the drillstring suddenly loses stability as axial compression exceeds a certain threshold. The drillstring first buckles sinusoidally inside the wellbore which is then followed by helical buckling. Buckling leads to accelerated joint wear, tool fatigue failures, and lower drilling efficiency. To better manage the buckling risk, this paper proposes a method of simulating drillstring buckling inception and post-buckling state using an advanced transient dynamics model.
A buckling and post-buckling analysis methodology was developed based on the finite element transient dynamics model. The model captures the enriched physics involved in the buckling phenomenon: the large deformation of buckled drillstring, the strong non-linearity of contact and friction forces, and the dynamically triggered buckling due to drilling rotation. Transient dynamics simulations are conducted for drillstring with the actual well trajectory and rotation speed. Weight on bit (WOB) is ramped up gradually, and the drillstring deformation is monitored to detect the onset of buckling. The post-buckling state is examined to evaluate drilling efficiency and string reliability.
To conduct the model validation, an extended reach drilling (ERD) job was analyzed by the model. A measurement while drilling (MWD) tool was deployed in BHA to measure the downhole weight and torque. The simulation implies the helical buckling occurs in drill-pipe and captures the drilling weight and torque loss due to buckled string. Most existing buckling theories use the analytical equations of critical buckling load, which were normally derived based on the idealized assumptions, such as perfect wellbore shape and uniform tubular geometry, but neglect friction and string rotation. The proposed method simulates the drillstring buckling in the actual field drilling conditions. It gives more realistic predictions of buckling inception load and post-buckling configuration. The transient dynamics model is capable of simulating drillstring whirl and weight lockup under the severe helical buckling. Based on the simulated the post buckling configuration of the string, an automatic interpretation method was proposed to detect the buckling mode and location along the drillstring.
Using the transient dynamics model, the simulation procedure presented in this paper can significantly improve drillstring buckling and post-buckling predictions and help mitigate buckling risk in well planning and execution phases.