Efficient Drillstring-Wellbore Contact Model and Implications for Real-Time Modeling of Complex Downhole Mechanics

Abstract Determining the contact forces between the drillstring and wellbore wall remains a computational challenge; one that prevents real-time estimation of complex downhole mechanics. In order to achieve automation of engineering analysis for real-time dysfunction detection and response, this is a limitation that must be overcome. While current models are capable of providing accurate results for complex scenarios, they can be quite costly, especially for larger drilling assemblies (i.e. full length drillstrings). For reference, a state-of-the-art nonlinear finite element model might take 2 hours to calculate the deflections/rotations and forces/moments of ~20,000+ ft of drillstring. The goal should be the development of a model that can obtain the same result within a minute, if not seconds. Using a validated nonlinear finite element model as an initial comparison, a new drillstring contact algorithm has been developed that can provide similar results in a fraction of the time. The new approach utilizes a direct integration scheme of forces, moments, rotations, and deflections along the drillstring. Contact forces are then determined iteratively over the length of the drillstring. This results in a performance improvement over traditional nonlinear approaches, which rely on the calculation of incremental displacements to determine the precise location and magnitude of contact forces. The new contact iteration is distinct from previous iteration approaches in that it can process multiple contact points in a single iteration, while previous algorithms are limited to adjusting only a single contact point per iteration. The results show a 100-300% improvement in computation time, depending on the individual scenario. For smaller drilling assemblies, such as Bottom-Hole Assemblies (BHAs) with total lengths of a few hundred feet, the computation time reduction is generally on the lower end. The larger time savings occur for full drillstring assemblies that are 10,000-20,000+ ft long. Direct comparisons are shown for increasingly complex scenarios, from deflections of BHAs in 3-dimensional wellbore profiles, to full drillstring assemblies in challenging horseshoe wells. The model is further compared directly to measured downhole bending moment data, with a very good agreement between field-measured and calculated values. This novel wellbore contact algorithm is presented to show what is possible when applying new methods to "old" problems. The new approach has enabled a drastic reduction in the amount of computation time needed to obtain a result. Promising results have set the stage for future development of modeling software and integration into real-time architectures.