Development of Automatic BHA Directional Tendency Prediction Based on Drill-Ahead Modeling
Authors: Suryadi Hendrik , Yu Tao , Shen Yuelin , Yang Jack , Chen Robin , Chen Wei , Khusaenov Timur 
Published: October 2019

Directional drilling enables reaching farther and more difficult targets and improves well production through increased reservoir contact. Drilling and steering a well with a 3D trajectory path has become very common to achieve multiple objectives such as surface versus target location, well anti-collision on a crowded platform, completion and artificial lift needs, landing the reservoir section in a favorable direction, and maximizing the length of the lateral for optimum production.

Those objectives will be a challenge for the bottomhole assembly (BHA) design, including the bit and steering tool selection. The planned BHA must be able to drill the actual wellbore as per the planned trajectory path. It is important to avoid the failure that result from an inability to follow the planned trajectory because it will cause the nonproductive time to change the BHA; introduce additional tortuosity in the well, which can cause other problems; and risk not reaching the target hence requiring a sidetrack and redrilling. Therefore, BHA design and modeling the directional tendency capability become an important aspect in the planning phase.

Advances in digital technology and modeling allow us to provide a better tool to design the BHA. Many tendency modeling applications today still use the three-point contact theory. In actual conditions, well propagation is a complex transient process, affected by the bit, BHA, formation drilled, and drilling parameters used, and therefore three-point contact theory does not always give satisfactory prediction due to oversimplification. A new directional tendency prediction workflow was developed based on the finite element method. Finite element modeling allows us to calculate BHA deformation and forces. During drilling, the BHA is subjected to axial loading, torsional loading, wellbore contact force, gravity force, etc. All these forces will affect the BHA tendency. Simulating this in drill-ahead/propagation mode will give us a better prediction of BHA tendency and capture the transient well propagation behavior. This new method has been implemented as an automatic analysis agent in a drilling engineering software platform where every time the BHA design is created or changed, the tendency is automatically calculated, and the results are displayed as traffic lights based on comparison with the planned trajectory. The modeling relies on detailed models of various downhole equipment including steering tools and bit cutting interaction with the rock. The modeling results were validated with extensive field data and there was a good match between prediction and the actual results.

The computation was optimized by smart selection of well sections to conduct tendency analysis to evaluate if the BHA can deliver the designed trajectory with good confidence. Computation performance becomes important because the analysis workflow is implemented in an automated planning system where any change of the BHA or other well design aspects will trigger the calculation automatically. This new modeling provides a better tendency prediction which is critical to the well success.