Recent advances in drilling and oil & gas extraction have altered the mindset among drilling engineers. One example is the recent trend to drill faster and minimize Non-Productive Time (NPT). This usually requires minimizing changes to the Bottom Hole Assembly (BHA) and improving its reliability. Directional drilling tools such as mud motors and Rotary Steerable Systems (RSS) have become a main stay in minimizing NPT. Moreover, understanding in planning stages the tools’ working envelope in downhole environment, is critical to reducing NPT. Conventional surface testing, however, have significant constraints when trying to determine the performance envelope of directional tools and BHAs.
Advances in numerical modeling enable evaluation of BHA performance under much more realistic downhole conditions. This paper discusses the advancements in the evaluation of directional drilling tools using advanced Time Domain Analysis (TDA). For example, time domain models allow exploration of the full range of BHA response under downhole conditions including the effects of formation changes. Drilling dysfunctions including stick-slip, whirl, and dynamic lateral vibrations can be realistically predicted before drilling. TDA models allow drilling engineers to explore the design space and also explore operating conditions to optimize performance and reliability of the BHAs.
This work describes a newly implemented TDA model based on rigid body dynamics (RBD) solved by finite element methods (FEM) to model drilling dysfunctions. The approach is significantly more accurate and faster compared to conventional models. Also shown is how the TDA model successfully predicted several drilling dysfunctions before drilling and reduced NPT. It is also used to analyze post drilling job cases and explain issues observed in the field.