Downhole Wireline Mechatronics and Drillstring Vibration Dynamics

Abstract

The work is divided into two parts: The First part discusses and documents simulation investigations on the interactive effect of the different conveyance accessories tools and their designs on the wireline cable tension force, and how it can influence the wireline cable performance especially in open hole logging operations with highly deviated and rugose zones. A computer simulation model was built to predict the cable tension force applied on conveyed wireline string so as to assess and analyze the effect of the different conveyance accessories, such as centralizers, bottom-nose tools, and wireline coating, on wireline penetration rates. A numerical computing approach was then utilized to represent and analyze the simulation studies output results in a friendly graphical form. Improving the wireline logging performance, especially in highly deviated rugose openhole wells, could increase the percentage of successful logging operations, reducing time, cost and improving data quality with the increased wellbore coverage. The second part discusses the possible violent drillstring vibrations encountered during drilling and its effect on the overall rate of penetration and sustainability. This entails a complete identification and modeling of the drillstring dynamics and the sources of vibrations excitation that include stick-slip, bit-bounce, and whirling with its two forward and backward types to better control its functional operation and improve its performance.

A Matlab numerical simulator model based on Finite-Element-Method of 3D- Timoshenko beam elements is developed for this purpose to predict and simulate the rotordynamic behavior of the bottom-hole-assembly (BHA) and the PDC-Drillbit cutting dynamics. The model also includes the coupling between the torsional and bending vibrations of drillstrings with the nonlinear effects of drillstring/wellbore friction contacts. The work extends previous models of drillstring vibrations in the literature to include the destructive drillstring vibration backward whirling type with Pure rolling behavior and answers some crucial questions: the operation conditions that possibly causes backward whirl vibrations, possible stabilizers’ configuration to reduce chance of backward whirl, best stabilizers locations in the BHA to minimize the sever vibration effects on the drillstring, and other arising questions.