Study on dynamic characteristics of drill string in deep-water riserless drilling

Abstract

The cost and security of ocean drilling are directly related to the efficient exploration and development of ocean resources. The riserless drilling system is usually adopted in the ocean drilling. With the consideration of marine environment load, a dynamic analysis model of drill string in deep-water riserless drilling is established. This model aims to analyze the dynamic characteristics of drill string in the water and down hole during the process of deep-water riserless drilling. The research results are as follows. For the drill string in water, its displacement increase with the increase of ocean current velocity, water depth, rotation speed, and WOB. But the rotation speed and WOB have less influence. The drill string in down hole shows the same pattern. However, the drill string in down hole is only affected near the mud line and the bit, and the rest of the drill string is almost unaffected. In deep-water riserless drilling, stress on the drill string at the wellhead, near the mudline, and at the bottom hole assembly (BHA) is complex. The safety of drill string at these locations should be given great attention.

An Analytical–Numerical Model for Determining “Drill String–Wellbore” Frictional Interaction Forces

“…The authors considered different curvatures of the rods to investigate the regularities of the "sticking-sliding" interaction of the drill string with the wellbore. Reference [13] is devoted to the study of transverse and torsional vibrations of a drilling tool armed with both ball and PDS bits. According to the results of these studies, the relationship between the vibration of the drill string and the specific mechanical energy of the blowout destruction was established.…”

“…Therefore, the advantages of the model developed by us over the well-known ones [9,13,15,20,69,82] lie in the possibility of estimating the parameters of stability and dynamic load, taking into account the frictional forces of parts of the drill string against the walls of vertical, curved, and inclined sections of the well. The information about the use of pipes made of various materials, aluminum and titanium alloys and steel, in the layouts of active drill strings gives special importance to this work.…”

“…providing the required torque on bits; -determination of the real axial loading on the bottom hole; -assessment of the drilling energy balance; -assessment of the drill string guaranteed resource; -selection of washing liquids compositions, etc. [12,13].…”