Buckling of Buoyancy-Assisted Tubulars

Abstract

Use of buoyancy provides multiple solutions to overcome the drag problem for wells with shallow and high step-out profiles. Although both full-and partial-flotation methodologies have been used successfully to extend the reach in many field cases, the influence of buoyancy on tubular instability has not been investigated yet. This paper presents an extensive experimental and analytical study, focusing on static tubular instability inside horizontal wellbores with emphasis on buoyancy. In terms of the experimental research, running tubulars into horizontal wellbores was simulated with four different pipes, varying buoyancy, and varying loading speed. Throughout the tests, axial loads both applied to the pipe and transmitted through the pipe were recorded simultaneously, with respect to pipe displacement. Experiments reveal that currently existing models give reasonable approximations as long as buoyancy is not included in the tests. The major interpretation from the experiments is contrary to what currently existing expressions imply (i.e., tubular buckles immediately as effective weight approaches zero; even for naturally buoyant conditions, considerable amount of axial load is still required for both buckling initiation and helix formation). As buoyancy increases further, results and predictions diverge from each other considerably. To eliminate the discrepancies between results and predictions, theoretical study was conducted. Empirical correlations that also consider the influence of buoyancy on critical buckling loads are presented. Finally, another pipe was also tested within different buoyancy conditions to validate the equations developed. Experimental results of this pipe closely match the new analytical findings. This experimental and analytical study provides useful results for future applications with buoyancy-assisted tubulars, in terms of practical engineering and design calculations.

Buoyancy effect dualism on drill string axial forces calculation

“…The effective force Feff is usually derived in calculations from the magnitude of the true force by taking into account the stability force Fbs according to expressions (6,8). Studies of the drill string stresses in the fluid have shown [8,9] that accounting for the stability force Fbs leads to the exclusion of the hydrostatic component from the stresses in the drill string, which does not affect the buckling of the drill string, as well as the strength of the plastic materials from which the drill string elements are usually made. Therefore, effective force is widely used to check buckling conditions, which is one of the most important requirements for the operability of the drill string.…”

Research on Buckling Behavior and Analysis of Sensitive Factors in Horizontal Well Drilling

“…Directing at the theoretical models above, Arslan [21] measured the buckling critical load of a horizontal string through an experiment with the experimental setup as shown in Fig. 2.…”

“…The parameters used in numerical simulation are as literature [21]. The length of the pipe is 28 m. Outer and inner diameters of the inner pipe are 19 and 17 mm, respectively.…”

“…This is because the radial deformation of the drill string is limited by borehole wall, and the increasing axial force leads to the increase of the radial force between drill string Fig. 2 Horizontal buckling facility [21] and borehole wall. Thus, it intensifies the frictional drag and also makes the axial force increase.…”

Dynamic buckling with friction inside directional wells

“…Recent works have focused in comparing results obtained from literature models with experimentally measured data, such as in Arslan et al (2014); or improving even further the models for the static configuration after buckling, as in Huang et al…”