Buckling of Tubulars in Actual Field Conditions

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractBuckling of tubulars inside wellbore has been the subject of many researches and articles in the past. However, these theories have always followed the same assumptions : the wellbore has a perfect and unrealistic geometry (vertical, horizontal, deviated, curved) and the friction is ignored, conditions relatively far from actual field conditions. How do tubulars buckle in actual field conditions, that is, in a naturally tortuous wellbore with friction and rotation ? Can we apply conservatively theories developped for perfect well conditions (no tortuosity, no friction) to actual well conditions ? This paper gives answers to these questions in comparing results obtained from existant models with results obtained from an advanced model dedicated to drillstring mechanics.Firslty, this paper presents the new developements integrated in a recently advanced model for drillstring mechanics and enabling to take into account the buckling phenomenom in any actual well trajectory. Secondly, this paper shows the influence of tortuosity and friction on the buckling phenomenom for some practical and critical case met in the drilling industry. These tortuosity and friction effects are demonstrated with an experimental set up that enables to confirm theoretical features. Lastly, we compare results obtained from existant models with results obtained from our new model to evaluate the tortuosity and friction effects on the critical buckling load found in the litterature.

How Drillstring Rotation Affects Critical Buckling Load?

“…In conducting laboratory experiments and numerical analysis in a perfect horizontal well without rotation, Menand et al 9 and Thikonov et al 10 found similar results about the relationship between λ number and the deformed shape of the drill pipes : λ close to 2.83 enables to predict the onset of the first helix, and λ close to 5.65 enables to predict the full helical drillstring deformation in a perfect wellbore geometry (without rotation). While many equations had been derived for perfect vertical, inclined, horizontal or curved wellbores, no theory were developed for actual well geometry, that is in a naturally tortuous wellbore.…”

“…The results obtained with a non-rotating pipe in a tortuous wellbore have already been presented in a previous paper 9 . The aim of this section is to present results for rotating pipes.…”

“…While many equations had been derived for perfect vertical, inclined, horizontal or curved wellbores, no theory were developed for actual well geometry, that is in a naturally tortuous wellbore. Based on a new numerical method and an experimental facility, Menand et al 9 have demonstrated the strong effect of tortuosity on the critical buckling load, showing for example that a helix could be formed at a load lower than the critical helical buckling load predicted by all equations found in the literature.…”

“…More details, such as main hypotheses and resolution steps, can be found in previous papers 9,22,23 . The numerical model ABIS is implemented in the BHA Management software 24,25 .…”

Drill string instability reduction by optimum positioning of stabilizers

“…Mitchel found that the critical load for a drill string with friction is less than that for a drill string without friction. Menand et al [18] used experimental data to compare them with the results obtained by an Automated Ballistic Identification Systems (ABIS) simulation for a horizontal drill string. He found that the critical axial force for a rotating drill string is much less than that for a non-rotating drill string.…”