Effect of Drillstring Vibration Cyclic Loads on Wellbore Stability

Abstract

Wellbore instability resulted in the largest percentage of non-productive time (NPT) during drilling stage in oil industry. Wellbore instability during drilling includes: wellbore pack-off, excessive torque and drag, blowout, stuck pipe and other related well problems. Many studies assumed that wellbore instability problems were due to physical and chemical interactions between rocks and drilling fluid; and neglected impact of drillstring vibration on wellbore stability. Drillstring vibration is usually mitigated while drilling not for wellbore stability issues; but to prevent drillstring fatigue and downhole tools failure by not exceeding vibration operation limits for drillstring. This work aims to develop a new approach studies the impact of drillstring vibration on wellbore stability by analyzing different rock failure mechanisms can happen to wellbore due to drillstring vibration; and computing drillstring vibration limits (acceleration values) that can collapse wellbore. Rock failure mechanisms and drillstring dynamic behavior while vibration was studied to understand consequences happened due to drillstring collision with wellbore. Authors innovated a new model to predict drillstring vibration hotspots values that can collapse wellbore. Results show that drillstring vibration can collapse wellbore by three failure mechanisms: a- when drillstring vibration applies stresses above rock strength, rock compressive failure will take place; b- if drillstring vibration applies repeated cyclic loads on rock continuously; rock fatigue will occur; c- when cyclic loads on rock are not strong enough to cause rock failure; rock fatigue will reduce rock strength and lead to rock shear failure. Model computes drillstring acceleration values that can fail wellbore by these failure mechanisms; and calculates mud weight needed to prevent rock shear failure before and after reduction in rock strength due to rock fatigue. Model outputs must be compared with drillstring vibration operation limits; and the lower value must be used as a boundary limit for drillstring vibration while drilling to prevent wellbore collapse and drillstring failure. These will make model results used as an early detector for harmful drillstring vibration shocks on wellbore.

Numerical Investigation of the Influence of the Drill String Vibration Cyclic Loads on the Development of the Wellbore Natural Fracture

“…The drill string vibration cyclic loads which are hitting the wellbore surface generate a decohesion in the preexisting wellbore natural fracture, then, the trend of the opening and closure of the wellbore natural fracture in function of the time also follows the trend of the drill string vibration oscillating profiles. Other studies in the literature have also highlighted the decohesion of the rock structure caused by the drill string vibration cyclic load [8,12,15]. The fluid pressure inside the fracture is highest near the wellbore, therefore, a la fracture width in that region is also expected.…”

“…Ref. [12] investigated the effects of the drill string vibration cyclic loads on the wellbore stability and they obtained slightly similar results with those of [8]. They found that wellbore failure occurred due to drill string vibration cyclic loads when: (i) the drill string vibration applied stresses on the formation exceeded the strength of the rock formation, (ii) the drill string vibration applied continuous cyclic loads on the wellbore resulted in the rock fatigue, (iii) the drill string generates cyclic loads which did not result in the rock fatigue, however, the strength of the rock reduced.…”

“…Although some studies in the past have already investigated the effect of the drill string vibration on the wellbore stability, some of those studies [6,7,10] only demonstrated that drill string vibration indeed had affected the wellbore stability. Other researchers [8,12] focused on the effect of the cyclic loads on the wellbore collapse pressure. Few studies investigated how the continuous cyclic loads can change the parameters of a naturally fractured formation such as its length and its width.…”

Transient response of near-wellbore supercharging during filter cake growth

“…It is well known that many activities, such as drilling, tunnel excavation, seismicity, geological energy exploitation and storage, and geological disposal of nuclear waste, can cause pore pressure to change, which may further change the structure and stress state of porous materials and may lead to shear failure or fracturing (Bruno and Nakagawa, 1991;Guayacán-Carrillo et al, 2017;Liu et al, 2013Liu et al, , 2020Mohajerani et al, 2012;Rice, 2006;Shi et al, 2021). In drilling engineering, there are many factors that can result in pore pressure variation near the wellbore, and these factors can be classified into physical (e.g., fluid flow into or out of the formation, time-dependent filter cake growth, capillary action, and hydrodynamic expansion), mechanical (e.g., drilling unloading, temperature change-induced thermal stress, and in-situ stressinduced stress concentration near the wellbore), chemical (e.g., interaction between the rock and drilling fluid), and engineering effects (e.g., surge/swab pressure during tripping operations, drill-string rotation or vibration, and the drill string colliding with the wellbore wall) (Jia et al, 2019;Khaled and Shokir, 2017;Ma et al, 2016;Meng et al, 2019;Roshan and Rahman, 2010).…”

A Transient Analytical Model for Predicting Wellbore/Reservoir Temperature and Stresses during Drilling with Fluid Circulation

“…Wellbore stability is affected by a variety of factors, such as mechanical impact as a result of drillstring vibration during drilling [6], formation material properties [7,8] and change in loading boundary conditions. Especially, with the exploration and development of unconventional energy resources such as shale gas/oil and geothermal energy, wells are being drilled deeper and at orientations with respect to the stress field that result in higher stress concentrations around the well.…”