• norsk
    • English
  • English 
    • norsk
    • English
  • Login
View Item 
  •   Home
  • Fakultet for ingeniørvitenskap (IV)
  • Institutt for geovitenskap og petroleum
  • View Item
  •   Home
  • Fakultet for ingeniørvitenskap (IV)
  • Institutt for geovitenskap og petroleum
  • View Item
JavaScript is disabled for your browser. Some features of this site may not work without it.

Analysis of Stick-Slip Effects During Oil-Well Drilling

Zhao, Dapeng
Doctoral thesis
View/Open
Fulltext not avialable (Locked)
URI
http://hdl.handle.net/11250/2448627
Date
2017
Metadata
Show full item record
Collections
  • Institutt for geovitenskap og petroleum [1853]
Abstract
The drilling operation is a costly portion of the upstream petroleum industry. It

is worth making efforts to reduce unwanted non-productive time (NPT), which

is often induced by downhole problems during drilling. In this thesis, dynamic

models of the drillstring to account for both axial and lateral motions have been

developed. Based on these models, problems related to surge and swab pressures

and equipment failures are addressed.

Downhole pressure variations are often caused by surge or swab pressure, from

the axial movement of drillstring during tripping in or out of the well, and also

from heave motion of the drillstring suspended from a heaving drilling vessel. In

this thesis, the Stribeck friction model is used to analyze the friction-induced selfexcitation

vibration (stick-slip) through four regimes of contact: sticking, boundary

lubrication, partial fluid lubrication, and full lubrication. The results indicate

a significant increase in the peak velocity of the drillstring compared to the heave

velocity of the vessel. In addition, axial tension induced geometrical stiffness has

been taken into account, which results in a time dependent normal force between

the drillstring and the borehole in the curved section of the borehole. Simulations

show that the elastic wave form of the downhole drillstring motion is different

from the surface motion. Due to the occurrences of abnormal downhole

pressure, the conventional method might lead to substantially over/underestimated

pressure. Comparing with field data, the theoretical results are matching the observed

downhole pressure. Moreover, based on this study, some recommendations

are further proposed for improving the model, experimental validation, and mitigating

of downhole pressure variations.

Another important study in this thesis is related to the potential failure of drill

collar connections, which is attributed to cumulative fatigue due to bending vibration. An important class of bending vibration is whirl, which is formed by

the eccentricity of the rotational drill collar. The contact between the drill collar

and the borehole causes an harmful backward whirl, even a chaotic whirl. A

two-degrees-of-freedom nonlinear lumped parameter model is utilized for representing

the whirl of the drill collar in this thesis. Different from other studies, the

stick slip vibration causing fluctuation of rotary speed is taken into account. It is

shown that the chaotic whirl happens at a lower rotation speed. In this lumped

element model, the contact forces obey the Hertzian contact law, which leads to

lateral bounce of the drill collar and impact borehole wall chaotically. The modified

Karnopp friction model is adopted to simulate the stick slip rotary vibration

of the bottom hole assemble (BHA). Based on the time domain responses of whirl,

the continuous bending stress history is broken down into individual stress ranges

with an associated number of stress cycles using the rainflow counting method.

The cumulative fatigue damage is estimated using Miner’s rule. Based on the

study, some of recommendations are introduced to further improve model and extend

the model application (such as snake motion of drillstring). In addition, some

mitigation solutions are proposed to expand fatigue life of drill collar.

The third contribution in this thesis is related to the axial vibration assisted drilling.

This technique has recently started to be implemented in gas/oil well drilling. The

application of the technology is validated to improve the drilling efficiency (increase

the rate of penetration) and performance (mitigation of the stick slip). In

this thesis, the mechanism underlying axial vibration assisted drilling is analyzed

using a cutting experiment with a single cutter. The cutter is connected to a microvibration

based piezoelectric actuator, which generates cyclic loads perpendicular

(normal) to the cutting path. The experimental results indicate that the cyclic loads

lead to decreasing both the shear force (30% reduction) and the normal force (50%

reduction)significantly. Simultaneously, the lateral vibration of the cutter, which

can be imaged as the drill bit stick slip results from cutter-rock interaction, is

clearly mitigated during the cutting process. Observations with a confocal microscope

show that the abrasion at the front of the cutter is increased due to the greater

surface roughness when rupture damage of rock occurs (increasing 7.5% area and

50% depth). Based on the analysis of cutting mechanism, the intrinsic specific

energy (or strength) of the rock sample is found with obvious deterioration when

increasing the frequency of the cyclic loads. According to the S-N curve of fatigue

life of Berea sandstone, it is concluded that this deterioration evolution process of

the rock sample is because the cyclic loads induced cumulative damage (up to

42% in maximum). Finally, in order to make this technology applicable, some potential

improvements in further work were listed including high temperature high

pressure influence, abrasion analysis, and 3D scan etc.

The main body of the thesis is given in chapter 3-5, which is fully based on the

publicized articles (I, II and III) 1. Some additional publications (IV, V and VI) are

presented in Appendix B (4, 5 and 6) as an expansion of my study.
Publisher
NTNU
Series
Doctoral theses at NTNU;2017:127

Contact Us | Send Feedback

Privacy policy
DSpace software copyright © 2002-2019  DuraSpace

Service from  Unit
 

 

Browse

ArchiveCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsDocument TypesJournalsThis CollectionBy Issue DateAuthorsTitlesSubjectsDocument TypesJournals

My Account

Login

Statistics

View Usage Statistics

Contact Us | Send Feedback

Privacy policy
DSpace software copyright © 2002-2019  DuraSpace

Service from  Unit