Abstract
<p class="1Body">This study analyses the stress-strain state of a drill string at the section of the borehole with a cavern/chute. The study was conducted to obtain analytical dependencies to determine normal bending stress in the cross section of the drill string and its downforces to the walls of the well. This will allow to compare these values with the critical ones, and draw conclusions about the possibility and duration of the drill string operation under these conditions.</p><p class="1Body">The study is based on modelling the drill string as a beam, which indicates longitudinal and transverse load and deforms in-plane.</p><p class="1Body">The formulas obtained to determine stresses and pressing forces apply to the following cases of the relative position of the drill string in a straight borehole and a curved borehole with a cavern/chute: a – the drill string touches only the bottom of the borehole; b – the drill string touches only the bottom of the borehole and the bottom of the cavern/chute; c – the drill string touches the top and the bottom of the borehole; d – the drill string touches the top and the bottom of the borehole and the cavern/chute.</p><p class="1Body">The calculations based on the dependencies obtained lead to the following conclusions: a – the cavern/chute in the inclined straight borehole causes bending stress value in the cross section of drill pipes proportional to the fatigue margin of the material; b – the cavern/chute in the curved borehole may increase normal bending stress in the cross section of the borehole up to five times.</p>
Highlights
The shape of a borehole significantly differs from cylindrical
Chutes/caverns significantly complicate the working conditions of the drill string, which under their influence may incur additional transverse strain both in a straight and a curved borehole
As the result of the analytical research conducted, the formulas for determining normal bending stress (12), (13), (17) and responses of the walls of the well (15), (19), (18) were obtained, depending on the functions of the elastic axis of the drill string, which is subject to strain both in a straight and a curved borehole with a chute/cavern
Summary
The shape of a borehole significantly differs from cylindrical. As a result of the drill string pressing to the walls of the well, and ravelling and erosion of softer rocks with the drilling fluid, chutes and caverns are formed. Chutes/caverns significantly complicate the working conditions of the drill string, which under their influence may incur additional transverse strain both in a straight and a curved borehole. In "Ukrburhas" Drilling Department, for the period of 2007 to 2009, there were 73 complications and 14 accidents (Gryciv, 2012). 39 of them were due to the formation of chutes and violation of the integrity of the borehole walls, which is 45% of the total amount of complications and accidents In "Ukrburhas" Drilling Department, for the period of 2007 to 2009, there were 73 complications and 14 accidents (Gryciv, 2012). 39 of them were due to the formation of chutes and violation of the integrity of the borehole walls, which is 45% of the total amount of complications and accidents
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
