<abstract xmlns="http://www.w3.org/1999/xhtml"><p>Wellbore collapse is an instability-event that occurs at low mud density and leads to unfavorable economic project, reaching billions of US dollars. Thus, it is important to accurately determine its value, especially in deepwater horizontal wellbores. The main reasons for nontrivial problems with such wellbores are evident: the shale encountered are anisotropic in nature and possess planes of weakness; they react with water-based mud, generate osmotic stresses, swell, and fall unto the wellbore bottom, thereby increasing the non-productive time. To this end, salts are added to reduce the collapse tendency, but it is not currently known what amount of salt addition maintains stability, and does not lead to wellbore fracture; in deepwater, the current trend in global warming means there is a future concern to the industry. As the climate temperature increases, more ice melts from the polar region, the seawater expands and the sea level rises. How to incorporate the corresponding effect on collapse gradient is scarcely known. This study captures the major concerns stated above into wellbore stability analysis. Following the classical approach for geomechanical analysis, Mogi-Coulomb criterion was combined with a constitutive stress equation comprising contributions from mechanical and osmotic potentials of mud and shale. A sophisticated industry model was used to consider the deepwater effect. The results show significant reduction in collapse gradient as the water depth increases, also, larger difference between the mud and shale chemical activities represents higher complexities in the wellbore. In addition, the reduction in the chemical activities of mud limited to 37.5% of the initial value can be practically safe.</p></abstract>

Wellbore collapse is an instability-event that occurs at low mud density and leads to unfavorable economic project, reaching billions of US dollars. Thus, it is important to accurately determine its value, especially in deepwater horizontal wellbores. The main reasons for nontrivial problems with such wellbores are evident: the shale encountered are anisotropic in nature and possess planes of weakness; they react with water-based mud, generate osmotic stresses, swell, and fall unto the wellbore bottom, thereby increasing the non-productive time. To this end, salts are added to reduce the collapse tendency, but it is not currently known what amount of salt addition maintains stability, and does not lead to wellbore fracture; in deepwater, the current trend in global warming means there is a future concern to the industry. As the climate temperature increases, more ice melts from the polar region, the seawater expands and the sea level rises. How to incorporate the corresponding effect on collapse gradient is scarcely known. This study captures the major concerns stated above into wellbore stability analysis. Following the classical approach for geomechanical analysis, Mogi-Coulomb criterion was combined with a constitutive stress equation comprising contributions from mechanical and osmotic potentials of mud and shale. A sophisticated industry model was used to consider the deepwater effect. The results show significant reduction in collapse gradient as the water depth increases, also, larger difference between the mud and shale chemical activities represents higher complexities in the wellbore. In addition, the reduction in the chemical activities of mud limited to 37.5% of the initial value can be practically safe.

Analysis of the Collapse Gradient of Deep Water Horizontal Wellbore and the Effects of Mud Chemical Activity and Variation in Water Depth

Department of Petroleum and Gas Engineering

Studia Geotechnica et Mechanica

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Wellbore collapse is an instability-event that occurs at low mud density and leads to unfavorable economic project, reaching billions of US dollars. Thus, it...

Analysis of the Collapse Gradient of Deep Water Horizontal Wellbore and the Effects of Mud Chemical Activity and Variation in Water Depth

Article Category: Research Article

Published Online: Apr 09, 2020

Page range: 232 - 241

Received: Oct 05, 2019

Accepted: Feb 02, 2020

DOI: https://doi.org/10.2478/sgem-2019-0040

Keywords
Mogi-Coulomb criterion, collapse gradient, horizontal well, deepwater, chemical activity

© 2020 Adewale Dosunmu et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Analysis of the Collapse Gradient of Deep Water Horizontal Wellbore and the Effects of Mud Chemical Activity and Variation in Water Depth

Article Category: Research Article

Published Online: Apr 09, 2020

Page range: 232 - 241

Received: Oct 05, 2019

Accepted: Feb 02, 2020

DOI: https://doi.org/10.2478/sgem-2019-0040

KeywordsMogi-Coulomb criterion, collapse gradient, horizontal well, deepwater, chemical activity

© 2020 Adewale Dosunmu et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Keywords
Mogi-Coulomb criterion, collapse gradient, horizontal well, deepwater, chemical activity