Masters Theses


"Wellbore instability problems play a major rule of increasing nonproductive time (NPT) during drilling processes. In most cases, the cost of drilling a well can be reduced by designing a suitable operational window using geomechanical models. Several wellbore instability problems have been encountered during drilling Nahr Umr Formation in an oil field in southern Iraq. These problems include but are not limited to, mechanical stuck, caving, and tight holes. Data from twenty vertical wells are investigated to reveal the major factors that control the instability problems and to design an optimum mud window. A geomechanical model is developed to determine the in-situ stress and induced stresses by using numerous field and laboratory data for Nahr Umr Formation. Mohr-Coulomb and Mogi-Coulomb failure criteria are used to predict the breakout profile and to estimate the optimum mud weight to avoid sticking. Our analysis shows that the majority of wellbore instability problems are mainly caused by, rock failure (shear failure) around the wellbore due to high stresses and low rock strength, and inappropriate drilling practice with respect to the heterogeneity of Nahr Umr Formation. Moreover, the wellbore failure analysis demonstrates the necessity of core analyses and field tests such as the triaxial test and the mini-frac. test to improve the geomechanical model when studying lithology with high heterogeneity"--Abstract, page iii.


Flori, Ralph E.

Committee Member(s)

Dunn-Norman, Shari
Heidari, Peyman


Geosciences and Geological and Petroleum Engineering

Degree Name

M.S. in Petroleum Engineering


Missouri University of Science and Technology

Publication Date

Summer 2017


xii, 85 pages

Note about bibliography

Includes bibliographical references (pages 78-84).

Geographic Coverage


Time Period



© 2017 Haider Qasim Mohammed, All rights reserved.

Document Type

Thesis - Open Access

File Type




Thesis Number

T 11195

Electronic OCLC #