Doctoral Dissertations

Keywords and Phrases

Clay Inhibit; Geomechanical Model; Rock Mechanical Properties; Safe Mud Weight; Wellbore Instability


”The Zubair Formation is the most prolific reservoir in Iraq, which is comprised of sandstones interbedded with shale sequences. Due to the weak nature of the shale sequence, the instability of a wellbore is one of the most critical challenges that continuously appears during drilling across this formation. Historically, over 90% of wellbore problems in the Zubair Formation were due to wellbore instability. Problems associated with wellbore instability, such as tight hole, shale caving, stuck logging tools along with subsequent fishing, stuck pipe, and sidetracking result in increasing the non-productive time. This non-productive time has cost an enormous amount of money.

The main objective of this research is to reduce the drilling time and cost for 8 ½” phase of wells in Zubair Formation by minimizing wellbore stability problems. This will be achieved by different laboratory tests on core samples from the targeted formation to obtain the rock mechanical properties and by applying a geomechanical model based on offset well data coupled with suitable rock failure criteria to obtain a safe mud weight and an appropriate well trajectory. Furthermore, this project presents some of the primary laboratory and wellsite testing techniques that are often used by mud engineers to characterize and remediate drilling fluids and shale interactions to improve the selection of chemical additives for clay inhibit.

The present research work can be applied as a cost-effective tool to assess and address existing wellbore instability problems and to guide future neighboring wells for better drilling efficiency by reducing the non-productive time and well costs”--Abstract, page iv.


Flori, Ralph E.

Committee Member(s)

Rogers, J. David
Wei, Mingzhen
Dunn-Norman, Shari
Al Saba, Mortadha


Geosciences and Geological and Petroleum Engineering

Degree Name

Ph. D. in Petroleum Engineering


Missouri University of Science and Technology

Publication Date

Summer 2020

Journal article titles appearing in thesis/dissertation

  • Integrated approach using core analysis and wireline measurement to estimate rock mechanical properties of the Zubair reservoir, southern Iraq
  • Estimating rock mechanical properties of the Zubair shale formation using a sonic wireline log and core analysis
  • Stability analysis of highly deviated boreholes to minimize drilling risks and nonproductive time
  • Laboratory analysis to assess shale stability for the Zubair formation, southern Iraq


xvii, 146 pages

Note about bibliography

Includes bibliographic references.

Geographic Coverage

Southern Iraq


© 2020 Ahmed Khudhair Abbas, All rights reserved.

Document Type

Dissertation - Open Access

File Type




Thesis Number

T 11733

Electronic OCLC #



Dissertation Location