TY - THES

T1 - Evaluation of wellbore cement integrity for groundwater protection

AU - Thonhofer, Christoph

N1 - embargoed until null

PY - 2015

Y1 - 2015

N2 - A lack of well integrity and resulting gas migration through the cemented sections of a well occurs in a large number of wells and can cause severe problems in either the well itself or, through contaminating cross flow, in the formation around the well. Also “Shallow Gas”, which naturally occurs in low depths, poses a potential threat. Especially the contamination of the ground water bearing zones in an area is one thing that must not be underestimated and should definitely be avoided. The quality of cement bonding is usually measured with so called “Bond Logs”. The working principles and accuracy of the most common log types will be discussed in order to clarify their strengths and limitations. This thesis will then investigate the reasons for insufficient cement bonding and micro channels in the cement which allow gas migration in the first place, with a focus on the surface casing section. Theoretical concepts of bonding or integrity models will be discussed to set boundary conditions for possible future FE simulations. Also possible experiments which could be helpful to improve wellbore integrity will be proposed. The main purpose is to increase awareness of the importance of proper cement placement within the well and the importance of the so called Minimum Bonded Interval.

AB - A lack of well integrity and resulting gas migration through the cemented sections of a well occurs in a large number of wells and can cause severe problems in either the well itself or, through contaminating cross flow, in the formation around the well. Also “Shallow Gas”, which naturally occurs in low depths, poses a potential threat. Especially the contamination of the ground water bearing zones in an area is one thing that must not be underestimated and should definitely be avoided. The quality of cement bonding is usually measured with so called “Bond Logs”. The working principles and accuracy of the most common log types will be discussed in order to clarify their strengths and limitations. This thesis will then investigate the reasons for insufficient cement bonding and micro channels in the cement which allow gas migration in the first place, with a focus on the surface casing section. Theoretical concepts of bonding or integrity models will be discussed to set boundary conditions for possible future FE simulations. Also possible experiments which could be helpful to improve wellbore integrity will be proposed. The main purpose is to increase awareness of the importance of proper cement placement within the well and the importance of the so called Minimum Bonded Interval.

KW - bond log

KW - Evaluierung der Zementation

KW - Mindeststrecke für Zementation

KW - well integrity

KW - minimum bonded interval

KW - bond logs

KW - cement sheath evaluation

M3 - Master's Thesis

ER -