TY - THES

T1 - Experimental Design to Investigate the Casing Smearing Effect

AU - Hirschl, Daniel Maria

N1 - embargoed until null

PY - 2017

Y1 - 2017

N2 - One of the main reasons why Casing while Drilling (CwD) was growing more and more interest in the oil and gas industry is the so called “smearing effect”. Due to the eccentric motion of the casing string crushing of the cuttings takes place along the string. It is assumed that the casing string smears the mixture of fine-sized cuttings and mud onto the wellbore wall. The result in most of the cases is a low permeability layer, which is assumed to stabilize the wellbore wall and consequently increases the overall drilling margin. This is in contrast to the ordinary methods of fluid loss prevention. Normally a filter cake develops due to the difference in formation and mud pressure. No mechanical action is involved in the creation of the cake. In this case, it is not desirable if the drillstring makes contact with the wellbore wall. Furthermore, the cuttings remain at its original size because no crushing action takes place. Therefore, the influence of the cuttings on the filter cake quality is negligible. The main goal for both methods is the same but the underlying mechanism is different. The thesis analyses the underlying mechanisms in theory and defines the most influential parameters for both methods. Furthermore, the geomechanical impact on the area surrounding the wellbore regarding CwD is analysed. Finally, an experimental design is proposed which, if implemented, enables the user to directly compare filter cakes created by one of the two methods.

AB - One of the main reasons why Casing while Drilling (CwD) was growing more and more interest in the oil and gas industry is the so called “smearing effect”. Due to the eccentric motion of the casing string crushing of the cuttings takes place along the string. It is assumed that the casing string smears the mixture of fine-sized cuttings and mud onto the wellbore wall. The result in most of the cases is a low permeability layer, which is assumed to stabilize the wellbore wall and consequently increases the overall drilling margin. This is in contrast to the ordinary methods of fluid loss prevention. Normally a filter cake develops due to the difference in formation and mud pressure. No mechanical action is involved in the creation of the cake. In this case, it is not desirable if the drillstring makes contact with the wellbore wall. Furthermore, the cuttings remain at its original size because no crushing action takes place. Therefore, the influence of the cuttings on the filter cake quality is negligible. The main goal for both methods is the same but the underlying mechanism is different. The thesis analyses the underlying mechanisms in theory and defines the most influential parameters for both methods. Furthermore, the geomechanical impact on the area surrounding the wellbore regarding CwD is analysed. Finally, an experimental design is proposed which, if implemented, enables the user to directly compare filter cakes created by one of the two methods.

KW - Drilling

KW - Exploration

KW - Casing

KW - Filtercake

KW - Bohren

KW - Exploration

KW - Verrohrung

KW - Filterkuchen

M3 - Master's Thesis

ER -