TY - THES

T1 - Cementing Geothermal Wells in the Molasse Basin and Development of Monitoring and Quality Assurance Practices

AU - Sonnleitner, Natascha

N1 - embargoed until 29-10-2018

PY - 2013

Y1 - 2013

N2 - Between the years 2009 and 2013 about 30 geothermal wells have been drilled in the vicinity of Munich. Several instances of collapse implied that the success of completing those wells highly depends on cementing practices. A detailed analysis of these casing collapse events showed that free fluid behind the casing had a significant influence on these failures. Therefore, the free fluid, resulting from insufficient cementing practices, should be avoided. The objective of this thesis is to ensure the success of future cement jobs and to minimize the risk of casing collapse especially in regard to the local geological setting. During former projects, cement jobs have often been performed following the procedures, which are common for oil and gas wells in the Molasse Basin. Most of them are applicable for geothermal wells; however, there is a difference in completing those wells, which requires more detailed consideration. The first step was to assess all factors influencing a properly placed cement sheath; a geothermal project drilled in the south of Munich served as the basis for research. Main problems were identified and characterized. Recommendations were then developed for an adjusted cementing program. In addition to that a standardized reporting system has been established in order to adequately utilize the know-how gained in preceding projects and to reduce the data complexity. Moreover, the cementing process itself has been split up into 4 main phases using a Gantt chart; each phase is again subdivided into different operations, which allow illustrating every kind of cementation using a varying sequence. Based on this sequence, the future outlook is to create an algorithm to simulate an ideal case of the cement job phase using rate, density and pressure curves. The other phases (call off, rig up, rig down) still need to be recorded and interpreted manually, using the standardized reporting system. Those procedures should be used as the basis for future cement quality evaluation.

AB - Between the years 2009 and 2013 about 30 geothermal wells have been drilled in the vicinity of Munich. Several instances of collapse implied that the success of completing those wells highly depends on cementing practices. A detailed analysis of these casing collapse events showed that free fluid behind the casing had a significant influence on these failures. Therefore, the free fluid, resulting from insufficient cementing practices, should be avoided. The objective of this thesis is to ensure the success of future cement jobs and to minimize the risk of casing collapse especially in regard to the local geological setting. During former projects, cement jobs have often been performed following the procedures, which are common for oil and gas wells in the Molasse Basin. Most of them are applicable for geothermal wells; however, there is a difference in completing those wells, which requires more detailed consideration. The first step was to assess all factors influencing a properly placed cement sheath; a geothermal project drilled in the south of Munich served as the basis for research. Main problems were identified and characterized. Recommendations were then developed for an adjusted cementing program. In addition to that a standardized reporting system has been established in order to adequately utilize the know-how gained in preceding projects and to reduce the data complexity. Moreover, the cementing process itself has been split up into 4 main phases using a Gantt chart; each phase is again subdivided into different operations, which allow illustrating every kind of cementation using a varying sequence. Based on this sequence, the future outlook is to create an algorithm to simulate an ideal case of the cement job phase using rate, density and pressure curves. The other phases (call off, rig up, rig down) still need to be recorded and interpreted manually, using the standardized reporting system. Those procedures should be used as the basis for future cement quality evaluation.

KW - cementing

KW - collapse

KW - geothermal well

KW - Molasse Basin

KW - Geothermie

KW - Zementation

KW - Rohr-Kollaps

KW - Molasse Becken

M3 - Master's Thesis

ER -