Operators in the Cardium formation of central Alberta are increasingly adopting a cemented-back monobore well design to reduce costs and improve operational efficiency. Extensive field data from more than 360 wells completed by an operator working in this formation demonstrates the operational advantages and substantial cost savings gained by adopting a monobore well design. This paper details the evolution of well construction for open hole horizontals in the Cardium, and provides cost and operational comparisons between drilling different wellbore sizes, running different casing sizes, and using different stage tools to cement from the heel of the well back to surface.

The operator completed 77 wells in the Cardium using 177.8 mm intermediate casing through the build section and a 159 mm open hole lateral with 114.3 mm liner before evolving to a cemented-back monobore design. Analysis of the field data determined that 171 mm vertical and build sections of the wellbore, and a 159 mm open hole lateral with 114.3 mm casing is the optimal cemented-back monobore design, allowing for easier casing installation and providing substantial cost savings by eliminating the intermediate casing.

Monobore ball-drop completion systems require a stage tool to cement from the heel of the well back to surface. By implementing a stage collar that closes mechanically rather than with a wiper plug or dart, the operator was able to reduce wellbore integrity risks and considerably lower drill-out costs before stimulating the well. The operator has completed more than 220 wells using this stage collar with 100% success.

The geology of the upper formations was managed using invert drilling mud to control wellbore stability and downhole pressure, rather than intermediate casing, to successfully adopt a cemented-back monobore well design. The steps detailed in this paper to eliminate intermediate casing from wellbore construction, identify optimal wellbore sizes and reduce drill-out costs have proven to be successful in the field and can be applied to a variety of formations around the world.

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