The common limitation with a casing string is its inability to maintain hole inside diameter (ID) when run through an existing casing string already installed within the wellbore. This instigated development of expandable metal tubulars to maximize the open interval below existing casing, ensuring conventional wellbore designs can be maintained as well as managing unexpected drilling hazards. With the introduction of expandable tubulars, existing wells could now be completed through the ability to include an additional casing without increasing top-hole design or compromising on the planned completion size.

Today’s industry demands further development in technology, with an ability to set a casing and run another casing string without the additional hole-size reduction experienced with conventional casing or standard expandables. A monobore solution is key to allowing operators increased control of the wellbore by isolating intervals, ensuring an efficient fluid-management system, and continuing with the existing tool assemblies. This requirement has led to the development of monobore expandable systems for intervals of the wellbore with common hole sizes of 12-1/4 in., 8-1/2 in., and 6-1/8 in.

Whether in their liner or clad form, isolating the respective interval without a loss in hole diameter provides new economies to operators when accessing deep and more complex reservoirs. Wellbores can now be engineered with contingency solutions without compromising on well objectives. Their ability to isolate intervals while not compromising on post-expansion hole size is providing operators the ability to mitigate drilling hazards, slim tophole casing designs, or increase completion diameters with minimal operational impact on their existing well plans. To date, operators have actively incorporated monobore expandable solutions to mitigate drilling hazards in Norway, Oman, Turkey, Australia, Saudi Arabia, and Azerbaijan, allowing for hazards to be overcome and well objectives achieved. This paper details design and implementation of such monobore expandable systems while providing real results on a global scale of their implementation, advantages, and operational efficiencies.

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