Optimizing the casing program is one of the most critical factors in well design for deepwater applications. Conventional design often dictates that very large surface casing be used to allow passage of a high number of subsequent casing strings telescoping down in size that are required to reach and penetrate target zones. The large casing, the larger surface facilities needed to handle the large casing, and the greater level of services needed to support drilling and completion of these larger holes increases exploration and field -development costs significantly. In ultra -deep drilling projects, a conventional design may require so many casing strings to reach the target zones that no additional strings are available should unexpected situations occur, such as sloughing, high pressure or lost circulation. Reaching the target zones may then become impossible, and potential production from the well may be severely reduced or completely unobtainable. The value of a revolutionary new technology, expandable tubulars, in reducing well costs and ensuring drilling success for deepwater applications has been commercially proven. With this technology, an expansion device known as the expansion cone is propagated through a new string of downhole tubulars to expand the tubulars. An expandable hanger anchors the expanded string to the previous string. Because an expanded string and hanger require less hole size for placement than a conventional string and hanger, smaller initial hole sizes and casing strings can be used to reach the target zone with the same size string as a conventional installation. Thus, appreciable cost savings can be realized. Alternatively, rather than to reduce the size of the initial hole and subsequent strings, the conservation in hole size afforded by expandable tubulars can be (1) reserved for additional strings that might be necessary for contingency operations or (2) used to increase the size of the final production tubulars thus allowing a significant increase in production flow rates. Hence, wells may be saved that might otherwise be abandoned. Clearly, well designs that utilize expandable tubulars can help reduce costs and increase success in deepwater applications. The paper discusses this new technology and gives examples of commercial installations of expandable tubular systems. These examples illustrate the value of including expandable tubulars in well designs and how these designs can be applied in deepwater drilling.
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