HIGH RATIO, ELASTIC REGION TUBULAR EXPANSION (Continued)

Some strength properties resulting from plasticized expansion are similarly not compliant with industry preferences. Strength of pre-expanded casing is based on specific performance of its originally intended form. The wall-thickness of a tubular device must increase in proportion to increases in its expanded radius, so as to maintain equivalent pressure ratings. This is not what results from the cold-work processes. Often, tremendously lowered pressure ratings occur in the expanded form. In order to provide more acceptable post-expansion properties, one potential solution is to substantially increase the beginning wall-thickness. This can increase the initiating force requirements and exacerbate local shrinkage issues, particularly in the threaded sections.

The simple goal of expandable technology is to lower costs and risks for drilling challenging wells. The first major approach towards this goal are proposals to develop monodiameter or nested-type well systems, where the diameters and volumes related to excavation work, casing sizes, drilling fluids, cement, and waste generation are significantly reduced. Monodiameter schemes are excellent in their numerous progressive goals, but those are very difficult to achieve due to the many issues already discussed and others not capable of being presented in a short article. There is increasing industry recognition that even the numerous incremental benefits of prospective MoD system realization will still not lead to step-changes in E&P economics. This is due partly to the ever-present reliability factors of current designs, but is mostly attributable to conventional expandable technology not providing actual solutions downhole and not providing efficient delivery of such an integrated solution. Currently, identical rig costs for time to repair trouble zones, condition, trip, and wait must still be incurred every time a casing or liner is run – whether expanded or not. R&D which merely improves the expansion method or the quality of the expanded casing is not enough to realize any meaningful goals.

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