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doi:10.2204/iodp.proc.301.104.2005

Some concluding comments and opinions

Importance of engineering support

We cannot overemphasize the critical importance to the overall ODP CORK effort of the support provided by three groups of engineers: those at the drilling operator, those associated with third-party instrumentation, and those associated with the submersible operators. The contributions of these engineers have been central to the scientific success of the CORK effort and are too important to merely list in a traditional acknowledgments section (as is done below). As has been alluded to earlier, the overall funding structure and support models for ODP allowed for the drilling operator to provide the engineering support for the original installations from commingled program funds, but only for limited postinstallation submersible activities and not for the scientific instrumentation. As IODP began, a similar support model was applied for the Expedition 301 installations (Fisher et al., this volume), but if IODP is to embrace observatory science and serve a wider scientific community, as described in the Initial Science Plan, better support models are probably needed (e.g., see Fisher and Brown, 2004). It is not yet fully clear how support for IODP borehole observatory efforts is going to be supplied via a more complex IODP management structure involving a central management organization (IODP Management International) and three implementing organizations as drilling operators. In an ideal world, the IODP program (via IODP Management International and the implementing organizations) would have sufficient program resources to support all the necessary engineering for borehole observatories, the associated instrumentation, and all postinstallation submersible operations. But this may be unrealistic to expect immediately given programmatic fiscal constraints, so some elements of the support model developed for ODP CORKs will probably remain important in the short term.

"Standard" CORK models for IODP?

At the beginning of IODP, there have been calls for the program to "standardize" on a few CORK models for IODP use in something akin to off-the-shelf mode and/or to provide a "primer" with a straightforward decision tree for selecting the model appropriate for given objectives. This has been motivated both from a program planning and budgeting perspective (partly to minimize the needs for new engineering support discussed above) and to assist a new generation of investigators in proposing sealed-hole hydrogeological monitoring experiments. Although these are laudable objectives, we are not sure it is useful to "standardize" beyond the basic configurations described in "CORK design summaries" for several reasons. These include

• The inherent flexibility in most of those basic configurations to tailor the instrumentation capabilities to the objectives (e.g., the modified CORK-II described by Fisher et al., this volume),

• The fact that IODP does not currently provide commingled program funding for the instrumentation or submersible time,

• The perspective developed in "A few scientific lessons learned and challenges for the future" that each design and instrumental advance has brought important new observations, and

• That "standardizing" could stifle initiatives to develop even more capable configurations of sealed-hole observatories.

At least two current examples of the last include an effort to marry long-term seismic monitoring capabilities with the formation-pressure monitoring CORK capabilities and an effort to design a simpler single-zone pressure-only monitoring installation that can be deployed in spatial arrays in both a time- and cost-effective manner. Thus, it is not clear to us whether scientific creativity would be served by standardizing on a few fixed models.

Nevertheless, the basic configurations described in "CORK design summaries" will probably serve as a basis for a majority of applications. Where monitoring a single zone is the objective, if the necessary instrumentation can be made at diameters of <3.75 inches, then minor modifications of the original single-seal CORK design would provide a well-proven and both time- and cost-effective technology, and the programmatic responsibilities could be assessed and budgeted in straightforward fashion. Where monitoring from multiple depth zones is the objective, options include the ACORK, CORK-II, or even closely spaced arrays of original CORKs, each extending to different depths. Where monitoring in a preexisting reentry hole is the objective, the wireline CORK is an option that does not require use of a drillship, and options from a drillship would include a single-seal original CORK or multilevel CORK-II. Choosing among these options depends on a variety of operational factors and on balancing programmatic cost considerations against scientific objectives. With respect to programmatic costs, we note here only that the ACORK may be perceived as much more expensive than other options, but that is partly because the ACORK itself comprises the main casing string; when true casing costs are added to the other designs, the cost differential is reduced considerably. Even if cost considerations are not the limiting factor, only a few easy rules can be developed. For example, if the prime objective is sampling formation fluids, especially in basement, then the CORK-II concept may be more suitable than the ACORK. On the other hand, if the prime objective is monitoring profiles of physical parameters like pressure, especially through a long sedimentary section, then the ACORK concept may be more appropriate. However, these are intended only as examples, not as fixed rules appropriate for every setting. The only easy conclusion is that the choice of a configuration must rely on careful consideration of specific scientific objectives and site-specific geological and operational constraints.

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