SODV - PAC REACTION PAPER SUBSEA VISUALIZATION SYSTEMS

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1 SODV - PAC REACTION PAPER SUBSEA VISUALIZATION SYSTEMS Prepared by David Christie for PAC Past and Future The predominant and essential requirement of subsea visualization in support of drilling operations is the ability to image the seafloor during some spud-in and all re-entry operations. This capability has been provided throughout ODP and IODP Phase 1 by the VIT (vibration isolated television) sled. This system consists of a steel frame that is constructed to enclose and freely move along the drill string. It is raised and lowered by a coaxial cable that carries power to and signal from the sled via a winch in the moon pool area. The VIT system includes several lamps, a black and white, non-adjustable TV camera, a sonar system, and a gyro or compass that has not worked for many years. There is a limited ability to use the VIT sled to place sonar beacons or other equipment on the seafloor. While the system has been used successfully for numerous routine re-entry operations and for occasional local visual surveys of the seafloor, image quality is very poor by modern standards, and an upgrade is clearly overdue. Preliminary discussions indicate that improved image quality, even for black and white, may require fiber optic cable given the cable length required. In considering a replacement system for the VIT, two clear paths emerge in the discussion documents: Sources A sled-based system that is effectively an updated version of the VIT system, with the possibility of some additional capabilities. A modern deep-sea ROV system with capabilities far beyond those of a basic sled system. Key added value capabilities, considered essential for some types of expedition, include the ability to deploy and manipulate instruments and other devices on the seafloor and an enhanced ability for monitoring environmental and operational conditions. The principal source of material presented here is the SODV Briefing Book. This is supplemented by input provided by the STP and EDP advisory panels. Most of this material is written in terms of required or desired equipment. In the following section, I have attempted to extract the operational and scientific tasks that these equipment items are required (or desired) to perform. Decision Points In a budget-limited situation, it is clear that there are two key decisions that have major budget implications, both for acquisition and for future operations: Page 1 of 5

2 A decision to install a permanent deep-sea ROV implies commitment to at least two dedicated personnel as well as significantly higher maintenance costs. A decision to maximize sled-system capability will almost certainly require deployment of a fiber-optic (as opposed to coaxial) umbilical. This implies significantly higher initial cost, as well as potentially higher maintenance and depreciation costs. The scientific and operational issues that ultimately should drive these decisions have not been discussed in cost-benefit terms. Scientific and Operational Justification In fact, very little direct scientific justification for subsea visualization capabilities emerges from the available documents. For some expeditions, the ability of an ROV to manipulate CORKs or other instruments will provide direct scientific benefits. For others an enhanced visual capability will allow better geological interpretation of local surveys, providing better context for bare-rock or other types of spud-in. In general, however, the principal scientific benefit appears to derive from faster, safer and more efficient operations. Tasks for Seafloor Imaging Systems Tasks that can be accomplished with an improved version of the present system This task list could be considered to be the minimum requirement for effective operation. Hole relocation and re-entry Seafloor survey, especially for spud in control in bare-rock or environmentally sensitive locations Monitoring or trouble-shooting hole or drill-string Emplacement of equipment onto seafloor and/or into hole Tasks that require ROV capability Items on this task list may be desirable at some level, but seem to be in excess of the minimum requirement for most sites. Monitoring hole at seafloor during active drilling Monitoring and/or interacting with seafloor equipment, especially CORKs Insertion of logging or other tools into hole Opportunistic tasks not directly related to drilling. These include water or rock sampling, physical chemical or biological monitoring and/or sampling. Page 2 of 5

3 In addition, all but the first item in the minimum task list would most likely be more effectively performed by an ROV. Stand-alone Tasks These tasks would require stand-alone devices to be deployed close to the hole and recovered later. Their utility is severely limited by the difficulty of real-time data transfer through the water. Critical Issues Wellhead monitoring during drilling. Of particular interest is the ability to monitor for hydrocarbon emissions during hydrate drilling. Sampling and monitoring of ambient conditions not directly related to drilling Three basic operational/budget issues will dominate any cost-benefit analysis: Type of umbilical. Coaxial cable is cheaper and more rugged than fiber-optic cable, but is bandwidth limited. Fiber optic cable is more expensive and more easily damaged but should provide effectively unlimited bandwidth. Fiber optic cable may also have minimum-radius requirements that significantly impact the space requirements and cost of the required winch systems. Providing heave compensation via a fiber optic cable may also present problems. Risk assessment associated with the use of ROVs while drill string is rotating Personnel issues associated with ROV operation. If a permanent ROV requires dedicated personnel, cost and berthing issues become major factors. Capabilities of Seafloor Imaging Systems Essential Components of a Sled-based System The following capabilities are specified in the briefing book to varying levels of detail. Items in [italics], sometimes with comments in parentheses, require careful specification and cost-benefit evaluation. Winch and umbilical operational to 7000 m water depth [and heave compensated]. Umbilical must be capable of re-termination onboard under adverse operational conditions. Shock-isolated frame compatible with all likely pipe, collar and casing diameters up to 16 inch [or larger?] casing. (No specs available for shock isolation this is currently achieved by the use of bungee cord to suspend the key components within the frame.) Gyro package for heading reference. Hi-resolution [color*] imagery with zoom pan and tilt. Color* sonar system (currently specified by brand-name, not by desirable specs). Page 3 of 5

4 * Although color is specified in the briefing book, a choice of coaxial over fiber optic cable most likely implies the use of BW rather than color imaging. Optional (Desirable) Components of a Sled-Based System Stereo camera system. Detachable, tethered camera system.* Expansion capability that will allow future or as-needed additional sensors and/or samplers. Ability to deploy and recover stand-alone instruments. * A detachable camera system is, in effect, a mini-rov (see ROV section). Topside Systems User-friendly control systems in a protected working environment. Data and video integrated into ship s data network and available real time to driller, bridge and science team as well as to the sled operator. Essential (Desirable) Components of a ROV System Note that these requirements could be fulfilled by either a sled-mounted or a surfacedeployed ROV. Fulfill all requirements of a sled-based system. Manipulation capability suitable for CORK manipulation, emplacing, and servicing a wide variety of seafloor instruments. Ability to collect and return fluid, sediment, rock, or biological samples. Umbilical management system capable of safe operation while drilling. Initial PAC Recommendations Many of the details of the seafloor visualization system have no impact on vessel construction and can be deferred until after the initial vessel design is completed. However, the two key Decision Points discussed earlier do affect ship design and construction and they must be resolved. Recommendations Affecting Construction (1) There is little support in any available document for permanent deployment of a ROV. There is, however, a clear potential need for ROV operations during certain expeditions. Therefore, the SODV should maintain the ability to mount and deploy a deep-sea ROV. At least initially, deployment should be on an as-needed basis. Page 4 of 5

5 (2) In the absence of a ROV, the SODV must have the ability to deploy a subsea visualization sled that uses the drill pipe as a guideway to the seafloor. The size of the sled will be determined by its required functions and by optimizing the design. Presumably other factors will dictate the size of the moon pool and hence the maximum sled size. (3) A cost-benefit driven decision on whether to employ a fiber-optic or coaxial umbilical must be made urgently. This decision will have a significant budget impact and may have important space implications due to a much larger fiber optic winch system. Downstream Recommendations (4) If there is a decision to acquire a fiber optic umbilical: a. The potential for using the winch and umbilical for future ROV operations should be explored. b. The sled design should incorporate maximum flexibility for deployment of additional devices, either permanently or on an as-needed basis. c. The possibility of a sled-mounted mini-rov should be explored. (5) If there is an initial decision to use a coaxial cable, the limited bandwidth must be thoroughly exploited through the creative use of electronics. (6) PAC urges the SODV JOI Alliance Project members to utilize the unparalleled and willing expertise and experience of the academic deep submergence community through the Deep Submergence group at Woods Hole and/or the ROV group at MBARI in exploring and defining options. Page 5 of 5