Transocean Sedco Forex Inc.'s Discoverer Deep Seas will utilize modern project-management techniques to shorten cycle time and improve workflow procedures.
This ultradeepwater vessel (Figs. 1 and 2), which uses a dual-activity design pioneered by the Discoverer Enterprise (OGJ, May 26, 1997, p. 69), will be delivered late in the fourth quarter to begin a 5-year contract with Chevron Inc. in the US Gulf of Mexico.
The Deep Seas incorporates two drilling packages under one derrick (Fig. 3). This layout allows crewmembers to conduct independent operations on either rotary table (International Petroleum Encyclopedia 2000, PennWell, p. 225).
In the initial process of a well start, for example, the forward rotary can be used to prepare the blowout preventer (BOP) stack and riser. At the same time, the aft rotary can pick up the bottomhole assembly (BHA) then spud in the well.
Once drilling personnel finish drilling the surface hole and set casing, the critical path can then advance to the forward rotary. At this point, the riser and BOP stack, already made up below the water line, can be quickly landed at the mud line by repositioning the drillship.
"We cannot over-emphasize the amount of detailed, well-specific preplanning that needs to be conducted by operator, drilling contractor, and third parties to realize the maximum benefit of 'dual-activity' capabilities," says Steve Woelfel, drilling engineer for the Discoverer Enterprise.
"Not only does preplanning apply to [the sequential and parallel] timing of operations for each rotary, it also applies to the design of casing strings, BHAs, and drillstrings so they can be efficiently interfaced with the rig equipment."
Both drilling packages, for example, share a single fingerboard that extends from one side of the derrick to the other. As a result, engineers developed a fingerboard management strategy for the entire well to optimize drill-pipe and casing stand placement from both rotaries.
Woelfel says this plan prioritizes tasks and applies risk analysis to the timing of critical path activities (see box). "It is based on advance completion or delay of operations in one rotary and the resulting effect on the other."
For example, both the Discoverer Enterprise and Discoverer Spirit, prior vessels of the same class, found that exploratory-type wells require more than 10,000 ft of 133/8-in. OD casing to reach the required depth.
Because the setback area holds only 8,500 ft of 135/8-in. casing, however, the limited capacity of the fingerboard requires additional stands of pipe to be built on the aft rotary then run intermittently in the string.
"We found that this works well and that the aft rotary is able to keep up with additional stand building without a negative impact on overall job time," says Mike Shaw, drilling engineer on the Discoverer Spirit.
The learning curve
"We are able to piggy back on the experience gained from the Discoverer Enterprise and the Discoverer Spirit," says Eddy Redd, rig manager of the Deep Seas. "This will allow us to optimize drilling and operational procedures where some 70% of our supervisors, both drilling and maintenance personnel, have spent time on the other rigs."
This experience has allowed engineers and drilling personnel to be more proactive in planning activities. "We have documented 147 equipment and procedural learnings from the Discoverer Enterprise after its first quarter of operations, then transferred these to the Discoverer Spirit and Discoverer Deep Seas," Woelfel said.
In comparison to traditional operations, Transocean's success with the "dual-activity" concept has shown clear results. "Through a productive time analysis, we determined that both the Discoverer Enterprise and Discoverer Spirit achieved a one-third time savings compared to the single-activity mode on plug-and-abandonment jobs," he added.
"And after setting the sixth casing string on an extended-length exploration well, we confirmed our original calculations with productive time savings of about 15%."
Transocean, however, expects to gain even larger time savings, as much as 40%, in development work. In this mode, batch-type work will keep the aft rotary busy for a greater percentage of time-as opposed to the exploration-type wells.
For example, Discoverer Enterprise-class rigs may be able to establish a well-cluster template by dynamically repositioning the vessel in a circular manner around the forward rotary. "We could batch-set eight wells or more while drilling ahead through the riser on a central well," Woelfel said.
According to Transocean, drillers should be able to batch set simultaneously this template and run 20,000 ft of casing in fewer than 60 days.
The dual-activity design may also lead to new work that has been traditionally handled by other sectors of the industry. "For example, the first rotary table may be dedicated to drilling operations while the second can be j-laying or back-laying subsea pipeline with the help of a boat and ROV," Redd said. "This will save the expense of a pipeline lay barge."
Although simultaneous pipe-laying and drilling activities have not yet been conducted, an in-house study that involves an unnamed operator is under way.
Project-management techniques and the learning curve have also helped, Transocean to reduce construction costs throughout the new-build cycle. In the case of the three Discoverer-class drillships, unit delivery was spaced far enough apart to allow "corrective actions to be implemented," said John Rouse, assistant vice-president of engineering at Transocean.
Transocean estimates it cost $440 million to build the Discoverer Enterprise, $375 million for the Discoverer Spirit, and $360 million for the Discoverer Deep Seas.
This is the result of several factors, including a focused internal effort to identify problem areas, the completion of engineering designs prior to construction, tighter project management control, equipment designs that minimized delivery and start-up problems, and shipyard personnel who clearly understood the scope of the work to be done.
"With mature engineering designs, strict control of design changes were required to prevent re-engineering," Rouse said.
The critical path
During the 1998-2000 drillship construction cycle, drilling contractors and operators applied a modern project-management technique called the Critical Path Analysis. This method, which plays a continuing role in reducing cycle times, has helped engineers to integrate vessel design with equipment selection in order to gain improvements in workflow activities.
The critical path focuses on the sequence of activities that must be completed in order before the next one can begin. Before surface casing can be run, for example, the rig must first be moved on to location and the well must be spudded in.
The critical path can be used to:
- Define those tasks that must be carried out.
- Show where parallel activities can be conducted.
- Specify the shortest time in which a project can be completed.
- Enumerate the sequence of activities and scheduling.
- Delegate resources for each activity.
- Indicate task priorities.
A quick "oil-patch" method used to "intuit" the critical path includes building a graphical illustration of the traditional depth vs. time curve. Wherever there are nondrilling flat spots along the graph, one can plainly see periods of downtime then gain insights into what causes them.
Yet because engineers cannot fine-tune precedent relationships with this method, it must be followed by more-thorough analyses using Gantt and PERT (program evaluation and review technique) charts.
With the Gantt technique, work activities are plotted on vertical axis and duration on the horizontal axis.1 In this way, early and late start schedules can be defined beforehand or in real time.
Yet because bar-graph schedules do not completely show task dependencies and time-resource tradeoffs, activity-on-arrow network techniques like PERT should also be employed.
By manipulating precedent relationships, drillers have found ways to reduce cycle times. An analysis with Gantt, for example, clearly shows the time savings when the proper configuration of piperacking and pipehandling equipment allows casing stands to be built offline and stood back in the derrick while drilling operations proceed unhindered.
Thus, when it comes time to run casing, instead of picking up tubulars joint by joint, vertical casing stands can be run straight into the hole in doubles or triples.
On the Discoverer Enterprise, crewmembers have run 16-in. OD casing stands at rates of up to 36 single joints/hr, compared with 12 joints/hr for singles.
1. Shtub, A., Bard, J.F., and Shlomo, G., "Project Management: Engineering, Technology and Implementation," Prentice Hall, pp. 322-23.