Jules Verne's intrepid adventurer would have been proud to learn of the work of a team of equally visionary pioneers.

One of the most interesting papers (OTC 15328) given at the recent Offshore Technology Conference revealed the progress of a joint industry project to develop a seabed located drilling rig (SDR). Sponsored by ITF Pioneer, DTI Smart and Maris, the project has the support of offshore heavyweights BG, BP, Conoco-Phillips, Kerr-McGee, Marathon and Shell. You may recall that Kerr-McGee is widely credited with drilling the first well out of sight of land in 1948. If this project is successful, KerrMcGee will add another accolade - drilling the first well out of sight.

Far from a science fiction concept, the seabed located drilling rig is based on solid engineering and draws heavily on recently developed robotics technology employed on today's modern drilling fleet. Since one of the compelling reasons given for developing iron roughnecks and automatic pipe handling systems is elimination of humans from the drill floor, once the humans are eliminated, why not take advantage of the situation and move the drillfloor closer to the worksite? The advantages are obvious.

* No rigid riser, handling or recoil system
* Reduced tubular inventory
* Single or dual gradient drilling
* Reduced weather downtime
* Wide vessel operating envelopes
* Well pressure control at the seabed
* Greater operating efficiency
* Lower capital and operating costs

Deployment of the SDR is facilitated by its modular design. Once the conductor is driven and dressed, rig modules are lowered from the rig support vessel. They are positioned and locked into place by an ROV, and a flexible triconduit is connected to provide paths for drilling fluid in, drilling fluid/cuttings out and power.

An elegant solution for handling tubulars has been proposed. Tubular goods are stored in honeycomb-style modules shaped and sized like standard sea/land containers. They are stacked vertically alongside the rig module, giving the pipe handling robot access to individual joints of pipe in any desired order. Orientation of the pipe handling system is software controlled as it is on surface drilling units so the robot can locate any joint of pipe and position it precisely for insertion into the drill string.

Everything is not cloned from surface equipment and techniques. A unique Continuous Circulation Coupler (CCC) is the key element that makes the SDR viable. This coupler effectively isolates the seawater from the drilling fluid while maintaining circulation and well control during connections. Operating like an air lock on a diving bell, the CCC consists of a series of rams that provide drillstring alignment and hydraulic isolation for the tool joint while it is introduced into the drillstring and made up. Once the connection has been made, mechanical force on the rams is relaxed so drilling can continue, but stripping elements remain in place, forming a dynamic seal that segregates the mud from the surrounding seawater. The CCC eliminates pressure surges and transients caused by circulation stops and starts. It allows trip margin to be reduced to drill at near-balanced condition using ECD control that facilitates drilling in narrow pore/frac pressure windows. It also allows longer reach sections to be drilled before casing.

Because only a flexible conduit connects the SDR to its support vessel, the vessel can safely operate in a much wider circle over the wellsite. This makes the system suitable for harsh environment or ultradeep water areas.

Much work remains to be accomplished, but the concept is sound and the proposed applications are feasible. A great leap forward has been provided by the development of rugged reliable robotics for handing of drill string components. Adapting these to work while totally submerged in near-zero temperature waters will be challenging. Figuring out a way to acquire and transmit well log data will keep engineers busy for a while. Some neat tricks will be required to complete the well once it has been drilled, but the partners are confident it will be done. Considering how far offshore technology has come in only 55 years, we should expect to see results shortly.

Many of Jules Verne's 19th century fictional ideas became realities. The indomitable Captain Nemo may still be out there somewhere, and if he had heard the OTC presentation, he'd be nodding in agreement, "Piece of cake!"


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