A new take on an old idea — conducting drilling operations on the seafloor in order to avoid the problems inherent in floating drilling operations — has recently bubbled to the surface.
Some interesting proposals in this area have popped up previously including a 2000 paper by C. T. F. Ross and G. Laffoley-Lane of the Department of Mechanical & Manufacturing Engineering at the University of Portsmouth. They describe a one-atmosphere design that is a cylinder with hemispherical caps surrounded by a toroid with connecting spokes (or tunnels) supported by four legs that could have come off any jackup rig.

The latest is contained in a paper (AADE-07-NTCE-30) presented at the 2007 American Association of Drilling Engineers National Technical Conference in April. In it, Adel Sheshtawy lists the problems of floating drilling operations: the riser and the mud column circulating through it, shutdowns caused by surface waves or strong current and the construction costs and limited availability of floating drilling vessels. Sheshtawy also believes 10,000 ft (3,050 m) is the technical and economical limit of floating drilling vessels.

To solve these problems, Sheshtawy proposes the Underwater Seafloor Drilling Rig (USDR). The name may be redundant, but outside-the-box ideas like this are always worth a look.
According to Sheshtawy, the concept uses proven components and technologies from “both the drilling industry and submarine vessel knowledge bases.” The paper describes two main components. The first is the Submersible Drilling Capsule (SDC). This contains a rack-and-pinion mast or hydraulic ram rig with top drive, iron roughneck, automated pipe handling system, mud pumps and mud-handling equipment. It also contains emergency electric power, air and hydraulic sources. A conventional blowout preventer (BOP) stack attached to the lower end of the SDC and a double spherical BOP, pipe ram and blind ram attached to the upper end allow tripping the drill string in sections up to 5,000 ft (1,525 m) long. The SDC is a cylinder with semispherical ends, about 20 ft (6.1 m) in outside diameter and 110 ft (33.5 m) long. Sheshtawy says the SDC will be double-hulled, with the space between the hulls pressurized to half the hydrostatic head pressure to increase the collapse safety factor. Three “support capsules” attached to the SDC increase the live load capacity of the SDC and control buoyancy from positive to neutral to negative.

The second component is the USDR support vessel, which Sheshtawy says can be one-fourth the size of a fifth-generation deepwater drilling vessel. Initially this could be a production spar, TLP or small scientific coring vessel. The support vessel has mud mixing and pumping capabilities, electric power generation and crew accommodations. Electric power, drilling fluids, air and control signals are transmitted through hoses and cables. Sheshtawy says these hoses and cables can be long enough to permit a wider range of support vessel positions relative to the SDC compared to a conventional floating vessel.

You may be wondering if there will be people down there. The USDR will first be used unmanned to drill the conductor pipe. Sheshtawy says manned operations for the hole sections below the surface conductor casing will be carried out only after proving the safety of the system under actual field conditions. The design calls for two emergency evacuation capsules attached to the SDC and “purified air rich in oxygen” continuously circulated from the support vessel to the SDC through the umbilical bundle.

Space prevents a description of the operational procedure, but it has some interesting components, which includes racking long sections of drill pipe on the seafloor. “Transport capsules” are used to provide buoyancy for moving them about.

What about safety? According to Sheshtawy, historical safety data from the years 1905 to 2000 for military and civilian submarines with operating water depth ranges from 700 ft to 2,460 ft (213.5 m to 750 m) is impressive. He states that there is no reported accident for a deep dive research submarine from 1934 to 2005 with water depth ranges from 1,000 ft to 35,800 ft (305 m to 10,919 m). Sheshtawy points out that all lost submarine accidents are related to factors like collision with other vessels during military maneuvers, explosion due to malfunction of ammunition, nuclear power generator failure and mutiny. Those factors don’t exist in USDR operations. Sheshtawy says the safety record and absence of historical accident factors “…indicates that the SDC will be safer than driving your car on any major city highway or flying from Houston to San Francisco.”

Sheshtawy realizes the challenges he faces. “I recognize…every operator in the petroleum industry wants to be number two in any new drilling technology application.”

Those challenges could be numerous, to say the least. But still, you have to admire the effort. After manned space capsules blasting off from the lunar surface or remotely operated vehicles crawling across the surface of Mars while busily performing experiments — not to mention all the tricks the industry routinely performs on earth — it’s getting harder and harder to say what’s feasible and what’s not.