The days when moving a drilling rig was a straightforward, low-key effort have disappeared for a number of reasons, with cost the primary one. The current cost of moving a drilling rig can easily be US $1 million per day if unproductive rig time and the rates for anchor handling vessels (AHVs), remotely operated vehicles (ROVs), helicopters and other ancillary operations are taken into account. And the availability of AHVs, costing more than $100,000 a day, cannot be taken for granted.

In the Gulf of Mexico, for example, the new guidelines introduced after hurricanes Katrina and Rita in 2005 requiring 12-point mooring systems on many rigs have placed a heavy workload on the region’s vessels, depressing availability.

The practical difficulties of moving a drilling rig have also escalated over the past several years because of the steep rise in the level of critical subsea infrastructure in most established oil and gas provinces and the increased use of floating production systems linked to the seabed by various risers and, of course, their own moorings.

To avoid interference with this existing infrastructure, a rig move may necessitate a series of tight, carefully choreographed maneuvers at the outset to pick up the anchors and then at the end to redeploy them at the rig’s new position. Rig moving exercises and rig mooring arrangements are both increasingly becoming non-standard.

Operators and contractors get top efficiency from rig moves if the right team works with the right plan. (Photo courtesy of Intermoor and Trident Offshore)


Furthermore, that new position may well be much more tightly specified than in the past, certainly on the occasions when a rig has to be situated over an existing subsea well in order to carry out intervention work. It is not uncommon to have to situate rigs within 16.4-ft (5-m) centers, and 3.28-ft (1-m) accuracy is sometimes required. Also, because of possible damage to subsea infrastructure, there is increased demand for more sophisticated mooring systems using lightweight polyester ropes or subsurface buoys. Acquiring the equipment can have lead times of up to a year.

In a discussion of the challenges connected with any activity in the oil industry at the moment, it is impossible to leave out the issue of human resources. In a highly cost-conscious industry environment, as with any expertise needed on the rig, it makes financial sense to bring the right people in only when they are needed. Consequently, many rigs no longer have the people permanently onboard with the knowledge, skills and experience either to conceive or execute an efficient rig move.

If these obstacles were not enough, more and more rig moves are being conducted at short notice in order to make maximum use of the rig. The temptation to cut preparation time in these cases is obviously high.

The solution is sophisticated planning. But just what actually is involved? In the view of twin Acteon mooring companies InterMoor and Trident, planning starts by ensuring that the right team of people is available, ideally within the same organization: mooring analysts and designers, experienced marine operations specialists, and someone with a good knowledge of drilling rig operations. Having this mix is essential to address two key questions: will the planned mooring arrangement station the rig effectively; and, is the arrangement practical from an operational standpoint — can the designed mooring be deployed safely and without damage to the rig, any subsea assets in the area and the AHVs employed in the exercise?

To help the team, it must have access to up-to-date site surveys that include the best information regarding the seabed topography and soil conditions, the situation regarding subsea infrastructure, and the presence of other obstacles and hazards at both the existing and new rig sites.

The team’s aim will be to use its knowledge, experience and the supplied information to develop a clear and detailed set of procedures for the rig move. Because of the issues described earlier, these are likely nowadays to be specific to the intended move. The importance of this set of procedures cannot be overstated, and every effort devoted to their preparation will certainly be repaid.

They will typically begin by defining the objectives of the move, the conditions under which it will be carried out and, naturally, the precise locations of the rig before and after the move. The roles and responsibilities of the various personnel involved will be covered — and there are lots of people with a serious interest: the rig’s offshore installation manager, the vessel masters, client representatives, the client’s drilling manager, and the move superintendents and their navigation officers. (There needs to be two of each of these to provide full cover for the move throughout the 24-hour period.)

The procedure will describe the AHV requirements for the move with particular attention to manning levels and the vessels’ navigational capabilities. All the mooring equipment, especially any unusual items, will also be detailed.

Knowing the precise position of the rig and the relative positions of the various marine assets at all times is vital to the success of the move. For this reason, it is important to specify carefully the positioning system to be placed aboard the rig, from where it will be linked to the navigation systems of the AHVs by telemetry. This is a particular interest of Trident Offshore, which, as customers’ needs have evolved over the years, has worked hard to build up a world-class capability in this area of technology.

Having set the scene, the written procedure will contain a cogent description, with detailed drawings, of every operation, in sequence, from the first move necessary to retrieve the anchors through to deployment of the new mooring and its final testing. Instructions to be followed in the event of a mishap must also be included, which can only be formulated by a process of scenario development in combination with formal risk assessments.

Once the procedure is finalized, it will form the basis for briefing sessions for all the parties involved. These will take place first onshore, when the procedures can still be modified, and then offshore, immediately prior to the move. Best practice dictates that the minutes of these meetings should be recorded.

It is our view that planning of this kind makes life easier for all the parties involved and goes a long way to ensuring moves are carried out safely, quickly and thus in the most cost-effective manner possible. From our experience, once involved in a well-planned rig move, people become hooked on the approach.

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