Pipeline Trenching Technology

Wed, 01/25/2012 - 11:27

Able to excavate sand, gravel, silt, rockdump, drill cuttings and firm clay, “mass flow excavators” provide a combination of non-contact excavation, real-time control and gyroscopic stability to successfully excavate in a variety of different conditions. Alternatives to the excavation technology offered for example by British company Rotech to Pemex can be useful in a variety of circumstances and conditions, but due to the very large number of pipeline crossings in the Campeche basin, this particular technology is an apt solution for Mexican shallow water projects.

Rotech has three different excavation tools, which can all be deployed with the use of a crane, and A-frame or davit, or from a drill string. The R2000 excavator can additionally be deployed by attaching it to the jib of a tracked excavator for work in shallow waters. The R2000, T8000 and T4000, different models of excavators, all have an extremely small deck footprint, allowing for deployment on a number of different vessels, from DSVs to barges, supply boats and jackup rigs. The largest of the excavators, the T8000, only has a 10m x 10m deck footprint.

The excavators also use an off-bottom technique, which means there is no requirement to make contact with the pipeline, structure or other target. This makes the excavators suitable for work on live pipelines, wellheads or other sensitive infrastructure. As José Luís Oviedo, Country Manager of Rotech Mexico, explains, “Our T-shaped system has two turbines on top, which suck water in to create a water flow of 8000 litres per second. What differentiates us from other subsea excavation systems is that the water does not come out under pressure; we can move a large volume of material with water flow so we don’t hit subsea structures with pressure or vibration.” Additionally, the excavators can be used in both shallow and deepwater conditions. Also, multibeam sonar images allow the excavation to be monitored in realtime. In 2010, Rotech’s excavators were used to trench two pipelines for Pemex at Cantarell, reaching a drilling rate of 1.27m/minute with the use of a Twin T8000. An average for the company in the Campeche basin is 1m/minute, which translates to an average 600m-800m/day, and up to 1.3km/day under the right conditions.