OES's Lead Keel Jet Trenching Systems
a) Shallow to moderate water depth version (1m to 100m)
OES have developed and successfully operate four lead keel jet trenching systems. These machines have many advantages over ploughs, jet sleds and jet machine stabilised with buoyancy tanks.
OES jet trenching machines can be operated from small barges and supply boats, thus they are ideal for shore approaches in very shallow water. They are suitable for both sands and clays up to 190 kPa undrained shear strength. For economic reasons, they are suitable for trenching near offshore platforms, for short pipelines (less than 30 km long) and for large pipelines (>30" OD) where very deep trenches are required (>1.7 m). In comparison, typical ploughs and jet sleds are unable to trench, or they are not economical to use to trench, pipelines under the above conditions. The larger barges required are more expensive, require 8-10 times the power and cannot operate in very shallow water depths. Also, jet sleds with buoyancy tanks are not able to operate in very shallow waters where the tanks are exposed to the air.
The OES jet trenching technology result in machines that are much smaller and lighter that jet sleds and ploughs. They are 3-6 metres long, weigh 3-9 tonnes and thus require lower pull forces. They can also be operated in deeper water from a small DP vessel.
The OES machines are capable of making very deep trenches with multiple passes because they roll along the pipeline and do not span the trench width like jet sleds do. A 5 metre deep trench has been made in sands with an OES machine at the shoreline. For this project, an equivalent jet sled would have had to have spanned at least a 20 metre wide trench, making it very large and heavy. Ploughs are unable to make more than one pass, so they are limited to a maximum of 2 metre deep trenches.
Also, the OES trenching machines are able to trench a wide range of pipeline sizes (up to 54" OD). Most ploughs are limited to a maximum pipeline OD of 30".
OES trenching machines are also generally more stable than jet machines stabilised with buoyancy tanks in strong currents or in large waves. This is because the lead keel concept results in a low centre of gravity and there are no buoyancy tanks to create a high current drag on the machine.
b) Deep water version (100m to 400m depth)
OES have pioneered another major innovation in that they have extended the water depth capability of their lead keel machines by adding deep water hydraulic powered subsea jet pumps as used successfully on their Tiger Prawn II jet sled. OES also improved the suction capacity of Tiger Prawn II for the lead keel machines by adding subsea hydraulic powered double intake/volute centrifugal pumps for soil eduction.
The new eduction system is much more energy efficient than the water eduction system which OES normally use quite well for surface supplied water. The increased efficiency, however, is necessary for deep water and a 100% increase in flow rate has been achieved.
The pipeline trenching systems OES currently own and operate are listed below. The systems have been used to trench over 52 submarine pipelines in the last eight years (1995 - 2003). Note that all machines can operate “diverless”.
- “Bengal Tiger” lead keel post trenching machine (30"-60" OD pipelines). Click to view image
- “Sumatran Tiger” lead keel bi-directional post trenching machine (20” – 42” OD pipelines). Click to view image
- “Siberian Tiger” lead keel machine (12”-30” OD pipelines). Click to view image
- “White Jaguar” lead keel bi-directional post trenching machine (12” – 30” OD pipelines). Click to view image
- “Arabian Leopard” lead keel post trenching machine (12"-30" OD pipelines). Click to view image
- “Tasmanian Tiger” lead keel post trenching machine (4"-14" OD pipelines). Click to view image
- “Tiger Prawn I” fluidised bed cable/flexible pipeline trenching machine (2"-8" OD cables/flexible pipelines). Click to view image
- “Tiger Prawn II” deep water (400m) hydraulic powered jet sled for a semi-rigid flexible flow line and “piggy-back” lines (2” to 10”). Click to view image
- “Brutus Maximus” post rock trenching machine for pipelines up to 36” OD (detailed development stage). Click to view image
- “Rock Eater” multi-soils (rock, clays & sands), multi-pass post trenching machine (36"-48" OD pipelines) – (developmental stage). Click to view image
- "Buaya Besar" - OES Innovative Catamaran Barge. Click to view image
- "Grande Jacare" - OES Innovative Catamaran Barge. Click to view image
- OES “ANACONDA” – Cable Lay Barge. Click to view images
- OES “Python” – Shallow Water Pipe Lay Barge & Work Barge. Click to view images
- OES Low Pressure Pump to 350 psi - 8 units. Click to view image
- OES Stainless Steel High Pressure Pump to 1,000 psi - 3 units. Click to view image