Pipeline Trenching Procedure

Pipeline trenching is the normal practice for every pipeline that has been used for the tranportation of oil and gas product from the offshore facility to the onshore facility especially in countries where the water depth is shallow like Malaysia. Trenching are made to protect the pipeline from exposure to any danger that will cause any damage to the pipeline like ship's anchor drag on the seabed. Discussed below is the principle and the procedure related to the post-lay pipeline trenching of an underwater pipeline.

Figure 1: Trencher Machine - Commerce 1

Figure 2: Commerce 1 under Testing

PRINCIPAL OF TRENCHING
The principle of trenching is to create a trench beneath an existing pipeline so that the pipeline will be lowered down into the seabed. The basic steps of trenching are:

1. Hydraulically driven mechanical cutter create two slot on both side of the pipeline.
2. Jets and eductors that are located behind the cutters will fit into the slots created.
3. Cutters will pave the way for the trenching machine to move forward.
4. Cutters will allow jet energy to be concentrated underneath the pipeline in a hard type of clays and underneath and also the side of the pipeline in soft and cohessionless type of soil.
5. Jet manifold incorporates nozzle to direct pressurized water to cut soils underneath and to the side of the pipeline.
6. Certain nozzles will be used depending on the type of soils and also the shape of the trench.
7. Eductors are used to remove the cut and liquefied soils from the trench and deposit soil to the side of the trenching machine. Eductors are powered by the pressurized water.

Trenching machine will move forward and leaves a trench behind and the weight of the pipeline will cause the pipeline to sag down to the bottom of the trench. Stresses on the pipeline are controlled by adjusting the trench depth created on each pass made by the trenching machine. The allowable trench depth is the function of the pipe properties and also the allowable trenching stresses. Hydraulically driven tracks is mounted on the machine for the movement of the machine on the seabed. A dedicated pump usually be equipped on each jets and eductors to provide the necessary presurrized water for the trenching operation. Various hydraulic cylinders are used to adjust the trench depth and height of the cutter, jets and also eductors. The trenching machine will be controlled by an operator for its forward speed, cutter speed, side loads on the pipeline and also the machine direction. The water pressure and flow rates of the jets and the eductors will be adjusted at pump control panel on each of the pump under the direction of the operator. The trenching operation will be performed by the trenching crew located on the baby barge. However, the launching and the recovering operation for the barge will be made using the mother barge since the size of the baby barge is smaller compare to the trenching machine.

ONSHORE AND OFFSHORE SITE PREPARATION
On shore, the Real Time Kinematic (RTK) contorl referance station will be set up, calibrated and fully operational prior to the arrival of the trenching barge at the location while divers will mark the pipeline around the starting location buoys so that it will serve as the visual marker for the barge during setting up at the intended location. The marking shall be completed before the arrival of the trenching barge.

Figure 3: Working Barge POE Giant 7

SETTING AND ANCHORAGE OF BARGE FROM THE START POINT

1. Trenching barge will be towed at the intended location and will be set up approximately 60m from the trencher location.
2. Upon arrival at the visual marked buoy location set up earlier by diver and assisted by the survey team, towing bridle will be switched to anchor cable #1 for final approach and shallow water Anchor Handling Tug (AHT) will deploy anchor #1 at the intended location.
3. The barge will be repositioned close to the shore with the assistance of a tug boat and the utility boat will deplo mooring anchor #3.
4. Shallow water AHT will run anchor #4 and the utility boat will deplot anchor #2 close to the shore. After all the anchor have been deployed barge will be repositioned at intended start-up location.

TRENCHING MACHINE BALLAST TANK
Every trenching machine has its own ballast tank for the purpose of buoyancy to provide acquired depth of trenching depth for every trenching operation. There are some procedures that are usually being practised by the trenching superintendant to float and also to sink the trenching machine for the purpose of the trenching operation.


<>Ballasting Procedure

1. Attach the 2" air and water supply hose to trencher intake line.
2. Make sure 3 of the 2" in line ball valve at left side and 3 at the right side in open position.
3. 3 of the 2" drain ponits ball valve at left side and 3 at the right side in close position.
4. 3 of the 1" air vent point ball valve at lesft side and 3 at the right side in open position.
5. Close the 1" air supply ball valve at main manifold.
6. Open the 2" water supply ball valve slowly to allow water flow to buoyancy tank.
7. Fill-up activities completed when the water flow out at 6 points of the 1" air vent points.
8. Close the 2" air and water supply ball valve.
9. Disconnect the 2" air and water supply hose from trencher.
10. Close all 6 of the the 1" air vent point.
11. Trencher ready to lower down to sea bed by crane.

<> Deballasting Procedure

1. Attach the 2" air and water supply hose to the trencher intake line.
2. Make sure 3 of the 2" in line ball valve at left side and 3 at right side in open position.
3. 3 of the 2" drain points ball valve at left side and 3 at right side in close position.
4. 3 of the 1" air vent point ball valve at left side and 3 at right side in close position.
5. The 2" water supply ball valve in close position (open manifold).
6. Open the 1" air supply ball valve slowly to allow air flow to buoyancy tank.
7. Drain out water completed when the air flow out at 6 points of the 2" drain point.
8. Close the 2" air supply ball valve.
9. Disconnect the 2" air and water supply hose.
10. Close 6 of the 2" drain point ball valve.
11. Trencher ready to lift up by crane to the barge.
    

TRENCHING PROCEDURE

1. The deployment of the trencher machine will be assisted by diver. Once the divers are back on board the work barge, the Superintendent will then commence the full function test of the trenching system.
2. Surveyor will then fine the tune of the Dual Profile to ensure the data obtain from the both profiles are synchronised.
3. Trenching operation will stop after completion of initial 20 meters to allow divers to inspect the status of the trench and to adjust the nozzle if required.
4. The Intergrated Trenching System will go online and ready to resume the trenching operations.
5. The jetting pumps will be restarted and the trenching work will be fully operated. The commencement and relevant monitoring of the trenching operations will be overseen by the trenching superintendent.
6. Diver inspection will be conducted regularly for every 30 meter of trenching to monitor the pipeline and the trench profile as required for the operations. This shall be done by using the pole and feel method to confirm the trench depth.
   

PIG is not an animal

From observation and few ask-around session in the office today, I manage to learn more about the oil and gas industry. The oil rig and pipeline construction has a lot of acronyms that are needed for the engineers to understand the terms and its meaning. Firstly I want to discuss about Pipeline Inspection Gauge (PIG). There will also be a brief discussion on the difference between an Oil Rig and also Oil Platform.

Pipeline Inspection Gauge (PIG)

The name came from the squeling sound it made while travelling through the pipeline during operation. PIG are used to perform various operations without stopping the product flow inside the pipeline. A PIG launcher is installed in the Y-shaped funnel section in a pipeline and usually a PIG are check very ocassionally but will remain to shuttle up in the pipeline. Installation of a PIG inside the pipeline has a certain purposes in the pipeline. In the Oil and Gas industry, the purposes of installing the PIG inside a pipeline and also the type of PIGs used for the purposes stated are listed below:

1) Bullet shaped polyurethane foam type of PIG are used for the purpose of separating different products of oil in a multiproduct pipeline.
2) Tungsten studs or an abrasive wire mesh are used for the purpose of internal pipe cleaning to remove contaminants like wax, foreign objects, hydrants etc.
3) SMART PIGS are used to inspect the pipelines for its geometry and also data recording for later analysis using Magnetic Flux Leakage (MFL), ultrasonic and some PIGs are equipped with calipers for geometry measuring purpose.

The safety issues when a PIG is installed along the pipeline is:
1) Pipeline must be depressure to ensure that the PIG will not be boost out of the pipeline and injured the workers
2) When the product is sour, the flare system must be placed to ensure all the sour gases be burnt

The advantage of installing a PIG inside a pipeline is
1) potential resulting product separation
2) much more rapid and reliable product changeover
3) reduce the usage of chemical solvent for cleaning purposes


Example of a PIG

Derrick Lay Barge (DLB)

DLB are used for the purpose of laying the pipeline and also to help during the installation of the platform of an oil rig or an oil platform. There are many types of DLB used in the Oil and Gas Industry. Some DLB may only execute the pipelay operation, some types may do the derrick job and lastly there are types of DLB that may do both the derrick and also the pipelaying job. DLB differs from the normal utility barge by its size and also its features. DLB usually being installed with a derrick and other construction utilities on the barge but the normal utility barge platform is usually empty and the construction utilities placed on top of it can be customised according to the need of the project.















Figure of a DLB

Remotely Operated Vehicle (ROV)
ROV is considered as an unmanned vehicle that are usually used for the purpose of underwater exploration and also for survey job especially for offshore hydrocarbon extraction exploration. Certain ROV may have the ability to to do underwater construction work. ROV are usually unoccupied, highly maneuverable and being controlled by a person on a vessel where the ROV will be connected to the vessel by a tether. Tether is a group of cable carrying electrical power, video and data signals back and forth between the operator and also the vehicle. Some ROV which may require high power applications will include hydraulics cable inside the tether. Equipments that are usually being installed on the ROV are:

1) Video camera
2) Lights
3) Sonars
4) Magnetometer
5) Manipulator or cutting hand
6) Water sampler

The ROV can be classified into its own category based on the size and also the ability of the ROV to finish a task. Listed below is the classification of ROV and its descriptions:

1) Micro
Usually less than 3kg. Used for exploration in small spaces that may not be entered by divers like sewer, pipeline and also small cavity.

2) Mini
Approximately 15kg. Being referred as an 'Eyeball' as well as the Micro ROV. Usually may be operated without any outside help.

3) General
With a propulsion power of less than 5HP, this type of ROV usually being installed with small three fingers manipulators and also gripper. It may carry sensor and usually used for light survey applications. Maximum work depth is less than 1000m.

4) Light Workclass
Propulsion power less than 50HP, it may carry some manipulators. Its chassis usually made from polymer like polyethylene instead of aluminium. Working depth to be at less than 2000m.

5) Heavy Workclass
With less than 220HP prpulsion power, this type of ROV may be installed with two manipulators and may be able to work for the sea depth of 3500m and below.

6) Trenching/Burial
Propulsion power in between 200HP and also 500HP, this class of ROV usually be installed with a cable laying sled on the bottom side. Its working depth believe to be up to 6000m depth.

For an Oil and Gas industry, the most widely used ROV are the Construction ROV which usually include a large flotation pack on top of the aluminium chassis that may provide enough buoyancy for the ROV. Usually a synthetic foam are used for the flotation purpose and a tool sled may be fixed on the ROV for the accomodation of the sensor. The orientation of the Construction ROV of light components on the top side and also heavy components on the bottom side are to produce a large separation between the center of buoyancy and the center of gravity. The large separation between this two are useful to create stability and also stiffness for underwater operations. Electrical cables that supply electrical power and also other type of cable may be placed in an oil filled tube to avoid corrosion to occur to the cables itself. Lastly a Construction ROV are included with a thruster for all the axes for full control of the ROV.















Figure of ROV

Oil Rig
The function of an oil rig is basically on the oil reservoir exploration. Oil rig usually will float to the designated location that has been located by the surveyor to do the drilling work. After the drilling work has been done, the drill hole that link the sea bed and the oil reservoir will be sealed and the oil rig will float to another location for oil exploration and drilling work.

Oil Platform
Oil Platform is a platform that will do the extraction job from the oil wells that has been made by the exploration oil rig. The crude oil that has been extracted from the oil reservoir through the oil wells will then be stored and will be supplied to the oil tanker through the Floating Production Storage and Offloading (FPSO) or directly to the onshore reservoir through the pipeline.





















Figure of an Oil Platform


This is as much information I can provide the reader this time around. I will provide with a more interesting details and explanations regarding the Oil and Gas Industry on my next post and also to share the experience that I have gain during my Industrial Training period in Ombak Marine Group Sdn Bhd.

Subsea Pipeline and Treanching

Today's lesson is about subsea pipeline and also treanching. It was explained by one of the Marine Executive, En. Fazli and also based on the assignment by trainee supervisor, En. Fahidin Ismail.

The day started off with the trainee participation in the Weekly Operation Meeting (WOM) chaired by the Trainee Supervisor, En. Fahidin himself. All the issues in regarding the operation of the company was discussed in the WOM divided by the department in the company which was Safety Department, Marine Department, Engineering Department and also the Administration Department. At the end of the meeting, En Fahidin arranged a meeting with the trainee and also the apprentice for a short briefing. En Fahidin told us that he was the first one to apply the writing of Minutes of Meeting concurrently with the progress of the meeting. He said that with this method, the time taken to prepare the Minutes of Meeting (MoM) can be reduced and the MoM may be distributed among the employees for their attention and also their immediate action. He expected us to be able to write the MoM in the coming meeting.

Later, I was assigned by En Fahidin to research through the Internet for supplier for the concrete collar used to weigh down the subsea pipeline. It was known that the concrete collar strap was required by Petronas for their project. I managed to find some suppliers who were able to supply collar strap that may work for subsea operation. The strap is required to fixed the concrete to the pipeline for area that have a strong water current. This is to ensure that the pipeline always be under the seabed for safety purpose.

Later in the day we were introduced by the process of treanching. Treanching was made using the treancher which will be placed and moved along the pipeline. The treancher consist of a pump that will shoot high velocity of water that will be able to penetrate the seabed to acquire the desired depth for the pipeline installation under the seabed. Treancher will be controlled by a computer and will be monitored by a skilled operator located on the work utility barge. The treanching process will end once the whole length of the pipeline has been submerged under the seabed and after the diver has checked the safety of the pipeline under the water.

I was also being educated with the project terms that might be useful in my future career. The terms and acronyms that I have learned for the day was

1) TCOT - Terengganu Crude Oil Terminal
2) MCOT - Miri Crude Oil Terminal
3) BCOT - Bintulu Crude Oil Terminal
4) LCOT - Labuan Crude Oil Terminal
5) SOGT - Sabah Oil Gas Terminal

It has been a great day in Ombak Marine Group. I have learned more every day while doing my industrial training in Ombak Marine Group other than obtaining the working experience and exposure. Hope to learn more about the Oil and Gas industry in the day after.

The Starting Point

The first day of Industrial Training. A total of two students reported for the industrial training in Ombak Marine Group Sdn Bhd. We were then taken into the meeting room for some briefing on the company background and its subsidiaries. Later we were introduced to the staff of the Ombak Marine Group. We were then shown to our station before our supervisor, En Fahidin, assigned us with a few assignments. I was assigned with a study on the procedure of the Anchor Handling Procedure on the Petronas Pipeline Replacement Project. Many detailed procedures and also safety precautions are needed to be taken to ensure the working barge is anchored to the designated place for working purposes. Relocating and also replacing the position of the anchor of the barge need more attnetion and also constant communication among the foreman involved including the winch operator, hoist operator and also the barge master. Some of the consideration that have to be taken during the procedure of anchoring the working barge into the designated place is listed as:

1) Subsea facilities
2) Subsea obstruction

Other than that, the procedure also include the contingency plan and procedures if any problem occured during work progress on the barge is also being discussed. The most important part in placing the working barge on the designated location is listed as:

1) Working barge
2) Anchor Handling Tug (AHT)

More explanation on the AHT were done by Encik Md Noh. He was in-charge in the subsea division in Ombak Marine Group. There were two types of AHT which were the Anchor Handling Tug (AHT) and also Anchor Handling Tug and Services (AHTS). The normal AHT may only be used for the anchor handling processes while the AHTS may be used in the anchor handling process and also be used for the purpose of transferring materials, machineary and also work force from one barge to another. The size of the AHTS is much bigger compared to the AHT.

That is all for the note on the first day. May tomorrow be another educational yet informative day for me.