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Seismic Survey In Australia – An Insight

This article will give an insight into the processes and day to day running of seismic data collecting crews. Seismic survey is used to collect data from below the ground without having to use more invasive methods such as drilling and blasting. It is a form of geophysics and uses seismology (sound/vibration waves) which is linked to a computer via cables and geophones to determine where the coal seam is located and also where the layers of rocks and water tables are. It is the preferred method of mining exploration in Australia due to stringent environmental requirements, but is also commonly used in Canada and the Arctic regions for natural gas exploration. This article will describe the methods used in Queensland, Australia primarily. Seismic exploration is used to explore for coal and gas in these areas. Queensland has some of the highest quality and abundant supplies of coking coal (anthracite) in the world and large reserves of coal seam gas in the south west of the state.

Geologists will determine which area that they want surveyed, and then plot areas from where they want the exact data. A plan is generated and then is given to the line clearing crew, who use bulldozers and slashers to create ‘seismic lines’ which are cleared using the coordinates on the map. They are slashed/dozed around 3-4 metres wide to ensure that the recording crew can work safely and efficiently. After the lines are slashed, the surveyors will proceed to set out the survey points. Depending on the nature of the job, these can be spaced at different intervals however 10 metres is usually a common measurement. The surveyor will plot these points and then spray paint a line to indicate where the seismic crew need to place their equipment. They will also place pegs at regular intervals indicating line and station numbers.

Personnel

The numbers of personnel can vary on any seismic recording crew due to the nature of the job, the terrain, the speed at which the job is required to be completed and availability of staff. All coal mine workers in Queensland must undertake a series of inductions and training in order to be able to work in the industry. They must also be able to pass a stringent medical test and chest x-ray. Each mine site also requires employees to undertake mine specific training and inductions in order for the personnel to be familiar with the standard operating procedures of the relevant site and tasks which they will be undertaking. All employees are required to wear reflective clothing whilst working on site, which is to be long sleeves and long pants. Safety glasses and hard hats are also obligatory along with steel toed boots and in some areas extra personal protective equipment is required.

All coal mine workers must abide by strict rules, as per outlined in the Coal Mining Act (1999). This act outlines the rights and responsibilities of each coal mine worker, and is regulated by the Mines Inspectorate. Queensland has some of the toughest and most stringent safety regulations of anywhere in the world, and this reflects on the vastly improved safety record that the industry now enjoys. Workers who are employed in the coal seam gas sector are also covered by similar laws and regulations. All workers must present to work in a fit for work state, which means that the worker must be free of any alcohol, illicit or prescription drugs. Random tests are carried out in all mine sites and also testing for cause is conducted after any incidents. Workers must also present for duty fatigue free, as this can impair judgement and risk the worker and their co-workers.

This article will use an average crew size as an example, which is around 22-24 personnel. Please see the different titles and roles as per below:

Supervisor

The supervisor is responsible for the day to day well being of the recording crew. The supervisor’s role begins back at the head office, where he/she is responsible for the preparation and availability of vehicles and personnel for the mobilisation of the job. The supervisor needs to first contact the mine site at which the job is to be undertaken and arrange any relevant inductions or specific training that is required and also agree on a start date for the project. Appropriate accommodation must be booked for all the workers, and this usually involves staying at purpose built mining camps.

These camps cater for all needs of the crew, including sleeping quarters, meals, laundries and cleaning. The rooms are predominately single person, each with a bed, desk, wardrobe, refrigerator, television, ensuite and air conditioning. These rooms are often referred to as ‘dongers’ and are approximately 5 metres by 10 metres and are usually made of up transportable buildings which have four to five rooms connected in each building. The meals are prepared and served at what is called the ‘mess’ and set out in a buffet style, with the crew helping themselves to a variety of hot and cold meals. The mess usually has several chefs and kitchen staff employed. There are also provisions in the mess for workers to prepare their lunches, with several types of meats, breads, salads and fruit available for lunches.

The rooms are cleaned weekly by dedicated cleaners, and the workers are responsible for doing their own washing in purpose built laundries which are fitted with several washing machines and clothes dryers. Some mining camps also have recreation areas which include pool tables and ping pong tables, and also gymnasiums, tennis courts, basketball courts and swimming pools. There are also some mining camps that have their own bar, however this can vary as some camps have policies regarding the consumption of alcohol. Not all mines have camp facilities, and due to the location of various sites the distances to camps may be too great. In this case the crew will stay in motels, which are twin share.

The supervisor then must ensure that each person on the crew is available for the upcoming job. Each job can vary in length from a few days to several months. Most companies have a policy which outlines the amount of days that can be worked before having a break, and this is usually set at around 21 days on and 7-9 days off. After assembling the crew and ascertaining availability, the supervisor must check that all the crew are up to date with their relevant inductions and medicals.

The supervisor will then ascertain whether mobilisation will be over one day or more. Drivers will be allocated to the various vehicles according to the licences that are held. If it is more than one day the supervisor will need to book accommodation in motels at a designated point which is usually half way to the destination. Once the crew has arrived on site, the supervisor must ensure that all staff have rooms allocated and that all the crew are fit and well. Before the crew head out to the mine site, the supervisor must ensure that all employees have the correct personal protective equipment and all of their paperwork is in order. Once the job has commenced the supervisor will continue to look after employees and liaising with other senior members of the crew and mine site supervisors. The supervisor will then repeat the process when the job is complete and the crew and equipment need to be returned to the head office.

Observer/Recording Manager

The observer has the task of staying in the recording van and ensuring all personnel and equipment are deployed to the correct areas whilst making sure that all the data is being fed correctly into the computer system. The observer will work closely with the supervisor and other senior members of the crew to ensure that the job goes smoothly. The observer has the responsibility of determining what times the crew start and finish for the day, and this can vary depending on a host of factors such as distances, weather and other logistical considerations. He/she will also work closely with the geophysicists both from their own company and the mining company.

Mechanic

Each crew will have a dedicated mechanic, who is required to provide maintenance on all company vehicles and repairs when necessary. They are also required to ensure that all crew are looking after their vehicles and doing pre-start checks and filling out the required paperwork. The mechanics are often required to undertake further inductions and training at mine site in order to comply with the relevant standard operating procedures.

Line Boss

The line boss has the task of allocating all the different personnel to their positions daily. They also need to ensure that all of the recording gear is placed properly and that the job is working as efficiently as possible. The line boss will often have many years of experience and is often the first person that the observer will turn to for troubleshooting. The line boss is also responsible for the counting, storage and deployment of gear and counting again at the end of the job so there is no equipment left behind.

Spread Checkers

Depending on the size of the job and available personnel, there may be one or two spread checkers on each job. Their job is to ensure that all equipment is placed correctly and are usually close at all times so they can remedy any problems that occur in the least possible time. The spread checkers will also have the responsibility of changing batteries and remedying power problems that occur from time to time. They will also help the crew when required, and the spread checkers are usually highly experienced staff.

Spread Truck Personnel

Typically there are a minimum of four spread truck personnel on each crew. Their job is to deploy all of the gear into the correct positions ready for the line crew to lay out. There is usually two spread truckers per vehicle, one will drive the vehicle at a slow pace whilst the other follows behind loading the gear onto the back of the utility vehicle. They will then take the gear to the designated area and do the same, one drives whilst the other deploys gear. It is the responsibility of the spread truckers to ensure that no gear is left behind and also that the gear is deployed into the correct positions. Usually spread truckers will be highly experienced, with a minimum of two years in the industry.

Front and Back Crew Bosses

Each job will have two types of line crew allocate. One is called the front crew who are responsible for laying out and unrolling the gear, and the other is the back crew, who are responsible for rolling up and gathering the gear ready for the spread trucks to pick up. Each crew will have a dedicated boss who ensures the well being of their staff and also allocating work groups. There will generally be approximately 4 people on front crew and approximately 6 on the back crew, as this is a slightly slower process.

Line Crew

The line crew are the personnel that are responsible for rolling out the cables and placing the geophones into the ground. The crew is usually made up of a mix of experienced and unexperienced crew and work in groups of two or three.

Shot Firer

In some cases where dynamite is used, there will be two or three shot firers on the crew. It is their responsibility to detonate the small charges in conjunction with the observer. These employees are often highly experienced and need to undertake extensive training in order to be able to perform this role.

Equipment

There are several types of equipment needed in order to collect seismic data. Listed below are the types of equipment that are commonly used in Australia.

Recording Van

The recording van, or which is sometimes called the ‘dogbox’ is the heart of the operation. All of the cables are connected to the recording van which uses a series of computers to interpret the data. The observer is always inside this van in order to ensure that all of the data is going to the computers in a correct manner.

Vibrating Trucks

The vibrating trucks are articulated trucks which weigh around 8 tonnes. They are fitted with a hydraulic cylinder which pounds down into the ground, which sends vibrations and soundwaves down through the various layers of rock which then get reflected back. These vibration sounds are picked up by the geophones which then send the data back to the recording van. These trucks are operated by a single person and most jobs will have two or three trucks operating. Most jobs will utilise these trucks, and they are effective when the coal seam is at a shallow to medium depth.

Dynamite

In some cases the coal seam will be at a depth which makes it impractical to use vibrating trucks. Before the recording crew starts a job, a crew of drillers and pre loaders will come and prepare the charges by drilling holes, lowering the charges whilst leaving the detonation wires outside of the hole and then backfilling the holes again. The shot firers will then use a detonator to deploy the charges.

Spread Trucks

The spread trucks are usually four wheel drive utility vehicles with a large rear tray. They have raised suspension in order to be able to safely carry the heavy loads of cables, geophones and batteries on the tray.

Crew Vehicles

Usually the line boss, spread checkers and shot firers will have utility vehicles similar to those that are used by the spread truckers. The line crew will have slightly different vehicles, which are usually dual cabs so that they can comfortably seat all of the line crew for breaks and during transport to and from site.

Batteries

Each job will have several 12 volt batteries, which are similar in size to car batteries and are used to provide power to the seismic lines and ensure that the data reaches the recording van.

X’s

The ‘X’ is a square box like port which is approximately 50cm x 50cm and is used to connect cables from various areas to a central hub, such as the recording van.

L’s

The ‘L’ is a terminal to which the battery is connected to the recording cables in order for the seismic lines to be powered. The batteries and L’s will be placed approximately every 40 stations.

Geophones

Geophones are approximately 8 inches in length and have a 4 inch spike which penetrates the ground. These can come in single packs or packs of 3, 6 or 12. The 3 pack is the most commonly used geophone. The geophones are connected to each other with wires and all connect to a single plug which is plugged into the FDU (see below). The line crew personnel will place the geophone’s spike in the ground by hand and then drive it into the ground using the heel of their boot. The geophones need to be upright and as close to 90 degrees as possible in order to obtain the correct data.

FDU’s

The FDU is a small electrical box (approximately 20cm x 10cm) and weighing around one kilo. On each side of the FDU there are electrical cables which are usually around 10 metres in length. The FDU is placed on the ground by the line crew near the surveyed paint mark and the geophone plug is inserted. The cables are then connected to each other, which creates the seismic ‘line’. All of these lines are joined together with the aid of X’s and connected to the recording van. The FDU’s are deployed rolled up, and it is the responsibility of the front line crew to unroll and connect the cables. Once the data is acquired the back crew will roll up the equipment ready to be picked up by the spread trucks.

The Process

Each morning before heading out to site, all workers will assemble at a predetermined area, which is usually at the camp at which they are staying for a 'toolbox' meeting. Each employee is required to undergo a alcohol breath analysis to prove their fitness for work. At this meeting the supervisor and the observer or line bosses will outline the plan for the day and also bring up any other issues such as safety concerns or other general business. The crew will then head out to site in their vehicles. As mentioned above, the FDU’s and geophones are deployed to the relevant ‘stations’ which have been predetermined by surveyors. The line crew unroll and connect the gear which is all connected back to the recording van. Once a certain area is connected, the line crew will retreat and the vibrating trucks will enter the line. They vibrate the ground and the data is sent back to the recording van. The positions that the trucks will vibrate are also predetermined by the geophysicists and plotted into GPS units which are mounted in the trucks. Once the trucks have cleared the area the line crew will re-enter and roll up all of the gear so that the spread trucks can deploy it at the next designated area. This process is repeated several hundred or thousands of time. It can also vary by the type of seismic data acquisition, which is either called 2D or 3D. Please see the descriptions below:

2D Data

A 2D job is a preliminary way to acquire data and is more cost efficient. 2D lines are prepared and plotted as straight lines, and can vary in length from a few hundred metres to tens of kilometres. These lines often run alongside roads and tracks in order to minimise the amount of clearing that is required. 2D jobs are also logistically easier as only a few hundred FDU’s are needed in order to perform this operation. This data gives the mining company a two dimensional picture of what is directly below the seismic line, and on the strength of this data they can determine whether or not to mine in this location or whether to implement a 3D seismic survey.

3D Data

3D seismic survey jobs are conducted in similar fashion to 2D jobs, however the data is collected from an area which is a few kilometres squared rather than in straight lines. The lines are positioned approximately 30 metres apart and run parallel to each other. All of the lines are joined together at the ends by FDU’s so it forms a grid pattern, similar to a snake-like pattern. 3D lines are usually no more than 2 kilometres in length, however the average job can have several hundred line running parallel. 3D jobs are often slower and more expensive than 2D jobs but the data acquired gives a much clearer picture for the mining companies to work with. 3D jobs usually require more personnel and needs a significant amount of equipment, usually at least 3,000 FDU’s. This also makes the deployment and packing up of equipment more time consuming.

Disclaimer

This is just an example of how seismic survey works in Australia. There are now different types of new equipment which are available and being used overseas, and this may be utilised in Australia. This information is based on first-hand knowledge and there may be errors or oversights.

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