PRIME DRILLING HDD Drill Rigs Used for Venting Coal Strata in Australia
The company PRIME DRILLING from Wenden near Olpe/Germany was founded in 1999 and specialises in the design and construction of fluid-assisted, horizontal, directional drill rigs (HDD) with up to 6,000 kN pulling force.
Profiting from the experience of meanwhile 80 highly qualified employees, PRIME DRILLING stands for drilling-technical expertise, high production quality and perfect service. More than 150 fluid-assisted HDD rigs manufactured by PRIME DRILLING are being operated around the globe. The enterprise owes its success primarily to two abilities: listening to the customers’ often technically challenging needs and responding by making machines which live up to these demands. Now PRIME DRILLING was able to give proof of its expertise once more, even outside its particular sector of industry.
At present, it looks like mankind will depend on the exploitation of fossil energy sources for quite a while yet. New raw material deposits are constantly being tapped all over the world, mineral oil, gas and coal in the first places. Australia is ‘blessed’ with resources, it is one of the leading mining countries in the world; 10 percent of all coal resources can be found in Australia. Thus it comes as no surprise that coal mining industry in Australia is a crucial economical factor for the country. In the fiscal year 2008/2009, 487 million tons of coal were mined, 261 million tons of these were exported, according to Wikipedia.) In New South Wales and Queensland, great deposits of high-quality bituminous coal are lying close to the surface; they shall be exploited by open pit surface mining. When exploiting these coal deposits, coalbed gas – a gas based on methane – accumulates. In Europe this gas is known as mine gas, its composition is very similar to petroleum gas. Coalbed gas is generated when organic material in the coal deposits is degraded. Formerly it was simply flared and not made use of at all, but in the past 10 years it was increasingly used for generating electricity. First, the water must be pumped out of the coal bed before you can win the gas. This action lowers the pressure and the gas can be extracted.
As a rule this gas is mined by drilling vertically into the coal bed. In this case the vertical bores had to reach 350 m into the coal bed to be connected to horizontal bore holes coming from the coal bed cover. Such a line system virtually allows outgasing the complete deposit. On the one hand the aim is to utilise the coalbed gas for producing electricity, on the other hand the gas contents in the coal deposit can be reduced sufficiently to mine the coal without safety hazards. The time it takes for outgasing is variable, it depends on the size of the deposit. Gas exploitation exceeding two years is planned for the project at hand.
The horizontal drilling operations are a major challenge and demand expert skills. So Ralf Kiesow, head of the PRIME DRILLING sales and service department, was surprised to receive a phone call from Australia and the invitation to take part in a conversation. Kiesow had been in contact with the operator of the deposit for quite a while by then. The preliminary talk proved to be worthwhile; with PRIME DRILLING, the customer was convinced to have found the perfect partner. With the special requirements of the customer in his luggage, ‘target specifications’ comprising 30 pages, Kiesow flew back home.
“After our engineering team had checked the customer requirements and strict safety compliance and found both technically feasible, we received the go-ahead in December 2011 for the order of two drill rigs. We developed a special version, based on the existing drill rig type PD 100/80 RPC 45 with a max. pulling and pushing force of 100 tons,” Kiesow explained.
The following details had to be considered for the design: a penetration angle of 6 to 45 degrees was required, a minimal drill speed of 25 mm/min. had to be achieved and a clamp and break-away facility with a clamp range of 105 mm to 405 mm was to be integrated. A self-centring pipe handling system without the need for readjusting the drill stems and casing pipes was one of the specifications. An explosion-protected work area in a radius of three metres around the drill shaft was also demanded. All welded supporting structures were exposed to a non-destructive material test, the results were recorded. The drilling mast for two different drill stem lengths is 18 m long. The strict Australian safety demands were even beaten by the Prime Drilling team in some of the options concerning safety. For instance a special parking brake with spring accumulator was developed to prevent slipping-down of the top drive weighing several tons, even in the event of a total failure.
In the summer of 2012, the two drill rigs were shipped from Hamburg. The sea passage to Brisbane took all of 45 days. Since that time, the drill rigs are in action. They perform drilling operations called horizontal blind bore holes with diameters of 3 ½ in., a drill length up to 1,800 m and a drill depth up to 350 m. The previously established vertical bore holes have to be connected with the horizontal bore holes, therefore they are equipped with reference transmitters to allow the horizontal drill rig to pick up the signals and drive toward them. In order to reach a vertical bore hole in a depth of 200 m, the cut-in must be smaller than 45 degrees in a distance 200 m away from the vertical hole. As soon as the installation depth in the cover layer of the coal strata is reached, the drill moves forward from one vertical bore hole to the next until it arrives at the target. Then a casing pipe is pushed in up to the bore head. Finally, the drill stems with the bore head are recovered under the protection of the casing pipe. Now filter pipes are driven into the empty casing pipes. This is carried out with special rollers which are mounted to the first pipe and driven by means of hydraulics. The drilling process is completed as soon as the casing pipes are pulled out.
At first, the slotted filter pipes take up the water and transport it to the vertical bore holes where it can be pumped out. After draining the water, the pipes are used for outgasing. The captured gas is then conveyed to the point of power generation.
Kiesow: “If everything works out as it should, the complete drilling process will take one week and a half at a drilling length of 1,800 m in day and night operation, without interrupting work.”
This way an interesting application was opened up and the job was executed without problems and to the full satisfaction of the mine operator.