PRIME DRILLING HDD-Drilling Rigs for Gas Drainage Drillings of Coal Seams in Australia
PRIME DRILLING GmbH in Wenden near Olpe was founded in 1999 and is specialized in the manufacture of HDD Horizontal Drilling Rigs of up to 6.000 kN pull force. PRIME DRILLING with its meanwhile 70 high- qualified employees and long experience stands for drilling competence, high production quality and perfect service. More than 150 HDD Horizontal Drilling Rigs manufactured by PRIME DRILLING are in operation around the world. The company´ s success is particularly due to its ability to respond to the mainly technically very demanding customer requests and to meet their expectations. PRIME DRILLING has just demonstrated this ability once more by an application outside its usual industry.
Mankind will obviously continue to be dependent on fossil fuels for a while. More and more new deposits of raw materials are exploited all over the world, especially deposits of oil, gas and coal. Australia is blessed with such deposits and one of the largest mining countries in the world. 10% of the global coal reserves are located in Australia. It is thus no surprise that coal mining is a major economic factor in the country. In the 2008/ 2009 accounting year about 487 million tons of coal were extracted and about 261 million tons of those were exported.*)
In New South Wales and Queensland exist large near- surface deposits of high- quality hard coal, which are to be extracted by open-cast mining. With mining of these coal deposits a gas based on methane is produced called coal seam gas, which is known as “mine gas “ in Europe and which is similar to natural gas in composition. Coal seam gas is produced by the decomposition of organic components within coal deposits. In the past this gas was simply burnt, but these last 10 years it has been used more and more often to generate electricity. To be able to extract the gas, the water in the coal seam has to be pumped out first to lower the pressure inside and thus to allow for extraction of the gas.
Usually the gas is extracted via vertical drillings of lengths of e.g. 350 m down into the coal seam, which are later linked to each other by horizontal drillings in the surface layer of the seam. By means of the thus created line system nearly the entire deposit can be degassed. The aim is on the one hand to use the coal seam gas for power generation and on the other hand to reduce the gas content in the deposit to such a degree as to allow mining without safety risks. The time expenditure for such degassing operation varies as per size of the coal deposit. The present project is planned over a period of 2 years of gas extraction.
Horizontal directional drillings are challenging and require expertise. So the responsible sales and service director at PRIME DRILLING, Mr. Ralf Kiesow, one day received a telephone call from Australia and an invitation for a meeting. Mr. Kiesow had already been in contact with the mine operator for quite a while. The preliminary discussions proved to be worthwhile as the customer was convinced to have found the right partner in PRIME DRILLING. Ralf Kiesow returned from Australia with a 30- pages specification document of specific customer requirements in the baggage.
„After our team of designers had checked the customer specifications with their strict safety provisions and judged them technically feasible, we received the firm order for two drilling rigs in December 2011 and started to develop a special version on the basis of the existing rig type PD 100/80 RP-C 45° with a maximum thrust/ pull force of 100 tons”, reported Ralf Kiesow.
With the design of the rigs the following needed to be observed: the penetration angle was to be between 6 – 45 degrees, a minimum drilling speed of 25 mm/ min. was to be realised and the breakout system to be installed should have a clamping range of 105 to 405 mm. Also a self- centering pipe handler without re-adjustment of the drill pipes and the casing pipes was required. Furthermore an explosion- proof safety area of 3 m radius around the drilling shaft needed to be provided. All load- bearing welded steel constructions had to be checked by non-destructive material testing and documented accordingly. The drill mast was designed for 2 different drill pipe lengths and was 18 m in length. With some safety- related options the Prime Drilling team even managed to exceed the strict Australian safety requirements, e.g. by the specially developed spring park brake that prevents the several tons heavy power rotary head from sliding down even in case of total failure of the hydraulic system.
In the summer of 2012 the two rigs were shipped ex Hamburg on a 45 days journey to Brisbane. Since then the drilling rigs are in operation in Australia. The drillings performed are horizontal blind hole bores of diameter 3 ½”, a length of up to 1,800 m and a depth of up to 350 m. The vertical drillings installed earlier need to be linked to the horizontal drilling and are equipped with reference transmitters to that effect so the horizontal directional drilling rig can receive and locate the signal. In order to reach a vertical bore in e.g. 200 m depth, penetration is to be made at an angle below 45° and in a 200 m distance from the vertical bore. Once the installation depth in the surface layer of the coal seam has been reached, the drilling can be continued from vertical bore to vertical bore until the target point is met. Then wash-over pipes are inserted up to the drill head, which allows for safe pull-back of the drill pipes including drill head. Finally filter pipes are installed into the now empty wash-over pipes by means of rollers that are fixed to the first pipe and are driven hydraulically. The drilling operation is then completed by pulling back the wash-over pipes.
The slotted filter pipes absorb and then transport the water to the vertical bores where it is pumped to the surface. After drainage of the water the pipes are used to extract the gas for power generation.
Ralf Kiesow says: “If no issues occur and provided the works are not interrupted and executed in day and night shift, the complete drilling procedure for a drilling length of 1,800 m will take about 1.5 weeks.”
This is how a specific application was realised to the entire satisfaction of the customer as quickly and simply as ever.