Drilling tools for RC-drilling

Around the world, mining companies are paying special attention to replenishment and exploration of reserves of mineral deposits.
Geological research and its technological assets play a special role in this issue. One of the most important elements in geological research and exploration of all types of minerals is experimental drilling. Modern economic reality dictates more and more stringent requirements for carrying out geological exploration work — increasing volumes, reducing costs and time of work. Until recently, one of the most used geological exploration methods was core drilling, the so-called sampling of core columns. Core drilling is a type of high-speed drilling in which rock destruction occurs in a ring, and not over the entire face area. The interior of the rock is formed and preserved as a column of undisturbed core structure. The core is periodically jammed to be separated from the bottom and raised to the surface. The main decrease in productivity during the core drilling process occurs during additional operations for disassembling and assembling the drill string and lifting the core receiver for sampling, which take considerable time.
Today, the reverse circulation drilling method, or RC drilling, is gaining increasing popularity. The economic efficiency and productivity of this method is significantly higher than core drilling. The point is that mineral deposits (ore, mineral, etc.) most often have an irregular shape, far from any geometric figure. The dimensions of deposits in regard to strike lines and slant vary from several tens to hundreds of meters, and individual deposits can extend up to several kilometers. The reserves of one ore body can range from a thousand to a million tons, and sometimes exceed billions of tons, which shall be analyzed during deposit development in order to make a correct assessment of economic efficiency.
All this led to the search and development of a more effective sampling method compared to core (diamond) drilling. The search and development of a new method began in the 1970s in Australia. In 1972, the reverse circulation method was developed for rotary drilling, the principle of which was to use double drill rods. By the end of 1980, this method had proven itself to be more productive and cost-effective compared to core drilling.
In 1980, RC drilling allowed Western Australia to significantly increase its mineral production.
The development of technology and the desire to improve the reverse circulation method to enhance the quality of samples led to creation of the first hammer for RC drilling in 1990. The same year, the technology of air hammer drilling with reverse circulation was supplemented with the application of high pressure air compressors, which led to even greater productivity and increased penetration rates. All this has made it possible to significantly increase the efficiency of geological exploration, and as a result, RC drilling has become one of the most economical and accurate drilling methods in prospecting surveys.
Reverse circulation sampling (RC drilling) is a type of drilling that uses compressed air to effectively obtain drilled rock from a well through the internal area of the tool used for the purpose of further collection of samples. The reverse circulation method is full-hole drilling without unnecessary auxiliary operations. The reverse circulation method is implemented by installing a drive shroud after the drill bit in the operational drilling part, which forms an enclosed work area. In this area there is created a differential pressure that is converted into aerodynamic lift force. This force lifts the cuttings up through the internal tubes located inside each rod.
The double beam rods consist of the outer and inner tubes. The use if the inner tube allows to divide the drill rod into two enclosed areas (tube routes). The intertube area (between the outer and inner tube) provides a continuous flow of high pressure compressed air from the compressor to the RC hammer. During drilling crushed rock is brought to the surface via the inner tube to collect samples.
The use of high-pressure compressors makes it possible to achieve not only high productivity of RC drilling, but also to obtain the effect of preliminary drying of undrilled rock mass in the working area in front of the drill bit. Air in the working area, where differential pressure is created, penetrates into fractures and pores, displacing water. Pre-dried and drilled rock immediately flows from the drill bit through inner tubes, first to the deflector, and then through sampling hoses to the cyclone and then to the divider, where it is directly collected into sampling bags. This sampling layout does not provide cross-contamination from the external drilled medium. The use of quality equipment, tools and skilled operators produces sampling results that rival the accuracy of the core method. Under With RC drilling, samples can remain dry even several hundred meters below the groundwater level. Dry samples are preferable as they are more accurately digested for subsequent analysis. The initial stage of sample preparation for chemical analysis during core drilling begins with grinding the sample (core) into pieces approximately 10–20 mm in size. RC drilling does not require this procedure, which significantly speeds up the process of obtaining data on mineral content.
The speed of drilling with reverse circulation is comparable to the speed of drilling with air hammers using high pressure compressed air, used mainly for blasting and technological wells, and at great depths it can even exceed it. The productivity of drilled meters per day ranges from 150 to 300 m, which is many times higher than core drilling. Reverse circulation drilling is applied not only for surface deposits (pits),, but also for mines. One of the goals of RC drilling method is providing operational information on the content of mineral resources in a particular site. High drilling productivity allows you to quickly collect samples and send them for evaluation, which in turn gives a clear picture of the distribution of the boundaries of ore bodies with an empty hole. Less time for processing and proper distribution of activities help reduce overall costs. Currently, RC drilling is the most productive and economical method for extracting rock samples. Until recently, drilling tools for RC drilling were presented only by foreign companies. The experience accumulated in the manufacture of mining equipment together with the experimental work held allowed Machine-Building Holding JSC, Yekaterinburg (MH JSC) to launch into production a whole range of drilling tools for RC drilling, which can be found on the company’s website.