Bulroc (U.K.) LTD

DTH Reverse Circulation Equipment

What is - Reverse Circulation Drilling?

Reverse Circulation Drilling has been in use for quite a long time in Canada and the USA, where it is referred to as "Center Sample Recovery" or "Dual Wall Drilling."

RC drilling employs a Dual Wall Pipe where the drilling medium, normally high pressure air, is passed between the outer and inner tubes, down to the face of the drilling bit, where it is returned up the center tube along with the sample cut by the drill bit.

The sample is directed through the center of the air inlet swivel, through the rotary head, and through the sample recovery swivel, from where it decelerates into a larger diameter hose and is delivered into a cyclone collection arrangement. From here the sample is collected either as a continuous sample in long sausage-type plastic bags or as a sample of a specific depth drilled.

From this it will be clear that the drilling rig will need to have certain features such as a hollow spindle rotary head of sufficient dimensions to accommodate the inner tube of the particular dual pipe to be used. It would also need to have a winch or rod handling facility since dual wall pipe is considerably heavier than conventional drill pipe. The rig would also need to be of substantial proportions so as to have the necessary rotary torque and pull back capabilities.

Good Reasons for Choosing Bulroc RC

No Contamination

The Bulroc RC System collects sample through the recovery holes in the face of the drill bit immediately as the cuttings or sample is formed. The sample then travels through the center of the hammer into the inner dual wall pipe and on to the cyclone collection point. Unlike the conventional hammer and crossover sub arrangement, the drilled sample does not have to travel the length of the hammer, where contamination and loss of sample take place.

Dry Sample

Even in certain water bearing strata it is still possible to collect a dry Sample because the cuttings (sample) are collected as they are formed through the face of the drill bit, and this system allows penetration of the dry sample ahead of the water. During rod changes it is inevitable that the sample will become wet, but will very quickly return to a dry sample as drilling recommences. Naturally a dry sample can only be obtained when the hammer is able to overcome the flow of water in the hole. Excessive volumes of water and inadequate operating pressures will affect the hammer's ability to maintain a dry sample.

Higher Production

The Bulroc RC System is considerably faster than tricone drilling in hard formations, but will still deliver an uncontaminated sample. Although conventional hammers with crossover subs may develop marginally higher penetration rates, the quantity and quality of sample cannot compare with that delivered by the Bulroc RC. In broken and fractured ground conditions the Bulroc RC will often outperform the conventional hammer in terms of penetration rates and the smooth contours of the Bulroc RC System make tripping out easier and quicker.

Higher Sample Recovery

Because the sample is collected through the face of the drill bit there is no loss of sample when drilling through broken or fractured ground. Even when drilling through old mine workings the Bulroc RC hammer will provide a sample up to the point of breaking through and will immediately pick up sample when the hammer reaches the other side of the stope or heading. And since the bit is matched to the chuck size there is very little bypass of sample, and recovery rates of up to 98% are generally achievable.

Tricone and Drag Bits When drilling in soft to medium formations it is normal practice to use a modified Tricone bit with an adaptor sub to suit the particular dual wall pipe. In particularly soft formations such as sand, shale, and coal, etc., a carbide inset Drag Bit can be used, again incorporating an adaptor to suit the Dual Wall Pipe size. Both modified Tricones and Drag type bits pick up sample directly from the bit face, and the uncontaminated sample passes directly into the inner tube of the Dual Wall pipe. However, in harder formations these types of drill bits become uneconomical as a result of escalating bit cost.	Conventional Hammers In harder formations it is necessary to change to a conventional Down Hole Hammer fitted with a crossover or interchangeable sub positioned between the backhead and the dual wall pipe. The hammer operates in the normal way, exhausting through the center of the drill bit, carrying the cuttings along the length of the hammer where a certain percentage will enter the crossover sub and be transported to the surface through the center of the Dual Wall Pipe. The percentage of sample recovered depends on various ground factors, but the weakness in this system is the inability to control the quality or purity of the sample recovered. Disadvantages Contamination of sample as it travels along the length of the hammer to the cross-over sub. Loss of sample through void and broken ground. Contamination of sample in water-bearing strata. Loss of sample through greater erosion of bore hole wall in soft broken strata.	BULROC RC System The Bulroc RC range of hammers operates in a similar way to conventional hammers, but in the case of the Bulroc RC the exhaust air is directed between the splines of the special drill bit and the chuck (Driver Sub). The air then travels over the face of the bit, through the center of the hammer, and into the inner dual wall pipe. The sample is collected immediately as it is formed and transported to the surface without any contamination, up to 98% of sample recovery. The Bulroc RC hammer can collect sample in broken and fractured ground. Even through old mine workings the sample will be picked up immediately when the bit reaches the other side of the stope or heading.

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BULROC - The Original RC Hammer

It has long since been accepted that the sample delivered by the conventional Down Hole Hammer with a Crossover or interchange sub will have some degree of contamination. The degree of contamination will be affected by the geological make up of the rock, as will the actual percentage volume of sample recovered per foot of hole drilled.

Several attempts had been made to construct a "Hollow" Hammer so that uncontaminated sample could be collected from the bit face and travel through the hammer, but no suitable alternative was found until in 1985, when Bulroc U.K. introduced the first prototype RC or CSR Down Hole Hammer. Initial development involved the 6" BRC6 Hammer, which provides a considerable amount of sample and required a substantial Rig/compressor package to operate it. Although the concept was welcomed by the geologist, there was a certain amount of resistance from some contractors due to the shear volume of sample, the weight of the equipment, and the cost of energy required to power this size hammer.

Bulroc U.K. therefore developed the 4" BRC4 model, which produced the same purity of sample, but with less volume and at a much reduced cost in terms of equipment and energy required. The BRC4 hammer became widely accepted throughout Australasia during 1987-88, particularly in grade control operations at existing open pit mines, but also for general mineral exploration work.

As the BRC4 became accepted the demand grew for a somewhat larger and more powerful RC Hammer, and from this demand, Bulroc UK developed the 5" BRC5 Hammer, thus completing the present range.

Mineral Exploration - Whether for initial exploration deposit or for in-fill drilling of an existing ore body.

Grade Control - RC Drilling provides quick and accurate information to assist decisions on Future mine planning and production.

Aquifer Determination - The RC system makes it possible to identify the quality and provide data on the potential yield of individual aquifers.

As an Alternative to Core Drilling - To obtain uncontaminated bulk samples from relatively shallow mineral deposits, the RC system is a quicker and more cost-effective option. In unconsolidated ground the RC system can often provide a superior sample to Core drilling.

BULROC - The Complete RC Hammer

RC Drilling is rapidly becoming a more widely accepted alternative method of producing accurate geological samples, particularly in the applications already mentioned.

Bulroc's commitment to RC Drilling is emphasized by the range of RC accessories offered - from the drill bit through to the collection cyclone - to suit all types of strata.

The Bulroc RC hammer is made to suit all types of dual wall drill pipes by means of a simple adapter sub. The subs also have a center sample tube which connects with the center tube of the hammer - via the valve seat - and the center tube of the particular dual wall pipe in use.

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Bulroc RC Hammers

Venturi Option

All Bulroc RC Hammers can be fitted with a modified valve seat which will develop a strong venturi action and assist in collecting loose and unconsolidated materials in the hole, at the same time improving up hole velocity within the inner tube and reducing the incidence of blocking off.

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