Impregnated Diamond Core Bits
The impregnated diamond core bit has emerged as the most commonly used type in the mineral exploration industry. The advantages of using impregnated diamond core bits over bits manufactured with other cutting media include:.
- An extremely wide range of application.
- A simple bit crown geometry that makes them less susceptible to in-hole damage than bits manufactured with other types of cutting media and as such are more tolerant of changing or banded geological formations.
- Their multi-layered cutter arrangement results in better overall bit life than bits produced with other types of cutting media.
- They are particularly well suited for drilling in hard, consolidated and non-abrasive formations.
Inside the Impregnated Diamond Bit Crown
The basic construction of these products features a powdered metal matrix-body bit crown that is fused to a steel tool body or shank. The matrix-body bit crown is composed of two layers that include:
- The “matrix” layer that cuts the rock and
- The “backing” layer that connects the matrix layer to the steel tool body and serves to support the gauge protection setting.
The cutting media that is used in the matrix layer of an impregnated bit is synthetic diamond. This material has a distinct advantage over the natural mined industrial diamond that is used in surface-set bits in that it is an engineered material that has measurable, controlled physical properties, particularly with respect to crystal friability and crystal geometry.
The matrix layer of the bit crown contains a uniform distribution of synthetic diamond crystals that are embedded in the matrix-body’s metal bond. The grit size, concentration and grade of the synthetic diamond crystals as well as the relative hardness of the metal bond materials in which they are suspended are all functions of the matrix type designation.
Dimatec manufactures a range of impregnated diamond matrices with matrix layer metal bonds that range from hard, abrasion resistant types to soft, ductile types. These matrix types are offered in three different series, namely, the S-Series, the HR-Series and the D-Series. Each of these series are geared towards specific applications that are discussed below. (Also refer to the “Matrix Selection Chart” under “Product Resources”).
Individual matrix types are identified by number designations within a given series. In general, a hard, abrasion resistant matrix such as the Dimatec “S3” would be used to drill a soft, unconsolidated formation while a soft, ductile matrix such as the Dimatec “HR12” would be used to drill an extremely hard, non-abrasive and consolidated formation. The relative hardness of the metal bond hardness decreases as the matrix number designations increase. The intent is to match the bit matrix hardness to the formation hardness so as to cause the metal bond of the bit’s matrix layer to erode at a controlled rate during normal drilling operation. This controlled erosion of the matrix layer will in turn, continually expose new layers of sharp synthetic diamond until the matrix layer of the bit crown is totally consumed.
Unlike the matrix layer, the “backing layer” does not contain synthetic diamond distributed throughout its volume. The backing layer is also composed of a powdered metal matrix-body; usually a bond type with good wear resistance properties. The exposed outer and inner gauge diameter surfaces are set with a combination of tungsten-carbide wear pads and thermally stable polycrystalline (TSP) diamond elements. These material assist in maintaining the critical gauge diameters throughout the operational life of the bit.
S-Series Impregnated Diamond Core Bits
Introduced in 2013, this series of products represents Dimatec’s most recent development in our diamond impregnated matrix offerings. This series of matrix types is well suited for use on high-powered hydrostatic drilling equipment. They are designed to offer superior durability and overall bit life without sacrificing overall production rates.
For optimum performance, the S-Series matrices typically require 15% to 30% more rotational torque than an HR-Series or D-Series matrix with an equivalent number designation. They are generally more adaptable to a broader range of drilling parameters (bit load, rotational speed, torque and circulation fluid rate) than the HR-Series or D-Series product ranges.
HR-Series Impregnated Diamond Core Bits
Dimatec’s HR-Series impregnated diamond core bits have been specifically designed for use in hard rock drilling applications where formation conditions are generally consolidated and fine grained with high compressive strengths and Mohs hardness values in the 5 to 7.5+ range. Traditionally, it has been necessary to apply higher bit loads when drilling under these conditions in order to achieve acceptable rates of penetration – usually at the expense of overall bit life and premature wear on the drill string components. HR-Series impregnated diamond core bits provide several performance benefits that include:
- Very smooth cutting characteristics throughout the life of the bit when drilling through even the hardest formations.
- A relatively low bit load (weight-on-bit) is required to maintain a high rate of penetration. In some cases, a reduction in bit load of between 20% to 30% has been realized with HR-Series bits while achieving or exceeding the penetration rates of competitive products. The application of lower bit loads results in less wear and tear on drill string components as there is less potential for flexure or over-tightening of the thread connections. In addition, the ability to apply lower than normal bit loads assists in reducing the potential for drill string vibration as well as hole deviation while drilling.
- Under most conditions, HR-Series bits are self-sharpening. Very little intervention by the drill operator is required to keep the bit cutting steadily.
- HR-Series bits have demonstrated the ability to drill through fractured formations with significantly fewer core blocks than competitive products.
- Improved overall bit life and exceptional production rates in harder, consolidated and fine grained formations.
For optimum performance, the HR-Series matrices require circulation fluid rates that are 20% to 30% higher than D-Series products with a similar matrix number designation. A lower torque setting should be applied in cases where a hydrostatic drill is in use. Also note that the application of unnecessarily high bit loads on HR-Series bits may actually slow penetration, create high, erratic torque loads and ultimately cause the bit to wear out prematurely.
D-Series Impregnated Diamond Core Bits
Originally developed in 2001, the products in this series are good all around proven performers in the Mohs 4 to 7+ rock hardness range. They are recommended for use in softer and somewhat abrasive formations.
The D-Series matrix types are well suited to the application of higher bit loads. They generally require a change in drilling parameters to sharpen the bit in the hole. (Example: A temporary reduction of the circulation fluid rate while drilling).
Product Selection Criteria for Impregnated Core Bits
There are four criteria that must be evaluated when selecting an impregnated core bit …
1. WHAT IS THE ROCK HARDNESS?
- For LOW rock hardness (≥ Mohs 4), use a matrix with a lower number designation. Appropriate selections may include: S3, S6, D2, D3 or D4. Consider the use of a ‘Regular’ (Style ‘W’) waterway configuration.
- For HIGH rock hardness (~ Mohs 7), use a matrix with a higher number designation. Appropriate selections may include S-Series products: S9, S10, S11, S12 or HR-Series products: HR10, HR11, HR12, HR13, HR14 or D-Series products: D9 and D10. Consider the use of a ‘Turbo’ (Style ‘T’) waterway configuration for thin-wall bits or ‘T-Turbo’ (Style ‘TT’) for wireline bits.
2. WHAT IS THE ROCK GRAIN SIZE?
- For a COARSE grain size formation, use a matrix with a lower number designation. Appropriate selections may include: S3, S6, S7 or possibly D2, D3, D4, D5 and D6.
- For a FINE grain size formation, use a matrix with a higher number designation. Appropriate selections may include S-Series products: S9, S10, S11, S12 or HR-Series products: HR10, HR11, HR12, HR13, HR14 or D-Series products: D9 and D10.
3. WHAT IS THE CONDITION OF THE FORMATION?
- For BROKEN and FRACTURED conditions, use a matrix with a lower number designation. Appropriate selections may include: S3, S6, S7 or possibly D2, D3, D4, D5 and D6.
- For MASSIVE and CONSOLIDATED conditions, use a matrix with a higher number designation. Appropriate selections may include S-Series products: S9, S10, S11, S12 or HR-Series products: HR10, HR11, HR12, HR13, HR14 or D-Series products: D9 and D10.
4. WHAT TYPE OF DRILL IS IN USE?
- For a LOW powered drill, adjust your selection by choosing a slightly softer (higher matrix designation number) D-Series or HR-Series matrix type.
- For a HIGH powered drill, adjust your selection by choosing a slightly harder (lower matrix designation number) S-Series matrix type. Keep in mind that S-Series matrices are well suited for use on high powered hydrostatic drills.
Fine Tuning Your Product Selection …
1. Drill with the matrix type that you have selected.
2. Monitor the rate of penetration (ROP) and overall bit life.
3. Is the performance satisfactory?
YES: Continue drilling with the product that you have selected.
NO, the ROP is too slow: Change to …
- A higher number S-Series, HR-Series or D-Series matrix type and/or
- A lower contact area waterway style such as Turbo or T-Turbo.
NO, the overall bit life is inadequate: Change to …
- A lower number S-Series, HR-Series or D-Series matrix type and/or
- A higher contact area waterway style such as Regular (Full-Face).