Recent advances in diamond bit technology have helped to bridge the gap between polycrystalline diamond compact (PDC) and diamond impregnated bit applications. A new type of diamond bit has been developed to effectively drill hard, abrasive formations, while retaining the ability to efficiently drill through non-abrasive sections. This new type of diamond bit utilizes a three part cutting structure consisting of PDC cutters, diamond impregnated blades, and hot pressed diamond impregnated inserts.
Technological advances in the design and manufacture of diamond bits have greatly expanded the applications of both PDC and diamond impregnated bits. However, there are still many intervals of hard rock drilling which have sections that are too hard or abrasive for a conventional PDC bit, but also contain sections that are not sufficiently abrasive to be effectively drilled with a conventional diamond impregnated bit. Drilling these types of intervals with conventional drill bits has proven very costly. Operators have been forced to choose between incurring expensive trip times, due to the need to frequently change out bits to maximize the rate of penetration (ROP) in the different formations, or suffering through the very slow penetration rates typical of conventional impregnated drilling in non-abrasive formations.
A very successful run has recently been completed with this new diamond bit in the Huamampampa formation in Tarija, Bolivia. In a long, 8 ½" hole size section, where the shale content ranged from 10 to 90%, this new bit type drilled to TD with a higher overall rate of penetration than any offset. The combination of PDC cutters with hot pressed diamond impregnated inserts in a diamond impregnated matrix has proven to be a very versatile cutting structure in variable formations.
The introduction and development of drag type drill bits with diamond cutting elements has greatly reduced the cost associated with many drilling programs. Due to the excellent abrasion resistance of diamond cutting elements, and to the fact that this type of drill bit has no moving parts, diamond bits are capable of drilling very long sections relative to roller cone type bits. The long bit life of a diamond bit has proven to greatly reduce the number of trips required to drill a given interval, particularly in areas where rig costs tend to be high.
Diamond bit technology has recently come full circle. As a result of material and manufacturing constraints, the first drag type drill bits that used diamonds for the cutting elements were of the impregnated type (diamond impregnated bits are constructed such that the diamond cutting elements are suspended throughout the tungsten carbide matrix blades).1 As materials and manufacturing processes advanced, the diamond bit drilling industry moved away from diamond impregnated bits into surface set diamond bits (surface set diamond bits use a single layer of fairly large natural diamonds arranged on the face of the bit). These surface set diamond bits are capable of retaining much larger diamonds for higher diamond exposure, which translates to a higher rate of penetration (ROP) potential for a given rotary speed.2 Therefore, surface set diamond bits provided the advantage of a fixed diamond cutter design (no moving parts), and also offered a reasonably wide range of diamond sizes for varying formation hardness.
The next major advancement in the diamond bit industry occurred with the introduction of PDC bits, which use relatively large (3/8" diameter to 1" diameter) diamond compact discs as the cutting elements. For a variety of reasons, when PDC bits were first introduced, they were limited to drilling soft to medium strength formations. At this stage in the development of diamond drilling technology, surface set diamond bits were used in medium hard to hard applications, while PDC bits were used in soft to medium applications.