1.Describe the design of an impregnated drill bit.
ü As the name implies the matrix in an impregnated diamond bit is thoroughly impregnated with small diamonds, much smaller than the diamonds used in a surface set bit. The diamonds used in impregnated bits are almost only artificial diamonds. Natural diamonds can be used as so called kicker stones who’s task is to keep the nominal diameter of the bit.
2. What does free cutting or self sharpening of an impregnated diamond mean?
Describe this process
ü The diamonds cut until they are worn
ü The matrix erodes and looses it’s grip on the worn diamonds
ü New sharp diamonds are exposed
ü These new diamonds cut the rock until they are worn
ü The matrix erodes and looses its grip on the worn diamonds
ü Etc, …
3. Which are the advantages of an impregnated diamond core bit as compared to a surface set diamond core bit?
ü A larger area of application as concerns geological formations
ü A more robust design that can handle drilling in broken and fissured formations
ü Can handle rough treatment
ü Will drill longer and faster in hard formations
4. Which properties of the rock have an influence on the choice of a suitable diamond drill bit?
ü Hardness: which is groped into soft, medium hard, hard, very hard and ultra hard rocks.
ü Grain size: which is groped into fine, medium and coarse grained rocks.
ü Abrasiveness: which is groped into non, slightly and very abrasive rock.
ü Tectonic properties: which are groped into very competent, competent, fairly
ü competent, fractured and highly fractured rocks.
5.How are these properties grouped?
ü •See the answers to question number 4 above.
6.What is the basic rule when choosing a suitable impregnated diamond drill bit?
ü In hard formations use a drill bit with a soft matrix and in soft formations use a drill bit with a hard matrix.
ü If we for example are drilling in a soft limestone, the diamonds can work during a comparatively long time before they are worn and it is then necessary that the matrix is hard in order not to erode too fast and thereby loosing the grip of the diamonds before they are worn.
ü If we on the other hand are drilling in a hard, fine grained, slightly abrasive volcanic rock the diamonds will wear out comparatively fast and it is then important that the matrix is soft enough to erode and expose new diamonds at the same pace as the old ones are worn.
7. Which are the most common impregnation depths (matrix heights) of an impregnated diamond bit?
ü 6 mm
ü 9 mm
ü 12 mm
ü 14mm
ü 16mm
8. What is the advantage of an extra high matrix height when drilling with wire line?
ü When drilling with wire-line systems a 16 mm matrix height is undeniably a great advantage. Compared to a 12 mm matrix drill bit, a 16 mm matrix drill bit will drill 20 – 40 more meters in a competent rock before it is worn and has to be exchanged. As everyone understands this mean less rod handling.
9.Which is the most common profile on an impregnated diamond core bit for wire line drilling?
ü The W-profile ( STD Profile )
10.Describe the difference between a front discharged drill bit and a drill bit with conventional waterways. Do also describe the formations that these two water way configurations are intended for.
ü When drilling in non-consolidated formations such as soil, sand, gravel, silt or clay there is a risk that the water will flush away part of the core.
ü A similar thing can happen when drilling in a fissured formation if the fissures are filled with a soft material. The water can flush away the soft material in the fissures and the rock mechanic has no way to tell whether the fissures where empty or filled.
ü For drilling under these circumstances front discharge flushing channels shall be used. In stead of passing in the annular space between the core and the inside diameter of the bit the flushing water will pass through channels inside the matrix and out via ports on the cutting surface. The contact between the flushing water and the very soft core is minimized and the risk for flushing away part of the core is much smaller.
ü Another advantage with front discharged drill bits is that the pressure drop over the ports is smaller than the pressure drop over the standard water slots. This will also contribute to a better core recovery in soft formations.
11. Which are the tasks for the reaming shell?
ü To ream the drill hole to the nominal diameter
ü To act as a stabilizer for the core barrel
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