Design and application of the bit for the hottest

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Design and use of drill bit for drilling "slip layer"

I. definition of slip layer

impregnated artificial diamond drill bits often slip in drilling various rock formations. The so-called slip is the phenomenon of low ROP and even no footage during drilling. There are many rock layers that can produce this phenomenon, such as hard quartz layer, granite, chert, limestone, marble, etc. Can we say that the rock layers that produce this phenomenon are all sliding layers? Of course not. There are many reasons for skidding. For example, the rocks in a mining area are limestone, marble, etc., and the exploration team working in this area can only use electroforming bits to drill. If the hot pressed sintered impregnated artificial diamond bits are used instead, the footage will not be advanced, and the diamond will not be exposed. The reason is that the emulsion cannot be used due to the leakage in the well, so the speed of the drilling rig cannot go up, and the actual linear speed of the bit rotation is only 0.5 0.8 m/s, The lip diamond of the hot pressed sintered bit, which causes the wear resistance of the matrix, does not go out of the blade and does not advance. Rock layers in such cases should not be called slip layers

the so-called slipping layer should be a rock layer with low ROP when normal impregnated bit and normal parameters are used, excluding various operating factors. The common characteristics of this kind of rock stratum are: the minerals that make up the rock are hard, the mineral particles are fine, and the structure is dense, such as quartzite, hard granite, chert, etc. Its main lithological indicators are: the indentation hardness is more than 4500mpa, the uniaxial compressive strength is more than 150MPa, and the abrasiveness is less than 15mg

II. Design principle of drill bit for sliding layer

the characteristics of sliding layer are that the rock is particularly hard, the structure is dense, the strength is high, and the abrasiveness is weak. According to these characteristics, good drilling effect can be achieved by reasonably designing bit parameters. The basic principles are:

1. Select high-grade synthetic diamond

high-grade synthetic diamond has the characteristics of good crystal shape, high compressive strength of a single grain, good thermal stability and so on. Drilling hard rock has particularly obvious advantages, which is unmatched by low-grade diamond

2. Select medium particle size artificial diamond

in terms of the characteristics of diamond growth and the current level of synthesis technology, with the increase of single crystal particle size, the content of inclusions in the crystal increases, and the trend of irregular growth of single crystal due to lattice distortion increases, which means that in the full particle size range, medium to fine-grained diamond monocrystals such as 50/60, 60/70, 70/80, 80/100 are the most complete and the impurity content is the lowest, that is, in single crystals of the same grade, This particle size has better compressive strength (specific pressure) and impact strength index per unit area than coarse particle size (35/35, 40/45, 45/50), This can be proved from the difference of the compressive strength (KGF)/pore area (UM) ratio of 45/50 and 50/60 particle sizes, which are of the same mbd12 grade:

the compressive strength (KGF)/pore area (UM) ratio of 45/50 particle size is 16/390=0.041

the compressive strength (KGF)/pore area (UM) ratio of 50/60 particle size is 14/275=0.051

the former is much smaller than the latter

in the rock crushing work under the same conditions, the medium to fine-grained diamond single crystal with better specific pressure has better sharpness and durability, while the coarse-grained diamond is easy to be blunt and cannot be threshed in time due to its low strength index per unit area, and the new cutting edge cannot be exposed in time, resulting in slipping

of course, too fine diamond particle size will also cause bit slippage due to insufficient cutting edge. What particle size can meet the requirements of normal drilling can be evaluated and roughly calculated by simulating the relationship between bit drilling process parameters

the drilling behavior of the drill bit can be described in the following ways: a diamond cutting edge on the lip of the drill bit is working in the form of a helix, that is, it is generated in two directions at the same time. This division is based on the use of the steel hammer to divide the displacement and force: one is along the drilling axis y, the other is the tangential direction X perpendicular to the axis, and the combined displacement and resultant force Z of the two represent the actual working state of the cutting edge. This state can be expanded according to the geometric model, such as the hook, strand and chord relationship, and there is the following relationship formula:


this relationship formula is substituted into the corresponding data for derivation, which can evaluate and roughly calculate the rationality of some design parameters of the drill bit, such as the selection of diamond particle size, concentration, strength, etc. the following is derived with the determination of particle size as an example

suppose a 75 diamond coring bit is designed. According to the normal drilling process, the bit speed is r/min, the footage speed is m/h, and the WOB is 150kgf/cm2. Taking a diamond cutting edge at the maximum outer diameter as the object, the displacement s in the X, y, and Z directions per unit time is calculated. Set the time t=1min, the bit speed v1=300r/min, and the footage speed v2=4000mm/h, then x, y The displacement s in the three directions of Z is respectively:

sx=75 300=70685mm

sy=4000 60=66.667mm

sz= 706852 + 66.6672=70685.8mm

diamond cutting edge processing of rock. The experimental method of high temperature resistance of fire smoke exhaust fan ga211 ⑴ 999 is the result of the comprehensive action of grinding, cutting, ploughing, crushing and other methods, and it is actually the working state of a group of cutting edges. It is difficult to accurately calculate its primary cutting depth working parameters, Therefore, only the idealized state, that is, single edge and cutting state, is used to quantify the corresponding data to obtain a conclusion. According to the above data, the drill footage per revolution is obtained as:


it can be considered that the maximum depth of a single diamond cutting edge cutting into the rock at one time is 0.133mm

experience shows that when the embedding depth of diamond single crystal in the matrix reaches 60%, it can ensure that there is no abnormal falling off, and 50% of the edge height is suitable as the chip holding height in cutting, so the one-time cutting depth design of diamond cutting edge can be 20% of the diamond particle size. According to this idea, substituting the above data of cutting into the rock depth once, the diameter of this diamond single crystal particle is:

d=0.133 4=0.532mm

this data is equivalent to 45/50 particle size

3. Select mixed particle size impregnation

in order to improve the broad spectrum of drill bit, it is an effective way to adopt different particle size mixing and inlay. In this way, it is possible to drill in sliding layer and non sliding layer, and the phenomenon of frequent drilling and bit replacement due to rock formation change is eliminated

4. Choose a lower concentration of diamond content

due to the low concentration, the diamond particles are relatively reduced, and the WOB of each diamond distributed on the lip will increase, which is conducive to the diamond cutting into the rock, so as to improve the ROP

5. Choose a reasonable distribution mode of diamond

adopting a reasonable distribution of diamonds to achieve balanced wear on the lip of the bit can increase the service life of the bit

6. Medium hardness carcass shall be selected

in the past, due to the low grade of diamond, soft matrix was often used in drilling to facilitate the exposure of diamond, which is undoubtedly correct. However, due to the continuous improvement of the grade of synthetic diamond, the continued use of soft matrix in the use of high-grade diamond is bound to cause premature threshing of diamond, which is not conducive to footage and waste. Therefore, according to the principle of matching the hardness of matrix with the grade of diamond, Medium hardness matrix should be selected to match high-grade diamond to drill into slippery rock stratum

7. Choose the lip shape with more free surfaces

when drilling into the complete sliding layer of the rock stratum, the lip shape of more free surfaces, such as ladder tooth type, sawtooth type and sharp tooth type, will be conducive to rock crushing. At this time, the diamond rock crushing method will change from simple surface crushing forms such as ploughing, pressing, crushing and scraping to more efficient volumetric crushing forms such as disintegration, which is conducive to improving the drilling speed. At the same time, considering the constant ROP, it is required that the change of the lip shape of the bit with time should be as small as possible, and the ladder tooth lip shape is an ideal choice

8. Adopt diamond single crystal to keep diameter

because the rock in the slip layer is particularly hard, the use of needle alloy or polycrystalline diameter preservation will often seriously affect the footage, while the diamond single crystal has a scraping effect on the hard shaft wall, which is conducive to improving the drilling rate

9. Select fan-shaped nozzle

the fan-shaped nozzle is particularly important for the wireline coring bit. Compared with the straight nozzle, the fan-shaped nozzle and the straight nozzle can make the inner and outer lip surfaces of the bit wear evenly with 20 trains of 350 km/h Alpine EMU and 20 trains of 250 km/h Alpine EMU. The number of nozzles should not be too large if it meets the conditions of powder discharge and cooling

10. The drill bit shall be pre sharpened

pretreatment is particularly important for drilling the slipping layer, so that the bit can directly advance without primary grinding, reducing the time of primary grinding and improving the drilling speed

III. several problems that should be paid attention to in the drilling operation of the sliding layer

1. Because the lithology of the sliding layer is particularly hard, the WOB is a key parameter in drilling. Without sufficient specific pressure, the sharp edge of the diamond cannot be pressed into the rock. At high speed, the diamond cutting edge is quickly polished and loses drilling ability

WOB p=f p

where: F is the annular lip area cm2,

p is the unit pressure value n/cm2. The WOB of sliding layer is required to be larger than that of drilling other rocks, which is generally about 882.6~1078.7n/cm2

2. The rotation of the drill bit in the slipping layer should not be too fast. Too fast rotating speed will affect the cooling of the cutting edge on the lip of the diamond bit, while the diamond cutting edge is generally low in the drilling of the slipping layer. This effect will be more obvious, which is easy to cause the cutting edge to be worn in advance and polished after grinding, resulting in artificial slipping. Generally, the linear speed is controlled between 1.5~2m/s

3. The pump volume should be small. Due to the low drilling speed in the slipping layer, the rock powder produced at the bottom of the well is relatively small. Larger pump capacity will further reduce the amount of rock powder at the bottom of the well, which is very unfavorable for diamond exposure and prone to slip. Moreover, excessive pump volume causes high pump pressure, which can offset part of the WOB, and the reduction of WOB will also cause slippage

empirical formula for calculating pump volume: q=k d

where: Q - pump volume l/min

d - outer diameter of drill bit cm,

k - coefficient (generally 4~6)

4. Because the rock in the slip layer is particularly hard, generally the shaft wall clearance is small, so when selecting the reamer, we should pay attention to the size matching between the outer diameter of the drill bit and the outer diameter of the reamer. The outer diameter of the reamer is generally 0.2~0.3mm larger than the outer diameter of the drill bit, which should not exceed 0.4mm, Otherwise, the footage will be affected

5. When drilling the slipping layer, the type of reamer should be diamond single crystal reamer (preferably electroplated), and polycrystalline reamer should not be selected. The reason is the same as that of drill bit diameter retaining material

6. The bent drill pipe and drilling tool cannot be used in drilling the slipping layer. The coaxiality of the drill bit should meet the design requirements to ensure the independent development of the rotation of the drilling tool. The long carbon chain 2-yuan acid stability is obtained by microbial fermentation with petroleum light wax, so as to prevent the occurrence of abnormal threshing of diamond in the drill bit. The specific indicators are: the bending of drill pipe per meter shall not exceed 1mm, the bending of drill tool per meter shall not exceed 0.75mm, and the coaxiality deviation of drill bit shall not exceed 0.2mm

7. Before the bit without pre cutting edge is put into the well, a small amount of quartz sand (particle size 0.5~1mm) should be put into the well. After the bit is put into the well, use small pump volume, light WOB, slow rotation drilling for 5~10 minutes, and then use normal parameters for drilling

8. In case of slipping during drilling, the common double pipe drilling should be carried out immediately, and the bit should be removed. When drilling with wireline coring, it can reduce the pump volume and increase the amount of rock powder at the bottom of the hole, so as to promote the diamond to return to normal after re cutting

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