Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186–192
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Int. Journal of Refractory Metals and Hard Materials
j ourna l homepage: www.e lsev ie r .com/ locate / IJRMHM
A new composite impregnated diamond bit for extra-hard, compact, andnonabrasive rock formation
Songcheng Tan a,b,c,⁎, Xiaohong Fang a, Kaihua Yang a, Longchen Duan a
a Faculty of Engineering, China University of Geosciences, Wuhan, Hubei 430074, PR Chinab Post Doctoral Work Station, CNPC Bohai Drilling Engineering Company Limited, Tianjin 300457, PR Chinac Post Doctoral Research Center, Southwest Petroleum University, Chengdu, Sichuan 610500, PR China
⁎ Corresponding author at: No. 1 Drilling Engineering CRoad, Dagang Oilfield, Binghai New District, Tianjin 3025924006.
E-mail addresses:[email protected] (S. Tan)[email protected] (K. Yang), [email protected] (L
0263-4368/$ – see front matter © 2013 Elsevier Ltd. All rihttp://dx.doi.org/10.1016/j.ijrmhm.2013.11.001
a b s t r a c t
a r t i c l e i n f oArticle history:Received 29 July 2013Accepted 7 November 2013
Keywords:Metal-bonded diamond toolsHard rock drillingSintered diamond-impregnated cutterStructural design
In this study, a new composite impregnated diamond bit was designed to solve the slipping problem when im-pregnateddiamondbit is used for extra-hard, compact, and nonabrasive rock formation. The newbit is composedof sintered diamond-impregnated (SDI) cutters and support body. The support body has weaker resistance toabrasion and would thus wear out faster than SDI cutters during drilling operation. Such design decreases thecontact area between the bit work layer and the rock formation and increases the unit load acting on the worklayer and the single diamond, thereby improving drilling efficiency. The design parameters and manufacturingtechnology of the new composite impregnated diamond bit were analyzed to achieve the desired performance.TwoФ41/27 mm laboratorial bits weremanufactured to conduct a laboratory drilling test on the rock specimensof fine-grainedmonzonitic granite rich in biotite. The laboratory drilling test indicated that both themanufactur-ing technology and the drilling parameters significantly affect the rate of penetration (ROP). The test also indicat-ed that the abrasive resistance of the bit work layer was proportional to the area ratio of SDI cutters to bit bottomface. A very small or very large area ratio in the radial direction causes annular groove or wale at that section, re-spectively. Therefore, optimization was conducted to coordinate the abrasiveness of the drilled rock formationand abrasive resistance of the bit work layer, and a Ф91.5/71 mm composite impregnated diamond bit wasmanufactured. The new bit was applied to a hydropower station drilling construction in Fujian Province,China. Field drilling application indicated that the ROP of the new bit was approximately three to four timesthat of the bits produced by other factories. The ROP relationship was completely similar to the ratio of the ap-plied load acting on a single diamond of the new composite to ordinary impregnated diamond bits.
© 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Drilling is the most important operation for mining and prospectingindustries. The probability of encountering slipping formation duringdrilling operations has increased because of the development of energyexplorations in deep rock formations. In the drilling community, slip-ping formation is the informal name for extra-hard, compact, and non-abrasive rock formation. This formation usually has three characteristics[1]. (1) Rock hardness is relatively high because of the high quartz con-tent. The rock hardness of slipping formations is approximately5000 MPa but reaches up to 7000 MPa for a number of special forma-tions. (2) Rock strength is high because the rock-formingmineral grainsare very small (with diameters ranging from 0.01 mm to 0.2 mm) andhave local siliceous cementation. Thus, an overall uniaxial compressivestrength of 150 MPa or higher can be achieved because of the compactstructure. (3) Rock abrasiveness is weak. The low rate of penetration
ompany, BHDC. No. 128 Hongqi0280, PR China. Tel.: +86 022
, [email protected] (X. Fang),. Duan).
ghts reserved.
(ROP) results in small rock debris. Therefore, the debris abrasivenessto the bit matrix is limited, and diamonds do not easily emerge fromthe bit matrix.
An essential feature of slipping drilling is that the diamond protru-sion height on the bit bottom face is too short or almost nonexistent.The bit bottom face appears somewhat like a mirror finish. Severalmethods have been employed in field drilling applications to addressthis issue [2]. These methods include grinding the bit matrix underdry condition drilling, putting quartz sand at the bottom of the well,hammering the bit bottom face, and using acid to treat the bit bottomface. However, thesemethods can only be used in shallowwells; other-wise, the drilling efficiency would be affected, the probability of drillingaccidents would increase, and a number of unnecessary difficulties andlosses may occur.
Numerous studies were conducted to address the difficulties in hardrock drilling. For instance, various indices, such as total silica content,grain shape factor, shore hardness, and abrasiveness, were found to beresponsible for the bits' wear rate in rock drilling [3]. The performanceof polycrystalline diamond compact cutters under different combinedloads of static thrust, impact, cutting, and water jets on Missouri redgranite and Halston limestone were investigated to verify the feasibility
Fig. 1. Configuration of the new composite impregnated diamond bit to illustrate the cut-ting structure for slipping formation.
Table 1Diamond grit parameters and concentration.
Diamondtype
Grit size(US mesh)
Toughnessindex (%)
Thermal toughnessindex (%)
Concentration(vol.%)
ZND2160 35/40 88 to 91 83 to 87 17.5ZND2160 50/60 80 to 83 77 to 78 7.5
187S. Tan et al. / Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186–192
and efficiency of rotary–percussive drilling assisted by water jets forvery hard rocks [4]. Laboratory tests were conducted on rocks (such assandstone, limestone, granite, and basalt) to investigate the applicabili-ty of ultrasonic percussive drilling with diamond-coated tools todownhole drilling [5]. Nonionic polymer was added to the flushingmedia to enhance the diamond drilling performance on phosphaterock [6]. Particle impact drilling was experimentally studied for deepwell hard formation [7]. Gao [8] designed a bionic coupling impregnateddiamond bit specifically for hard rock formation drilling. However, theslipping formation differs from these ordinary hard rock formations interms of nonabrasive property.
This study presents a new diamond bit structure to solve the drillingdifficulties in extra-hard, compact, and nonabrasive rock formation. Thisdesign steadily maintains a small contact area between the diamond bitwork face and the rock formation during drilling to increase the unitload acting on the single diamond and improve the ROP.
2. Design of the new diamond bit
2.1. Methodology
Several commonly accepted principles in the drilling industry are re-lated to the manufacture of impregnated diamond bits for slipping for-mations. For example, a diamond bit with heterogeneous bottom facecan be employed to decrease the contact area between the bit workface and the rock formation, thereby increasing the free surfaces whenbreaking rocks [9]. Choosing a matrix with low abrasive resistance canimpel the diamond protrusion, and decreasing the diamond concentra-tion can improve the load acting on each single diamond [10].
In terms of diamond parameters, high quality and strength are usu-ally required; however, the required particle size remains debatable. Ye[11] used theoretical calculation to show that a macrograined diamondimproves the average load acting on the single diamond of the bit bot-tom face; such improvement benefits the diamond protrusion.
Moreover, severalmethods, such ashot-pressed or electroplated bitswith weak diamond retention [12,13] and hot-pressed diamond bitswith principal and secondary abrasives [14], have been employed to en-sure that weaker abrasives participate in wearing out the bit matrix.
After a comprehensive review of previous studies, we found thatthree aspects were important for bit structural design. (1) Diamondswith high quality, high strength, and large particle size were requiredto resist the high bit load. (2) The capacity of the bit matrix resistanceto abrasion should be weaker because the rock debris is very small.Thus, the debris abrasiveness to the bit matrix should be enhanced.(3) The contact area between the bit work face and the rock formationshould be as small as possible to increase the unit load acting on thebit work face.
Wedesigned a new composite impregnated diamond bitwithweak-er matrix resistance to abrasion and sintered diamond-impregnated(SDI) cutters to achieve the desired design objectives. The configurationof the new composite bit work face is shown in Fig. 1.
As shown in Fig. 1, two sets of drills, namely, one with (a) arrange-ment and one with (b) arrangement, were used. The SDI cutter wasmanufactured through hot pressing, and it could be either cuboid or cy-lindrical. The support body was the bit matrix with lower hardness andweaker abrasiveness, andwas designed to embed SDI cutters andmain-tain a connection between the bit blank body and the bit work layer.
2.2. Diamond parameters and matrix formula
Previous studies [15] indicated that diamonds normally present sixdifferent states during cutting operation: emerging grit, integral grit,smoothed grit, micro-fractured grit, macro-fractured grit, and pull-out.These states are usually closely related to the properties of diamondgrits. Higher diamond compression strength and impact toughness cor-respond to less diamond breakage during operation, resulting in tool
property improvement [16]. In this study, we selected the ZND2160 di-amond type (Zhongnan Diamond Co., Ltd., China) for the SDI cutters be-cause of its high quality (diamond concentration: 25 vol.%). Mixedmesh consisting of 40/45 US mesh (17.5 vol.%) and 50/60 US mesh(7.5 vol.%) was used in this study. The mechanical parameters of twoUS mesh size diamonds are shown in Table 1.
The bit matrix is the component that embeds the diamond grits andconnects the bit's blank body. The adaptability between the bit matrixand the drilled rock formation properties plays an important role inbit quality. In other words, difficulties in slipping drilling indicate thatthe properties of bit and rock formation are not adaptable. Thus, thema-trix formula for the SDI cutters and the support body should be sepa-rately designed.
The metallic matrices of tungsten carbide, cobalt, and iron are themost frequently used matrices for impregnated diamond bits. In con-trast to other matrices, the tungsten carbide-based matrix has highsintering temperature, excellent hardness, and strong abrasive resis-tance. Cobalt is widely regarded as the best metal material for metallicmatrices [17]. Cobalt-basedmatrix has good toughness, moderate hard-ness, and average abrasive resistance. Similar to cobalt, iron is an eighthgroup element; thus, these elements have similar properties. Iron-basedmatrix has relatively weak hardness and abrasive resistance but is re-cently widely used because of its low cost and availability [18,19]. Thehardness and abrasive resistance of the support body should be weakerso that the support body can beworn outmore easily than thematrix ofSDI cutters and the bit load can be focused on the SDI cutters. Thus, aniron-based matrix was preferred.
SDI cutters are the cutting parts during the drilling process. The ma-trix of the cutters should be sufficiently hard and strong to resist thehigh bit load on the cutters' bottom faces and to embed the diamondgrits strongly. Therefore, a tungsten carbide-based matrix would bepreferable. The matrix formulae for the SDI cutters and the supportbody are shown in Table 2.
Table 2Manufacture technologies and gauges of new composite impregnated diamond bit for laboratory drilling tests.
Item Matrix formula Specification and size Sintering temperature Retention time Sintering pressure
(wt.%) (mm) (°C) (min) (MPa)
SDI cutter WC50(663Cu)30Co5Ni7Fe3Ti2Mn3 3.5 × 3.5 × 6 980 4 18Supporting body (bit #1) Fe48(663Cu)32Co2Ni15Mn3 Φ41/27 850 4 18Supporting body (bit #2) Fe48(663Cu)32Co2Ni15Mn3 Φ41/27 830 3 16
663Cu is a kind of pre-alloyed metal powder, with weight content of Cu85Sn6Zn6Pb3.
188 S. Tan et al. / Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186–192
Phosphorus decreases the melting point of the Cu–Fe alloy [20] andthe sintering temperature of the diamond bit matrix [21]. Thus, theoverall component of iron powder consisted of Fe–P alloy powder(25%), reduced iron powder (57%), and atomized iron powder (18%).The phosphorus content was 5.5% of the total mixed iron powder.
2.3. Manufacturing technology and equipment
The diamond bit matrix is manufactured through transient liquidphase sintering. The three key factors in diamond bit manufacture aresintering pressure, sintering temperature, and retention time. Duringthe sintering process, the powders in the graphite mold generatedisplacement and deformation under high sintering temperature andpressure. Thus, densification and abrasive resistance can be improvedbecause of the decrease in powder contact surface area and pore vol-ume. The strengthened connection between the bit matrix and theblank body can also be obtained.
According to the main components of the matrix formula, sinteringtemperature is determined by the eutectic temperature of metal pow-ders. For the iron-based matrix rich in phosphorus, the sintering tem-perature was decided by the melting point of 663-Cu. The mutualmelting ability is good among copper, iron, and nickel. Zak-Szwed [22]performed hot-pressing experiments and found that the Cu–Fe alloyachieves the best bond strength and ductility under sintering tempera-tures between 820 °C and 900 °C. Xie [23] indicated that the Fe–Co–Cualloy achieves the best bending strength under sintering temperaturebetween 750 °C and 850 °C. During the hot-pressing process, themetal powders of the bonding component present a liquid phase afterthe sintering temperature is achieved, whereas other components stillpresent a solid phase. By maintaining the high temperature and pres-sure, the bonding liquid fully permeates into the other components,and the overall strength is improved.
Laboratory drilling test was performed on two manufacturedlaboratorial bits to verify whether our design methodology for a new
Fig. 2. The overall bit mounting of SDI cutters, support body, and bit blank body.
composite diamond bit is efficient for slipping formation. As shown inTable 2, the geometries of the SDI cutter are 3.5 mm × 3.5 mm × 6 mm,and the inside and outside diameters of the laboratorial bits are 27 and41 mm, respectively. The overall bitmounting of the SDI cutters, the sup-port body, and the bit blank body are shown in Fig. 2. The sinteringequipment for the SDI cutters was the Automatic Controlled SM100-AResistor Furnace (Hubei Changjiang-Jinggong Materials Technology Co.,Ltd., China). The resistor furnace is a contact heating equipment exten-sively used for metal matrix composite sample manufacturing. Thesintering equipment for the laboratorial bits was the AutomaticControlled ZPM Intermediate Frequency Furnace (Hubei Changjiang-Jinggong Materials Technology Co., Ltd., China). The intermediatefrequency furnace is an induction heating equipment extensively usedin diamond tool production.
The retention time was designed to be 4 and 3 min on the basis ofheating speed, SDI cutter and bit geometries, matrix compositions,and other factors. The detailed parameters of the manufacturing tech-nology are shown in Table 2.
3. Drilling test and application
3.1. Laboratory drilling test
3.1.1. Drilling conditionsThe rock specimens for the laboratory drilling test were fine-grained
monzonitic granite rich in biotite. The mineral compositions are shownin Table 3, and the granite photomicrograph is shown in Fig. 3. Accordingto the rock drillability grading standard for diamond drilling promulgat-ed by the Ministry of Geology and Mineral Resources of China in 1984,rock drillability could be divided into 12 grades [24]. The granite speci-mens were hard rock formations belonging to the seventh and eighthgrades. The specimen size of the granite was 10 cm × 10 cm × 20 cm.
The SGZ-I8 laboratory bench was employed for the laboratory dril-ling test under the following conditions: bit load: 4 kN; rotationspeed: 400 rpm; and cooling fluid: 5 L/min.
3.1.2. Test results and analysesEach laboratorial bit drilled three granite specimens under the de-
signed drilling parameters. Bit #1 initially performed poorly under theabovementioned conditions. Thus, the rotation speed was increased to600 rpm. Consequently, the ROP exceeded 2 m/h. The detailed drillingparameters and test results are shown in Table 4. The wear on the two
Table 3Mineral composition of the fine-grained monzonitic granite rich in biotite.
Composition Volumetric content (%) Particle size (mm)
Hypautomorphic–xenomorphicgranular orthoclase
65 1 to 5
Quartz 15 0.5 to 1.5Plagioclase 15 0.5 to 2.5Biotite 5 0.1 to 1
Fig. 3. Photomicrograph illustrating the grain structure of the granite rock. Note thewidelyvarying shape, color, content, and size of various grains.
189S. Tan et al. / Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186–192
laboratorial bits after the drilling test is shown in Fig. 4. The followingpreliminary findings were obtained from the laboratory drilling test.
1. Analysis of Tables 1, 2, and 4 indicated that although the bit matrixformula and the diamond parameters were identical, the ROP ofthe two bits can be significantly affected by the manufacturing tech-nology because the higher sintering temperature, greater sinteringpressure, and longer retention time can improve the abrasive resis-tance of the support body. Thus, the diamond protrusion is impededand the ROP is remarkably decreased.
2. High rotation speed increases the broken volume of rock formationper unit time and enhances the abrasion of the bit work layer. There-fore, the ROP of the bit can be significantly improved by increasingthe rotation speed. The bit matrix formula and the manufacturingtechnology should be coordinated to achieve a high ROP and longbit service life under high rotation speed.
3. The area ratio of the SDI cutters to the bit bottom face significantly in-fluences the abrasive resistance of the bit work layer. For example,the area ratio at the inside diameter of bit #1 was small; thus, theabrasive resistance of the bit work layer at that area was weak andan annular groove was produced. By contrast, the area ratio at themiddle diameter of bit #2 was large because of the overlap of theSDI cutters; thus, an annular wale was produced at this section.
3.1.3. Optimization of bit designThe optimizationof the newcomposite impregnated diamond bit in-
cludes improving the performances of the SDI cutters, the support body,and the internal structure of the bit work layer, aswell as the adaptationbetween those three aspects. The new bit was designed mainly for theextra-hard, compact, and nonabrasive rock formation. Thus, the designphilosophies consisted of increasing the unit load acting on the SDI cut-ters and decreasing the abrasive resistance of the support body so thatthe diamond grits could continuously maintain the appropriate
Table 4Drilling parameters and test results of the laboratory drilling test.
Bitnumber
Bit load(kN)
Rotationspeed (rpm)
Cooling fluidflow (L/min)
Drillingdistance (cm)
Rate ofpenetration (m/h)
Bit #1 4 400 5 16 0.87Bit #1 4 600 5 19 1.91Bit #1 4 600 5 19 2.16Bit #2 4 400 5 19 1.76Bit #2 4 400 5 18 1.84Bit #2 4 400 5 19 1.86
protrusion height. We mainly considered the following aspects inconducting the optimization, and the bit design itinerary map isshown in Fig. 5.
1. The area ratio of the SDI cutters to the bit bottom facewas decreasedto reduce the contact area between the SDI cutters and the rock for-mation. The area ratio along the radial direction should be relevantwith the radius.
2. SDI cutters were used in all the cutting operations in the drillingprocess. The diamond parameters for this purpose were as follows:high concentration, large grit size, strong abrasive resistance, andhigh quality.
3. The abrasive resistance of the support body should be weak and fitfor SDI cutters.
4. The matrix property and diamond parameters of the SDI cutters, in-cluding the protrusion height of the SDI cutters to the bit bottomface and the protrusion height of the diamond to the SDI cutters,should be coordinated.
5. The waterway number or waterway width should be increased toensure the cleaning of the well bottom and to avoid burning the bit.
3.2. Field drilling application
3.2.1. Applied rock formationField drilling application was conducted at a hydropower station in
Fujian Province, China. Over 10 bit factories participated in the project;however, all of them failed because of the low ROP ranging from0.30 m/h to 0.40 m/h.
The applied rock formation was denominated as acid lithic crystaltuff and structured as porphyritic clastic texture with microcrystallineand tuffaceous structure in matrix material. The photomicrograph ofthe rock formation is shown in Fig. 6, and the mineral composition isshown in Table 5. Fig. 6 and Table 5 indicate that this crystal tuff isone of the most typical slipping formations. According to the rock drill-ability grading standard for diamond drilling promulgated by theMinis-try of Geology and Mineral Resources of China in 1984 [24], this acidlithic crystal tuff is an extra-hard rock formation belonging to the 11thgrade.
3.2.2. Bit designThe basic bit design for the crystal tuff included decreasing the con-
tact area between the SDI cutters and the rock formation and employingweak abrasive resistance for the support body. These two aspectsshould be combined to improve the drilling efficiency in field drilling.The arrangement and gauge of the SDI cutters in the bit work layerwere similar to those in the (b) type shown in Fig. 1, with the arearatio of the SDI cutters to the bit bottom face ranging from 45% to 50%.This kind of bit can also be applied to hard rock drilling under low rota-tion speed and small bit load.
The new composite impregnated diamond bit had a diameter ofФ91.5/71 mm, a bit work layer width δ of 10.25 mm, and 10waterwayswith awidth of 8 mmeach. The detailedmatrix compositions of the SDIcutters and the support body were the same as those of the aforemen-tioned two laboratorial bits. The manufacture technology parameterswere as follows: sintering pressure: 16 MPa; sintering temperature:850 °C; and retention time: 6 min.
3.2.3. Drilling results and discussionThe total service life of this new composite impregnated diamondbit
was 17.8 m, with an average ROP of 1.23 m/h (three to four times thatof the ROP manufactured by other bit factories). Bit wear was normal,and approximately 1.5 mm height of work layer was left.
The new bit can efficiently drill the crystal tuff because the bit struc-ture ensures that the bit load is focused on each single diamond of thebit bottom face. In addition, the ordered disperse arrangement of the
Fig. 4. Photograph illustrating thewear of two laboratorial bits after drilling test. Note the annular groove of bit #1 and annularwale of bit #2 on bit bottom faceswhichwere caused by thedifferent abrasive resistance of the bit work layer.
190 S. Tan et al. / Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186–192
SDI cutters, which was beneficial to diamond protrusion and cuttingsremoval, improved ROP.
Two standard impregnated diamond bits with diameter ofФ91.5/71 mm were assumed. Bit A was the ordinary impregnateddiamond bit. Weak abrasive resistance of bit matrix, low diamondconcentration of 20 vol.%, and fine-grained diamond of 50/60 USmesh were employed for normal diamond protrusion. Bit B wasthe new composite impregnated diamond bit designed in thisstudy. The area ratio of the SDI cutters to the bit bottom face was50%. The diamond concentration of the SDI cutters was 25 vol.%,with 40/45 US mesh content of 17.5 vol.% and 50/60 US mesh con-tent of 7.5 vol.%. The density of the diamond grits was 3.52 g/cm3.The average grit size of the 40/45 and the 50/60 US mesh was 408and 289 μm. If the work layer height of the two bits is 6 mm andnumber of waterways is 10 with a gauge of 10.25 mm × 8 mm,then the annular area of the bit bottom face is
S1 ¼ π D2−d2� �
=4−n � δb ð1Þ
where S1 is the annular area of the bit bottom face, mm2; D is theoutside diameter of bit, mm; d is the inside diameter of bit, mm; nis the number of waterways; δ is the width of bit work layer, mm;and b is the width of waterway, mm.
If D is 91.5 mm, d is 71 mm, n is 10, δ is 10.25, and b is 8 mm, thenthe annular area of bit bottom S1 is 1796 mm2.
The total number of the diamond grits within bit A is
NA ¼ 6S1hcA=πd350=60 ð2Þ
whereNA is the total number of 50/60 USmesh diamond grits within bitA; h is the height of the bit work layer, mm; cA is the diamond volume
Design of new
composite
impregnated
diamond bit
Rock abrasiveness
Abrasive resistanc
Rock hardness Required bit load
Abrasive resistanc
SDI cutters
Fig. 5. Itinerary map showing the coordination bet
concentration of bit A, %; and d50/60 is the average grit size of 50/60 USmesh.
If h is 6 mm, cA is 20%, and d50/60 is 0.289 mm, then the total numberof diamond grits embedded in the work layer of bit A is 170528, with atotal mass of 7.59 g.
The total number of diamond grits embedded in bit B (i.e., SDIcutters) is
NA ¼ 6S1hcP=πð Þ= cB1=d340=45 þ cB2=d
350=60
� �ð3Þ
where cP is the area ratio of the SDI cutters to the bit bottom face, %;cB1 is the diamond volume concentration of 40/45 US mesh in bit B,%; cB2 is the diamond volume concentration of 50/60 US mesh in bitB, %; and d40/45 is the average grit size of 40/45 US mesh, mm.
If cP is 50%, cB1 is 17.5%, cB2 is 7.5%, and d40/45 is 0.408 mm, then thetotal number of diamond grits embedded in bit B is 58,489, with a totalmass of 4.74 g. The 40/45 USmesh diamond grits had a total number of26,515, with a total mass of 3.32 g, whereas the 50/60 US mesh dia-mond grits had a total number of 31,974, with a total mass of 1.42 g.
If the diamond grits were dispersed uniformly within the bit worklayer, then the total number of diamond grits on the bit bottom facethat participated in rock cutting can be counted. The total numbers ofbit A and bit B were counted using Eqs. (4) and (5).
nA ¼ NA= S1hð Þð Þ2=3 � S1ζ ð4Þ
nB ¼ NB= S1cPhð Þð Þ2=3 � S1cPζ ð5Þ
where ζ is the ratio of diamond grits on the bit bottom face that partic-ipated in the cutting operation. This ratio is caused by the heterogeneous
e of support body
Area ratio of SDI cutters
to support bodyDrilling capacity
e of
Matrix formula of support body
Diamond parameters
Matrix formula of SDI cutters
ween bit design method and rock properties.
Fig. 6. Photomicrograph of the field test rock formation showing the shape, color, content,and especially the extra small size of various grains.
191S. Tan et al. / Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186–192
diamond protrusion, with a value ranging from 1/2 to 1/3. When mixedmeshes were employed, ζ was 1/3 [25].
If ζ is 1/2 for bit A and 1/3 for bit B and the numbers of NA and NB aresubstituted into Eqs. (4) and (5), then the number of diamond grits thatparticipated in the cutting operation of bit A is 5660, whereas that of bitB is 1468.
The recommended bit load for the ordinary impregnated diamondbit with a diameter of Φ91 mm should range from 8 kN to 15 kN [24].The drilled crystal tuff was classified as extra-hard rock formation;thus themaximum bit load was employed. The load on each single dia-mond of two bits participating in the cutting operation can be respec-tively counted using Eqs. (6) and (7).
PA ¼ P=nA ¼ 15;000=5;660 ¼ 2:65 N=gritð Þ ð6Þ
PB ¼ P=nB ¼ 15;000=1;468≈10:22 N=gritð Þ ð7Þ
k ¼ PB=PA≈3:86 ð8Þ
where P is the total bit load (15 kN in this study); PA is the load on eachsingle diamond of bit A that participated in the cutting operation(2.65 N); PB is the load on each single diamond of bit B that participatedin the cutting operation (10.22 N), and k is the ratio of PB to PA.
A greater load on each single diamond corresponds to a deeper pen-etration of the rock formation by the diamond. Eq. (8) indicated that theload on a single diamond of bit B was 3.86 times that of bit A; such rela-tionship is similar to the ROP relationship between the two bits. Theabovementioned theoretical calculation quantitatively proves that thenew composite impregnated diamond bit is better than the ordinaryimpregnated diamond bit.
In addition, the totalmass required for bit Awas7.59 g,whereas thatfor bit B was 4.74 g; thus, the product cost can be reduced by 37.55%from the usage of diamond.
Table 5Mineral composition of the applied crystal tuff.
Composition Volumetric content (%) Particle size (mm)
Hemicrystalline and tuffaceous 80 b0.02Microcline 5 0.1Allomorphic orthoclase 4 0.6Hypidiomorphic plagioclase 5 0.9 to 1Limestone lithic 3 1 to 2Fine-grained diorite lithic 3 3
4. Conclusions
In this study, laboratory drilling test in granite and field drilling ap-plication in crystal tuff were conducted. Test results indicated that thediamond parameters, metal matrix formula, bit structure, manufactur-ing technology, and drilling parameters were all significant factors inachieving efficiency drilling for extra-hard, compact, and nonabrasiverock formations. The following conclusions were drawn afterconducting the experiments and analyzing the results.
1. Laboratory drilling test indicated that high sintering temperature,high pressure, and long retention time can improve the abrasive re-sistance of the bit support body, impede diamond protrusion, and de-crease ROP remarkably. Higher rotation speed or greater bit loadshould be employed to increase wear of the support body and to en-sure that bit load is focused on SDI cutters.
2. The abrasive resistance was significantly proportional to the arearatio of SDI cutters to bit bottom face. A small area ratio impelswear, causing an annular groove. Meanwhile, a large area ratio im-pedes wear, causing an annular wale. These phenomena are abnor-mal and would decrease bit service life.
3. The major advantage of the new composite impregnated diamondbit over the ordinary bit is that the structure of the new bit increasesthe load on each single diamond of the bit bottom face that partici-pated in the rock cutting operation. In addition, the new bit structurecan also minimize the consumption of diamonds.
4. Having a shorter service life is the main disadvantage of this newcomposite diamond bit. However, service life can be extended in fu-ture applications by increasing thebitwork layer height or regulatingthe area ratio of the SDI cutters to the bit bottom face.
Acknowledgments
The authors gratefully acknowledge theNational Scientific Foundationof China (NSFC; contract no. 50904052) for the financial support and theLaboratory Open Foundation of China University of Geosciences (Wuhan;contract no. SKJ2011084). Also, the authors wish to thank Mr. XiaosongChen and Dr. Wenjiao Zhang (China University of Geosciences, Wuhan)for their assistance and discussion on laboratory drilling test.
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