57, PR Ch
Keywords:Metal-bonded diamond toolsHard rock drillingSintered diamond-impregnated cutterStructural design
te impregnated diamond bit was designed to solve the slipping problem when im-
Drilling is the most important operation for mining and prospecting the bit matrix.
e bottom of the well,to treat the bit bottomshallowwells; other-
e probability of drilling
Int. Journal of Refractory Metals and Hard Materials 43 (2014) 186192
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Int. Journal of Refractory M
l seare 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 compact
accidents would increase, and a number of unnecessary difculties andlosses may occur.
Numerous studies were conducted to address the difculties in hard. (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 grains
dry condition drilling, putting quartz sand at thhammering the bit bottom face, and using acidface. However, thesemethods can only be used inwise, the drilling efciency would be affected, thindustries. 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
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 nish. Severalmethods have been employed in eld drilling applications to addressthis issue . These methods include grinding the bit matrix understructure. (3) Rock abrasiveness is weak. The
Corresponding author at: No. 1 Drilling Engineering CRoad, Dagang Oileld, Binghai New District, Tianjin 3025924006.
E-mail addresses:email@example.com (S. Tan)firstname.lastname@example.org (K. Yang), email@example.com (L
0263-4368/$ see front matter 2013 Elsevier Ltd. All rihttp://dx.doi.org/10.1016/j.ijrmhm.2013.11.001(ROP) results in small rock debris. Therefore, the debris abrasivenessto the bit matrix is limited, and diamonds do not easily emerge from1. Introductionof 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 efciency. The design parameters and manufacturingtechnology of the new composite impregnated diamond bit were analyzed to achieve the desired performance.Two41/27 mm laboratorial bits weremanufactured to conduct a laboratory drilling test on the rock specimensof ne-grainedmonzonitic granite rich in biotite. The laboratory drilling test indicated that both themanufactur-ing technology and the drilling parameters signicantly 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 91.5/71 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.Received 29 July 2013Accepted 7 November 2013
pregnateddiamondbit is used for extra-hard, compact, and nonabrasive rock formation. The newbit is composed
Article history: In this study, a new composiA new composite impregnated diamond binonabrasive rock formation
Songcheng Tan a,b,c,, Xiaohong Fang a, Kaihua Yang 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 3004c Post Doctoral Research Center, Southwest Petroleum University, Chengdu, Sichuan 610500, P
a b s t r a c ta r t i c l e i n f o
j ourna l homepage: www.elow rate of penetration
ompany, BHDC. No. 128 Hongqi0280, PR China. Tel.: +86 022
, firstname.lastname@example.org (X. Fang),. Duan).
ghts reserved.or extra-hard, compact, and
ngchen Duan a
etals and Hard Materials
v ie r .com/ locate / IJRMHMrock 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 . 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
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 . 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 sufciently 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 1Diamond grit parameters and concentration.
Grit size(US mesh)
Thermal toughnessindex (%)
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) 186192and efciency of rotarypercussive drilling assisted by water jets forvery hard rocks . 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 . Nonionic polymer was added to the ushingmedia to enhance the diamond drilling performance on phosphaterock . Particle impact drilling was experimentally studied for deepwell hard formation . Gao  designed a bionic coupling impregnateddiamond bit specically 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 drillingdifculties 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
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 . 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 .
In terms of diamond parameters, high quality and strength are usu-ally required; however, the required particle size remains debatable. Ye 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 benets 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 , 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 congurationof 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  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 toolproperty improvement . 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, difculties 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-
Fig. 1. Conguration of the new composite impregnated diamond bit to illustrate the cut-ting structure for slipping formation.
Phosphorus decreases the melting point of the CuFe alloy  andthe sintering temperature of the diamond bit matrix . Thus, theoverall component of iron powder consisted of FeP 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
Table 2Manufacture technologies and gauges of new composite impregnated diamond bit for laboratory drilling tests.
Item Matrix formula Specication 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 41/27 850 4 18Supporting body (bit #2) Fe48(663Cu)32Co2Ni15Mn3 41/27 830 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) 186192The 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, densication 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 performed hot-pressing experiments and found that the CuFe alloyachieves the best bond strength and ductility under sintering tempera-tures between 820 C and 900 C. Xie  indicated that the FeCoCualloy 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 newFig. 2. The overall bit mounting of SDI cutters, support body, and bit blank body.composite diamond bit is efcient 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 diamete...