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Procedia Engineering 73 ( 2014 ) 134 – 142

1877-7058 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of Geological Engineering Drilling Technologydoi: 10.1016/j.proeng.2014.06.181

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Geological Engineering Drilling Technology Conference (IGEDTC), New International Convention Exposition Center Chengdu Century City on 23rd-25th May 2014

Design & Application of Diamond Bit to Drilling Hard Rock in Deep Borehole

Jia Meiling a,* , Cai Jiapina, Ouyang Zhiyonga, Shen Linaa, Wu Haixiaa, Li Chuna a. Beijing Institute of Exploration Engineering, 100083, Beijing, China

Abstract

Aiming to the drilling characteristics of hard rock in deep borehole, a new kind of impregnated diamond bit was redesigned from structure, matrix formula, parameters of diamond and etc. in the paper. According to the design, the new long life impregnated diamond bit was developed, which could significantly improve drilling efficiency and reduce drilling construction cost in deep borehole. Compared with the conventional bit, the lifetime of the new diamond bit increased by over 1.5 times, and its drilling rate was improved by over 20%. With the new bit, the drilling efficiency in deep borehole hard rock could be improved immensely. © 2014 The Authors. Published by Elsevier Ltd. Selection and peer-review under responsibility of Geological Engineering Drilling Technology.

Key words: Hard Rock; Diamond Bit; Bit Life; Deep Hole

1. Introduction

With the exploration drilling towards deep direction continuously, the complexity of drilling stratum is increasing, especially the extra-hard and weak-abrasive stratum. There are lots of studies suggesting that, with the increasing of borehole depth, the rock compactness in the deep borehole would be increasing under the pressure of overlying strata, not only the rock density and hardness will be increased, but also the rock should has the tendency transforming from brittle to plastic compact rock. Meanwhile, the forming-rock minerals of the strata are hard (with high content of quartz), and have small granularity and high cementation strength (generally siliceous cement). With

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© 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).Selection and peer-review under responsibility of Geological Engineering Drilling Technology

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135 Jia Meiling et al. / Procedia Engineering 73 ( 2014 ) 134 – 142

the impregnated diamond bit, the drilling rate on these strata is too slow, and the drilling cuttings are fine and its number is few, meanwhile erosion and wear of the bit matrix is little, so the bit should be polished and slipping. In order to resume the bit drilling, some abrasive stones need to be put in the borehole which may cause the bit serious and abnormal wear.

The basic principle of diamond drilling is that the rock surface is consecutively broken using the exposed diamonds on bit lip surface under the axial pressure and rotational torque. The fragmentation process not only depends upon the drilling conditions, the physical and mechanical properties of rock, and but also is closely related to the properties of diamond bit.

The footage and duration of each drilling roundtrip should be as long as possible in the condition of drilling a deep borehole. The performance of diamond bit is one of the most important factors influencing the drilling efficiency, the quality of borehole and the cost of drilling. This paper pays attention to the drilling characteristic of hard rock in deep hole, focuses on rock samples in Wugang region of Henan Province and Chengde region of Hebei Province, analyzes the micro characteristic of mineral composition of rock samples and discusses its genesis. The rock drillability is classified by experimental results of indentation hardness, spring back number of pendulum ball and its plastic coefficient. The adaptability of the bit to the formation has been increased after optimal design of impregnated diamond bit.

2. Characteristics of Formation

2.1. Lithology Analysis

Wugang Region, Henan Province The hard rock formation in Wugang region belongs to metamorphic series, microscope analysis on the hard rock

showed that the mineral composition is given priority to with quartz, k-feldspar and plagioclase. The rock sample was a mixed biotite-mont-granulite, which had granoblastic texture with unequal grain size ranged from 0.3mm to 1mm (Fig. 1, Table 1). The sample was composed of original metamorphic rocks and new veins, and the new veins were k-feldspar veins and quartz veins within (or developed from) remelting or regeneration k-feldspar were aggregated crystal, and quartz was podiform. So, through a long-term diagenesis, the rock is very hard (Mohs Hardness 6~7 grade), which is a drilling handicap in this area.

(a) Photo of HENJSS-3 sample (b) Micrograph of HENJSS-3 sample Fig. 1 Photo and micrograph of rock sample in Wugang region, Henan Province

Table 1 Mineral composition and percentage of the HENJSS-3 sample

Mineral quartz k-feldspar plagioclase biotite muscovite metallic mineral

Content percentage (%) 40 35 20 4 - micro

Chengde Region, Hebei Province


a Photo of HEBCDKC-1 sample b Micrograph of HEBCDKC-1 sample Fig. 2 Photo and micrograph of rock sample in Chengde region, Hebei Province

The hard rock formations in Chengde area were quartzite, its microscope analysis showed that the main mineral was quartz (silica content more than 95%) with a small amount of feldspar, calcite and trace amounts of muscovite and iron. They were formed from metamorphic recrystallization of quartz-sandstone, which hassub-rounded granular with granularity ranged from 0.2 to 0.6 mm (Fig. 2, Table 2). Secondary enlargement structures could be found which indicates that the tight mosaic granoblastic texture was generated through secondary enlargement edges within the metamorphic recrystallization of cementing materials of original rocks. The samples were hard and compact with Mohs Hardness grade 7, which led to slipping and footage problem of bit. So, these kinds of formations were typical hard and slipping ones.

Table 2 Mineral composition and percentage of the HEBCDKC-1 sample

Mineral quartz k-feldspar calcite muscovite

Content percentage (%) 95 3 1 micro

2.2. Drillability Evaluation

The paper classified the drillability grade of rock with the main indexes of indentation hardness, the spring back number of pendulum ball and the plastic coefficient. The main characteristic parameters of the rock samples discussed above had been measured, and then the rock’s drillability grade was calculated through the formula 1, the results are shown in the Table 3.

K=3.1980+0.008854HY+0.02578Hn (1) Where:

K ——drillability grade; HY——indentation hardness (kg/mm2); Hn——the springback number of pendulum ball on a standard rock sample.

Table 3 Main indexes and drillability grade of the samples

Samples Indentation hardness (HY)

Resilience frequency of ball pendulum on standard diameter rock sample (Hn)

Drillability grade of sample

HeNJSS-3 453.2 57.5 9

HEBCDKC-1 610 67 10


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3.2.1 Application of Superfine Alloy Powder

The composition of superfine alloy powder is uniform. In order to observe the element distribution of pre-alloyed powder, designated phase analyses on the fine grains of alloy powder have been carried out. As the test results shown, there were various kinds of metal elements in the powder grains (Fig. 5).

(a) Micrograph of superfine alloy powder (b) Energy spectrum of superfine alloy powder Fig.5 Energy spectrum analysis results of superfine alloy powder

Sintering properties of the superfine alloy powder is high. The SEM morphology is shown in fig. 5 and Fig. 6, which is a larger version of particle. As shown in the SEM morphology, the grain sizes are in nanoscale, it has a large surface area and its density is high in low sintering temperature due to its open-structure (Fig. 7).

Fig. 6 SEM morphology of alloy powder Fig. 7 Sintered density curve of superfine alloy powder

3.2.2 Selection of Matrix Material with Good Performance

The matrix material used in hard rock drilling should have a good mechanical performance and little interaction with diamond. There are four basic principles should have been followed in the design.

Design matrix material with high elastic limitation and low plasticity, improve the retention to diamond Research results indicated that high elastic and low plastic matrix material could improve the holding force to

diamond largely. Plastic deformation of matrix material holding diamond is little, and diamonds don’t easily fall off. During drilling operations, the matrix holding diamonds is eventually formed tadpole-shape support. Exposed degree of diamonds is high, and the diamonds do not fall off from the matrix. The diamonds impregnated in matrix


could give full play to cutting action (Fig. 8a). On the contrary, the diamonds impregnated in matrix which material has high plasticity should fall apart early and could not drill continually (Fig. 8b).

(a) Matrix material with wrapped diamond (b) Matrix material with high plasticity Fig. 8 Matrix material types of diamond

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and uniform (Fig. 9). The matrix has a high impact toughness and uniform hardness in a wide range of sintering temperature (Fig. 10).

Fig. 9 Microstructure of matrix material Fig. 10 Sintered hardness curve of superfine alloy powder

Little influence to diamonds during sintering There are not chemical reactions between diamonds and matrix material at the sintered temperature. Diamonds in

the matrix section are still with bright yellow shine, and the graphitization is little, the diamonds could be kept to have a good cutting performance during the drilling process (Fig. 11).

Fig. 11 Crystal morphology of the diamond after sintering

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rate and its own quality. And that was one of the main factors during drilling in extra-hard and compact formations. Appropriate diamond concentration should be designed to make sure that there is enough pressure on a single diamond, and the diamond could be pressed in the hard rock.

Two diamond bits with different diamond concentrations have been produced, through stereomicroscope, the distribution and exposure characteristics of diamonds can be gotten and shown as in Fig. 14. The drilling efficiency of the bit in fig. 14a was higher, while the life of the bit in fig. 14b is longer. Experiments show that the most appropriate diamond concentration is 60%~80%, the optimal diamond granularity is 30/40 mesh.

(a) Bit with 60% diamond concentration (b) Bit with 80% diamond concentration Fig.14 Distribution and exposure characteristics of bits with different diamond concentration

4. Application Result of the Bit

Aiming at the extra-hard and compact formation, the diamond bits with high working layer had been designed and produced based on the principles motioned above, and then had been used in Benxi, Liaoning province, Wugang, Henan province, Dulan, Qinghai province and Chengde, Hebei province. The drilled rocks were silicated quartzite,


maganetite quartzite, biotite plagiogranite, granite porphyry and etc. The accumulated footages of diamond bits were 6542 m. Compared to the conventional bit, the drilling efficiency and life of the new bit were significantly improved by 30% 100%. Its application effect data are listed in the Table 5.

Table 5 Application effect data of diamond bits with high working layer

Drilling site Conventional bit Developed Increased percentage (%)

Average drilling rate (m/h)

Average life(m)

Average drilling rate (m/h)

Average life (m)

Average drilling rate Average life

Benxi, Liaoling Province 0.62 26.2 1.25 70.0 101.6 167.2

Dulan, Qinghai Province 1 24 1.3 80 18.2 233.3

Chengde, Hebei Province 0.8 20 1.2 75 50 275

Wugang, Henan Province 1 25 1.2 70 20 180

5. Conclusions

Applying the ultrafine alloy powder which had excellent mechanical properties and could obviously improve the holding force to diamonds, can reduce diamond’s graphitization degree, and then increase the bit’s breaking ability and life; Increasing the height of diamond bit’s working layer can improve its service life, and improve the drilling efficiency in hard rock deep hole; High grade diamonds should be adopted to produce diamond bit for drilling the extra-hard and weak-abrasive formation; With development of powder metallurgy technology and application of new materials, the height of a new diamond bit’s working layer could be one or a few times higher than the conventional bit, which will obviously improve the diamond bit’s lifetime.

References:

[1] Wang Da. Key techniques of deep hole drilling [J]. Exploration engineering, 2009, 37 (S1). [2] Zhang Li, Yang Kaihua. Progress of the research on diamond drilling bits for extro-hard, compact and weak-abrasion rock

formation[J].Diamond & abrasives engineering, 2003(01).