Experimental study of rock-breaking with an offset single cone bit

Petroleum Science, May 2008

An experimental study of rock-breaking with an offset single cone bit was completed on the bit bench test equipment. Data such as transmission ratio, weight on bit (WOB), rate of penetration (ROP) and torque on bit were acquired in the experiments. Based on analyzing the experimental results, several conclusions were drawn as follows. The transmission ratio of the offset single-cone bit changed slightly with rotary speed of bit, weight on bit and offset distance. The rate of penetration of the offset single-cone bit increased with increase of WOB and offset distance. The torque on bit increased with increase of offset distance under the same WOB and bit rotary speed, decreased with increase of bit rotary speed under the same WOB. The rock-breaking mechanism of the offset single-cone bit was a scraping action. This indicates that the offset single-cone bit is a chipping type bit.

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Experimental study of rock-breaking with an offset single cone bit

Pet.Sci. Experimental study of rock-breaking with an offset single cone bit 0 School of Mechanical and Electronic Engineering, China University of Petroleum , Beijing 102249 , China An experimental study of rock-breaking with an offset single cone bit was completed on the bit bench test equipment. Data such as transmission ratio, weight on bit (WOB), rate of penetration (ROP) and torque on bit were acquired in the experiments. Based on analyzing the experimental results, several conclusions were drawn as follows. The transmission ratio of the offset single-cone bit changed slightly with rotary speed of bit, weight on bit and offset distance. The rate of penetration of the offset singlecone bit increased with increase of WOB and offset distance. The torque on bit increased with increase of offset distance under the same WOB and bit rotary speed, decreased with increase of bit rotary speed under the same WOB. The rock-breaking mechanism of the offset single-cone bit was a scraping action. This indicates that the offset single-cone bit is a chipping type bit. Offset single-cone bit; transmission ratio; rate of penetration; torque on bit 1 Introduction In order to accelerate the exploration and development of China’s oil and gas resources, especially the deep offshore reservoirs and complex reservoirs, it is necessary to develop new drilling technology and equipment. Since the 1990s, the slim hole drilling technology is the focus of research for new drilling technology, the development of a new type of bit is the key to slim hole drilling technology (Fletcher, 2003; Langford Jr, 1999; Li and Tan, 2000; Qiu, 2000; Wu and Liu, 2000; Yu et al, 1994) . Compared with conventional single-cone bit (with no offset), the offset single-cone bit has new structural characteristics, providing more selections of bit types for modern slim hole drilling (Deng et al, 2001; Ma et al, 2004; Moran and Witman, 2004; Witman et al, 2006; Xia et al, 2002; Yu and Yu, 2007) . However, the rock-breaking mechanism and drilling characteristics of the offset singlecone bit are still issues to be studied. The transmission ratio (i.e. the ratio of cone rotary speed to bit rotary speed) is a key parameter for bit design, which is essential to analyzing the trajectory of teeth on the cone. Therefore, it is a vital parameter for the design of cutting structure (Yu et al, 1995) . In general, transmission ratio for offset single-cone bit under practical conditions cannot be obtained from theoretical study, so the effect of offset distance on transmission ratio can be obtained only through bench tests. Compared with conventional single-cone bit, the offset single-cone bit is characterized by an asymmetrical structure, so the rate of penetration (ROP), torque and rock-breaking characteristics must be investigated experimentally through bench tests. At the same time, the bottom hole tracks crushed or cut by offset single-cone bits can also be analyzed. 2 Experimental apparatus and procedures The experiment was performed on bit bench test equipment, developed by Southwest Petroleum University. Fig. 1 shows its schematic diagram. The offset single-cone bit used is shown in Fig. 2. The bit bench test equipment is composed of a threephase silicon-controlled recti er control box 1, direct current electromotor 2, gear box 3, lower rotary table 4, sensors 7 and 8, joint 9, measuring joint 10, hydraulic cylinder 11, centralizer 12, upper rotary table 13, kelly bar 14, balance beam 15, and a swivel 16. During testing, the upper rotary table 13 was locked by pin and was stationary. The lower rotary table 4, on which the rock 5 was held by a clamping device, was driven by a direct current electromotor 2 through gearing. The rotational speed of the electromotor was adjusted by a three-phase siliconcontrolled rectifier. Then the bit could rotate relative to the rotary table. The hydraulic cylinder 11 could provide the given weight on bit (WOB) and control the vertical movement of bit. Sensors 7 and 8 were installed to monitor rotary speed of the bit and cone. WOB and torque were measured by resistance strain gauges on the measuring joint, and the linear strain was then converted into voltage signals with dynamic strain gauges. 3 Analysis of the experimental results Four single-cone bits with offset distances, d, of 0, 3.2, 5.8, 3 4 5 6 7 1-Silicon-controlled rectifier control box; 2-Direct current electromotor; 3-Gear box; 4-Lower rotary table; 5-Rock; 6-Single-cone bit; 7, 8-Sensor; 9-Joint; 10-Measuring joint; 11-Hydraulic cylinder; 12-Centralizer; 13-Upper rotary table; 14-Kelly bar; 15-Balance beam; 16-Swivel 9.0 mm, were tested respectively. The journal angles of these bits used were 40o, and their diameters were 152.4 mm. The rock sample was limestone. 3.1 Measured signals of WOB, torque on bit and bit rotary speed 60 rpm and 2 tonnes respectively. As shown in Fig. 3, the actual acquired signal of WOB had similar tendency with that of (...truncated)


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Yinghua Chen. Experimental study of rock-breaking with an offset single cone bit, Petroleum Science, 2008, pp. 179-182, Volume 5, Issue 2, DOI: 10.1007/s12182-008-0028-y