EFFECT OF CUTTING PARAMETERS ON TEMPERATURE OF A SINGLE POLYCRYSTALLINE DIAMOND COMPACT (PDC) CUTTER
H. Abdullah and M.A. Maoinser
Department of Petroleum Engineering, Universiti Teknologi PETRONAS, Malaysia Email: [email protected]
ABSTRACT
The usage of polycrystalline diamond compact (PDC) drill bit has significantly increased in the petroleum industry due to its high rate of penetration and long life. However, it is becoming increasingly difficult to ignore the temperature effect to PDC bit, specifically its cutter during the drilling operation. The temperature causes the degradation of the PDC cutter by reducing its lifespan. A thorough understanding of factors that affect the temperature of a PDC cutter is crucial in predicting the optimum cutting parameters. Hence, the objective of this study is to evaluate the effect of cutting parameters on the temperature of a single PDC cutter in rock cutting. In this study, a rock cutting experiment by using a lathe machine tested on a single PDC cutter. The parameters involved rotational speed and depth of cut. The temperature was measured using an infrared thermographic camera, FLIR T640 and the spot measurement to pinpoint the temperature readings at the tooltip of PDC cutter. As a result, the depth of cut had more significant influence on the temperature when measured over a range of 16 levels as the temperature increases in a linear trend with increasing depth of cut as well as the high correlation of the plot (R2=0.98). However, tests for rotational speed showed less significant influence on the temperature when measured over a range of four levels where the percentage of error of the temperature for each rotational speed was less than 10%. To conclude, only the depth of cut has a significant effect on the temperature of a single PDC cutter.
Keywords: Rock cutting, temperature, Polycrystalline Diamond Compact (PDC), rotational speed, depth of cut
INTRODUCTION
Polycrystalline diamond compact (PDC) drill bit has been extensively used in drilling operations due to its high rate of penetration and long life than another type of bit [1]. The requirement to extend the bit of life has drawn significant attention to producing economical and efficient drilling operations in the oil and gas industry. Various studies have been conducted on PDC bit performance by using different means such as whole PDC bit studies using field data, simulation studies and laboratory experiments. These studies were conducted to analyse and increase the understanding of bit performance which was typically in terms of temperature, forces and wear.
The previous study conducted has focused more on a single PDC cutter experiment [2]-[6]. The main advantage of single PDC cutter-rock interaction study is that the complex cutting condition during drilling operation will be overcome such as uncontrolled variables discovered in whole bit studies will be eradicated and grant a direct measurement of single PDC bit performance [4]. Moreover, mechanisms of rock cutting can be efficiently understood in single PDC cutter rock interaction which will help the bit designer in designing the optimum drill bit design for a certain drilling application [7]. Analysing the geometrical performance of PDC bit resulted in lower cost through a single PDC cutter rock interaction method [4].
In single PDC cutter rock interaction, it is observed that the temperature has a direct effect on the bit performance as it wears down the cutter during rock cutting [8]. Glowka and Stone [9]-[10] observed that the cutter starts to wear at 750ºC due to frictional heating. This will cause the cutter to lose its diamond layer and reduce its capabilities to excavate the rock. Several researchers [4], [10]-[13] have also studied the temperature at the diamond layer and tungsten carbide substrate (WC-Co) substrate to find an appropriate solution for better PDC cutter performance. Hence, it is the objective of this study to analyze the effects of various parameters such as rotational speed and depth of cut on the temperature at the interface of the single PDC cutter during rock cutting. The temperature responses were evaluated after conducting rock cutting experiment using lathe facing operation.
Diamond layer
Tungsten carbide substrate (WC-Co)
Figure 1 PDC cutter
Figure 2 Indiana limestone rock cylinder MATERIALS
As shown in Figure 1, the PDC cutter with a diameter of 13.44 mm provided by Glynn Technical Diamonds Ltd, has a 2 mm diamond layer thickness attached to a 6 mm tungsten-carbide (WC) stud. The rock samples used were Indiana limestones rock cylinder with 101.6 mm diameter and 101.6 mm height provided by Kocurek Industries Inc., as shown in Figure 2.
Limestone is a homogeneous carbonate formation that has 2-4 mD permeability and porosity of 12-14%.
Almost 60% of oil and 40% of gas in the whole world are extracted from the carbonate reservoir [14]. It is the advantage of the study in analysing the cutting mechanisms on a rock using limestone.
EXPERIMENTAL SETUP
The cutting operation of limestone rock using a single PDC cutter was conducted using a heavy-duty lathe machine with a maximum rotational speed of 1000 rpm. Limestone rock samples were clamped at the three-jaw chuck, and polycrystalline diamond compact (PDC) cutter was positioned at the rock’s face diameter using a custom tool holder (Figure 3).
The study employed the face turning operation where the cutter cuts the rock along its face diameter until it reaches the centre of the sample [15]. The cutting experiments were conducted in a dry condition at ambient temperature. Rotational speed and depth of cut varied at 4 and 16 levels were selected as shown in Table 1. For each combination between rotational speed and depth of cut, the experiments were repeated three times to increase the accuracy and minimise errors.
Table 1 Cutting speed and depth of cut used in rock cutting experiment
Rotational Speed (rpm) 355, 500, 710, 1000
Depth of Cut (mm) 0.254, 0.508, 0.762, 1.016, 1.270, 1.524, 1.778, 2.032, 2.286, 2.540, 2.794, 3.048, 3.302, 3.556, 3.810, 4.064
Figure 3 Experimental setup of single PDC cutter rock interaction
These factors were varied at 4 and 16 levels, as shown in Table 1, based on the existing literature [3], [5], [6], [16]-[18]. The rotational speed was limited to four levels as these values are relevant to the field drilling operation [19]. A large range of depth of cut was chosen to analyse the effect of depth of cut to the temperature of PDC cutter. These values were scattered in the previous study [13], [20] and no significant interconnection between the depth of cut and the temperature has been conducted. Thus, it is necessary to combine all these values in this study, and the results were analysed.
The temperature of the PDC cutter was measured by using FLIR T640 thermal imaging camera with an image resolution of 640 x 480 pixels and field of view 15º x 11º. This camera can measure the temperature ranging from -40ºC to 2000ºC with an accuracy of
±2ºC. The camera is placed at the distance of 30 cm
to the cutter-rock interface by using a unique stand and covered by a transparent acrylic box preventing from rock’s chip damaging the equipment, as shown in Figure 4.
Figure 4 FLIR T640 thermal imaging camera used to measure the temperature of PDC cutter during rock cutting
Figure 5 Temperature measurement using FLIR software The camera lens is focused at the tooltip of PDC
cutter through built-in unique spot measurement, and the full-colour infrared image represents the cutter temperature, as shown in Figure 5. The FLIR interface shows three different temperatures, such
as temperature at the PDC cutter rock interaction, maximum and minimum temperature of the surrounding area of the experimental setup. Thus, the temperature measured at the PDC cutter rock
interaction, i.e. 65.5ºC as shown in Figure 5 was recorded in this study. The emissivity value of 0.63 was set at the camera feature to measure the thermographic surface of the PDC cutter, as suggested by Siegal et al. [21].
EXPERIMENTAL RESULTS AND DISCUSSION The temperature variation with respect to the time shown in Figure 6 explains the mechanism of cutter- rock interaction of this study. It was observed that the temperature plot is classified into four phases.
In Phase 1, as the cutter starts to cut the rock, the temperature starts to increase from the ambient temperature of 26°C to almost 44°C in 30 seconds.
Then, the temperature is consistent for 15 seconds in the second phase, followed by a gradual decrease at approximately 10 seconds in Phase 3. In Phase 4, the temperature starts to maintain at around 28°C before the cutter stops cutting the rock and reach the ambient temperature. In this study, the temperature measured at Phase 2 was recorded to evaluate the effect of rotational speed and depth of cut on the temperature of a single PDC cutter. The rock mass is reduced when the cutter cut towards the centre of the rock. Hence, it is believed that the decrease in mass of rock contributes to the decline in the temperature of the PDC cutter. Overall, one successful run takes about 160-180 seconds. It is also observed that the temperature versus time of the other experimental procedure conducted in this study has the same trend as in Figure 6.
Figure 6 Variation of temperature with time for Test 1
Effect of Rotational Speed on Temperature
A series of tests were conducted at a different rotational speed of 355, 500, 710 and 1000 rpm. Various rotational speeds were employed at a constant depth of cut, particularly at 0.254, 0.508 and 0.762 mm to observe the effect of rotational speed on the temperature response.
It was observed that the rotational speed has an insignificant effect on temperature at a constant depth of cut due to the brittle failure mode of rock (Figures 7,8 and 9) [15]. Thus, only three different depth of cut was used for this analysis. The results are also in agreement with the study conducted by Wilson & Vorono [20].
Effect of Depth of Cut on Temperature
In studying the effect of depth of cut on temperature, the rotational speed was kept constant at 710 rpm due to the insignificant effect of this parameter on temperature and the value falls within the range employed by the industry for drilling operation [19]-[20]. Figure 10 shows that the temperature increases linearly with increasing depth of cut due to larger expose area of the cutter that may impose a higher temperature and increase the friction between the cutter rock interaction [3]. The results obtained from this experiment is in parallel with the study conducted by [20], [22]. It is also observed that high R2 is obtained and almost equivalent to the previous study [3], [6].
Rotational Speed (rpm) Temperature (oC)
Figure 7 The temperature measurement with the different rotational speed at 0.256 mm depth of cut
Rotational Speed (rpm) Temperature (oC)
Figure 8 The temperature measurement with the different rotational speed at 0.508 mm depth of cut
Temperature (oC)
Rotational Speed (rpm)
Figure 9 The temperature measurement with the different rotational speed at 0.762 mm depth of cut
Figure 10 The temperature measurement for different depth of cut at 710 rpm
CONCLUSİON
In conclusion, the rock cutting experiment was successfully conducted to measure the temperature of a single PDC cutter. The effect of rotational speed and depth of cut on the temperature of single PDC cutter in rock cutting experiment was obtained and analysed. It is clearly observed that the rotational speed has less influence on the temperature in the rock cutting process due to the brittleness properties of the rock.
On the other hand, the temperature increased linearly with increasing depth of cut from 0.254 mm to 4.064 mm at the rotational speed of 710 rpm. As the depth of cut increases, the bigger the area of the rock sample needs to be cut. Hence, the friction between the PDC cutter and the rock sample increase and caused the temperature to increase. In the future, it is recommended that the other parameters such as rake angles, cutter material density and chamfer geometry be considered to study the most influential parameters in the rock cutting. It is also suggested that the influence of the various type of rocks on temperature needs to be included in a future study. Furthermore, it is advisable to include the study of wellbore temperature effect on PDC cutter
performance since the real operation involves drilling in deeper formation which has high temperature and high-pressure environment.
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