Experimental Investigation of Bit Vibration on Rotary Drilling Penetration Rate

Transcription

1 ARMA Experimental Investigation of Bit Vibration on Rotary Drilling Penetration Rate Heng Li, Stephen Butt, Katna Munaswamy, Farid Arvani. Memorial University of Newfoundland, St John s, NL, Canada Copyright 2010 ARMA, American Rock Mechanics Association This paper was prepared for presentation at the 44 th US Rock Mechanics Symposium and 5 th U.S.-Canada Rock Mechanics Symposium, held in Salt Lake City, UT June 27 30, This paper was selected for presentation at the symposium by an ARMA Technical Program Committee based on a technical and critical review of the paper by a minimum of two technical reviewers. The material, as presented, does not necessarily reflect any position of ARMA, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of ARMA is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgement of where and by whom the paper was presented. ABSTRACT: This investigation evaluated the influence of bit vibration on penetration rate for laboratory rotary core drilling. Laboratory core drill was modified and instrumented to drill under conditions of constant Weight on Bit (WOB) and varying levels of axial vibration amplitudes. Experiments were conducted at 300 RPM and 600 RPM with no vibration and with 60 Hz of vibration at amplitudes of 0.09, 0.29 and 0.44mm. Results show that for WOB less than the founder point, the rate of penetration (ROP) increases proportionally to the amplitude of the vibration. Some tests show that ROP increase is greater near the peak of the ROP-WOB curve. Further laboratory experiments and numerical simulations are planned to investigate this vibration assisted rotary drilling technology. 1. INTRODUCTION Rate of penetration (ROP) is a major factor affecting the overall drilling performance and field drilling operation cost. It is known that there are several factors affecting the performance of conventional rotary drilling e.g. WOB, bit rotary speed, hydraulic power and type of drilling fluid. Vibration drilling technology is believed to be greatly beneficial to the ROP advancement. Depending on the amplitude and frequencies, vibration drilling could be classified into many different mechanisms pure percussion drilling, rotary percussion drilling and sonic drillings. The most popular technology in this domain is the percussive drilling, which works at high amplitude and low frequency. It breaks the rock mainly by a specialized bit impact into the rock and causes both tensile and shear failure. Another mechanism called sonic drilling, represented by Sonic Drilling Ltd [1], resonates soil and shallow, soft formations by its ultra high frequency. Thus it could achieve a fast rate of penetration. However, these technologies have their own limitations. The down hole percussive drilling tools have compatibility issues with the existing circulation and well control systems; top hammer percussion tool has power transfer problems because the blow energy need to be transferred along the long drilling string. Sonic drilling technology is only suitable for soft and shallow formations and is rarely applied in the oil and gas drilling industry. Many investigations and publications are done for these two types of vibration drilling technologies. The earliest percussion drilling publications could trace back to the late 1940s. Guarin et al. [2] investigated the performance of specialized chisel and bottom bits for the percussive drilling applications. Pennington [3] in his report, gave an introduction to the concept of indexing angle, which is believed to be another important factor affecting the percussion drilling. He also tested the vibration drilling at a high frequency range up to 1400 Hz; this high frequency technology was then progressed to the applicable technology of sonic drilling [1]. Heartman [4] carried out some investigation to the parallel indexing distance; Yange [5] investigated the rock failure mechanism with single blow impact under confining pressure. Although most researchers have focused on the technology of percussive drilling, there could be possibilities for other types of vibration drilling tools with different mechanisms introduced in the oil and gas drilling industry. Ishikawa [6] has designed a combined frequency vibration drilling device for the purpose of 1

2 material fabrication; several benefits (high ROP, little deviation and reduced bit wear) were reported. The Advanced Drilling Group of the Faculty of Engineering, Memorial University has launched a research project called Vibration Assisted Rotary Drilling (VARD). The ultimate goal of this project is to develop a down hole vibration instrument which creates vibration near the bit. The vibration characteristic of this instrument will be investigated by both numerical simulations and laboratory scale experiments. Two laboratory scale experimental setups are planned for this purpose. The first setup, which is introduced in this publication, investigates the performance improvement with added vibration based on a rotary coring bit. This setup could not study the effect of the drill string; however it is capable of simulating the near bit vibration effect due to its vibration source position. 2. EXPERIMENTAL SETUP The laboratory scale experimental facility of the VARD project (Fig.1) is built up from a Milwaukee 4079 electrical powered coring drill rig. The rig has two rotary speeds (300 and 600 RPM). The drill and motor assembly travels along a rail guide. A wheel with hanged weight at side is mounted instead of the original handle bar as the source of constant weight on bit (WOB). An electromechanical axial shaker is mounted at the bottom of the drill stand as the vibration source. Several clamps hold the shaker (Fig.2) and wooden blocks isolate the vibration from the drill stand. The rig is mounted with a 2-inch diamond coring bit. Several other type of bits (flat bottom bit, full face diamond impregnated bit) are planned to be used as well, however these experiments are going to be reported in later publications. After the VARD experimental set up assembly was completed, a set of drilling experiments based on low strength cemented sand samples was conducted to investigate the rate of penetration (ROP) as a function of WOB and rotary speed. The results are plotted in fig.3, which show patterns typical for conventional rotary drilling [7]. Vibration characteristic of the shaker table is monitored using a group of accelerometers. These sensors detected the fact that the shaker works at a constant vibration frequency of 60Hz. A knob controls the shaker s vibration amplitude. An LVDT is mounted on the shaker to characterize the amplitude at different knob positions. During the vibration assisted drilling test, the vibration amplitude fluctuates in a small range with the change of WOB (shaker load). However the most determinant factor to the amplitude is the shaker controller s knob position. For example, at shaker knob dial position 10 it reaches average amplitude of 0.09 mm (varies from mm), position 30 has 0.29 mm (varies from mm), and position 50 has 0.44 mm (varies from mm). Fig.4 shows the signal collected from LVDT at zero load with 3 levels of shaker controller knob positions. The amplitude with no load is found to be smaller than the amplitude under loaded condition (while drilling). This is due to increased inertia brought by the loaded mass. The magnitude of off-axial shaker vibration was also analyzed. The measurements were done by an accelerometer, which has been mounted in three directions. It is found that the acceleration brought by the vibration in lateral directions have a maximum ratio of 4.04% to the main direction of vibration. Fig.1 VARD laboratory scale experimental setup 2

3 Rate of Penetration (cm/min) Displacement (mm) \ Fig.2 Vibration shaker modified with the sample bracket fixed on the vibrating table. Except the LVDT and accelerometers, several other type of sensors were used in the VARD experimental assembly. A rotary encoder is fixed with the drill bit and travels along the rig frame, which provides accurate displacement readings for the bit. It examines the consistency of the ROP during drilling. A digital tachometer is placed near the drill shaft and measures the rotary speed WOB (N) Fig.3 Result from conventional rotary drilling shows ROP as a function of RPM and WOB Time (s) Fig.4 Voltage signals collected from LVDT showing variable vibration amplitudes at a fixed frequency. 3. SAMPLE PREPARATION The long term plan for laboratory VARD experiments includes a wide range of rock strengths (ranging from 10 MPa to 100 MPa). This publication focuses on samples prepared using a commercial quick-setting concrete sieved to remove the aggregates larger than 2.36 mm, then casted into 6-inch diameter cylindrical molds. The drilling tests were done at the seventh day after casting where UCS tests following ASTM D indicate a material strength of 20 MPa. 4. EXPERIMENTAL PROCEDURE AND RESULTS The VARD experimental facility is designed with the capacity of varying several rotary drilling and vibration parameters (multiple levels of vibration amplitude and WOBs, two levels of rotary speeds), while keeping the vibration frequency and drilling fluid flow rate constant. Water was used as the drilling fluid. The bit type was kept the same during the experiment. Bit wear factor was analyzed while the experiment is underway and will be published in another publication. The first set of VARD experiments was conducted at 300 RPM rotary speed. The flow was adjusted to a sufficient level for the bottom hole cleaning and kept constant during the experiment. The experiment began with conventional rotary drilling with no vibration, followed by vibration assisted drilling with three levels of amplitude. The experiment was designed so that 5-6 runs with different WOB are done for each level of vibration and rotary speed. For a fixed combination of rotary speed and vibration amplitude, the WOB was 3

4 progressively increased until a clear reduction of ROP was obtained. The remaining tests were then concentrated in the range of WOB observed at the founder point (defined as the WOB at the maximum ROP under certain drilling condition) to locate the peak value of ROP. Based on the results of 300 RPM experiments, the next set of experiments with 600 RPM were redesigned with a different set of WOBs and only two levels of vibration amplitudes to provide a better resolution of WOB near founder point. The level of vibration amplitude was reduced to two (0.09 and 0.29 mm) instead of three in order to protecting the motor bearings. Due to the increment of ROP at 600 RPM, the flow rate is also increased to provide sufficient bottom hole cleaning. The results of 300 RPM and 600 RPM tests are shown in Fig.5. The shape of the ROP-WOB curve obtained from the 600 RPM tests has some difference in shape compared with the 300 RPM a rapid increase in the ROP near the founder point is observed in all three curves. One of the reasons is due to the increased number of tests conducted near the founder point. For the ROP-WOB curve at 300 RPM, 15 mm vibration, this rapid increment near the peak is observed as well. This suggests that for the 300 RPM test this may be as well the nature of the curve, even though, the rapid changes near the peak of the 600 RPM curves are much steeper than the 300 RPM curves. This may be due to the variations in the drilling fluid flow rates, which were observed during the experiments. In future experiments a flow meter and a pressure gauge will be used to monitor and control flow conditions. For WOB less than the founder point, the ROP is nearly proportional to rotary speed. The two levels of vibration assisted drilling however, varied greatly with their founder bit weight. The maximum penetration rate appeared at N and N for 0.1mm and 0.29mm of vibration at 300 RPM, while for 600 RPM it reduced to N and N respectively. It is also shown in Fig.5 that the maximum ROP for each ROP- WOB curve does not increase linearly with increasing amplitude. Both the 300 and 600 RPM experimental results suggest that at their highest vibration amplitude (0.44 mm and 0.29 mm separately), the curve is obviously compressed both the incline and decline portion are becoming sharper and steeper; it is also observed that the peak of ROP-WOB curves for both Fig.5 Experimental results of vibration assisted rotary drilling at 300 and 600 RPM, 2-3 levels of vibration amplitude. 4

5 sets of rotary speeds at the high vibration level is lower than the mid-level vibration ROP-WOB curves. This suggests that the drilling performance does not increase linearly with the vibration amplitude and an optimal level for vibration amplitude might exist under different levels of rotary speeds. Although the peaks of ROP-WOB curves under different vibration amplitude in Fig.5 do not increase linearly with vibration amplitude, the ROP increment at a low level of bit weight is obvious. Fig.6 re-plots the data of ROP vs. the vibration amplitude at N bit weight and 300 RPM. A linear trend can be observed from Fig.6; compared to the non-vibration drilling, more than 100% ROP increase to the rotary drilling is obtained at maximum amplitude. Fig.6 ROP increase with the vibration amplitude at fixed WOB and rotary speed. 5. PROSPECT AND CONCLUSION The VARD experimental system was designed to investigate the vibration assisted rotary drilling at a limited range of amplitudes for 60Hz vibration. It was found that VARD technology can provide a significant increase in ROP at low levels of WOB. With increasing WOB, a curve which is similar to those in conventional drilling could be obtained. Higher ROP is achieved with increase in WOB, rotary speed and vibration amplitude. However the slope near the founder point in ROP-WOB curves changes dramatically which is not normally observed for rotary drilling without vibration. Further investigation of this phenomenon is recommended for future research. The founder WOB decreases at higher levels of vibration and the maximum ROP increases at low levels of vibration. In summary, the conclusions are as follows: 1) ROP increases with increasing WOB up to a founder point where ROP decreases with further increase in WOB. This is the typical pattern observed in conventional rotary drilling. 2) ROP increases proportionally with increasing rotary speed. Again this is a widely observed pattern in rotary drilling. 3) ROP increases with increase in vibration amplitude. This increase is approximately linear until close to the peak ROP, where the rate of increase in ROP is noticeably higher. 4) There appears to be an optimal value of vibration amplitude at a given WOB and rotary speed, where ROP will decrease with higher vibration amplitude. These last points deserve further investigation. The studies in future based on the next phase of experimental assembly will give a better explanation to the phenomenon captured in this experiment. 6. FUTURE WORK Up to the date of this publication, a short term modification for the VARD experimental setup is underway. A flow meter and a pump is planned to provide a stable and controllable fluid source. A load cell and its adapter will be mounted between the motor and the drill string to track down the axial force during the vibration drilling. Bit wear investigation based on the same drilling condition is in progress. The wear will be analyzed by dimensional and geometric measurements and SEM analysis. An operation cost optimization model is planned based on the bit wear and ROP advancement. For a longer term prospect, an ultimate solution- Phase II experimental facility for the laboratory scale research of the VARD project is under intensive development. It is designed with a wide range of amplitude, adjustable frequency and multiple level of rotary speed. A pressure chamber is under development to simulate in-situ stresses, formation pore pressures and bottom hole pressure. 7. ACKNOWLEDGEMENT This investigation has been funded by the Atlantic Innovation Fund (contract no ), Industrial Research and Innovation Fund, Husky Energy and Suncor Energy. 5

6 8. REFERENCES 1. Resonant Sonic Drilling, prepared for U.S. DOE, April P.L. Guarin, H.E. Arnold, W.E. Harpst and E.E. Davis Rotary Percussion Drilling. Twenty-ninth Annual Meeting, Chicago, I John V. Pennington Some results of DRI Investigations- Rock Failure in Percussion. Thirtythird Annual Meeting of the Institute 4. H.L. Hartman The effectiveness of indexing in percussion and rotary drilling. Int. J. Rock. Min. Sci. Vol. 3.pp J.H. Yang, K.E. Gray Single-Blow Bit- Tooth Impact Tests on Saturated Rock Under Confining Pressure. SPE Ken-ichi Ishikawa, Hitoshi Suwabe, Tetsuhiro Nishide and Michio Uneda A study on combined vibration drilling by ultrasonic and low frequency. Process Engineering. 22: Adam T. Bourgoyne Jr., Keith K. Millheim, Martin E. Chenevert, F.S. Young Jr Factors Affecting Penetration Rate. In Applied Drilling Engineering,