Full-scale Drilling Tests Research Articles

Sensitivity investigation of drilling efficiency to operational parameters of a drifter

Drilling operations are extensively used for underground excavation, and their efficiency has a direct impact on project duration and expense. Adjusting the operational parameters during the drilling process is important for improving drilling efficiency. In this study, the sensitivity of drilling efficiency to operational parameters was investigated. Full-scale drilling tests for a dolomite block were conducted using a hydraulic drifter, and the ‘measurement while drilling’ system was used to record the drilling data. Orthogonal schemes were designed to arrange the tests, and the penetration rate, specific energy and rate–energy ratio were regarded as evaluation indices to assess the drilling efficiency. The sensitivity of the evaluation indices to operational parameters was analysed using both range analysis and variance analysis. Results show that the optimal combination of parameters within the test range was determined to be the propelling pressure of 8.5 MPa, percussive pressure of 17.5 MPa and rotary speed of 250 r/min to obtain the maximum drilling efficiency. The sensitivity sequence of the rate–energy ratio was propelling pressure, percussive pressure and rotary speed, with weights of 54.0, 38.7 and 7.3%, respectively. These findings can provide a valuable reference for adjusting the operational parameters of hydraulic drifters to optimise drilling efficiency.

Statistical Analysis of the Capabilities of Various Pattern Recognition Algorithms for Fracture Detection Based on Monitoring Drilling Parameters

Ground conditions, including characteristics of fractures, joints, bed separations, and strengths of rock layers, are critical factors for proper design of openings in underground mining and construction projects. Correct understanding of geologic conditions allows for improvement and optimization of ground support design and minimizing incidents of ground failure and instabilities in underground workings. Rock bolts have been widely accepted as the preferred method of ground support in almost all forms of rock excavation applications. The concept of monitoring drilling data to evaluate characteristics of geological features of interest in the rock surrounding the underground opening is a very attractive option for developing the geological model of the ground on real-time basis. This includes information on distributions of joints and bed separations, locations of voids, and strengths of rock layers, which enables the automated and rapid evaluation of ground conditions while drilling is in progress. Several smart drilling systems have been developed and proposed to detect joints; however, they offer limited capabilities and have exhibited difficulties in identifying joints with small apertures. The current study was focused on developing a more sensitive method to locate joints with smaller apertures along the hole being drilled with an instrumented roof bolter. A series of full-scale drilling tests were carried out in samples which contained simulated joints with different inclined angles in controlled laboratory conditions. New joint detection programs, with improved capabilities based on various pattern recognition algorithms, have been developed and used for analysis of data recorded in the full-scale drilling tests. To precisely locate joints, composite parameter was also used to offer more accurate detection. This paper reviews the laboratory testing program, data analysis, logic/algorithms used in the programs, statistical analysis of the detection results, and comparison of the various algorithms for this application.

Improving the capability of detecting joints and fractures in rock mass from roof bolt drilling data by using wavelet analysis

To optimise ground supporting and mitigate ground instability, a proper understanding of the ground conditions is critical. The concept of monitoring drilling parameters of a bolter for ground characterisation, which refers to identifying geological features included locations of joints and strengths of rock layers, has been studied in the past few decades. Several intelligent drilling units have been developed for joint detection but have limited capabilities. For instance, the existing systems fail to discriminate joints with the aperture of less than 3.175 mm and tend to generate false alarms. The objective of this research was to develop more efficient and sensitive detection programs for joint detection. To achieve this objective, a series of full-scale drilling tests with various simulated joint conditions have been conducted, and new detection programs have been proposed based on pattern recognition algorithms. Moreover, wavelet analysis has been applied to pre-process data to further promote detection programs. [Received: July 15, 2017; Accepted: November 18, 2017]

Improving the Capability of Detecting Joint and Fractures in Rock Mass from Roofbolt drilling Data by Using Wavelet Analysis9

To optimise ground supporting and mitigate ground instability, a proper understanding of the ground conditions is critical. The concept of monitoring drilling parameters of a bolter for ground characterisation, which refers to identifying geological features included locations of joints and strengths of rock layers, has been studied in the past few decades. Several intelligent drilling units have been developed for joint detection but have limited capabilities. For instance, the existing systems fail to discriminate joints with the aperture of less than 3.175 mm and tend to generate false alarms. The objective of this research was to develop more efficient and sensitive detection programs for joint detection. To achieve this objective, a series of full-scale drilling tests with various simulated joint conditions have been conducted, and new detection programs have been proposed based on pattern recognition algorithms. Moreover, wavelet analysis has been applied to pre-process data to further promote detection programs. [Received: July 15, 2017; Accepted: November 18, 2017]

Wear of cemented tungsten carbide percussive drill–bit inserts: Laboratory and field study

Design of the drill–bit and selection of the Cemented Tungsten Carbide (CC) grade for drill–bit inserts are crucial for efficient percussive drilling. This study presents the results of an experimental campaign executed with the aim to identify the distinctive wear mechanisms and behaviour of different CC grades. Three laboratory and one full–scale drilling tests were performed using nine CC grades with different binder contents, binder chemical compositions, mean tungsten carbide (WC) grain sizes, and grain size distributions. Wear traces found on the drill–bit inserts after the full–scale drilling test show noticeable differences depending on their position on the drill–bit. Tensile forces present on the leading edge of the inserts due to the sliding contact with rock are suspected to play a significant role. Laboratory tests performed include: (i) single impact tests using a modified Split Hopkinson Pressure Bar (SHPB) apparatus, (ii) Abrasion Value (AV) rotating disk tests, and (iii) impact abrasion (LCPC) tests. Volume loss and shape change were used as macroscopic measures of wear. Greater volume losses were found for the grades with nickel–based binders compared to those with pure cobalt binder. The use of a narrower WC grain size distribution leads to lesser volume loss in drilling and AV tests. Surface analysis of the damaged microstructure was performed using scanning electron microscope. Distinct meso–scale (few dozens of WC grain sizes) patterns of damaged microstructure zones surrounded by the intact surface were found on the surfaces of specimens after single impact test. The pattern indicates the potential influence of a non–uniform contact due to the rock roughness and internal rock heterogeneities, which is supported by the study of the rock crater roughness. Size of such zones could be seen as a certain length–scale, which determines the insert–rock contact behaviour. A specific “peeling” mechanism of material removal was observed in the full–scale drilling test, where portion of the CC microstructure fused with the rock tribofilm gets removed when that tribofilm peels off.

Ground characterization and roof mapping: Online sensor signal-based change detection

Measurement while drilling systems are becoming an important part of excavation operations for rock characterization and ground support design that require reliable information on rock strength and location & frequency of joints or voids. This paper focuses on improving rock characterization algorithms for instrumented roof-bolter systems. For this purpose, an improved void detection algorithm is proposed, where the underlying theory is built upon the concept of mean change detection based on the feed pressure signals. In addition, the application of acoustic sensing for void detection is examined and it is shown that the variance of the filtered acoustic signal is correlated to the strength of the material being drilled. The proposed algorithm has been validated on the data collected from full-scale drilling tests in various concrete and rock samples at the J. H. Fletcher facility.

Feasibility study on roller-cone bit wear detection from axial bit vibration

Previous studies reported that the peaks of a power spectrum for roller-cone bit axial vibration move to higher frequencies with the progression of bit-tooth wear. This result implies that monitoring and analyzing roller-cone bit vibration could be a new real-time detection method for downhole bit wear conditions.In this study, the dynamics of roller-cone bit axial vibration were modeled to quantitatively evaluate bit-tooth wear. The model includes the kinematics of roller-cone bit motion and a model for bit-tooth/rock interaction that considers the detailed geometry of a worn tooth. By sequentially solving the equation of motion with increments of cone rotation angles, the time history of axial bit vibration was simulated.The developed model was validated by comparing the power spectral densities for the simulated time histories of axial bit vibration with the experimental results of full-scale drilling tests. Detection of bit-tooth wear, bearing failure, and broken teeth was studied from a feasibility perspective.

ローラーコーンビットの軸方向振動に関する動力学モデル

It has been reported in previous studies that dominant peaks of a power spectrum for roller cone bit axial vibration moved to higher frequencies as the bit tooth wear progressed. This experimental result implies that monitoring and analyzing roller cone bit vibration could be a new real-time diagnosis method of downhole bit wear conditions.In this paper, dynamics of roller cone bit axial vibration was modeled to make a quantitative evaluation of bit vibration characteristics. The model includes kinematics of roller cone bit motion, and a model for bit-tooth/rock interaction in consideration of worn tooth geometry and inclination of tooth penetration. Sequentially solving the equation of motion with increments of cone rotation angles under some constraints on cone rotations, time history of axial bit vibration was simulated.The developed model was validated by comparing the power spectral densities for simulated time histories of bit displacement and weight on bit with experimental results in full-scale drilling tests. Simulation study revealed that the characteristics of roller cone bit axial vibration was very sensitive to a small variation of cone rotation speed, and that bit tooth tracking on bottomhole craters could constrain the cone rotation speeds depending on the situation.

Optimum bit selection and operation for the rotary blasthole drilling using a Horizontal Drilling Rig (HDR) - A case study at KBI Murgul Copper Mine

ABSTRACT This paper describes a new method to optimise roller-cone bit selection and operation by means of achieving the highest rate of penetration and bit life in a given formation that results in the lowest total cost for the hole. The performance in both areas can be ma×imised by controlling the weight applied and the rotary speed for the selected bit providing ideal hole cleaning. A Horizontal Drilling Rig (HDR) designed and used to perform full scale drilling tests in the laboratories of ITU Faculty of Mines. The block sample size of appro×imately 1.5 × 1.0× 1.0 m was taken from KBI Murgul Mine and the geotechnical parameters of the samples were investigated. According to the values obtained, the appropriate roller-cone bits were initially selected from the product lists of four different manufacturers. The optimum operating parameters were sought for each bit on the HDR as rotational speeds and weight applied on bit were the controlled parameters and the penetration rate, torque, power consumption are recorded with the aid of an advanced data acquisition system. Finally, field tests were carried out to determine the bit life under the optimum operating conditions obtained in laboratory as this leads to the optimum bit selection and operation at KBI Murgul Copper Mine.

Clear Brine Drilling Fluids: A Study of Penetration Rates, Formation Damage, and Wellbore Stability in Full-Scale Drilling Tests

Summary The performance of CaCl2/CaBr2 clear brine fluid was compared with that of lignosulfonate-water-based and oil-invert-emulsion-based fluids in a series of full-scale laboratory drilling tests. Sandstone and shale rock samples were drilled with a clean CaCl2/CaBr2 brine, a solids-contaminated CaCl2/CaBr2 brine, a water mud, and an oil mud, all at 13-lbm/gal [1558-kg/m3] density. Penetration rates were measured under various conditions of weight on bit, fluid flow rate, and differential wellbore/pore pressure. Drilling fluid filtration into the sandstone was measured under both drilling and circulating (nondrilling) conditions. After drilling, 2-in. [5.08-cm] radial cores taken from the sandstone specimens were studied for permeability damage caused by the drilling fluids. In a separate test, shale specimens were exposed to circulating drilling fluids to examine wellbore stability effects.

Laboratory Evaluation of PDC Drill Bits Under High-Speed and High-Wear Conditions

Summary Recently, five experimental polycrystalline diamond compact (PDC) bit designs were tested in the laboratory, at 100 and 500 rpm in three different types of rock: Nugget sandstone. Crab Orchard sandstone, and Sierra White granite. This paper describes the testing procedures, summarizes bit performance and wear procedures, summarizes bit performance and wear characteristics, and correlates these experimental results with specific design options such as rake angle, bit profile, and material selection. profile, and material selection. Introduction The significant improvements in turbodrill technology over the past few years have generated a great deal of interest in the development of drill bits capable of operating at the high speeds typically associated with these downhole motors. Because of severe wear of moving parts such as bearings and seals, tricone rock bits generally have performed poorly on high-speed turbines. PDC drag bits, on the other hand, have no moving parts and have been used successfully on turbines in the North Sea and elsewhere overseas. In 1979, Sandia Natl. Laboratories initiated a program to investigate the limitations of PDC drill bits as applied to high-speed, high-temperature geothermal drilling.Recently, five different experimental PDC bit designs were tested in the laboratory under atmospheric conditions at both 100 and 500 rpm. Four of the designs were developed by commercial bit manufacturers, while the fifth was developed at Sandia. In general, the designs were very diverse and used different bit profiles, cutter rake angles, cutter positioning strategies, material selection rationales, etc. This diversity allowed the comparison of different design concepts. General Description Two 6.75-in.-diameter PDC drill bits were procured from each of the following commercial bit manufacturers: American Coldset Corp., NL Hycalog, Smith Intl. Inc., and Dresser Industries Inc./Security Div. In a parallel effort, two 6.5-in.-diameter PDC bits were parallel effort, two 6.5-in.-diameter PDC bits were designed and built at Sandia. All of these experimental drill bits were developed specifically for high-speed operation (greater than 300 rpm). The five different designs are pictured in Figs. 1 and 2.A typical PDC cutter assembly (Fig. 3) consists of a PDC drill blank bonded to a support post or stud using PDC drill blank bonded to a support post or stud using either General Electric Co.'s high-temperature LS-brazing process or a diffusion-bonding technique developed at Sandia. For purposes of comparison, the 10 drill bits fabricated for this experiment used both bonding techniques. In addition, both steel and tungsten carbide support posts or studs were used. Six of the bits had all LS-brazed carbide cutters (a PDC drill blank attached to a tungsten carbide stud using GE's LS-brazing process), one had all diffusion-bonded steel cutters, and the process), one had all diffusion-bonded steel cutters, and the other three bits had some combination of LS-brazed carbide cutters, diffusion-bonded steel cutters, and diffusion-bonded carbide cutters. All 10 bits are described in detail in Table 1. The full-scale drilling tests were conducted at the Drilling Research Laboratory in Salt Lake City under atmospheric conditions and using water as the drilling fluid. The flow rate was held constant at 200 gal/min for all tests. For these PDC bits, the hydraulic pumpoff effect was found to be insignificant with respect to the bit weights used. The hits were tested in Nugget sandstone, Crab Orchard sandstone, and Sierra White granite at two different rotary speeds: 100 and 500 rpm. The unconfined compressive strength of these three types of rock was found to be 18,000, 20,800, and 24,000 psi, respectively. Depending on the type of rock, rotary speed, and bit design used, the weight or vertical force on each cutter varied from 30 to 1,500 lbf. JPT P. 2316

Effects of Bit Hydraulics on Full-Scale Laboratory Drilled Shale

Summary The effects of bit hydraulics while drilling shale with a standard three-cone bit are examined in this paper. Tests were conducted by drilling into large-diameter, intact shale samples at simulated downhole conditions in Drilling Research Laboratory's wellbore simulator. The shale samples were recovered from massive surface outcroppings and preserved for laboratory use. The effects of hydraulic horsepower from 20 to 400 hhp and bit weights from 20,000 to 50,000 lbm on rate of penetration are presented. Introduction Most deep shales and some intermediate shales found in the U.S. are typically "slow" drilling formations. Efforts to improve rate of penetration in shale have been performed in both field tests and small-scale laboratory investigations. Until recently, laboratory drilling studies on shale have been confined to microbit1 or single-cutter2 studies because the ability to obtain and preserve large, intact shale samples had not been developed. In addition, laboratory facilities where full-scale drilling tests could be conducted at simulated deep-well conditions did not exist. Massive surface shale formations have been located and techniques have been developed to extract and preserve large-diameter, intact samples. With these samples and the ability to simulate full-scale drilling conditions, a systematic, technical approach was taken where the effects of drill bit hydraulics were examined while drilling shale at simulated downhole conditions. Background and Definitions The in-situ conditions of a typical deep wellbore and surrounding rock formation are illustrated in Fig. 1. The formation is subjected to overburden stress, confining stress, wellbore pressure, and formation pressure. As previously demonstrated,3–5 rate of penetration is influenced strongly by the bottomhole conditions and appears to be most sensitive to the differential pressure between the wellbore and formation. These effects, however, can vary widely depending on rock properties such as rock type, strength, density, permeability, and mud properties such as composition, filtration rate, viscosity, solids content, and particle size.6 Bit hydraulics - i.e., the means of removing cuttings from the hole bottom and cleaning the bit with the drilling fluid - are a key factor in improved bit performance. Bottomhole cleaning theories,7 microbit studies,8 and full-scale laboratory drilling experiments in hard, impermeable rock9 have shown the need for adequate bit hydraulics to maximize rate of penetration and avoid bit balling. Field tests with extended nozzles10 also have demonstrated great potential for increasing rate of penetration in certain formations with improved bit hydraulics. Some nondrilling laboratory studies have shown the effects of nozzle size on pressure distribution at the hole bottom.11