Zhiyue Xu

Specific energy for pulsed laser rock drilling

Application of advanced high power laser technology to oil and gas well drilling has been attracting significant research interests recently among research institutes, petroleum industries, and universities. Potential laser or laser-aided oil and gas well drilling has many advantages over the conventional rotary drilling, such as high penetration rate, reduction or elimination of tripping, casing, and bit costs, and enhanced well control, perforating and side-tracking capabilities. The energy required to remove a unit volume of rock, namely the specific energy (SE), is a critical rock property data that can be used to determine both the technical and economic feasibility of laser oil and gas well drilling. When a high power laser beam is applied on a rock, it can remove the rock by thermal spallation, melting, or vaporization depending on the applied laser energy and the way the energy is applied. The most efficient rock removal mechanism would be the one that requires the minimum energy to remove a unit ...

Laser spallation of rocks for oil well drilling

Laser rock spallation is a rock removal process that utilizes laser-induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. High intensity laser energy, applied on a rock that normally has very low thermal conductivity, concentrates locally on the rock surface area and causes the local temperature to increase instantaneously. The maximum temperature just below the melting temperature can be obtained by carefully controlling the laser parameters. This results in a local thermal stress in subsurface that is enough to spall the rock. This process continues on a new rock surface with the aid of the high pressure gas purging blowing away the cracked fragments. Laser parameters that affect the laser spallation efficiency will be discussed in the paper. Also reported in the paper is the multi laser beam spot spallation technique that has been developed for potentially drilling large diameter and deep gas and oil wells.Laser rock spallation is a rock removal process that utilizes laser-induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. High intensity laser energy, applied on a rock that normally has very low thermal conductivity, concentrates locally on the rock surface area and causes the local temperature to increase instantaneously. The maximum temperature just below the melting temperature can be obtained by carefully controlling the laser parameters. This results in a local thermal stress in subsurface that is enough to spall the rock. This process continues on a new rock surface with the aid of the high pressure gas purging blowing away the cracked fragments. Laser parameters that affect the laser spallation efficiency will be discussed in the paper. Also reported in the paper is the multi laser beam spot spallation technique that has been developed for potentially drilling large diameter and deep gas and oil wells.

Rock perforation by pulsed Nd:YAG laser

In gas and oil well completion, perforation channels must be made through the steel casing wall and cement and into the rock formation in the production zone to allow formation fluid to enter the well. This paper will present study results on using a pulsed Nd:YAG laser to drill the perforation channels through reservoir rocks. With fiber optic cable delivery capability, an Nd:YAG laser beam has the potential to be delivered to deep oil production zones. Effects of laser pulse parameters, beam properties, and assistant gas purging on the perforating efficiency and rock permeability will be reported. Unlike the conventional explosive charge perforation that often causes great reduction of rock permeability, laser perforation would enhance the rock permeability, therefore increasing the oil or gas production rate of the wellIn gas and oil well completion, perforation channels must be made through the steel casing wall and cement and into the rock formation in the production zone to allow formation fluid to enter the well. This paper will present study results on using a pulsed Nd:YAG laser to drill the perforation channels through reservoir rocks. With fiber optic cable delivery capability, an Nd:YAG laser beam has the potential to be delivered to deep oil production zones. Effects of laser pulse parameters, beam properties, and assistant gas purging on the perforating efficiency and rock permeability will be reported. Unlike the conventional explosive charge perforation that often causes great reduction of rock permeability, laser perforation would enhance the rock permeability, therefore increasing the oil or gas production rate of the well

Drilling large diameter holes in rocks using multiple laser beams

Studies on drilling petroleum reservoir rocks with lasers show that modern infrared lasers have the capability to spall (thermally fragment), melt and vaporize natural earth materials with the thermal spallation being the most efficient rock removal mechanism. Although laser irradiance as low as 1000 W/cm2 is sufficient to spall rock, firing the beam on a single spot for too long at that intensity causes rock melting and reduces removal efficiency. Also, it is difficult to visualize an efficient way to create a six or eight inch hole by sending one large beam down hole. Alternatives are either to raster the beam to cover the 20 cm hole area or, using a pattern of many small beams illuminated sequentially or in groups, create a nearly circular work face. This paper will present the testing results of the multiple small beam method. The effect on rock removal efficiency of several parameters, including relaxation time between laser bursts, basic patterns of multiple beams, and beam spot overlapping amounts are determined and presented.Studies on drilling petroleum reservoir rocks with lasers show that modern infrared lasers have the capability to spall (thermally fragment), melt and vaporize natural earth materials with the thermal spallation being the most efficient rock removal mechanism. Although laser irradiance as low as 1000 W/cm2 is sufficient to spall rock, firing the beam on a single spot for too long at that intensity causes rock melting and reduces removal efficiency. Also, it is difficult to visualize an efficient way to create a six or eight inch hole by sending one large beam down hole. Alternatives are either to raster the beam to cover the 20 cm hole area or, using a pattern of many small beams illuminated sequentially or in groups, create a nearly circular work face. This paper will present the testing results of the multiple small beam method. The effect on rock removal efficiency of several parameters, including relaxation time between laser bursts, basic patterns of multiple beams, and beam spot overlapping amounts ...

The effect of laser welding process parameters on the mechanical and microstructural properties of V-4CR-4TI structural materials.

V-Cr-Ti alloys are among the leading candidate materials for the frost wall and other structural materials applications in fusion power reactors because of several important advantages including inherently low irradiation-induced activity, good mechanical properties, good compatibility with lithium, high thermal conductivity and good resistance to irradiation-induced swelling and damage [1]. However, weldability of these alloys in general must be demonstrated, and laser welding, specifically, must be developed. Laser welding is considered to be an attractive process for construction of a reactor due to its high penetrating power and potential flexibility. This paper reports on a systematic study which was conducted to examine the use of a pulsed Nd:YAG laser to weld sheet materials of V-Cr-Ti alloys and to characterize the microstructural and mechanical properties of the resulting joints. Deep penetration and defect-free welds were achieved under an optimal combination of laser parameters including focal length of lens, pulse energy, pulse repetition rate, beam travel speed, and shielding gas arrangement. The key for defect-free welds was found to be the stabilization of the keyhole and providing an escape path for the gas trapped in the weld. An innovative method was developed to obtain deep penetration and oxygen contamination free welds. Oxygen and nitrogen uptake were reduced to levels only a few ppm higher than the base metal by design and development of an environmental control box. The effort directed at developing an acceptable postwelding heat treatment showed that five passes of a diffuse laser beam over the welded region softened the weld material, especially in the root region of the weld.

Procedure development of laser welding of V–4Cr–4Ti alloy

Abstract V–4Cr–4Ti alloy is selected as the structure material for the first wall/blanket in a fusion power reactor. A systematic study was conducted to develop a laser welding procedure for fabrication of vanadium alloy for the first wall/blanket systems. A 1.6 kW pulsed Nd:YAG laser with fiber optic beam delivery was used to carry out the bead-on-plate welding on 4 mm thick V–4Cr–4Ti plates. The process parameters, such as laser schedule power settings, beam travel speed, and welding atmosphere control, and their effects on weld quality, such as weld depth, porosity, and oxygen uptake were studied. Results from metallurgical characterization of the welds are presented. An innovative laser welding procedure has been developed to obtain deep penetration, defect-free, and oxygen contamination-free welds.

Efficiency of concrete removal with a pulsed Nd:YAG laser

The mechanism and efficiency of ablating concrete surfaces with a pulsed Nd:YAG laser were studied. Ablation efficiency and material removal rates were determined as functions of irradiance and pulse overlap. The ablation mechanism was dominated by fragmentation and disaggregation of the concrete. The ablation efficiency was insensitive to peak laser irradiance over a range from 0.2 to 4.4 MW/cm2. Excessive pulse overlap (>60%) caused a significant decrease in ablation efficiency by inducing melting. In concrete samples, the cement phase of the material responds in various ways to the laser energy, including disaggregation, melting, and vaporization, but the aggregate portion (sand and rock) mostly fragments. The ablation effluent therefore consists of both micron-size aerosol particles and chunks of fragmented aggregate material.

Laser Based Ignition of Natural Gas-Air Mixtures

In current natural gas engines, lean operation to reduce NOx emissions along with the requirement to maintain high specific power results in in-cylinder conditions that demand spark voltages beyond the capabilities of present ignition systems. Unable to overcome such limitations, presently these engines are operated well below their full potential (about 15% less). Additionally, undue maintenance demands are placed for the upkeep of ignition systems. Laser based ignition (LBI) on the other hand, overcomes the above limitations and potentially reduces emissions and increases efficiency. Experimental studies were performed to identify such potential benefits while using lasers to ignite quiescent methane-air mixtures. Quiescent methane-air mixtures at various conditions (φ = 0.6–1.0, fill pressure = 2–20 Bar) were established in a pressure vessel and were ignited using lasers and by conventional ignition systems. Such tests showed lasers to ignite mixtures with initial pressures 30% higher than those limiting ignition by conventional ignition systems. However, extension of the lean ignition limit appeared to be marginal and was defined by φ = 0.675. Also, for single point ignition followed here, the rates of pressure rise and ignition delays were identical and did not depend upon the method of ignition. Other characteristics in terms of (a) effect of focal length, (b) effect of fuel composition, and (c) effect of laser beam polarization are presented. In practice, in-cylinder conditions such as turbulence, velocity and temperature are likely to have an additional bearing on the ignition characteristics. Such effects will be determined through future investigations.© 2003 ASME

Two-dimensional modeling of laser spallation drilling of rocks

High power lasers can weaken, spall, melt and vaporize natural earth materials with thermal spallation being the most energy efficient rock removal mechanism. Laser rock spallation is a very complex phenomenon that depends on many factors. Computer numerical modeling would provides great tool to understand the fundamental of this complex phenomenon, which is crucial to the success of its applications. Complexity of modeling laser rock spallation is due to: 1) rock is a porous media, to which traditional theories of heat transfer and rock mechanics can not be directly applied, 2) the laser rock removal process involves a variety of physical phenomena, and 3) thermolphysical property data for rocks are lacking, particularly the data at elevated temperatures. In this paper, we propose a combined approach to this complex problem, that is establishing models for each of the physical phenomena based on the finite difference method (FDM), then combining them into one numerical procedure using the Constrained interpolation profile-Combined Unified Procedure (C-CUP). The transient temperature and stress distributions in dry or water-saturated rocks exposed to a laser beam are calculated. The spallation boundary and rock removal efficiency are determined. The modeling results provide a better understanding of laser rock spallation and guidelines for selecting processing parameters for fast rock removal.High power lasers can weaken, spall, melt and vaporize natural earth materials with thermal spallation being the most energy efficient rock removal mechanism. Laser rock spallation is a very complex phenomenon that depends on many factors. Computer numerical modeling would provides great tool to understand the fundamental of this complex phenomenon, which is crucial to the success of its applications. Complexity of modeling laser rock spallation is due to: 1) rock is a porous media, to which traditional theories of heat transfer and rock mechanics can not be directly applied, 2) the laser rock removal process involves a variety of physical phenomena, and 3) thermolphysical property data for rocks are lacking, particularly the data at elevated temperatures. In this paper, we propose a combined approach to this complex problem, that is establishing models for each of the physical phenomena based on the finite difference method (FDM), then combining them into one numerical procedure using the Constrained int...

Effect of Laser Glazing and Laser Shock Peening on Tribological Performance of 1080 Carbon Steel

High-power laser surface treatments in the form of glazing, shock peening, cladding, and alloying can significantly affect material tribology. In this paper, effects of laser glazing, laser shock peening, and their combination on the tribological behavior of 1080 carbon steel were investigated. Laser glazing is a process in which a high-power laser beam melts the top layer of the surface, followed by rapid cooling and resolidification. This results in a new surface layer microstructure and properties. Laser shock peening, on the other hand, is a mechanical process in which a laser generates pressure pulses on the surface of the metal, similar to shot peening. Five conditions were evaluated: untreated (baseline), laser shock peened only (PO), laser-glazed only (GO), laser-glazed then shock peened last (GFPL), and laser shock peened then glazed last (PFGL). In pin-on-disc testing, all laser-treated surfaces reduced dry friction, with the GFPL surface having maximum friction reduction of 43%. Under lubricated conditions, all laser-treated surfaces except the PO sample lowered friction. Similarly, all glazed samples reduced wear by a factor of 2–3, while the PO sample did not change wear significantly. These tribological results are associated with changes in the near-surface microstructure and properties.Copyright