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 volume of rock. Samples of sandstone, shale, and limestone were prepared for laser beam interaction with a 1.6 kW pulsed Nd:yttrium–aluminum–garnet laser beam to determine how the beam size, power, repetition rate, pulse width, exposure time and energy can affect the amount of energy transferred to the rock for the purposes of spallation, melting, and vaporization. The purpose of the laser rock interaction experiment was to determine the optimal parameters required to remove a maximum rock volume from the samples while minimizing energy input. Absorption of radiant energy from the laser beam gives rise to the thermal energy transfer required for the destruction and removal of the rock matrix. Results from the tests indicate that each rock type has a set of optimal laser parameters to minimize specific energy (SE) values as observed in a set of linear track and spot tests. As absorbed energy outpaces heat diffusion by the rock matrix, local temperatures can rise to the melting points of the minerals and quickly increase observed SE values. Tests also clearly identified the spallation and melting zones for shale samples while changing the laser power. The lowest SE values are obtained in the spalling zone just prior to the onset of mineral melt. The laser thermally spalled and saw mechanically cut rocks show similarity of surface microstructure. The study also found that increasing beam repetition rate within the same material removal mechanism would increase the material removal rate, which is believed due to an increase of maximum temperature, thermal cycling frequency, and intensity of laser-driven shock wave within the rock.
Approximate, but accurate, analytical expressions for the far-field divergence angle of a Gaussian beam normally incident on a circular aperture are derived. A first equation is obtained based on the concept of Gaussian transform, in which the Bessel function present in the far-field diffraction integral is approximated by a Gaussian function. Refining this approach yields another simple, practical closed-form formula with such a level of accuracy that we propose that it can be used as an exact reference. All approximations hold for any combination of Gaussian beam width and aperture radius.
There is increasing interest in the petroleum industry in the application of fiber-optic sensing techniques. In this paper, we review which sensing technologies are being adopted downhole and the drivers for this deployment. We describe the performance expectations (accuracy, resolution, stability and operational lifetime) that the oil companies and the oil service companies have for fiber-optic sensing systems. We also describe the environmental conditions (high hydrostatic pressures, high temperatures, shock, vibration, crush, and chemical attack) that these systems must tolerate in order to provide reliable and economically attractive reservoir-performance monitoring solutions.
The combined water (H2O+) in 30 geochemical standards having known and unknown water contents was determined by an elemental analyzer on 1 day during each of 6 weeks over a period of several months. The analysis of variance of the data measured in the form of a Youden square shows an extremely significant variation due to some unknown cause during the weeks in which the data were obtained. The higher water contents of the first two sets were obtained in the fall season when this area (Reston, Va.) has high and variable humidity, whereas the last four sets were measured during winter months. Humidity, however, was not included as a variable in the design and was not measured. The first two of three average blanks for H2O+, measured after determining H2O+ contents of about 11 percent for two samples, are noticeably higher than the third average blank. Similarly, the first of two average blanks for H2O+, measured after determining the H2O+ content (4.70 percent) of PCC‐1, is higher than the second. Data for the last 4 weeks were used to calculate the line of regression and the extremely significant correlation coefficient. The line is used to predict suggested revisions of the “best” H2O+ contents of the standards. Coefficients of variation calculated from the data for the last 4 weeks indicate that there is no severe sampling problem due to the small sample size (20 mg) taken for the determinations. The coefficients follow the general trend of large coefficients for samples containing the least amount of the constituent (BHVO‐1: x̄= 11.76% H2O+; C.V. = 7.3%) and of small coefficients for samples containing the greatest amount (BX‐N: x̄= 11.76% H2O+; C.V. = 0.4%).
Films of silicon nitride have been grown in an ultrahigh vacuum system by the reaction of silane with nitrogen remotely excited in a microwave plasma at pressures in the range 0.1–0.9 Torr with substrate temperatures in the range 70–350 °C. Growth rates have been determined as a function of silane–nitrogen flow ratio, pressure, microwave power, and substrate temperature in order to give some insight into the growth mechanism. Results indicate that the rate of film deposition is governed by the arrival rate of active nitrogen species at the surface. The films have been characterized by 15N nuclear reaction profiling and Rutherford backscattering analysis to determine the hydrogen, silicon, and nitrogen contents. Hydrogen contents are comparable to those obtained with parallel-plate plasma enhanced chemical vapor deposition reactors while near stoichiometric, nitrogen rich films can be obtained over a wide range of deposition parameters. Floating double probe measurements used to obtain the electron temperatures and ion densities verify that substrate bombardment by charged or energetic particles is not a factor in the growth of these films.
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