Rogerio T. Ramos

Production and wetting properties of fluorinated diamond-like carbon coatings

Abstract The control of hydrophobicity of diamond-like carbon (DLC) surfaces has been studied by the use of CF4 etching plasma and by the deposition of fluorinated DLC (a-C:F) using mixtures of CF4 with butane and acetylene. The results indicate that the degree of fluorination (F:C ratio), and the hydrophobicity of the surface depend critically on both the elemental composition of the gas feedstock and the deposition parameters. There is a correlation between high levels of fluorination and hydrophobicity, although at high F:C ratios, the mechanical stability of the fluorinated surface may be compromised. A possible mechanism for the production of hydrophobic fluorinated surfaces is proposed.

Optical injection locking and phase-lock loop combined systems

Optical injection locking and optical phase-lock loops have been used for laser synchronization. The use of a combined optical injection locking and phase-lock loop system is proposed here. We have taken into account the modification of the slave laser phase response induced by the injection locking to calculated the phase-error signal spectrum and the phase-error variance for an optical injection locking and phase-lock system. They show that this system presents both a wide locking range, given by the optical injection locking action, and a low phase error for low frequencies, given by the optical phase-lock loop action. These results can improve the system tracking capability and decrease the final phase-error variance compared with those in isolated systems.

A local optical probe using fluorescence and reflectance for measurement of volume fractions in multi-phase flows

Three-phase volume-fraction measurement can be obtained by a combination of reflectance and fluorescence methods. Fluorescence from oil can be detected by an optical fibre probe placed in the flow, while reflectance at the end of the same fibre probe is also detected. The method is demonstrated by preliminary experiments.

Comparison between first-order and second-order optical phase-lock loops

A comparison between the performance of modified first-order and second-order optical phase-lock loops (OPLLs) is made, revealing that the modified first-order loop offers better performance when long loop delay time is present and a wide bandwidth loop filter is used. The introduction of a 10 dB gain margin from the critical gain can be used to keep the damping close to that expected when the delay time is negligible. If OPLL design is optimized for this gain margin and 5 MHz linewidth lasers are used, the increase in the phase-error variance with delay time is 54 rad/sup 2///spl mu/s for a modified first-order and 80 rad/sup 2///spl mu/s for a second-order loop, confirming that modified first-order loops are less sensitive to loop delay.<<ETX>>

Fiber optic sensors for oil field services

The international oilfield service industry has used a large variety of sensing devices for the exploration of oil and gas in the last 70 years. These include sensors that range in the measurement of nuclear information, resistivity, acoustic, seismic, E & M fields including most recently optical sensors. The environments are very demanding in temperature, pressure, and vibration which, in general, describes the difficulty in converting current laboratory or commercial sensors for the oilfield industry. Applications where optical sensors have been successfully used and the potential future of fiber optic sensors for this industry will be reviewed.

Corrections of gradiomanometer data for volume fractions in two-phase flows

For typical applications of the gradiomanometer in laboratory two-phase flows, we analyse major contributions to the measured differential pressure. Application for estimation of the fluid-phase volume fraction is valid only when terms representing friction and differential momentum flux (acceleration) are negligible or can be corrected for. The importance of friction is commonly recognized, but that of acceleration in developing flows is less so. Order-of-magnitude estimates of friction and acceleration are given for typical cases of (i) air/water and (ii) kerosene/water two-phase flows. We point out that the acceleration term could be significant in developing liquid/liquid flows of weak density contrast. For the liquid/liquid case, it is therefore important that measurements be made in a fully developed region of the flow. Results for several multi-phase flows are compared with data from local optical fibre probes in a series of companion articles.

Transversely loaded Bragg grating pressure transducer with mechanically enhancing the sensitivity

In this paper, we describe a transversely loaded Bragg grating pressure transducer with mechanically enhanced the sensitivity utilizing fiber Bragg gratings written onto a single mode fiber, and demonstrate pressure sensitivity up to 5k psi with low temperature sensitivity.

Survivability of Optical Fiber for Harsh Environments

Today, optical-fiber systems are used in the oilfield for sensing and telemetry applications. The most commonly used downhole is the distributed temperature sensing (DTS) system which collects permanent real-time temperature well logs. These logs are extremely useful for real-time production allocation, heavy oil thermal recovery (e.g., steam-assisted gravity drainage, SAGD), steam-well management, and well-integrity monitoring. Unfortunately, optical fibers are not immune to degradation under downhole conditions. Hydrogen, present in the wells because of corrosion or other factors, can attack the optical-fiber components causing attenuation increase. This attenuation can have a negative effect on the performance of the system, such as decreasing accuracy or resolution. Understanding the process and the impact of this degradation is of great importance to the reliable operation of these optical-fiber systems. This article shows how a combination of controlled testing and modeling calculations can be used to provide an estimation of the attenuation increase expected from the fiber with time and downhole conditions. Test results for attenuation of optical fiber in hydrogen atmospheres and under downhole temperatures will be shown. The article also provides results from the testing of a new optical fiber that was designed to give a considerable improvement in resistance to hydrogen attack. These results give an order of magnitude improvement in comparison with commercially available optical fibers. Early field tests are consistent with the results of the study.

A local optical probe using fluorescence and reflectance for measurement qf volume fractions in multi-phase flows

Three phase volume fraction measurement is demostrated in three-phase flows using an optical fiber probe placed into the flow. Fluorescence from oil and reflectance signal from gas are detected from the same probe end.

Continuous-phase fluid velocity measurement for oil field flows using local optical probe and tracing method

The measurement of the velocities of oil and water phases in the bore-hole of a producing well, together with volume fraction measurement, gives the flow rate of each fluid phase. Even though radioactive tracers methods provides a good velocity measurement, safety concerns and regulations makes their use unattractive. We propose a method of measuring fluid velocity using local optical fiber probes and tracer techniques. A fluorescence dye is injected into the bore-hole where it is mixed with the fluid of interest. An optical fiber probe is positioned down-stream from the point of injection detects the passage of the tracer with the flow. The time between injection and detection enables one to calculate the flow velocity for a given distance between injector and detector. The same local probes cold also be used for hold-up estimation. We describe laboratory experiments using a flow loop, fluorescence dye as tracer and an optical fiber probe. The dependency of the injection to detection distance to the flow mixing is observed. Best results for average velocity estimation can be achieved for long distances. Measurements at short distances are possible but some kind of flow model may be needed to interpret the results.