Experimental Investigation of Seepage Mechanism on Oil-Water Two-Phase Displacement in Fractured Tight Reservoir

As a type of unconventional oil and gas resources, tight sandstone reservoir has low permeability and porosity properties and thus is commonly necessary to develop through hydraulic fracturing treatment. Due to the coexistence of natural fractures and induced hydraulic fractures, the heterogeneity of reservoir permeability becomes severe and therefore results in complicated fluid seepage mechanism. It is of significance to investigate the oil-water two-phase seepage mechanics before and after the hydraulic fracturing stimulation with the aim of supporting the actual production and development of oilfield. This paper experimentally investigated the influences of fracture system on seepage characteristics of two-phase displacement in sample cores of fractured tight sandstones. In details, the changes of injection rate, cumulative production rate, recovery ratio, and water content were analyzed before and after the hydraulic fracturing treatments. To further analyze the displacement characteristics of the sample core, the displacement indices of four rock samples in different displacement stages were investigated. The sensitivity of sample core displacement indices to many key factors, including injection time, oil production rate, oil recovery factor and injection multiple factor, and moisture (i.e., water content was 95%, 98%, and 99.5%, respectively), before and after the hydraulic fracturing treatments were obtained synthetically. Besides, the relationship between recovery difference and contribution of fracture to permeability was explored at different water contents. The experimental results reveal that the fracture system shortens the water-free production period and hence reduces the recovery rate. The greater the contribution of fractures to permeability, the lower the recovery of water during this period.

Analysis of gas preparation processes for improvement of gas transportation technology

At production, collection and transport of low – pressure gas to deep water offshore platforms in sea conditions because of thermodynamic indices change in the system, complications are generated in connection with liquid phases – separation. These complications disturb normal operational well behavior, gas preparation unit and trunk (main) pipeline conditions. As a result of these phenomena high – volume losses of gas, gas condensate and chemical reagent take place. In the process of testing, the following process parameters were determined: pressure, gas temperature, facility performance, regeneration temperature, amount of absorbent injected into the gas flow, concentration of regenerated and saturated absorbent, dry gas dew point and so on. In the process of investigating the effect of the amount of inhibitor on the degree of corrosion prevention, hydrate formation and salt deposit at the facilities, regression equations. That is why, to guarantee uninterrupted transportation of low-pressure gas in field conditions, new methods are required for these phenomena prevention. On the basis of field study results some variants of calculation were given to increase efficiency of low-pressure gas transportation system in offshore oil and gas field’s conditions. Results of high-pressure gas optimal working pressure calculation for precipitated liquid phase displacement at low-pressure petroleum gas transportation to deepwater offshore platforms are shown in the article. As well, method for precipitated liquid phase displacement from low-pressure gas pipeline with usage of high-viscosity elastic gelling compositions on the basis of domestic petrochemical products

Experimental Study and History-Match of Near-Miscible WAG Coreflood Experiments on Mixed-Wet Carbonate Rocks

Water-alternating-gas (WAG) injection, both miscible and immiscible, is a widely used enhanced oil recovery method with over 80 field cases. Despite its prevalence, the numerical modeling of the physical processes involved remains poorly understood, and existing models often lack predictability. Part of the complexity stems from the component exchange between gas and oil and the hysteretic relative permeability effects. Thus, improving the reliability of numerical models requires the calibration of the equation of state (EOS) against phase behavior data from swelling/extraction and slim-tube tests, and the calibration of the three-phase relative permeability model against WAG coreflood experiments. This paper presents the results and interpretation of a complete set of two-phase and thee-phase displacement experiments on mixed-wet carbonate rocks. The three-phase WAG experiments were conducted on the same composite core at near-miscible reservoir condition; experiments differ in the injection order and length of their injection cycles. First, the two-phase water/oil and gas/oil displacement experiments and first cycles of WAG were used to estimate the two-phase relative permeabilities. Then, a synchronized history-matching procedure over the full set of WAG experiments and cycles was carried out to tune Larsen ans Skauge WAG hysteresis model—namely the Land gas traping parameter, the gas reduction exponent, the residual oil reduction factor and three-phase water relative permeability. The second part of this paper deals with the multiphase upscaling of microscopic displacement properties from plug to coarse grid reservoir scale. The two-phase relative permeability curves and three-phase WAG parameters were upscaled using a sector model to preserve the displacement process and reservoir performance. The result of the coreflood calibration indicate that the two-phase displacement and first cycles of WAG yield a consistent set of two-phase relative permeabilities. Including the full set of WAG experiments allowed a robust calibration of the hysteresis model.

Why Should We Test the Wideband Transformation Accuracy of Medium Voltage Inductive Voltage Transformers?

In this paper the results of the tests of the wideband transformation accuracy of medium voltage (MV) inductive voltage transformers (VTs) in the frequencies range from 50 Hz up to 5 kHz are presented. The values of voltage error and phase displacement for transformation of the harmonics of distorted primary voltages are determined. In the case of a typical 50 Hz-type inductive VT with a rated primary voltage equal to (15/Ö3) kV and (20/Ö3) kV manufactured by an international company the limiting values of the accuracy classes extension for quality metering required by the standard IEC 61869-6 for the Low Power Instrument Transformers (LPIT) were not exceeded. While, in the same test other MV inductive VTs show poor accuracy and even resonance at multiple frequencies. Unfortunately, this problem also arises from nonlinearity of the magnetization characteristic of their magnetic core. Therefore, for transformation of the sinusoidal voltage in the secondary voltage significant but not easily detectable values of the low order higher harmonics are present. Moreover, for transformation of harmonics of distorted primary voltage the influence of connected capacitance on the obtained values of voltage error and phase displacement was tested.

Metrological characterisation of current transformers calibration unit for accurate measurement

<p class="Abstract"><span lang="EN-US">The manuscript presents a method for the metrological characterisation of the commercial AC comparators used to calibrate current transformers. The theoretical basis for simulating the difference between two almost identical currents has been outlined, as well as the mathematical models for both a ratio error and a phase displacement has been derived. The measurement setup, consisting of conventional measuring instruments, has been described with a detailed presentation of its parameters. The sources of uncertainty have been distinguished and analysed with determining the current phase shift which led to a significant increase of relative measurement uncertainty. The simulation of measurement results was yielded in two ways: physically using a method presented and virtually using a Monte Carlo method. The second method confirmed that evaluating the measurement uncertainty through derived sensitivity coefficients is correct enough. The simulation results in the range from 1 to 1200 parts per million for both ratio error and phase displacement motivated the use of a comparator characterised through the proposed method for accurate measurement, especially for very low errors.</span></p>

Common-Mode Voltage Harmonic Reduction in Variable Speed Drives Applying a Variable-Angle Carrier Phase-Displacement PWM Method

Electric variable speed drives (VSD) have been replacing mechanic and hydraulic systems in many sectors of industry and transportation because of their better performance and reduced cost. However, the electric systems still face the issue of being considered less reliable than the mechanical ones. For this reason, researchers have been actively investigating effective ways to increase the reliability of such systems. This paper is focused on the analysis of the common-mode voltage (CMV) generated by the operation of the VSDs which directly affects to the lifetime and reliability of the complete system. The method is based on the mathematical description of the harmonic spectrum of the CMV depending on the PWM method implementation. A generalized PWM method where the carriers present a variable phase-displacement is developed. As a result of the presented analysis, the CMV reduction is achieved by applying the PWM method with optimal carrier phase-displacement angles without any external component and/or passive filtering technique. The optimal values of the carrier phase-displacement angles are obtained considering the minimization of the CMV total harmonic distortion. The resulting method is easily implementable on mostly off-the-shelf mid-range micro-controller control platforms. The strategy has been evaluated in a scaled-down experimental setup proving its good performance.