SAG Process Research Articles

Investigation of active voltage support control approach of DC distribution networks based on virtual inertia coordination

AbstractDC distribution networks (DCDNs) possess the advantages of high power efficiency, low operation loss, and favourable control flexibility, and are regarded as an essential form of future power distribution systems. In order to increase the voltage transient performance of DCDNs against disturbances, this paper proposes a methodology for realising the active voltage support control of DCDNs based on virtual inertia coordination. Firstly, the impact of the inertia of DCDNs towards the transient voltage change is analysed, and the active voltage support mechanism considering the variable droop inertia control and virtual DC motor inertia (VDCMI) control is explored. Then, a time sequence coordination strategy based on the voltage grading of DCDNs is developed, and an adaptive inertia coefficient is designed to achieve the inertia adjustment in terms of the voltage sag and recovery processes. Using MATLAB/Simulink, a detailed model of the double‐terminal DCDNs is created to check the efficacy of the proposed approach. Different voltage disturbance scenarios are imitated, and the comparative simulations demonstrate that the proposed approach can fully utilise the inertia potential of the DCDNs to suppress the voltage sag and smooth the voltage recovery procedure. The proposed method's validity and feasibility can be well validated.The cover image is based on the Original Article Investigation of active voltage support control approach of DC distribution networks based on virtual inertia coordination by Lei Chen et al., https://doi.org/10.1049/esi2.12123.

Oil production enhancement, asphaltene precipitation and permeability damage during CO2-SAG flooding of multi-layer sandstone reservoirs

The process of CO2-SAG flooding involves conventional miscible CO2 flooding until breakthrough (BT), followed by a period of CO2 soaking or shut-in, and then a continuation of the miscible CO2 flooding. The SAG process provides different improvements in the oil recovery for different positions of each layer in multilayer reservoirs, and has different effects on the distribution of pore throat blocking and adsorption of asphaltene to mineral surfaces. In this paper, both miscible CO2-SAG and conventional CO2 flooding experiments have been carried out at reservoir conditions and on multi-layer systems composed of 3 long cores each with increasing porosities and permeabilities, which were connected in parallel. After CO2-SAG flooding oil recovery factors (RF) of the low, medium and high permeability cores were 7.7%, 8.3%, and 7.6% higher compared to the RFs after CO2 flooding, respectively. The respective fractional oil production (FOP) of each long core was 10.6%, 27.7%, and 61.6% after CO2-SAG flooding, with less difference between each long core than for CO2 flooding. After CO2 flooding, the permeability of the high permeability core at the injection end dropped by 24.5–25.8%, which is 5.5–14.3% higher than the value at the outlet. The permeability decrease due to CO2-SAG flooding was 0.7–9.7% higher than that due to CO2 flooding, and the distribution of permeability decline was more homogeneous. The contribution of the total permeability decrease attributable to asphaltene particle blockage due to CO2 flooding was 84.7–62.7%, 5.2–10.1% higher than that due to CO2-SAG flooding, gradually decreasing along the flow direction. Complex two-phase flow of oil and gas is more likely to cause pore throat blockage instead of causing the adsorption of asphaltene precipitation.

Using carbon isotopes and organic composition to decipher climate and tectonics in the Early Cretaceous: An example from the Hailar Basin, Inner Mongolia, China

When conducted in tandem, organic petrography and isotopic analyses can be used to interpret regional tectonics and palaeoclimate within a global context. As an example, a sequence of lignite (vitrinite reflectance average = 0.27%) in the Lower Cretaceous Yimin Formation, Inner Mongolia, China, was investigated. The study area is within the intracratonic Hailar Basin and was situated at ~45°N palaeolatitude. Globally warm temperatures allowed temperate to tropical vegetation such as ferns, cycads and gymnosperms to form thick, laterally extensive palaeomires within the basin. Probabilistic assessment indicates that the lower, thick (~40 m) Seam #16 may have accumulated over a time span between 174 (P10) to 481 (P90) thousand years, whereas the thin (~6 m) overlying Seam #16 Upper took between 20 (P10) and 96 (P90) thousand years. Thermal sag processes were active in the basin during these time periods, with subsidence rates balanced to allow enough accommodation space to accumulate thick peat, but not so fast as to induce flooding and burial by clastics. A high proportion of fossil charcoal (‘inertinite’) in both seams indicate that throughout the peat-forming period, fire was an important part of the mire ecology. This is consistent with global high oxygen content and an in-land continental palaeogeographic position with seasonal precipitation. Stable isotopes of carbon indicate periods of high precipitation but also times of significant relative dryness. The palaeoclimatic conditions are likely to be both seasonal as well as longer term, possibly decadal to millennium in scale and would have occurred over the whole region, not just mire specific.

Modeling and simulation of barite deposition in an annulus space of a well using CFD

In drilling industry, barite particles settling and barite sag as a major problem can potentially impose significant operational issues. Static conditions, in which well undergoes an extended shut-in period, could occur during different drilling and completion operations such fishing operation, tripping, and logging. Despite its importance, such phenomenon is not well understood yet. To avoid issues related to barite settlement and barite sag, a good understanding of the impact of different drilling parameters on barite settlement and sag phenomenon is required. Recently, the mathematical formulation and modeling of settlement and sag processes have gained more attention. In order to better design the drilling fluids and to optimize the operational conditions such as flow rate and drill pipe rotation speed, as well as drilling well trajectory design to avoid barite settlement, the mathematical formulation and modeling of such physical phenomena is required. This study is aimed at mathematically describing and analyzing the settling of barite particles in annular concentric space without axial flow by the means of computational fluid dynamic (CFD) simulation. The modeling approach consists of two main steps: a) simple vertical annular domain and b) complex three dimensional barite settlement process in a deviated well with rotational drill pipe. The current work is based on Eulerian two phase model. The settling of the single particle and the hindering effect of other particles on settling velocity have been investigated. Based on single particle model, the rate of barite settlement and fluid pressure reduction have been modeled. However, the single particle model cannot describe the particle to particle interactions and their impacts on settlement such as particle shearing viscosity, kinetic particle viscosity, and collisional effects. In this study, the accurate and comprehensive modeling of barite settlement has been done by applying the Eulerian-Eulerian approach. The models have been validated against available published experimental data in the literature. In addition, in order to further validate the model presented here, drill pipe rotation, fluid rheology, and inclination angle impacts have been experimental investigation and compared with results of the proposed model. The results indicate that the model based on using Eulerian-Eulerian approach accurately predicts the experimental data results. Afterward, the sensitivity analyses were carried out to show the impact of inclination angle, inner pipe rotation, fluid rheology, and barite content on the rate of settlement. This study showed that drag forces induced resuspension plays a vital role in barite settlement inside a deviated well. The results reveal that the settling rate is decreased with increasing the inner pipe rotation and the vortex effect created by inner pipe rotational, play a major role in the reduction of barite settlement. The results also show that the maximum settlement rate accrues at the deviation angles between of 45–60°.

Surfactant foam flushing for in situ removal of DNAPLs in shallow soils

An innovative process combining surfactant foam and surfactant flushing (SF) for the remediation of a shallow saturated soil contaminated with a dense non-aqueous phase liquid (DNAPL) residual was investigated at bench-scale. First, foam was formed by injecting DHSS surfactant and nitrogen in alternation in soil (SAG process) at constant pressure. The effect of pressure gradients set point (≤90kPam−1) on DNAPL recovery was investigated. Foam front mobilized DNAPL with a piston-like fast propagation (1.8md−1) despite the low pressure gradients. 34–60% of DNAPL residual was extracted with low surfactant consumption (<0.4kgkg−1 DNAPL removed). Then, a solubilizing agent (Tergitol) was injected into soil, previously treated with foam, to improve the DNAPL removal. It led a removal up to 95% whereas only 2 porous volume (PV) of solubilizing solution were injected. As a comparison, when the solubilizing agent was injected without foam pre-treatment, 40 PV would have been required to lead the removal up to 90%. Considering the overall treatment, the technology we developed requires 10-times less surfactant than the traditional SF technology. This technology is especially suitable for very shallow soils where injection pressure has to be kept at a low level to avoid soil heaving.

Ensemble-Based Optimization of the Water-Alternating-Gas-Injection Process

Summary CO2-water-alternating-gas (CO2-WAG) flooding generally leads to higher recovery than either continuous CO2 flooding or waterflooding. Although CO2 injection increases microscopic displacement efficiency, unless complete miscibility is achieved, suboptimal sweep efficiency may be obtained because of gravity segregation and the channeling of CO2 through high-permeability zones or by viscous fingering. Alternating water injection with CO2 injection results in better mobility control and increases sweep efficiency. Water injection also increases pressure that promotes miscibility. However, poorly designed WAG parameters can result in suboptimal WAG performance. In this work, given the number of WAG cycles and the duration of each WAG cycle, we apply a modification of a standard ensemble-based optimization technique to estimate the optimal well controls that maximize life-cycle net present value (NPV). By optimizing the well controls, we implicitly optimize the WAG ratio (volume of water injected divided by the volume of gas injected). We apply the optimization methodology to a synthetic, channelized reservoir. The performances of optimized WAG flooding, optimized waterflooding, and optimized continuous CO2 flooding are compared. Because of the similarity between WAG and surfactant alternating gas (SAG foam), we also optimize the SAG process and provide a more computationally efficient way to optimize the SAG process with the optimal well controls obtained from WAG as the initial guesses for the optimal controls for SAG.

Magnetic Susceptibility Studies of the Upper Albian-Danian Sediments of Cauvery Basin, South India

Abstract: The Cauvery basin of the Indian Peninsular shield, formed during the fragmentation of the Gondwana Supercontinent, continued to evolve until the end of Neogene through rift, pull-apart, shelf sag and tilt processes. The basin witnessed many cycles of transgression, regression, erosion and deposition. A more or less complete succession of upper Cretaceous–Paleocene sediments is exposed in the Ariyalur–Pondicherry depression of the basin. Anisotropy of magnetic susceptibility (AMS) technique is applied in an attempt to examine the depositional and eustatic conditions prevailed during the formation of these sedimentary sequences. AMS results point to the sedimentation history dominated by marked sea level changes with several phases of transgression and regression. The sedimentation occurred mainly in a shallow epicontinental sea which has been punctuated with terrigenous supply more often. Greater utility of magnetic fabrics is suggested as a tool to trace fluvial responses to tectonic and climatic changes.

Injectivity errors in simulation of foam EOR

Injectivity is a key factor in the economics of foam enhanced oil recovery (EOR) processes. Poor injectivity of low-mobility foam slows the production of oil and allows more time for gravity segregation of injected gas. The conventional Peaceman equation (1978), when applied in a large grid block, makes two substantial errors in estimating foam injectivity: it ignores the rapidly changing saturations around the wellbore and the effect of non-Newtonian mobility of foam. When foam is injected in alternating slugs of gas and liquid (“SAG” injection), the rapid increase in injectivity from changing saturation near the well is an important and unique advantage of foam injection. Foam is also shear-thinning in many cases. This paper considers the two problems in turn: non-Newtonian effects and foam dry-out. In studying non-Newtonian effects we use the method-of-characteristics approach of Rossen et al. (2011), which resolves both changing saturations and non-Newtonian rheology with great precision near the wellbore, and compare to conventionally computed injectivity using the Peaceman equation in a grid block. By itself, the strongly non-Newtonian rheology of the “low-quality” foam regime makes a significant difference to injectivity of foam. However, one could estimate this effect using the equation for injectivity of power-law fluids, i.e. without accounting for changing water saturation near the well, without much error. In SAG processes, however, non-Newtonian rheology is less important than accounting for foam collapse in the immediate near-wellbore region. Averaging water saturation in a large grid block misses this dry-out very near the well and the Peaceman equation grossly underestimates the injectivity of gas. This error is similar in kind to, but much greater than, that in conventional gas-injection EOR. The magnitude of the effect on the overall simulation decreases as the simulation grid is refined around the well; this grid refinement is especially important for simulating foam SAG processes. We illustrate with examples using foam parameters fit to laboratory data.

Wedges and buffers: some new structural observations from the Dnieper–Donets Basin, onshore Ukraine

Abstract The onshore Ukraine Dnieper–Donets Basin (DDB) is a large partially inverted late Palaeozoic intracratonic basin. Rifting began in the late Devonian when two evaporite sequences were deposited, and Carboniferous post-rift thermal sag was accompanied in some areas by some extension. Although important quantities of Devonian salt are calibrated by wells and diapirs have been documented, classic salt diapirs are probably not as common as suggested by the literature. Indeed, in several parts of the basin salt movement was stopped and buried by up to 5 km of overburden. Four important tectonic events related to salt movement have been documented over the DDB: Tournaisian–Early Visean extension, Middle Serpukhovian extension, Late Carboniferous–Early Permian movements mostly documented recently as extension and uplift and Alpine compression. Seismic imaging of the basin has not traditionally been of the highest quality, but the reprocessed seismic data made available over several parts of the DDB as part of a Ferrexpo/RDS multi-licence project has enabled three new structural observations of the basin to be made. Firstly, it is proposed that basin margin extension, facilitated by listric faulting with thin-skinned décollement on Devonian salt and exemplified by well-imaged Tournaisian syntectonic wedges, is linked to thick-skinned partial inversion of some basement rift faults. Secondly, it is proposed that these thick-skinned faults acted as obstacles or buffers, where monoclines began to develop. These folds were exaggerated by the later tectonic movements. Thirdly, we propose that these linked tectonic events may have been caused by pulses of sag which punctuated the Lower Carboniferous post-rift thermal sag process. These three observations fit neatly with published interpretations of Tournaisian–Lower Visean and Middle Serpukhovian extension. Finally, however, a literature review and new seismic interpretation also clearly show that Late Carboniferous–Early Permian movements inverted marginal listric faults and their Tournaisian wedges, and also inverted the downdip thick-skinned faults causing the monoclines to further develop prior to the Alpine overprint. This, contrary to many published papers over the last 15 years or so, suggests that this Late Carboniferous–Early Permian event brought shortening rather than extension to the DDB.

Multifunction SAG process for high-yield, low-cost GaAs microwave integrated circuits

A new fully planar, multifunction refractory self-aligned gate (MSAG) technology suitable for the fabrication of GaAs small-signal and power microwave monolithic integrated circuits (MMICs) is demonstrated in a manufacturing environment. Data on the distribution of DC and RF performance and yield for pilot production of discrete FETs and MMICs are presented. The heart of the MSAG process is a planar, self-aligned gate FET. It uses a refractory TiWN Schottky gate and exhibits high performance for small-signal microwave, power microwave, and digital circuit applications. Lots with good wafer yields have demonstrated average chip yields on PCM good wafers of 45%, 49%, and 36% for 2-10-GHz distributed amplifiers, 1-W C-band power amplifiers, and 4-W power amplifiers, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

C-band 10 W MMIC class-A amplifier manufactured using the refractory SAG process

The authors describe the design, fabrication, and test results of a C-band single-chip GaAs monolithic microwave integrated circuit (MMIC) class-A amplifier manufactured using a multifunctional self-aligned gate (MSAG) process. The amplifier demonstrates a 10-W power output (0.625 W/mm power density) at 5.5 GHz with an associated gain of 5 dB and a power-added efficiency of 36%. The average functional yield of the IC is above 70%. This excellent performance is attributed to an accurate model for 4-mm FETs, the IC design method used, simple circuit topology, and high-yield, high-performance MSAG processing. >

Nonequivalent cylinder models of neurons: interpretation of voltage transients generated by somatic current injection

1. Numerical methods were used to simulate the voltage responses to an intrasomatic current step of neuronal models that incorporated tapering dendrites, dendrites of unequal electrotonic length, nonlinear membrane properties, and regional differences in specific membrane resistivity (Rm). A "peeling" technique was used to estimate the time constants (tau 0 and tau 1) and coefficients (a0 and a1) of the first two exponential terms of the series of exponential terms whose sum represented the slope of the voltage response. 2. The electrotonic structure of models with a uniform Rm was calculated using equations derived by Rall or Johnston or Brown et al. The adequacy of these methods were tested using a wide variety of models that conformed to the equivalent cylinder approximation of Rall. Johnston's method provided the most reliable estimate of electrotonic length (L) and the ratio of the dendritic conductance to the somatic conductance (rho). However, if L exceeded 2 and rho was eight or larger, the equations derived by Johnston could frequently not be solved due to small errors in the peeled values of tau 0, tau 1, a0, and a1. Although the method suggested by Brown et al. could be applied to all models, this method invariably underestimated L and rho. These errors were particularly large for model neurons with L values of 1.5 or larger and rho values of four or larger. Estimates of L using Rall's method were only reliable if rho was large and L was two or less. 3. Changing the geometry of the dendritic tree (dendritic tapering or dendrites of unequal L) or the addition of a time- and voltage-dependent conductance designed to mimic a sag process commonly seen in spinal motoneurons caused systematic changes in tau 0, tau 1, a0, and a1. The sag process always led to an underestimate of tau 0 even after applying a correction procedure. On the other hand, the ratio, tau 0/tau 1, was not affected by the sag process or dendritic tapering.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in somatic and dendritic specific membrane resistivity of spinal motoneurons: an electrophysiological study of neck and shoulder motoneurons in the cat.

1. The voltage response to a hyperpolarizing current step was used to estimate the electrotonic structure of neck and shoulder motoneurons in anesthetized cats. The coefficients (a0 and a1) and time constants (tau 0 and tau 1) of the first two exponential terms of the series of exponential terms whose sum represented the slope of the voltage response were calculated using a standardized "peeling" technique. 2. Input resistance, membrane time constant, and electrotonic length were similar to values reported for other spinal motoneurons. The voltage response of most neck and shoulder motoneurons had a slow, nonlinear component, commonly known as sag, which is also a feature of other spinal motoneurons. Estimates of motoneuron surface area were up to two times larger than the surface area of hindlimb motoneurons. 3. It was possible to estimate electrotonic length and the ratio of the dendritic conductance to the somatic conductance using Johnston's technique for only 6 of 51 motoneurons examined. The responses of these motoneurons were identical to the responses of equivalent cylinder models that had an electrotonic structure derived from the application of Johnston's technique. 4. We were unable to use Johnston's technique for the remaining motoneurons because the ratio, a1/a0, exceeded 2.0. For these motoneurons it was usually impossible to find an equivalent cylinder model whose response matched the experimental data. The failure of equivalent cylinder models to accurately predict the responses of neck and shoulder motoneurons could not be attributed to the sag process or the dendritic geometry of these cells. 5. The electrotonic structure of a group of these motoneurons was further examined using the somatic shunt model developed by Durand and Kawato. After shifting the base line of the experimental records by 1-2 mV in the depolarizing direction, it was possible to find a somatic shunt model whose response was identical to the experimentally recorded voltage response.(ABSTRACT TRUNCATED AT 400 WORDS)

Factors determining the variation of the afterhyperpolarization duration in cat lumbar α-motoneurons

The duration of the afterhyperpolarization (AHP) in cat spinal α-motoneurons varies systematically with motoneurone type, being shorter in motoneurones projecting to fast-contracting muscle units. Recent experiments have shown that the AHP duration is correlated with the amount of sag found in the voltage response to injected constant current pulses. Using a model of the sag process, the present study shows that this correlated is likely to be causal to a substantial extent. Short AHP durations in fast motoneurones may thus be as much, or more, a consequence of a more developed sag process than of faster kinetics of the K conductance process underlying the AHP. This notion is also supported by the experimental observation of a decreased amount of sag and a prolonged AHP duration after axotomy.

Evolution des propriétés rhéologiques de différents types de sangs conservés à + 4°C

Apparent stationary viscosity, viscoelasticity and thixotropy measured with a Couette viscosimeter have been determined on blood samples stored in eight anticoagulant and/or preservative solutions. All the results as well as those obtained in a previous morphological study show clearly the advantages of the SAG or PAGGS storage processes. It is observed that the rheological parameters of RBC stored in protein poor media are, between the 30 th and 35 th days, identical on CPD at the first week and with that measured in CPD concentrates between second and third week (for a same hematocrit value). We want to emphasize that the erythrocytes stored in these new media retain for a long time their ability to circulate in the capillary system.