Fixed Injection Rate Research Articles

Numerical study on nonisothermal reactive viscous fingering

The numerical study examines the dynamics of viscous fingering in a miscible flow displacement involving an exothermic reaction between displacing and displaced fluids producing nanoparticles. The exothermic reaction alters fluid properties by producing nanoparticles and/or by releasing heat at the front, both competitive in nature. The front changes from stable to forward (reverse) fingering when the contribution of temperature (concentration) to the viscosity dominates. For a fixed viscous behavior, decreasing reaction rate weakens the forward movement of fingers and reverse fingering is obtained. For a fixed injection rate, the thermal diffusivity can weaken the thermal gradients leading to a stable displacement even when the system is viscously unstable and can also trigger double-diffusive instability in a viscously stable system. Overall, the study suggests that the interplay between the mass and thermal contribution to the fluid properties and chemical reaction rates governs the fingering dynamics.

Mitigation of Gravity Segregation by Foam to Enhance Sweep Efficiency

Foam-assisted gas injection exhibits promising potential for enhancing sweep efficiency through the amelioration of gravity segregation, particularly within reservoirs characterized by heterogeneity. In this work, the implicit-texture (IT) model featuring two flow regimes is employed to examine the impact of heterogeneity on gravity segregation. The validation of the numerical results for water–gas coinjection and pre-generated foam injection is accomplished through a comparative analysis with analytical solutions. A hypothetical two-layer model with varying permeabilities and thickness ratios is used to examine the impact of foam on gravity segregation. The numerical findings demonstrate satisfactory conformity with analytical solutions in homogeneous reservoirs. A high-permeability top layer in a layered model with a fixed injection rate results in sweep efficiency similar to that of a homogeneous reservoir with each individual permeability. A low-permeability top layer could increase the sweep efficiency, but with severe permeability contrast, the bottom high-permeability layer could impact the displacement process, even with a thin thickness. The sweep efficiency increases with the thickness of the high-permeability top layer and decreases with a thicker low-permeability top layer under fixed injection pressure. The predicted segregation length through a single-layer approximation cannot match the results of the layered models where the permeability contrast is too great or the thickness of two layers is comparable.

λ-Navier-Stokes turbulence.

We investigate numerically the model proposed in Sahoo et al. (2017 Phys. Rev. Lett. 118, 164501) where a parameter λ is introduced in the Navier-Stokes equations such that the weight of homochiral to heterochiral interactions is varied while preserving all original scaling symmetries and inviscid invariants. Decreasing the value of λ leads to a change in the direction of the energy cascade at a critical value [Formula: see text]. In this work, we perform numerical simulations at varying λ in the forward energy cascade range and at changing the Reynolds number [Formula: see text]. We show that for a fixed injection rate, as [Formula: see text], the kinetic energy diverges with a scaling law [Formula: see text]. The energy spectrum is shown to display a larger bottleneck as λ is decreased. The forward heterochiral flux and the inverse homochiral flux both increase in amplitude as [Formula: see text] is approached while keeping their difference fixed and equal to the injection rate. As a result, very close to [Formula: see text] a stationary state is reached where the two opposite fluxes are of much higher amplitude than the mean flux and large fluctuations are observed. Furthermore, we show that intermittency as [Formula: see text] is approached is reduced. The possibility of obtaining a statistical description of regular Navier-Stokes turbulence as an expansion around this newly found critical point is discussed. This article is part of the theme issue 'Scaling the turbulence edifice (part 2)'.

Contrast media injection protocol for portovenous phase abdominal CT: does a fixed injection duration improve hepatic enhancement over a fixed injection rate?

To assess whether a fixed contrast media (CM) injection duration improves the magnitude and inter-patient variability in hepatic enhancement over a fixed injection rate. Outpatients who underwent portovenous phase abdominal CT (fixed duration, February-November 2018; fixed rate, January-July 2020) with 1.22mL/kg iohexol 350 were included. Subjects with liver, kidney or heart disease were excluded. The number of subjects and injection protocols were as follows: fixed duration arm, 56 women, 60 men, 35s injection duration; fixed rate arm, 66 women, 62 men, 3mL/s injection rate. Liver attenuation measurements were obtained from regions of interest on pre- and post-contrast images. Mean hepatic enhancement (MHE) and MHE normalized to iodine dose (MHE/I) were compared (unpaired t-tests and F-tests). There was no statistically significant difference in age, weight, body mass index or CM dosing (p > 0.05). Enhancement indices were significantly lower in the fixed rate group as compared to the fixed duration group, as follows: MHE, 50.0 ± 12 vs. 54.8 ± 11 HU (p = 0.001); and MHE/I, 1.53 ± 0.43 vs. 1.66 ± 0.51 HU/g, (p = 0.04). However, there was no significant difference in the variances of MHE (p = 0.51) and MHE/I (p = 0.08). A fixed CM injection duration yields a greater magnitude in hepatic enhancement indices than a fixed injection rate. Inter-patient variability in hepatic enhancement indices do not significantly differ between the two injection protocols.

Creating a Predictive Model of the Contrast Enhancement for Coronary CT Angiography by Using Statistical Analysis and Machine Learning

The purpose of this study was to calculate statistically significant patient data and test bolus (TB) parameters in order to predict the contrast enhancement of main bolus (eMB) in coronary computed tomography (CT) angiography, and to create a predictive model of eMB with the calculated parameters by machine learning. A total of 126 patients underwent coronary CT angiography. Contrast material was administered at a fixed injection rate and volume. The peak enhancement (PE) and the time needed to reach peak (TP) of the TB were calculated for each patient. The dependency of MB contrast attenuation on these parameters was evaluated. Significant correlations were obtained among PE, TP, and the patient body surface area (BSA) with the eMB. The coefficient of determination of the linear regression model to estimate eMB by machine learning using the above three variables was 0.70 for the training data and 0.55 for the test data. For comparison, the coefficient of determination of the model using only BSA was 0.55 for the training data and 0.36 for the test data; the accuracy of the model created during this time was confirmed.

Numerical Study of the Comparison of Symmetrical and Asymmetrical Eddy-Generation Scheme on the Fire Whirl Formulation and Evolution

A numerical study of the fire whirl formation under symmetrical and asymmetrical entraining configuration is presented. This work aims to assess the effect of eddy-generation configuration on the evolution of the intriguing phenomenon coupled with both flow dynamics and combustion. The numerical framework implements large-eddy simulation, detailed chemistry to capture the sophisticated turbulence-chemistry interaction under reasonable computational cost. It also adopts liquid-based clean fuel with fixed injection rate and uniformed discretisation scheme to eliminate potential interference introduced by various aspects of uncertainties. The result reveals that the nascent fire whirl formulates significantly rapidly under the symmetrical two-slit configuration, with extended flame height and constrained vortex structure, compared with the asymmetrical baseline. However, its revolution orbit gradually diverges from domain centreline and eventually stabilises with a large radius of rotation, whereas the revolution pattern of that from the baseline case is relatively unchanged from the inception of nascent fire whirl. Through the analysis, the observed difference in evaluation pathway could be explained using the concept of circular motion with constant centripetal force. This methodology showcases its feasibility to reveal and visualise the fundamental insight and facilitate profound understanding of the flaming behaviour to benefit both research and industrial sectors.

Estimation of time to peak contrast enhancement of the aorta and liver for dual-phase computed tomography on the basis of contrast medium arrival time, injection duration, and injection technique in dogs.

OBJECTIVE To evaluate the accuracy of estimating time to peak enhancement (TPE) of the aorta and liver parenchyma on the basis of contrast medium arrival time in the aorta, injection duration, and injection technique in dogs. ANIMALS 18 dogs of specific body weight categories (≥ 2 dogs/category) with no liver abnormalities detected via CT. PROCEDURES Dogs were randomly assigned within weight categories to receive contrast medium IV at a fixed injection rate (5 mL/s) or fixed injection duration (20 seconds). Time-contrast attenuation curves were generated from dynamic CT scans acquired at the hepatic hilus. Data collected for contrast medium arrival time and injection duration were used to estimate TPEs of the aorta and liver, and results were compared with the observed TPEs for the aorta and liver. RESULTS Contrast medium arrival time, injection duration, and injection technique were significantly associated with observed values for aortic TPE and explained 96.1% of variation in TPE. For the fixed rate technique, the regression equation for estimating aortic TPE was 0.8 × (injection duration + contrast medium arrival time) + 1.6. For the fixed duration technique, the regression equation changed by only the constant (-2.6). However, the hepatic TPE estimated from the 3 predictor variables was not significantly different from the mean of observed TPEs. CONCLUSIONS AND CLINICAL RELEVANCE Aortic TPE could be accurately estimated from contrast medium arrival time, injection duration, and injection technique in dogs with apparently healthy livers. The regression equations derived from this relationship can be used to improve the efficiency of dual-phase CT of the liver in dogs.

Analysis of capillary pressure and relative permeability hysteresis under low-salinity waterflooding conditions

In this work, we analyze measurements of drainage, spontaneous imbibition and forced imbibition capillary pressure curves in conjunction with two-electrode resistivity on sandstone core samples under low- and high-salinity waterflooding conditions. State-of-the-art laboratory equipment able to work with actual reservoir fluids at reservoir conditions was designed and built to conduct these measurements. Unsteady-state coreflooding experiments under similar experimental conditions to those in the capillary pressure tests were also carried out. A black-oil reservoir simulation model was set up to history match experimental production and pressure data to obtain multi-phase flow functions. Two experiments were conducted on Minnelusa formation (eolian sand) rock samples at 93°C with TC crude oil and synthetic brines. Placement of an oil-wet membrane on one plug end and a water-wet disk on the other end guaranteed that only one phase was able to flow through each sample end at any given time. In one experiment, a 57,491ppm-brine (High-Salinity) was used during the imbibition process, while a 20-fold dilution of the High-Salinity brine (Low-Salinity) was used in the other experiment. Correspondingly, two unsteady-state experiments at fixed injection rate were completed on Minnelusa formation rock samples placed in the coreflooding system using comparable experimental conditions as those in the capillary pressure experiments. Comparison of high- and low-salinity experimental results shows that more noticeable capillary hysteresis toward water-wetness arose in the low-salinity experiment. High-salinity experiment results showed that the imbibition resistivity index was higher than that corresponding to drainage. History matching of the transient production data in capillary pressure experiments along with end-points obtained from unsteady-state core flooding experiments was used to obtain relative permeability curves. Availability of high-quality capillary pressure data at reservoir conditions improved the accuracy of relative permeability curves obtained from history matching unsteady-state core flooding experiments. Our results show a substantial improvement in obtaining both capillary pressure and relative permeability curves at reservoir conditions resulting from a combination of steady- and unsteady-state experiments. Capillary pressure results confirm that hysteresis is more prominent under low-salinity conditions and apparent higher oil trapping is observed during imbibition, compared to high-salinity conditions. Unsteady-state coreflooding results also show that low-salinity brine is not conducive to enhanced oil recovery in low-salinity waterflooding. Geochemical effects appear to negatively impact beneficial interfacial mechanisms proposed to benefit oil recovery such as the formation of more viscoelastic interfaces under low-salinity conditions. We conclude that coupling of fluid–fluid and rock–fluid interactions, including geochemical reactions, needs to be accounted for to better explain low-salinity waterflooding mechanisms.

Gas-Injection Rate Needed for SAG Foam Processes To Overcome Gravity Override

Summary Gravity override is a severe problem in gas-injection enhanced-oil-recovery (EOR) processes, especially in relatively homogeneous formations. Foam can reduce gravity override. Shan and Rossen (2004) show that the best foam process for overcoming gravity override is one of injecting a large slug of surfactant followed by a large slug of gas, injected at constant, maximum-allowable injection pressure. This process works because foam collapses near the injection well, giving good injectivity simultaneously with mobility control at the leading edge of the gas bank. The supply of gas that would be needed to maintain constant injection pressure is a concern for EOR processes in which gas is produced industrially or from a separations plant with limited capacity: The available gas stream may not be sufficient for the optimal process. We show that for such a process, the pressure drop across the foam bank back to the injection well, at fixed injection rate, is nearly constant as the foam bank propagates radially outward. From this result, one can derive a simple formula to predict the rate of gas injection required for each of two limiting cases: An extremely strong foam at the foam front, many times more viscous than the fluids it displaces. In this case, the rate of gas injection required to maintain constant injection pressure is nearly constant, but injection rate is low. A foam just strong enough to maintain mobility control at its leading edge. In this case, injection rate required to maintain constant injection pressure increases steeply with time. Use of the formulae provides a quick initial estimate of how gas-injection rate must vary over the duration of the EOR process to maintain an optimal process. The fit to simulations of surfactant-alternating-gas (SAG) foam-injection rate in a five-spot pattern is remarkably good, especially for strong foam, given the simplicity of the model. In addition, we illustrate how one would determine the properties of a foam that would fit the available gas stream. This criterion then could guide the development of a surfactant formulation with these properties.

Compact-bolus dynamic CT protocol with a test bolus technique in 64-MDCT coronary angiography: comparison of fixed injection rate and duration protocol

We compared the fixed injection rate protocol (P2) with the fixed injection duration protocol (P1) for coronary CT angiography using the test bolus technique. We randomly assigned 100 patients to one of two protocols. In P1, they received 0.7 mL/kg Iohexol-350 in an injection duration of 9 s, and we selected a delay of 3 s after peak enhancement of test bolus scan. In P2, they received 0.7 mL/kg Iohexol-350 at an injection rate of 5 mL/s, and we selected a delay after peak enhancement of test bolus scan using the following formula: TID/2-2 s, where TID is the injection duration of full bolus. We compared attenuation values in the ascending aorta and coronary arteries and patient-to-patient enhancement variability at each segment. At all segments, CT attenuations of P2 were significantly greater than those of P1 (ascending aorta 400 ± 64 vs. 368 ± 60, P = 0.01; left main trunk 399 ± 67 vs. 369 ± 55, P = 0.02; proximal-RCA 393 ± 66 vs. 363 ± 56, P = 0.01). There was no significant difference in patient-to-patient enhancement variability at all segments between the two groups (P > 0.05). P2 yielded superior vessel enhancement and comparable patient-to-patient enhancement variability compared with P1 in thin patients.

FIVE-SPOT INJECTION/PRODUCTION WELL LOCATION DESIGN BASED ON FRACTURE GEOMETRICAL CHARACTERISTICS IN HEAVY OIL FRACTURED RESERVOIRS DURING MISCIBLE DISPLACEMENT: AN EXPERIMENTAL APPROACH

Mapping fracture characteristics by using seismic acquisition and processing is important not only to identify sweet spots, but also to optimize production, especially for unconventional heavy oil reservoirs. In this experimental work we used five-spot micromodels initially saturated with heavy oil to find the optimum well locations during first-contact miscible displacement. The experiments were performed at a fixed injection rate on fractured micromodels with various patterns. The optimum location for injection/production wells was found in the pattern where fractures make an angle of 45° with the mean flow direction. Moreover, oil recovery was increased with the density, length, level of scattering, and discontinuity of fractures. The analysis of the experimentally measured recovery curve revealed that there are three distinct stages for each displacement. The efficiency of the first stage was found to be dominated by dispersion and diffusion. However, the recovery of the second stage was significantly affected by the fracture orientation. The displacement efficiency of the third stage was controlled by solvent dispersion, which is at maximum for the pattern with higher density, length, scattering, and discontinuity of fractures. Saturation monitoring showed that the fracture geometrical characteristics strongly affected the splitting, spreading, and shielding of the produced fingers and solvent front shape and consequently affected the recovery factor. As a result, five-spot micromodels can be used to investigate the optimum location of injection/production wells during miscible displacements in fractured heavy oil reservoirs.

EFFECT OF CONTRAST MEDIUM INJECTION DURATION ON PEAK ENHANCEMENT AND TIME TO PEAK ENHANCEMENT OF CANINE PULMONARY ARTERIES

Our goal was to investigate the effect of contrast medium injection duration on pulmonary artery peak enhancement and time to peak enhancement. Fourteen dogs were allocated into one of seven predefined weight categories, each category contained two dogs. Dogs in each weight category were assigned to group A or B. Animals in each group received a different contrast medium injection protocol. In group A, a fixed injection rate of 5 ml/s was used. In group B, the contrast injection rate was calculated as follows: flow rate= contrast volume/scan duration + 10s. Time to peak enhancement and peak enhancement of the main left and right pulmonary arteries were measured on single-level, dynamic CT images for a fixed time of 30s. Rank correlation (Spearman's) coefficients between injection duration and time to peak enhancement and between body weight and peak enhancement were calculated. For group A, there was a significant negative correlation between peak enhancement and weight (r = -0.94; P = 0.005), while for group B, there was no significant correlation (r = -0.64 and P = 0.18). There was a significant correlation between time to peak enhancement and injection duration in both groups (group A: r = 0.99; P = 0.006 and group B: r = 0.85; P = 0.02). In conclusion, injection duration is a key feature in a CT angiography injection protocol. A protocol with an injection duration adjusted to the scan duration seems to be particularly suitable for veterinary applications where a population with great weight variability is studied.

Effect of contrast medium injection duration on peak enhancement of canine pulmonary arteries

Our goal was to investigate the effect of contrast medium injection duration on pulmonary artery peak enhancement and time to peak enhancement. Fourteen dogs were allocated into one of seven predefined weight categories, each category contained two dogs. Dogs in each weight category were assigned to group A or B. Animals in each group received a different contrast medium injection protocol. In group A, a fixed injection rate of 5ml/s was used. In group B, the contrast injection rate was calculated as follows: flow rate1⁄4contrast volume/scan durationþ10s. Time to peak enhancement and peak enhancement of the main left and right pulmonary arteries were measured on single-level, dynamic CT images for a fixed time of 30 s. Rank correlation (Spearman’s) coefficients between injection duration and time to peak enhancement and between body weight and peak enhancement were calculated. For group A, there was a significant negative correlation between peak enhancement and weight (r1⁄4

Foam Delivery of Amendments for Vadose Zone Remediation: Propagation Performance in Unsaturated Sediments

Foam delivery of remedial amendments is potentially useful for vadose zone remediation because aqueous amendments are delivered while a low water content is maintained in the treated zones. The transport behavior of foam in the vadose zone has not been well studied. Benchtop‐scale column tests were conducted to investigate foam transport, foaming gas and liquid propagation, pressure buildup and distribution, the influence of foam quality and sediment permeability on foam injection pressure, and liquid uptake and distribution during foam flow in unsaturated sediments. Results indicated that under unsaturated conditions, the foaming gas front traveled much faster than the foam front where bubble rupture was significant. A liquid front was formed ahead of the foam flow front. The accumulated liquid in this front was mainly composed of the water injected with the foam. The foam injection pressure was primarily attributed to the resistance to foam flow by the sediment but not to the movement of the water ahead of the foam front. The foam had a high effective viscosity compared with water. A near‐linear pressure distribution within the foam‐occupied column section was observed. At a fixed injection rate, higher foam quality resulted in lower injection pressure. Higher permeability sediments did not necessarily have a lower foam injection pressure because other factors, such as the foam injection rate, foam bubble diameter, and sediment pore size, also influenced the pressure. In the foam flushed region, the liquid uptake and water content distribution in the sediment was negligibly affected by the initial water content and the foam injection rate within the ranges tested in this study. The implications of these findings to field remediation application were considered.

冠動脈ＣＴＡ検査のための至適造影剤注入法の検討：テストボーラスパラメータと被検者の性差，ＢＳＡを用いた注入ヨード量調整法

The purpose of this study was to correlate test bolus (TB) parameters and patient information and cardiac function with main bolus (MB) contrast density for 64-slice computed tomography, and to evaluate MB contrast density on a fixed injection rate, in comparison with an injection rate adjusted with TB parameters and patient information. A total of 256 patients underwent coronary CT angiography. In 126 patients (group 1), contrast material was administered at a flow rate of 4 ml/sec. The peak enhancement, the time needed to reach the peak of the TB and cardiac function of the MB were calculated for each patient in this group. The dependency of MB contrast attenuation on these parameters was evaluated. Significant correlations were obtained between the peak density of the TB and the patient's body surface area (BSA) with the enhancement of MB. Furthermore, females showed a higher peak enhancement of MB than males. In view of the results of group 1, in the other 130 patients (group 2) injection protocols were computed by using regression analysis of each patient's attenuation response to a TB and patient sex and BSA. Compared with group 1, the variations of MB contrast density of group 2 were reduced. Optimized contrast injection protocols are useful to reduce variations of MB contrast density, by taking these TB parameters and patient sex and BSA into account.

Does iodine concentration affect the diagnostic efficacy of biphasic spiral CT in patients with hepatocellular carcinoma?

We investigated the effect of iodinated contrast medium concentration on increased neoplastic lesion enhancement and its direct relation to diagnostic efficacy in biphasic spiral computed tomography for detection of hepatocellular carcinoma. A pilot, single-center, randomized, double-blind, crossover, comparative study was performed and included 22 participants. Each patient underwent two separate biphasic contrast-enhanced spiral computed tomographic examinations. Scans were performed with iomeprol containing 400 (iomeprol 400) or 300 (iomeprol 300) mg of iodine per milliliter (Iomeron, Bracco Imaging SpA, Milan, Italy) with a 2- to 12-day window scan; patients were given an equal total dose of 45 g of iodine at a fixed injection rate of 4 mL/s. Comparison included assessment of quantitative and qualitative parameters. Lesion density and lesion-to-liver contrast increased more markedly with the higher concentration of contrast medium during the arterial phase (p = 0.0016 and 0.0005, respectively). There was no significant difference in any parameter between the two concentrations during the portal phase. Number of lesions detected during the arterial phase increased from 37 with iomeprol 300 to 42 with iomeprol 400; in the portal phase, the respective numbers were 34 and 36. Even though a small number of patients was examined, our study suggests that, in patients with cirrhosis, an increased concentration of iodine improves liver-to-lesion contrast and may improve the detection of hepatocellular carcinoma.