Water Fingers Research Articles

Self-induced Hot Water Finger Burn Trying to Get Feeling Back after Ropivacaine Block

Summary: This case report is about a patient with self-induced hot water burns several hours after an infraclavicular block with ropivacaine for a scaphoid fracture operation. This patient was honest about what happened. However, some patients are too embarrassed to admit what they did to themselves. The injury may be misdiagnosed by the emergency department physician or by the surgeon because the history is incomplete. The resulting burn, which can lead to fingertip loss when severe, can be erroneously misdiagnosed as an ischemic injury after lidocaine with epinephrine local anesthesia. Most hand surgeons have seen ischemic finger injuries the morning after failed finger replantation. Acutely ischemic fingers from arterial insufficiency do not have parallel hot water burn lines, reactive hyperemia at the base of the burn, or burn blisters at the fingertips. The purpose of this article and its video is to help physicians and nurses recognize the three signs of self-induced hot water finger burns after local anesthesia: (1) a parallel hot water line in the fingers at the proximal burn level; (2) reactive hyperemia just proximal to the burn line; (3) burn blisters in the submerged fingertips. When seeing postoperative patients with these signs, the examining clinician may tactfully ask: “Did you try to get the feeling back in your fingers by warming them?” It is hoped that the patient may then reveal that he tried warming the finger in water, and that may lead to the truth that the water was indeed too hot.

Short-term cocoa bioflavanol supplementation does not improve cold-induced vasodilation in young healthy adults.

Cold-induced vasodilation (CIVD) is an oscillatory rise in blood flow to glabrous skin that occurs in cold-exposed extremities. Dietary flavanols increase bioavailable nitric oxide, a proposed mediator of CIVD through active vasodilation and/or withdrawal of sympathetic vascular smooth muscle tone. However, no studies have examined the effects of flavanol intake on extremity skin perfusion during cold exposure. We tested the hypothesis that acute and 8-day flavanol supplementation would augment CIVD during single-digit cold water immersion (CWI). Eleven healthy adults (24 ± 6years; 10M/1F) ingested cocoa flavanols (900mg/day) or caffeine- and theobromine-matched placebo for 8days in a double-blind, randomized, crossover design. On Days 1 and 8, CIVD was assessed 2h post-treatment. Subjects immersed their 3rd finger in warm water (42°C) for 15min before CWI (4°C) for 30min, during which nail bed and finger pad skin temperature were measured. Flavanol ingestion had no effect on CIVD frequency (Day 1, Flavanol: 3 ± 2 vs. Placebo: 3 ± 2; Day 8, Flavanol: 3 ± 2 vs. Placebo: 3 ± 1) or amplitude (Day 1, Flavanol: 4.3 ± 1.7 vs. Placebo: 4.9 ± 2.6°C; Day 8, Flavanol: 3.9 ± 1.9 vs. Placebo: 3.9 ± 2.0°C) in the finger pad following acute or 8-day supplementation (P > 0.05). Furthermore, average, nadir, and apex finger pad temperatures during CWI were not different between treatments on Days 1 or 8 of supplementation (P > 0.05). Similarly, no differences in CIVD parameters were observed in the nail bed following supplementation (P > 0.05). These data suggest that cocoa flavanol ingestion does not alter finger CIVD. Clinical Trial Registration Clinicaltrials.gov Identifier: NCT04359082. April 24, 2020.

Linear Stability of Filtration Flow of a Gas and Two Immiscible Liquids with Interfaces

The stability of the vertical flow that occurs when gas displaces oil from a reservoir is investigated. It is assumed that the oil and gas areas are separated by a layer saturated with water. This method of oil displacement, called water-alternating-gas injection, improves the oil recovery process. We consider the linear stability of two boundaries that are flat at the initial moment, separating, respectively, the areas of gas and water, as well as water and oil. The instability of the interfaces can result in gas and water fingers penetrating into the oil-saturated area and causing residual oil. Two cases of perturbation evolution are considered. In the first case, only the gas–water interface is perturbed at the initial moment, and in the second case, small perturbations of the same amplitude are present on both surfaces. It is shown that the interaction of perturbations at interfaces depends on the thickness of the water-saturated layer, perturbation wavelength, oil viscosity, pressure gradient and formation thickness. Calculations show that perturbations at the oil–water boundary grow much slower than perturbations at the gas–water boundary. It was found that, with other parameters fixed, there is a critical (or threshold) value of the thickness of the water-saturated layer, above which the development of perturbations at the gas–water boundary does not affect the development of perturbations at the water–oil boundary.

New Mathematical Technique for Step Rate Test Analysis Aids Determination of Fracture Pressure and Overcomes the Uncertainty of Conventional Analysis.

Experience in the oil industry has shown that it is challenging to sustain successful long-term matrix injection, as injection water quality cannot be maintained rigorously due to facility hiccups and membrane clogging. Most oil field operators have resolved this problem of injectivity decline by increasing the surface injection pressure to part the formation and inject just above the fracture gradient with strict offtake management for zonal conformance. This is not an easy task as injection much above fracture opening pressure can lead to water fingering and poor sweep that results in uneconomical waterflood recovery. The operators, thus, strive to inject at a pressure just above the fracture opening pressure so that the fracture opens near the wellbore but does not extend and then maintain the pressure just above the fracture closing pressure. Therefore, determination of the fracture opening pressure and fracture closing pressure has remained critical data for the success of waterflood projects. The most reliable industry approach to estimating fracture opening and fracture closing pressures comes from the step rate test (SRT). This traditional approach of Cartesian analysis of pressure-rate plot fits straight lines through the data in a plot of injection pressure against injection rate and then estimates the fracture pressure from the intersection of these lines having different slopes. The data received often do not exhibit one clear change in slope, thus resulting in multiple possible solutions, making it difficult for the operator to use the data for high CAPEX facilities design. Most past studies indicate the subjectivity of this Cartesian slope fitting technique. Alternative solutions through multirate superposition analysis found limited application in the analysis of SRT data due to considerable sensitivity to the value of initial pressure used for superposition and lack of stability of rate and pressure data. In this article, a new technique of SRT analysis is presented, which provides a unique solution for fracture opening and fracture closing pressures. It helps to overcome the limitations of the traditional technique of arbitrary fitting of straight lines. It uses the mathematical understanding of cumulative derivatives to recognize that the matrix opens when the cumulative growth of the rate of injectivity shows a change. It estimates the derivative of the injection rate with respect to injection pressure at each step. Then, it estimates the fracture pressure from the plot of the cumulative of this derivative against pressure at each step. It helps to overcome the challenge SRT solutions posed by the nonlinear trend of pressure data at each injection step both before fracture and after fracture is initiated. It also overcomes the limitations of the multirate superposition technique, as it is not sensitive to the value of initial pressure used for superposition.

Application of rectal balloon ice water stimulation for the rehabilitation of stroke patients with neurogenic bowel dysfunction.

Neurogenic bowel dysfunction (NBD) is a common complication in stroke patients. To investigate the effect of rectal balloon ice water stimulation on the rehabilitation of patients with NBD after a cerebral stroke. Forty stroke patients with NBD were selected between March and August 2022 and randomly divided into a study group (n = 20) and a control group (n = 20). Based on routine rehabilitation training, rectal balloon ice water stimulation or finger rectal stimulation were performed on the study or control group, respectively. After two weeks, the changes in the NBD, self-rating depression scale (SDS) and self-rating anxiety scale (SAS) scores were compared between the two groups. Before the intervention, there were no significant differences in age, sex ratio, and NBD, SDS and SAS scores between the two groups (p > 0.05). The NBD, SDS and SAS scores of both groups were significantly decreased following intervention (p < 0.05). After 2 weeks of intervention, the NBD score of the study group was significantly lower than that of the control group (5.50±1.28 vs 6.45±1.05; p = 0.014). The SDS score of the study group was lower than that of the control group, and the difference was statistically significant (32.30±2.81 vs 44.05±2.19; p = 0.014). The study group also had significantly lower SAS scores than the control group (p = 0.024). In addition, the incidence of dizziness, headaches, nausea, vomiting and abdominal pain and distension in the study group was significantly lower than in the control group (p < 0.05). Rectal balloon ice water stimulation can significantly improve stroke patients with NBD's intestinal function and psychological status.

A novel topographically patterned MXene@MnO2/PVDF piezo-active hybrid for flexible real-time and sensitive force sensor

Flexible force sensors capable of real-time and sensitive analysis have gained immense popularity because of their great potential to be integrated into potable and wearable electronics. Herein, a novel flexible force sensor constructing from topographically patterned piezo-active MXene@MnO2/poly(vinylidene fluoride) (PVDF) hybrid that allows for real-time precise pressure detection is proposed. Benefiting from the synergistic effect of topographical patterning and nano-reinforcement filling, the piezo-active hybrids with convex microarrays patterns demonstrate outstanding piezoelectric coefficient d33 (49 pC/N) and output upon mechanical stimuli, enabling the resultant force sensors with high voltage sensitivity of 0.450 V/N, fast response time of 16–19 ms and excellent operation stability. Furthermore, the feasibility of sensors in effectively detecting water droplets, gas flow and finger bending is demonstrated, confirming their viability for real applications.

Experimental and simulation analysis of liquid capillary fingering process in the gas diffusion layer

In a proton exchange membrane fuel cell (PEMFC), water movement through the gas diffusion layer (GDL) is essential for water management. Using a combination of experiments and simulations, this paper investigates the capillary fingering process of liquid water within the GDL and analyzes the effects of flow field type, GDL compression ratio, and contact angle on the capillary fingering of liquid water within the GDL. The results reveal finger-stopping, splitting, and fusion during the injection of non-wetting liquid, which is not conducive to rapid water movement within the GDL. When water breaks through the top layer of the fibers, a finger path between the inlet and the gas channel is formed, and the liquid preferentially migrates along this path. Due to the existence of air cross-flow, the GDL water saturation for the serpentine/cross-finger flow field is 17.2%. The water preferentially produces directional flow in the through-plane direction as the compression ratio rises, and the GDL water saturation falls to 24.18%. The distribution of anisotropic contact angles determines the flow state of liquid water, making water removal from the GDL easier. The results and findings here are expected to lead to more reliable water management and related high-power technologies of PEMFCs.

Dietary Bioflavanol Supplementation Does Not Improve Cold‐Induced Vasodilation in Healthy Adults

BackgroundCold‐induced vasodilation (CIVD) is a cyclical rise in blood flow to glabrous skin that occurs during cold exposure of the extremities. Nitric oxide (NO) is a proposed mediator of the CIVD response through active vasodilation and/or withdrawal of sympathetic vascular smooth muscle tone. Dietary flavanols augment bioavailable NO by upregulating NO synthase, the main source of NO in the vasculature, and by enhancing removal of reactive oxygen species that are known to breakdown NO. Although acute dietary flavanol intake has been shown to augment skin blood flow, at least in part through increased NO, no studies have examined the impact of flavanol intake on skin perfusion during cold exposure. Improving skin blood flow to the extremities may enhance manual dexterity and reduce the risk of peripheral cold injury, benefits pertinent to warfighters or other populations that spend time in cold environments.PurposeTo examine the effect of high‐dose flavanol supplementation on CIVD. We hypothesized that acute and 8‐day flavanol supplementation would augment CIVD during single‐digit cold water immersion.MethodsEleven healthy adults (24±6 yrs; 10M/1F) ingested cocoa‐based flavanols (FLV; 900 mg/d) or caffeine and theobromine‐matched placebo (PLA) for 8 days in a double‐blind, randomized, crossover design. On Days 1 and 8, CIVD was assessed 2 hours after treatment ingestion. Subjects immersed their middle finger in warm water (42°C) for 15 minutes before cold water immersion (4°C) for 30 min, during which nail bed and finger pad skin temperature were measured continuously.ResultsFlavanol ingestion had no effect (all P &gt; 0.05) on CIVD event frequency (Day 1, FLV: 3±2 vs. PLA: 3±2; Day 8, FLV: 3±2 vs. PLA: 3±1) or amplitude (Day 1, FLV: 4.3±1.7 vs. PLA: 4.9±2.6 °C; Day 8, FLV: 3.9±1.9 vs. PLA: 3.9±2.0 °C) in the finger pad following acute or 8‐day supplementation. Furthermore, average (Day 1, FLV: 9.2±1.5 vs. PLA: 9.2±1.8 °C; Day 8, FLV: 8.3±1.7 vs. PLA: 8.9±1.9 °C), maximum (Day 1, FLV: 11.9±3.0 vs. PLA: 11.2±2.3 °C; Day 8, FLV: 10.1±1.9 vs. PLA: 10.6±2.3 °C), and minimum (Day 1, FLV: 6.2±1.3 vs. PLA: 6.0±1.5 °C; Day 8, FLV: 5.8±1.8 vs. PLA: 6.2±1.7 °C) finger pad temperatures during cold water immersion were not different (all P &gt; 0.05) between treatments on Day 1 or Day 8 of supplementation. Similarly, no differences (all P &gt; 0.05) in CIVD parameters were observed in the nail bed following acute or 8‐day supplementation.ConclusionDietary ingestion of cocoa‐based flavanols does not improve the CIVD response to single‐digit cold water immersion.

Molecular dynamics simulations of the evaporation of hydrated ions from aqueous solution

Although important for atmospheric processes and gas-phase catalysis, very little is known about the hydration state of ions in the vapor phase. Here we study the evaporation energetics and kinetics of a chloride ion from liquid water by molecular dynamics simulations. As chloride permeates the interface, a water finger forms and breaks at a chloride separation of ≈ 2.8 nm from the Gibbs dividing surface. For larger separations from the interface, about 7 water molecules are estimated to stay bound to chloride in saturated water vapor, as corroborated by continuum dielectrics and statistical mechanics models. This ion hydration significantly reduces the free-energy barrier for evaporation. The effective chloride diffusivity in the transition state is found to be about 6 times higher than in bulk, which reflects the highly mobile hydration dynamics as the water finger breaks. Both effects significantly increase the chloride evaporation flux from the quiescent interface of an electrolyte solution, which is predicted from reaction kinetic theory.

Hygienic disposal of stools and risk of diarrheal episodes among children aged under two years: Evidence from the Ghana Demographic Health Survey, 2003–2014

BackgroundMost childhood diarrheal illnesses are a result of the faeco-oral transmission of infected food, water, and unclean fingers. The present paper was conducted to estimate the prevalence of hygienic disposal of stools (HDS) and its associated factors, and further quantify the impact of HDS on diarrheal diseases among children under two years.MethodsA cross-sectional design was used to evaluate three rounds of the Ghana Demographic Health Survey (GDHS) from 2003–2014 involving 4869 women with children aged under two years. The outcomes were prevalence of HDS and diarrheal diseases. Poisson regression model was employed to assess risk factors associated with HDS and dominance analysis was used to rank the important risk factors. Inverse Probability Weighting Poisson Regression Adjustment (IPWPRA) with Propensity Score 1:1 density kernel-based matching was employed to assess impact.ResultsThe pooled prevalence rate of HDS was 26.5%(95%CI = 24.6–28.4) and it ranged from 18.7% (95%CI = 16.4–21.2) in 2014 to 38.8%(95%CI = 35.3–42.4) in 2003. Diarrhea diseases pooled prevalence was 17.9%(95%CI = 16.4–19.5) and ranged from 13.3%(95%CI = 11.1–15.9) in 2014 to 25.4%(95%CI = 22.2–28.9) in 2003. The overall growth rate for HDS and prevalence of diarrhea diseases, decreased by 21.6% and 11.4% respectively. The most important risk factors of HDS from dominance analysis included; age of the child, wealth index, and differences in region. From pooled data wealth index, increasing age of the child, and regional disparity constituted approximately 72% of the overall impact (Weighted Standardized Dominance Statistics (WSDS) = 0.30, 0.24, and 0.19 respectively). In 2014, they constituted approximately 79% (WSDS = 0.139, 0.177 and 0.471 respectively). The average prevalence of diarrheal diseases among children of women who practiced HDS reduced over the period of the GDHS compared to those whose mothers did not practice HDS [2008 ATE(95%CI) = -0.09(-0.16–0.02), 2014 ATE(95%CI) = -0.05(-0.09–0.01) and Pooled data ATE(95%CI) = -0.05(-0.09–0.02)].ConclusionThis analysis has provided empirical evidence of the impact of practicing HDS in Ghana from a national household survey. Implementation of the WASH agenda in this low-income setting requires a synergy of interventions and collaborations of actors (government, private and development partners) to improve water and sanitation facilities and to increase hygiene education to prevent the spread of diseases including diarrhea by 2025.

The Role of Immiscible Fingering on the Mechanism of Secondary and Tertiary Polymer Flooding of Viscous Oil

Immiscible viscous fingering in porous media occurs when a low viscosity fluid displaces a significantly more viscous, immiscible resident fluid; for example, the displacement of a higher viscosity oil with water (where μo > > μw). Classically, this is a significant issue during oil recovery processes, where water is injected into the reservoir to provide pressure support and to drive the oil production. In moderate/heavy oil, this leads to the formation of strong water fingers, bypassed oil and high/early water production. Polymer flooding, where the injected water is viscosified through addition of high molecular weight polymers, has often been applied to reduce the viscosity contrast between the two immiscible fluids. In recent years, there has been significant development in the understanding of both the mechanism by which polymer flooding improves viscous oil recovery, as well as in the methodologies available to directly simulate such processes. One key advance in modelling the correct mechanism of polymer oil recovery in viscous oils has been the development of a method to accurately model the “simple” two-phase immiscible fingering (Sorbie in Transp Porous Media 135:331–359, 2020). This was achieved by first choosing the correct fractional flow and then deriving the maximum mobility relative permeability functions from this. It has been proposed that central to the polymer oil recovery is a fingering/viscous crossflow mechanism, and a summary of this is given in this paper. This work seeks to validate the proposed immiscible fingering/viscous crossflow mechanism experimentally for a moderately viscous oil (μo = 84 mPa.s at 31 °C; μw = 0.81 mPa.s; thus, (μo/μw) ~ 104) by performing a series of carefully monitored core floods. The results from these experiments are simulated directly to establish the potential of our modified simulation approach to capture the process (Sorbie, et al., 2020). Both secondary and tertiary polymer flooding experiments are presented and compared with the waterflood baselines, which have been established for each core system. The oil production, water cut and differential pressure are then matched directly using a commercial numerical reservoir simulator, but using our new “fractional flow” derived relative permeabilities. The use of polymer flooding, even when applied at a high water cut (80% after 0.5 PV of water injection), showed a significant impact on recovery; bringing the recovery significantly forward in time for both tertiary and secondary polymer injection modes—a further 13–16% OOIP. Each flood was then directly matched in the simulator with excellent agreement in all experimental cases. The simulations allowed a quantitative visualisation of the immiscible finger propagation from both water injection and the banking of connate water during polymer flooding. Evidence of a strong oil bank forming in front of the tertiary polymer slug was also observed, in line with the proposed viscous crossflow mechanism. This work provides validation of both polymer flooding’s viscous crossflow mechanism and the direct simulation methodology proposed by Sorbie et al. (Transp Porous Media 135:331–359, 2020). The experimental results show the significant potential for both secondary and tertiary polymer flooding in moderate/heavy oil reservoirs.

Triggering the Splitting Dynamics of Low-Viscous Fingers through Surface Wettability Inside Bifurcating Channel

This work presents the splitting dynamics of low-viscous fingers inside the single bifurcating channel through the surface wettability of daughter branches. The propagation of low-viscous fingers inside branching microchannels have importance in many applications, such as microfluidics, biofluid mechanics (pulmonary airway reopening), and biochemical testing. Several numerical simulations are performed where a water finger propagates inside the silicon oil-filled bifurcating channel, and at the bifurcating tip, it splits into two fingers and these fingers propagate into the separate daughter branches. It is noticed that the behaviour of finger splitting at the bifurcating tip depends upon numerous parameters such as surface wettability, capillary number, viscosity ratio, and surface tension. This study aims to trigger the behaviour of finger splitting through the surface wettability of daughter branches θ 1 , θ 2 . Therefore, a series of numerical simulations are performed by considering four different surface wettability configurations of daughter branches, i.e., θ 1 , θ 2 ∈ 78 ° , 78 ° ; 78 ° , 118 ° ; 78 ° , 150 ° ; 150 ° , 150 ° . According to the results obtained from numerical simulations, finger splitting may be categorized into three types based on splitting ratio λ , i.e., symmetrical splitting, nonsymmetrical splitting, and reversal (no) splitting. It is noticed that the surface wettability of both daughter branches is either hydrophilic 78 ° , 78 ° or superhydrophobic 150 ° , 150 ° , providing symmetrical splitting. The surface wettability of one of the daughter branches is hydrophilic and another is hydrophobic 78 ° , 118 ° , providing nonsymmetrical splitting. The surface wettability of one of the daughter branches is hydrophilic and another is superhydrophobic 78 ° , 150 ° , providing reversal splitting. The findings of this investigation may be incorporated in the fields of biochemical testing and occulted pulmonary airways reopening as well as respiratory diseases such as COVID-19.

Insights into oil recovery mechanism by Nothing-Alternating-Polymer (NAP) concept

This paper introduces new oil recovery mechanisms for oil recovery by polymer injection in heavy oil reservoirs with strong bottom aquifers. Due to unfavorable mobility ratio between aquifer water and oil and the development of the sharp cones significant amount of oil remains unswept. To overcome these issues, for the case demonstrated in this paper, a polymer injection pilot was executed with three horizontal injectors, located a few meters above the oil/water contact. The injectivity issues resulted in frequent shutdowns of the injectors. Interestingly, the water cut reversal and oil gain continued during the shut-in periods. This observation has led to the development of a new cyclic polymer injection strategy, in which the injection of polymer is alternated with intentional well shut-ins. The strategy is referred to as Nothing-Alternating-Polymer (NAP).It was found that during polymer injection, the oil is recovered by conventional mobility and sweep enhancement mechanisms ahead of the polymer front. Additionally, during this stage the injected polymer squeezes the existing cones and creates a barrier between the aquifer and the oil column, suppressing the aquifer flux and hence the negative effect of the cones or water channels (blanketing mechanism). Moreover, injection of polymer pushes the oil to the depleted water cones, which is then produced by the water coming from the aquifer during shut-in period (recharge mechanism). During the shut-in or NAP period, the aquifer water also pushes the existing polymer bank and hence leads to extra oil production. The resistance caused by polymer adsorption reduces the extent of fingering of water into polymer bank. The NAP strategy reduces polymer loss into aquifer and improves the polymer utilization factor expressed in kg-polymer/bbl of oil, resulting in a favorable economic outcome.

Effect of water injection on subsequent polymer floods in viscous oil reservoirs

Waterfloods (WF) in viscous oil reservoirs (>100 cp) are unstable and usually bypass a large amount of oil. Polymer floods (PF) often follow waterfloods and improve oil recovery through improved sweep efficiency. This study examines the effect of prior waterflood on the subsequent polymer flooding. The displacement of a viscous oil by water and polymer solution is studied in a custom-built 2D porous medium. Floods are conducted at the interstitial velocity of 1 ft/day with the oil viscosity (μo) of 390 cp at 25 °C. The extent of waterflood beyond the water breakthrough (WBT) is varied from 0 to 0.5 injected pore volume (PV). Polymer injection after the waterflood displaces the oil which further pushes the brine in the established water fingers and is reflected in a decrease in the water cut down to 0–0.3. After dewatering of the fingers, the polymer solution displaces the oil across the whole cross-section. The final recoveries range from 73 to 83 % of the original oil in place (OOIP). Injecting the viscous solution at earlier stages results in earlier production, higher crest of oil cut (fo) and slightly higher cumulative oil production (NpD). This work can help engineers optimize the strategy of polymer flooding in viscous oil reservoirs.

Research on Water Invasion Mode and Water Control Counter Measures of Geological MX Gas Reservoir

The MX gas reservoir is a typical carbonate gas reservoir and there are three types of water production characteristics in producing wells during the development process: fast rising type, slow rising type and stable type. The overall water invasion mode is dominated by the edge water invasion mode, with four types of water invasion modes including bottom water cone type, edge water finger type, edge water tongue type and native movable water tongue type. In this paper, numerical simulation techniques are used to investigate water management countermeasures for MX gas reservoirs based on the dynamic identification of water invasion. The results show that, after optimisation of the drainage and water control plans, the gas reservoir can produce steadily until the end of 2025 at a recovery rate of 3.06%, extending the time of steady production by about 9 months. In view of the relatively uniform advancement of fracture water channel and edge water into the interior of the gas reservoir, it is feasible to adopt active drainage and edge water control measures respectively to reduce the risk of water intrusion in the gas reservoir and ensure stable gas production.

Viscous Fingering of Irreducible Water During Favorable Viscosity Two-Phase Displacements

Multiphase displacements in porous media are expected to be stable if the injectant has a smaller mobility than the resident phase and injection velocity is small. We investigate two-phase displacements (aqueous phase displacing oleic phase) at favorable mobility ratios, which are expected to be stable, and find that the presence of low-viscosity irreducible water promotes the formation of viscous instabilities. Microfluidic experiments and Lattice Boltzmann (LB) simulations were utilized to identify the effects of pore-scale mobilization of irreducible water on centimeter-scale flow patterns during favorable displacements. Displacements in glass micromodels showed the presence of low viscosity irreducible water resulted in fingering and early breakthrough compared to experiments with high viscosity irreducible water (glycerol solution). The LB simulations were used to explain that fingers formed because irreducible water was mobilized ahead of the injected water. The low viscosity aqueous front fingered through the oil as the viscosity of the oil was larger than that of the low viscosity aqueous phase bank. Additionally, we conducted a coreflood that showed breakthrough of the aqueous phase occurred slightly earlier when irreducible aqueous phase viscosity was low (1 cp) than when irreducible aqueous phase viscosity was large (69 cp). The novelty of this work lies in showing that presence of low viscosity irreducible water may result in an unstable displacement of medium viscosity oil by high viscosity aqueous solution at small flooding velocities.

The Impact of Rheology on Viscous Oil Displacement by Polymers Analyzed by Pore-Scale Network Modelling.

Several experimental studies have shown significant improvement in heavy oil recovery with polymers displaying different types of rheology, and the effect of rheology has been shown to be important. These experimental studies have been designed to investigate why this is so by applying a constant flow rate and the same polymer effective viscosity at this injection rate. The types of rheology studied vary from Newtonian and shear thinning behavior to complex rheology involving shear thinning and thickening behavior. The core flood experiments show a significantly higher oil recovery with polyacrylamide (HPAM), which exhibits shear thinning/thickening behavior compared to biopolymers like Xanthan, which is purely shear thinning. Various reasons for these observed oil recovery results have been conjectured, but, to date, a clear explanation has not been conclusively established. In this paper, we have investigated the theoretical rationale for these results by using a dynamic pore scale network model (DPNM), which can model imbibition processes (water injection) in porous media and also polymer injection. In the DPNM, the polymer rheology can be shear thinning, shear thinning/thickening, or Newtonian (constant viscosity). Thus, the local effective viscosity in a pore within the DPNM depends on the local shear rate in that pore. The predicted results using this DPNM show that the polymer causes changes in the local flow velocity field, which, as might be expected, are different for different rheological models, and the changes in the velocity profile led to local diversion of flow. This, in turn, led to different oil recovery levels in imbibition. However, the critical result is that the DPNM modelling shows exactly the same trend as was observed in the experiments, viz. that the shear thinning/thickening polymer gave the highest oil recovery, followed by the Newtonian Case and the purely shear thinning polymer gave the lowest recover, but this latter case was still above the waterflood result. The DPNM simulations showed that the shear-thinning/thickening polymer show a stabilized frontal velocity and increased oil mobilization, as observed in the experiments. Simulations for the shear-thinning polymer show that, in high-rate bonds, the average viscosity is greatly reduced, and this causes enhanced water fingering compared to the Newtonian polymer case. No other a priori model of the two-phase fluid physics of imbibition, coupled with the polymer rheology, has achieved this degree of predictive explanation, of these experimental observations, to our knowledge.

Recent progress in simulating microscopic ion transport mechanisms at liquid-liquid interfaces.

Transport of ions through liquid-liquid interfaces is of fundamental importance to a wide variety of applications. However, since it is quite challenging for experimentalists to directly and selectively observe molecules at the interfaces, microscopic mechanisms of ion transport have been largely presumed from kinetic information. This Perspective illustrates recent examples that molecular dynamics simulations with proper free energy surfaces clarified mechanistic pictures of ion transport. The key is a proper choice of coordinates and defining/calculating free energy surfaces in multidimensional space. Once the free energy surfaces for realistic systems are available, they naturally provide new insight into the ion transport in unprecedented details, including water finger, transient ion pairing, and electron transfer.

The Effect of Flow Swing on Waterflood Under Oil-Wet Conditions: A Pore-Level Study

The stability of the waterfront in a heterogeneous porous medium and in the absence of gravity effects is controlled by capillary and viscous forces. Under oil-wet conditions, waterflood is a drainage process and the displacement front advances in zones with larger pores where capillary forces are lower, and the rate of displacement is higher compared to zones with smaller pores. Hence, in a waterflood process, a transition zone is formed where the water saturation gradually decreases from a trailing front to the leading end of advanced water fingers. In a heterogeneous medium, oil–water capillary pressure fluctuates due to variations of pore sizes in flooding paths. The difference in the capillary pressures between leading and trailing zones can help with the stability of the waterfront when the capillary pressure in frontal zones is increased by displacing oil through smaller pores. However, this mechanism creates a limited pressure gradient in the oil phase, so the waterfront instabilities continue to grow, especially at the adverse mobility ratio and high displacement rates. In this study, different oil samples with low, medium and high viscosities are displaced by water in an oil-wet medium containing pore-level heterogeneities. Herein, the effect of flow swing, which is introduced to the direction of oil–water displacement, on waterflood performance is investigated. Under flow-swing conditions, we reverse the fluid flow direction periodically; however, the overall volume of injected water is maintained the same for all scenarios by adjusting the periods of the forward and reverse steps. The flow reversal promotes the refill of water paths with oil, hence attenuating the advanced fingers. Consequently, the sweep efficiency of waterflood is improved and higher oil sweep efficiency is obtained at the time of breakthrough. The flow-swing mechanism is more effective when oscillations of capillary pressure result in a faster flow of oil between trailing and leading zones, thus decreasing the waterfront instabilities. The new process can be optimized and utilized at larger scales for improving the sweep efficiency of flooding operations.

Characterization and likelihood application of extracted mucilage from Hollyhocks plant as a natural polymer in enhanced oil recovery process by alkali-surfactant-polymer (ASP) slug injection into sandstone oil reservoirs

Injection of water-based polymeric solutions into oil reservoirs is a common way to enhance oil recovery in the tertiary oil production stage. Polymers are normally injected under different scenarios individually, or with surfactants and alkalis, or both as a slug. Adjusting the ratio of water and oil mobility, preventing the phenomenon of fingering and early production of injectable water by increasing water viscosity are the most important mechanisms of polymer injection in enhanced oil recovery (EOR) process. In this study, the possibility of using extracted mucilage from Hollyhocks plant as a natural polymer for injection as a slug with surfactant and alkaline in sandstone reservoirs was investigated. The plant polymer was characterized by Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Analysis (EDAX) and Thermal Gravimetric Analysis (TGA) after extraction and preparation. Viscosity tests were performed at different shear rates and the effects of polymer concentration, polymer hydration time, temperature and salinity on the viscosity of the polymeric solutions were investigated. Finally, a polymeric slug containing the polymer, an anionic surfactant at the critical concentration of micelle (CMC) and NaOH alkali at the optimum concentration was injected into a sandstone plug to calculate the oil recovery rate by the Alkali-Surfactant-Polymer (ASP) slug injection process. The novelty of this research is the introduction and use of a new, affordable and inexpensive polymer for use in ASP-slug injection into sandstone reservoirs, which can solve many of the challenges in this method. Based on the results, TGA analysis confirms the stability of the polymer at reservoir temperatures. Decreased viscosity versus increased shear rate shows non-Newtonian behavior of the polymeric solutions. The viscosity values of the polymeric solutions are several tens of times more than the surfactant solutions viscosities even at the low concentrations. Therefore, the polymer can be considered suitable for use in the ASP-slug injection process. The viscosity of polymeric solutions decreases with increasing temperature and salinity. However, the final values are not low enough to counteract the polymer effect. Finally, an increase in oil recovery of 27.9% is achieved under the ASP slug injection process containing an anionic surfactant synthesized from waste chicken fat at CMC, NaOH alkali at 2500 ppm and the polymer extracted from Hollyhocks at 2000 ppm. At last, it should be mentioned that the main purpose of this study was to introduce a new polymer for EOR process by injecting ASP slug. However, its application does not lead to this only. Polymers are used in various oil and gas industries. Due to the properties and behavior of the polymer solution, it can be used to reduce water production from oil reservoirs, improve the properties of drilling fluids and inject it with other additives to increase oil recovery.