Injection Mode Research Articles

Huff-n-puff gas injection or gas flooding in tight oil reservoirs?

Because of the ultra-low permeability of tight formations, gas injection is believed to be an effective method to enhance oil recovery (EOR). However, it has two modes: huff-n-puff injection (HNP) and continuous flooding. Which mode is more efficient? This study aims to answer this question through an experimental and simulation study. In the experimental study, tight core samples of permeabilities of 0.16 mD, 0.045 mD, 0.001 mD, and 0.00029 mD were used to compare the oil recovery from huff-n-puff gas injection with flooding. The gas used was nitrogen. Both flooding and huff-n-puff experiments were conducted on the same core in each core sample. Experimental results show that gas flooding had higher recovery in the cores than HNP with the permeability above 0.001 mD, but lower when the permeability was lower 0.00029 mD. To further analyze the gas injection performance, a numerical simulation was performed. The conducted experiments were used to validate the numerical models by historically matching the experimental data. Based on the validated simulation models, HNP is optimized. Simulation results show that optimized HNP is superior to gas flooding when the permeability is lower than 0.001 mD core. Finally, based on published data, a filed-scale model consisting of two well-propped fractures was established to compare the performance of the two gas injection modes. Filed-scale simulation results show that gas flooding can achieve a higher recovery when the matrix permeability is above 0.01 mD, while HNP injection can yield more oil when the matrix permeability is lower than 0.001 mD. However, from an economic point of view, the HNP performance is more justified than the corresponding flooding when the permeability is higher than 0.01 mD, and it is difficult to be economic for both HNP and flooding when the permeability is lower than 0.001 mD. • Two injection modes are compared by experiments and numerical simulation. • Gas huff-n-puff can yield more oil in a low-k reservoir (<0.001 mD). • Gas flooding performs better in a high-k reservoir (e.g., >0.01 mD). • Neither HNP nor flooding is economical in a reservoir <0.001 mD. • HNP shows better economic superiority in a reservoir of <0.01 mD.

Application of monitoring method in the establishment and maintenance of gas cap injection barrier in a Oilfield

In order to make technical reserves for developing gas cap and buffer zone in A Oilfield and explore effective development methods of gas cap reservoir, according to the overall development idea of oil-gas ring, a field test of gas cap injection and polymer barrier development buffer zone in Layer B was carried out in the structural axis of South Block in 2006. The test adopted the development mode of gas cap injection and polymer barrier development buffer zone, that is, the barrier was established by injecting polymer solution at the oil-gas boundary to separate natural gas from crude oil in buffer zone and keep relatively stable. In this paper, the morphological changes during the establishment and maintenance of barriers are found out by means of monitoring.

Achieving Wide Operating Voltage Windows in Non-Carrier Injection Micro-LEDs for Enhancing Luminance Robustness

Since the luminance of Micro-LEDs is highly dependent on the injected current density, inevitable voltage fluctuations will lead to luminance fluctuations and weak luminance robustness. In this work, Micro-LED chips working in non-electrical contact and non-carrier injection (NEC and NCI) mode is proposed, which is totally different from the current-injected mode. The luminance of NEC and NCI Micro-LEDs first increases with the increase of the voltage, and the saturation luminance can be obtained during a relatively large voltage range, which is defined as an operating voltage window. Then the luminance decreases when the voltage is further increased. It is demonstrated that the operating voltage windows can enhance luminance robustness. Finally, the insulating layer that is crucial for the operating voltage windows is optimized. And the working mechanisms related to the existence of operating voltage windows are discussed.

Study on Injection-Production Adjustment Technology in Sanduo Oilfield

On the basis of understanding the geological characteristics of low permeability oil fields with scattered sand bodies, this paper studies the water injection policy, response characteristics and the oil fields entering the middle water cut stage since the production. Affected by the scattered underground sand bodies, it is exposed to the influence of low water flooding control degree and less water flooding direction. After water breakthrough, it is difficult to adjust the water well scheme and the formation pressure level is low. In order to alleviate the above contradictions, oil wells are converted to injection, water drive control degree is improved, and formation energy is increased. In order to improve the control degree of sand bodies, several schemes are compared to find out the transfer injection mode suitable for oil fields with scattered sand bodies, increase the proportion of multiple connections and improve the oil recovery ratio.

Pan-Sharpening Framework Based on Multiscale Entropy Level Matching and Its Application

Current remote sensing hardware technology is not yet able to acquire multiband remote sensing images with both high spatial and spectral resolution. As an important tool to compensate for the lack of spatial information acquisition of multispectral (MS) images, pan-sharpening has been an important and continuously active research area in remote sensing image processing. Although many methods have emerged, the problem of how to obtain high spatial resolution while effectively maintaining the spectral information of MS images has not been well solved. Many aspects still need further research. In this article, we first investigate the essential properties and rationality of two common framework types in the multiresolution analysis (MRA) sharpening method of pan-sharpening from the source perspective—the identical-resolution framework (IRF) derived from the generalized fusion application and the different-resolution framework (DRF) exclusive to the sharpening application, and show that the core difference between the two frameworks lies in the different ideas of utilizing the multiscale transformation, i.e., they tend to expand the scale space and model the spatially blurred degradation relationship between the sources, respectively. Both of them have their own advantages and disadvantages in handling detailed information, and neither of them can effectively deal with the “detail exclusivity” problem. Based on this, the idea of “entropy level matching” (ELM) of pan-sharpening is presented, and a comprehensive framework that can combine the advantages of the two types of frameworks is constructed, namely, the multiscale ELM framework. Furthermore, as an application of this framework, we propose a sharpening method shearlet transform-based entropy matching (STEM) built on the nonsubsampled shearlet as a multiscale transformation method. According to the difference in detail injection mode in it, it can be further divided into two sharpening methods based on additive mode and substitutive mode. The comparison experiments with 11 popular methods show that the proposed two sharpening methods can effectively improve the spatial resolution of MS images while keeping the spectral information well, and the comprehensive performance advantage is obvious. The source code of the proposed method can be downloaded from <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/JZ-Tao/STEM/</uri> .

Research on the Technology of Profile Control and Flooding in JY Oilfield to Stabilize Production

JY oilfield is mainly an ultra-low permeability reservoir with low reservoir permeability. As the permeability decreases, the starting pressure gradient rises sharply, and the establishment of an effective displacement pressure system is slow. The main reservoir has entered the medium water-cut development stage. On the plane, water flooding intrudes along the dominant channels such as fractures and high-permeability strips, resulting in plane contradictions; on the profile, the production degree decreases, and the injection-production profile is unbalanced. In this paper, through the study of reservoir physical properties, water flooding and control and flooding mechanism and the implementation of fine profile control and flooding on a large scale, the well selection conditions of different reservoirs are obtained, and differentiated countermeasures are formulated. Four optimizations of injection mode to ensure continuous improvement of injection effect and economic benefits.

Experimental study on a modular thermo-activated building system for improving indoor thermal environment and energy saving

Thermo-activated Building Systems is an energy-efficient envelope insulation technology. In this paper, the Modular Thermo-activated Building Systems (MTABS) is proposed to enable flexible installation and maintenance of embedded pipe. Two scaled-down experimental rooms of the same size were built, in which the normal energy-saving wall (NW) and the MTABS wall were applied to the south-facing wall respectively. The MTABS for impacting on the indoor thermal environment and energy saving were measured in continuous low-grade heat injection mode under winter outdoor conditions in Hefei, and were analyzed in comparison with the NW. Experimental results show that MTABS can effectively improve the indoor thermal environment. The average temperature difference between indoor and outdoor of MTABS is 6.72 °C higher than that of NW; when the heat source temperature is 25 °C, the cumulative daily heat fluxes of MTABS is 44.0 kWh·m-2, which providing auxiliary indoor heating while significantly reduces energy consumption.

Experimental investigation of the heat transfer from the helical coil heat exchanger using bubble injection for cold thermal energy storage system

This study investigates cold thermal energy storage (CTES) using a helical coil heat exchanger modified with bubble injection. One of the effective methods for increasing the heat transfer rate in heat exchangers is using bubble injection. A helical coil heat exchanger is immersed inside a cylindrical water storage tank, where the helical coil is the evaporator of a vapor compression refrigeration cycle (VCRC) and provides the designed cooling. Experimental studies were carried out to examine the impact of bubble injection on Nusselt number, the temperature differences in the storage tank, exergy degradation in the evaporator, and cycle coefficient of performance (COP). The bubbles were injected from the bottom of the storage tank in four different geometries at airflow rates ranging from 3 to 11 L/min. The experimental results of this study revealed that bubble injection could significantly increase the COP and heat transfer rate from the storage tank, as well as the exergy destruction and Nusselt number (Nu). This increase was highly dependent on the geometry and flow rate of the bubble injection. The results also indicated that the bubble injection has an optimal flow rate value, which was 9 L/min in this study. More specifically, the COP of the refrigeration cycle and the Nu number increased by 124% and 452%, respectively, compared to the non-bubble injection mode. Finally, for calculating the outside Nusselt number of the helical coil, an empirical correlation as a function of bubble flow rate and bubble injection angle was proposed.

Exergy analysis in diesel engine with binary blends

Investigation on Diesel engine with minimized fuel consumption rate and increased output power is not the meaningful procedure if irreversibility in the thermodynamic system is ignored. This current procedure is aimed to signify the importance of exergy analysis in Diesel engine performance on the perspective of Second law of thermodynamics analysis. In this study, diesel-cotton seed oil blends were tested on engine running with direct fuel injection mode of operation. The experiments were conducted with diesel (D), 5% cotton seed oil-95% diesel (CB5), 10% cotton seed oil-90% diesel (CB10), and 15% cotton seed oil-85% diesel (CB15) for estimation of brake power, energy rate, and exergy rate in the fuel and exhaust, heat release rate, exergy destruction, ideal efficiency (I law), and actual (II law) efficiency. The results outcome that an increase in trend was observed in the fuel exergy and thermal exergy loss with engine speed for D, CB5, CB10, and CB15. The loss of exergy, heat release rate, percentage of exergy and exergy transferred through exhaust gases decreased for CB5, CB10, and CB15 compared to diesel.

Research and effect analysis on improving injection mode of weak alkali ASP flooding in poor oil layer block

In view of the large proportion of thin and poor layers in the weak-alkali ternary flooding block, the statistical analysis method is used to optimize the division of well groups with injection capacity, establish a strategy chart for different types of groups to maintain injection and tap potential, and optimize the well groups of different sand body connectivity types. The fracturing method strengthens the whole process of fracturing in the well area with poor injection capacity. The effective thickness water absorption ratio is over 80%, the maximum water cut reduction in the stage is 9.65%, the low water cut stable period is 16 months, and the recovery factor is increased by 8.77 percentage points. development effect.

Technical Analysis of Enhanced Oil Recovery by Polymer Flooding

Polymer flooding is one of the effective technologies to improve oil recovery. This paper briefly introduces the mechanism of polymer flooding, and describes the application advantages of polymer flooding in heavy oil sandstone reservoirs in China. Combined with the application practice of polymer flooding EOR technology, the scheme of polymer flooding EOR technology is further explored from the aspects of polymer flooding oil supply, polymer flooding oil injection mode and polymer solution mass concentration, hoping to provide some references for the improvement of reservoir recovery.

Capsaicin determination from pain patch for the calculation of Scoville heat units by gas chromatography-mass spectrometry

Background and Aims: A sensitive, accurate and precise method has been developed for the determination of Capsaicin from pain patches by Gas chromatography Mass Spectrometry (GC-MS). Capsaicin has irritant effects in high concentrations, so these effects can be minimized by knowing the amount present in pain patches for the efficacy and safety of patches. Methods: Capsaicin was extracted by using liquid-liquid extraction from patches. The Gas Chromatographic separation was performed by using 5% diphenyl 95% dimethylpolysiloxane column with high a purity 2 mL/min flow rate helium gas. The separation was made with a gradient oven temperature program. The oven temperature started at 250°C and was increased to 275°C at 10°C.min-1 ramp rate and held at 275°C for 2.5 min. The injection port was adjusted at 300°C and a split injection mode was used. The analysis was carried out in a split mode of 5:1. MS ionization potential was determined at 70 eV. Results: The calibration curve was found to be linear in the range 5 - 50 μg/mL. The limits of detection and quantification for capsaicin was found to be 3.46 μg/mL and 5 μg/mL, respectively. The method developed was validated and successfully applied to the patch analysis. Conclusion: This method is simple, reproducible, and can be used safely for the routine analysis of Capsaicin without derivatization. This study has the potential how to calculate the Scoville Heat Units (SHU) of pain patches that contain Capsaicin. The amount of Capsaicin in the pain patch, its irritant effects, and its efficacy and safety appear to be low when evaluated by the SHU.

Magneto-tunability of photocurrent in Zn0.3Ni0.7Fe2O4/ZnO-rGO composite heterojunction device

We studied light and magnetic field dependent DC transport properties of Zn0.3Ni0.7Fe2O4/ZnO-reduced graphene oxide composite heterojunction. Current through the heterojunction is expected from the carrier injection and tunneling in forward and reverse bias, respectively. Application of magnetic field has shown both negative magnetoresistance (MR) at forward bias and positive MR at reverse bias. The negative MR is attributed to the reduction of spin dependent scattering in the bulk of Zn0.3Ni0.7Fe2O4 layer. On the other hand, under reverse bias, a magnetic field dependent increase of depletion region in Zn0.3Ni0.7Fe2O4 side is supposed to take place, resulting in a positive MR. Under 660 nm visible light illumination, photoresponse has been observed. Under illumination, negative MR is found in reverse bias. This negative MR is expected to be associated with the magnetic field dependent widening of reverse bias depletion region. In forward bias voltages, under strong illumination of 3.08 mW/cm2 of 660 nm light, a positive MR is found. This positive MR is associated with the light dependent enhancement of depletion width at Zn0.3Ni0.7Fe2O4 side under high injection mode. When the applied voltage is swept along a cycle, irreversible nature of I-V characteristics is observed.

Removal of Fluorine from RECl3 in Solution by Adsorption, Ion Exchange and Precipitation

In this paper, methods of effective removal of fluorine from rare earth chloride solution by adsorption, ion exchange and precipitation with lanthanum carbonate or CO2 gas as fluorine-removal agent, respectively, were studied. The relevant parameters studied for fluorine-removal percentage were the effects of the type and dosage of fluorine-removal agent, the injection flow and mode of CO2, the initial concentration of rare earth solution and initial pH value, contact time, temperature and stirring. XRD, SEM and EDS were used to analyze and characterize the filter slag obtained after fluorine removal. SEM and EDS results showed that RECO3(OH) with a porous structure was formed in rare earth chloride solution when lanthanum carbonate was used as fluorine-removal agent, and it had strong selective adsorption for F−. The XRD spectra showed that F− was removed in the form of REFCO3 precipitates, which indicates that the adsorbed F− replaced the OH− group on the surface of RECO3(OH) by ion exchange. The experimental results showed that a fluorine-removal percentage of 99.60% could be obtained under the following conditions: lanthanum carbonate dosage, 8%; initial conc. of rare earths, 240 g/L; initial pH, 1; reaction temperature, 90 ∘C; reaction time, 2 h. Simultaneously, a fluorine-removal process by CO2 precipitation was explored. In general, RE2(CO3)3 precipitation is generated when CO2 is injected into a rare earth chloride solution. Interestingly, the results of XRD, SEM and EDS showed that the sedimentation slag was composed of REFCO3 and RE2O2CO3. It was inferred that RE2(CO3)3 obtained at the initial reaction stage had a certain adsorption effect on F− in the solution, and then F− replaced CO32− on the surface of RE2(CO3)3 by ion exchange. Therefore, F− was finally removed by the high crystallization of REFCO3 precipitation, and excess RE2(CO3)3 was aged to precipitate RE2O2CO3. The fluorine-removal percentage can reach 98.92% with CO2 precipitation under the following conditions: venturi jet; CO2 injection flow, 1000 L/h; reaction temperature, 70 ∘C; initial pH, 1; reaction time, 1.5 h; initial conc. of rare earths, 240–300 g/L; without stirring. The above two methods achieve deep removal of fluorine in mixed fluorine-bearing rare earth chloride solution by exchanging different ionic groups. The negative influence of fluorine on subsequent rare earth extraction separation is eliminated. This technology is of great practical significance for the further development of the rare earth metallurgy industry and the protection of the environment.

Simultaneous Estimation of Genotoxic Impurities 4-Nitrobenzene Trifluoride, 4-Aminobenzene Trifluoride, and Benzo Trichloride in Cinacalcet Hydrochloride by GC-MS/MS Method

The main objective of this study is to develop and validate a novel, fast, and more sensitive gas chromatography-mass spectrometry (GC-MS/MS) method for the simultaneous estimation of 4-Nitrobenzotrifluoride (4-NBTF), 4-Amino-benzotrifluoride (4-ABTF), and Benzotrichloride (BTC) impurities in Cinacalcet hydrochloride (CH). The chromate-graphic separations were performed on a DB-624, 30m × 0.32mm × 1.8µm column with injector temperature of 150°C, and mode of injection is split with asplit ratio 1: 20. The carrier gas used was helium with a flowrate 1.5 mL/min, and theinjection load was 1.0 µL. Mass spectrometry quantitation was achieved by aquadrupole analyser with EI (Electron Ionization) ion source atasource temperature of 250ºC and interface temperature of 250ºC. The retention times for 4-NBTF, 4-ABTF, and BTC were at 6.13, 6.74and 7.64min, respectively. The calibration curve was linear over the concentration ranging from LOQ level to 150 % level with the correlation coefficient (r) of &gt; 0.99. The percentage recovery was found to be within the specified range, i.e., 70.0 to 130.0 for the three impurities. The limit of detection (LOD) was established to 0.19, 0.19, and 0.18 ppm, whereas thelimit of quantification (LOQ) was obtained to 1.14, 1.12, and 1.11 ppm for 4-NBTF, 4-ABTF, and BTC, respectively. The test solutions with impurities were found to be stable in the diluent for 24 hours. A simple GC-MS/MS method was developed and validated for simultaneous estimation of three impurities in CH. The method was accurate, precise, linear, specific, sensitive, robust, and rugged as per ICH guidelines. The method has been applied to the real-time batch analysis and found to be suitable for routine quality control analysis of CH.

Experimental analysis of oil displacement by hybrid engineered water / chemical EOR approach in carbonates

Fast depletion in oil reserves has steered the petroleum industry towards developing novel enhanced oil recovery (EOR) techniques. The standalone EOR methods have associated merits and demerits. For example, the chemical EOR (CEOR) methods have very limited applications in high salinity, high temperature carbonate reservoirs because of increased chemical adsorption and high project costs. In this study, hybrid approaches utilizing engineered water (EW) and CEOR were investigated for carbonate reservoirs. The synergetic effects of EW and chemicals such as polymer, alkali, and surfactant were analyzed. Phase behavior analysis, aqueous stability study, surfactant static adsorption test, and polymer rheological characterization were conducted to select the optimum alkali/surfactant/polymer formulation. To evaluate the increase in oil recovery, wettability alteration, and extent of mobility control, various EW/CEOR combinations were designed for oil displacement experiments, including EW/surfactant flooding (EWSF), EW/polymer flooding (EWPF), EW/surfactant/polymer flooding (EWSPF), and EW/alkali/surfactant/polymer (EWASP) flooding. The EWASP flooding was executed in both continuous and slug-wise injection modes, and the best hybrid EW/CEOR design was selected. 10 times diluted Caspian seawater spiked with optimized active ions was used as the EW. Based on phase behavior and static adsorption tests, 1 wt% Soloterra 113-H was used as a surfactant, while 1 wt% sodium carbonate was used as an alkali. Flopaam 5115 was employed as a polymer with an optimum concentration of 1500 ppm, as established from rheological experiments. The best combination in terms of oil recovery, stability of polymer and surfactant, and chemical consumption was the hybrid EWASP flooding in slug-wise injection mode. This injection scheme resulted in 36% OOIP incremental recovery, 7% higher than the EWPF and EWSPF scenarios and 3% higher than hybrid EWASP flooding in continuous injection mode. Hybrid designs proved to be more effective in recovering residual oil because of better mobility control, reduced capillary trapping, wettability modification, lower surfactant adsorption, and ultra-low interfacial tension (IFT). Our studies showed that the application of hybrid EW/CEOR for carbonate formations, as a novel approach, can expand the application envelope of chemical methods to challenging carbonate formations by making the EOR projects technically and economically viable.

METHOD DEVELOPMENT FOR THE DETERMINATION OF METFORMIN IN HUMAN PLASMA BY CAPILLARY ZONE ELECTROPHORESIS

Background: Metformin is an oral antidiabetic drug from the biguanide class and it is the first-line drug chosen for the treatment of type 2 diabetes. This is a drug on the list of pharmaceutical substances required to report bioequivalence study data when registering the drug. Objectives: (1) To develope a capillary zone electrophoresis method for determining metformin hydrochloride in human plasma. (2) To validate the method. Materials and methods: Human plasma, metformin hydrochloride, ranitidine hydrochloride. The method was developed and validated according to US-FDA 2018 and EMA 2011. Results: The procedure was developed by using the Agilent 7100 CE electrophoresis system with ranitidine hydrochloride as an internal standard. Sample preparation was accomplished through protein precipitation with acetonitrile. The optimal electrophoresis conditions are as follows: uncoated fused-silica capillary column of a total length of 40 cm (31.5 cm effective length, inner diameter 100 μm), phosphate buffer solution 100 mM (pH = 4), the voltage applied to both capillary ends of 15 kV, the inlet end of capillary dipped in water before sample injection, sample injection mode of 50 mBar in 7 seconds, using a PDA detector at 232 nm. The analysis method was validated according to the requirements of the US-FDA 2018 and EMA 2011 with the following criteria: system suitability with RSD &lt; 3%; good specificity; the calibration curves were linear (r2 ≥ 0.98) in the concentration range of 0.1 – 4.0 μg/ml for metformin in human plasma; the lower limit of quantification was 0.1 μg/ml; the intra-day and inter-day accuracy were 99.41 – 105.28% and 92.47 – 106.26%, respectively; the intra-day and inter-day precision were 1.99 – 4.03% and 3.11 – 6.05%, respectively; the mean recovery of ranitidine (internal standard) was 86.2%, the mean recoveries of metformin at three levels LQC, MQC, and HQC were 72.9%, 75.9%, and 77.4%, respectively; plasma samples were stable to analysis. Conclusions: The developed method meets the requirements of US-FDA 2018 and EMA 2011 to determine metformin in plasma. Key words: Capillary zone electrophoresis, plasma, metformin

An experimental investigation of the foam enhanced oil recovery process for a dual porosity and heterogeneous carbonate reservoir under strongly oil-wet condition

In this study, we investigate the feasibility of foam enhanced oil recovery (EOR) for a dual porosity and heterogeneous carbonate reservoir in the Middle East with medium temperature (55 °C) and high formation salinity (16% TDS). An Alkyl Poly-Glycoside (APG) surfactant was firstly selected based on the solubility tests and bulk foam tests. Afterwards, a series of core flooding experiments both in the absence and in the presence of crude oil were performed on Estaillades limestone, a dual-porosity and heterogeneous carbonate presenting reasonable similarities with the actual formation. In these foam tests, the influence of surfactant concentration, foam quality, injection velocity, brine composition, injection mode and permeability on foam strength and incremental oil recovery were systematically investigated. The optimal foam quality is found to be around 60–70% from foam quality scan tests in the absence of crude oil. Moreover, foam can still be generated in Estaillades under strongly oil-wet conditions, and the foam strength in the high-quality regime is largely dependent on surfactant concentration. More than 10% original oil in place (OOIP) of the water flooded residual oil was recovered after co-injecting 2.0 total pore volume (TPV) of nitrogen and 0.5 wt% APG surfactant (in synthetic seawater brine) at 65% foam quality and 4 ft./d. Interestingly, it was observed that the presence of lauryl betaine (LB) can significantly enhance the stability of APG foam in the presence of crude oil, though LB surfactant itself is not a good foamer. At last, the three phase co-injection tests proved the presence of foam at approximately 70% oil saturation. The results of this study may provide insights into the foam transport behavior in a dual porosity and heterogeneous porous media under strongly oil-wet condition.

Ultrasensitive Detection of Ruthenium by Coupling Cobalt and Cadmium Ion-Assisted Photochemical Vapor Generation to Inductively Coupled Plasma Mass Spectrometry

An extremely sensitive methodology for the determination of Ru was developed by coupling photochemical vapor generation (PVG) analyte introduction with inductively coupled plasma mass spectrometry (ICPMS). PVG was undertaken with a thin-film flow-through photoreactor in a medium comprising 8 M formic acid in the presence of 10 mg L-1 Co2+ and 25 mg L-1 Cd2+. The volatile product (presumably ruthenium pentacarbonyl) was generated in a flow injection mode, yielding an overall efficiency of 29% at a sample flow rate of 1.4 mL min-1. The presence of both Co2+ and Cd2+ sensitizers enhanced PVG efficiency by 3,200-fold, permitting a 31 s irradiation time. Although enhanced efficiency (≈40%) could be obtained with increased Co2+ concentration, this was not suitable for routine use due to co-generation of cobalt carbonyl. Excellent repeatability (<2.5%) and reproducibility (4%) were achieved for 200 ng L-1 Ru3+. Limits of detection ranged from 20 to 42 pg L-1 (10-21 fg absolute) depending on the measured isotope and operational mode of the ICPMS reaction/collision cell. Interferences from inorganic acids and their anions, several transition metals, and metalloids were investigated. Practical application of the methodology was demonstrated by the analysis of seven water samples of various matrix complexities (well water, spring water, contaminated water, and seawater).

Experimental investigation of the leak-off effect on proppant transportation and distribution in a vertical fracture

Proppant placement inside hydraulic fractures is a key factor during gas production from unconventional gas reservoirs. Fracturing fluid somewhat leaks off through natural fractures when fracturing naturally fractured reservoirs, which affects proppant transportation and distribution. However, this phenomenon has often been neglected in existing experimental fracture models for simplicity. To date, the influence of leak-off on proppant placement remains unclear. This study aimed to build a leak-off vertical fracture model. Laboratory tests on proppant transportation and distribution were conducted using this model at different locations and controlled rates of fluid leak-off through valves simulating natural fractures. The experimental results showed that when the leak-off at the front was more severe than other leak-off locations, the deep fracture suffered the problem of large empty areas and thus ineffective proppant support. The interaction between leak-off location and alternating proppant injection mode was also studied to mitigate the adverse effect of leak-off. Accordingly, the pumping of small-sized proppant particles and then large-sized proppant particles was proposed for the case of severe leak-off in the front fracture. Such a mode led to a uniform proppant distribution throughout the fracture.