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Underground coal fires, which are widely distributed and cause serious resource waste and environmental hazards, have become a common concern of the international community. This paper aims to reveal the mechanism of coal spontaneous combustion and the expansion law of underground coal fires. A void rate model from the goaf to the ground surface and a multi-field coupling model for underground coal fires were established. Based on which, the combustion process from the beginning of oxidation to the formation of large-scale fire of the remaining coal in goaf was analyzed. Furthermore, the evolution law of underground coal fire after nitrogen injection and the influence of different nitrogen injection parameters were analyzed. The results show that the coal spontaneous combustion can be divided into three stages: slow reaction stage (stage Ⅰ), violent combustion stage (stage Ⅱ), and stable combustion stage (stage Ⅲ), and the transformation of different stages is mainly controlled by the oxidation reaction rate of coal. To obtain the optimal parameters for nitrogen injection for fire suppression, the fire extinguishing efficiency concerning nitrogen injection time, nitrogen injection amount and nitrogen injection position, as well as the distribution law of nitrogen in rock strata were analyzed. Through range analysis, it is determined that the most effective fire extinguishing occurs with the injection rate of 0.15 m3/s in stage I, and the injection position has little influence on the fire extinguishing effect. This understanding contributes to a deeper understanding of the multi-field coupling mechanism of underground coal fires and provides a guidance for extinguishing and preventing underground coal fires.

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Extensive studies have been conducted on effect of sealing ratio on combustion process and temperature field of pool fire, while still lacking emergency rescue research after the failure of the original fire extinguishing system. Therefore, a series of tests were carried out in a 1/3 reduced-scale tunnel to explore the nitrogen injection into the closed tunnel on the effectiveness of fire-fighting. The results show that, the presence of nitrogen not only significantly lowers the oxygen concentration and mass loss rate of the air drawn into the combustion area, but the flame continues to entrap the polluted low-oxygen air, resulting in the continuous inadequate combustion of the fire and a large amount of asphyxiating smoke, thus shortening the self-extinguishing time. The concentration range of oxygen concentration of flame extinguishing during nitrogen injection is 11.13 %–14.98 %. Simultaneously, an analytically derived model to estimate the extinction time of nitrogen injection into the closed utility tunnel was developed, which is found that the deviation between the improved classical model and the experimental data within 10 %. The present work positively provides a tool for the assessment of thermal environment and estimation of fire detection time in engineering practice.

Gas flooding is a key technique for increasing coalbed methane (CBM) production of declining wells in coal mining areas. Nitrogen is clean, pollution-free, low-cost, and relatively safe compared with carbon dioxide. In this study, nitrogen drive experiments were conducted under different conditions using a coal–gas–liquid relative permeability device and gas chromatography. The effects of the temperature, intermittent time, nitrogen purity, and displacement pressure on the output characteristics were investigated, and then, field tests were conducted. The results show that with increasing displacement time, the produced gas volume and flow rate are dominated by methane at the beginning and then quickly transform into nitrogen. The volumes of both methane and nitrogen are positively correlated with the displacement time via a power function. Additionally, increasing the nitrogen temperature, intermittent time, nitrogen purity, and injection pressure can effectively increase methane production. In the field test conducted in the Fanzhuang block in the Qinshui Basin, China, the methane production of 10 monitoring wells was 11,700 m3/day , which was 2,700 m3/day higher than that before nitrogen injection. This paper provides an optimized scheme for the stimulation of CBM via nitrogen displacement in coal mining areas, which has a good application prospect. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to explore the evolution of coal cracks during nitrogen injection, the resistivity response tests of coal during nitrogen injection were carried out. The research shows that during the nitrogen injection process, the resistivity of the coal remains basically unchanged at first, then increases slowly, and increases suddenly and stabilizes at about 1.2finally. The nitrogenadsorption ofcoal leads to a decrease in resistivity, and the higher the nitrogen pressure is, the greater the decrease in resistivity will be. The development of fissures in the coal will affect the conduction channel, resulting in an increase in resistivity. In the process of nitrogen injection, the resistivity change of the loaded coal is the result of the combined effect of the nitrogen adsorption of coal and the expansion of the fissures of the coal. [ABSTRACT FROM AUTHOR]

Recent decades have seen the development of many effective and innovative technologies for extra virgin olive oil (EVOO) extraction. Various solutions have been proposed to remove dissolved oxygen from the oil. Given these issues, we have designed and developed a system that can be added to the centrifuges that are already used in the olive oil industry. The system reduces the oxidative impact through the release of a technical gas inside the separator, and consequently delays the onset of defects related to oxidation. The experiment tested different N2 flow rates, directly into the vertical centrifuge, and four levels of N2 were tested–a control level (no N2 injection); low (20 L/min), medium (40 L/min), and maximum (80 L/min)–in order to evaluate the effectiveness of this new technique on EVOO quality. This experiment demonstrates that the objectives have been achieved. The EVOO produced using our system had lower dissolved oxygen content with N2 injection, along with an enriched volatile fraction, and higher biophenol concentrations. The chemical analyses were confirmed by a sensory analysis, with an increase in fruity intensity and bitter taste. [ABSTRACT FROM AUTHOR]

After the water release in the waterlogged mining area, the residual coal is prone to spontaneous combustion after being air-dried. To investigate the law of spontaneous combustion of residual coal in water immersed goaf during drainage, experimental studies, field observations and numerical simulations were used to analyze the effect of drainage on the spontaneous combustion characteristics of residual coal. Nitrogen injection parameters were optimized based on the results of the study. The experimental results show that: the spontaneous combustion tendency of soaked coal is enhanced compared with that of raw coal, and the spontaneous combustion tendency of soaked coal in goaf is stronger than that of the laboratory prepared soaked coal, because the immersion time of field-immersed coal is longer than that of laboratory-prepared coal samples. The simulation results of oxygen concentration and pressure distribution during goaf drainage show that: compared with that without drainage, the pressure in goaf decreased by 270 Pa, the air leakage in the goaf increased, the area of oxidation zone expanded by 5.2 times, and the possibility of spontaneous combustion of residual coal increased. Injecting nitrogen during the drainage was proposed to suppress the oxidation of the residual coal. The effect of nitrogen injection was measured on site and numerically simulated. After nitrogen injection were taken, the pressure dropped by 130 Pa after water release and the area of oxidation zone expanded by 1.5 times, indicating that nitrogen injection measures can effectively suppress the water-gas replacement. In addition, for this flooded goaf, the optimized nitrogen injection rate is 600 m3/h. This study provides an important reference for the prevention and control of spontaneous combustion hazards of residual coal in the short-distance composite coal seam during drainage of water immersed goaf. [ABSTRACT FROM AUTHOR]

To study the distribution law of coal spontaneous combustion zone in goaf of two intake and one return ventilation working face, the oxygen concentration under different working conditions during the mining of the 8301 working face of Tashan Coal Mine was simulated, the danger zone of spontaneous combustion of coal was determined and corresponding fire prevention measures were proposed. The spontaneous combustion danger zone of coal in the goaf of two intake and one return ventilation working face is large, and the spontaneous combustion zone reaches 96 m when the mining distance is 150 m; nitrogen injection can greatly change the distribution of spontaneous combustion zones and reduce the spontaneous combustion of coal in the goaf. For the two intake and one return ventilation working face, nitrogen injection should be considered on both sides of the goaf; increasing air volume allows the boundary of the spontaneous combustion zone to extend deep into the goaf and increase the distance of the front end from the working face.

High temperature nitrogen, injection into coal seams is supposed to improve the permeability and thus maintain the safety of underground mining. A novel triaxial apparatus is recently developed, aiming at providing the effective method to evaluate the effect of high temperature nitrogen injection. The main feature of this novel apparatus is its high confining pressure, gas injection with high pressure as well as the high temperature. This new device can be either used for natural coal samples (e.g. intact or fractured) or the synthetic coal samples. A series of leakage tests were conducted to verify the feasibility of this instrument, the results of which have confirmed that the maximum pressure (i.e. 10 MPa) can be reached. In addition, the high temperature and pressure of nitrogen gas can also be sustain at the requested level. Based on the preliminary tests on the instrument, a large amount of tests were carried out to evaluate the effect of nitrogen injection in enhancing the permeability of coking coal from the Pingdingshan coalfield, China, and the influence of high temperature nitrogen injection on mechanical parameters of coal was obtained. [ABSTRACT FROM AUTHOR]

In the petroleum industry, nitrogen is often used to improve the recovery of unconventional oil and gas resources such as heavy oil, tight oil, and shale oil. When nitrogen is injected into the oil and gas layers along the horizontal section of the wellbore, its pressure and temperature and other physical parameters all change with coordinates and time. These changes of pressure and temperature will have certain impact on the recovery efficiency. Therefore, it is necessary to simulate the non-isothermal variable mass pipe flow process of nitrogen in the horizontal wellbore. Based on the principles of conservation of energy and momentum, this paper establishes a nitrogen flow model in the horizontal wellbore by coupling sub-models such as the reservoir suction model. Results show that: (a) when the number of grids reaches 100, the degree of agreement between the predicted pressure value and the measured value of the model has met the requirements of engineering calculation accuracy. (b) when the injection pressure is lower than 2.7 MPa, the temperature gradient at the heel end and toe end of the wellbore is similar, while when the injection pressure is high (equal to 2.9 MPa), the temperature gradient at the toe end of the wellbore is significantly higher than that at the heel end. [ABSTRACT FROM AUTHOR]

This paper reports a study that employed a digital three-dimensional model of the gas condensate reservoir to investigate the process of nitrogen injection at the boundary of initial gas-water contact at different values of the injection duration. The calculations were performed for 5, 6, 8, 10, 12 and 14 months injection duration. Based on the modeling results, it was found that increasing the duration of the nitrogen injection decreases the operation time of production wells until the breakthrough of non-hydrocarbon gas. Based on the analysis of the technological indicators of reservoir development, it was established that the introduction of technology of the nitrogen injection into a reservoir ensures a reduction in the volume of reservoir water production. The cumulative water production at the time of nitrogen breakthrough to the production wells at the nitrogen injection duration of 5 months is 197,3 thousand m3; of 14 months – 0,038 m3. According to the results from the statistical treatment of estimation data, the optimal value for the nitrogen injection duration was determined, which is 8,04 months. The ultimate gas recovery factor for the optimal period of the non-hydrocarbon gas injection is 58,11 %, and in the development of a productive reservoir for depletion – 34,6 %. Based on the research results, the technological efficiency of nitrogen injection into a productive reservoir has been determined at the boundary of initial gas-water contact in order to slow the movement of reservoir water into gas-saturated horizons. This study results allow the improvement of the existing technologies of hydrocarbon fields development under conditions of water drive. The use of the results of the research carried out in production will make it possible to reduce the volume of cumulative water production and increase the ultimate gas recovery factors to 23,51 %. [ABSTRACT FROM AUTHOR]

For the special case above the working face of Tashan Coal Mine, the numerical simulation software was used to study the distribution of oxygen molar concentration in the goaf under different mining distances and different amounts of nitrogen injection and determine the coal spontaneous combustion danger zone in the goaf. Results show that long-distance extraction of gas makes the coal spontaneous combustion danger zone larger. As the mining distance increases, the spontaneous combustion danger zone gradually widens. When the mining distance is 50 m, the rate of widening the spontaneous combustion zone suddenly becomes larger. The ratio of the width of the spontaneous combustion zone on the inlet side to the length of mining distance is 180% higher than that of the mining distance of 30 m to 50 m, and the return side is 140% higher, causing larger risk of spontaneous combustion of coal; nitrogen injection can greatly reduce the coal spontaneous combustion danger zone in the goaf.

Prior to start any Enhanced Oil Recovery (EOR) process, it is desirable to characterize the flow pattern within the affected reservoir volume. This becomes of critical importance for in situ combustion in heavy oil reservoirs, where the mobility ratio is highly unfavorable, oftentimes resulting in channeling or early breakthrough. An inter-well connectivity test through immiscible gas injection aids improving the characterization of the flow distribution, in addition to: 1) calibrating estimates for sweep efficiency; 2) evidencing geological features that may lead to preferential flow towards a particular well or group of them, or lack of connection amongst them; 3) creating a gas path between the injector and producer wells to enable a safe progression of the combustion front; and 4) evaluating the performance of artificial lift and well control systems under high gas-liquid ratio conditions. A connectivity test using nitrogen was designed, implemented and evaluated at the Chichimene field, prior to the ignition of the in situ combustion pilot. This process is summarized and described in this paper. This will be the first in situ combustion trial in a deep (˜ 8000 ft.), extra-heavy oil reservoir, and will serve as a data source to evaluate the development of resources under similar conditions in the eastern plains basin of Colombia. This set of reservoirs bears a significant fraction of the hydrocarbon resources in the country and under Ecopetrol operation. The importance of this pilot makes this connectivity test of even larger relevance to reduce the subsurface and operational uncertainty, identifying potential risks, and increase the probability of success of the combustion process as an option to economically produce these resources.

Nitrogen injection is widely applied to enhance oil recovery, but the corrosion failure risk of tubing and casing is increased by residual oxygen in nitrogen. In this study, the corrosion behaviors of P110 steel under dynamic conditions with different oxygen partial pressures (2.5–0.003 MPa) simulating high‐pressure (30 MPa) nitrogen injection were studied. The morphology and composition of corrosion products were characterized by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and energy‐dispersive X‐ray analysis methods; furthermore, the localized corrosion rate and three‐dimensional surface morphologies were analyzed. The results show that the general corrosion rate decreased significantly with decreasing O2 partial pressure, especially when O2 partial pressure was below 0.5 MPa, and there is a corrosion morphology change from general corrosion to localized corrosion (pitting). Besides, the localized corrosion rates are about 20 times the general corrosion rates. The corrosion products are mainly FeOOH and Fe3O4. In addition, the scales in the intact area are relatively flat and dense, whereas the damaged scales are porous and brittle. Fluid flows not only changed the morphologies and microstructures, resulting in a more protective product layer but also promoted the transfer of the corrosive mediators and affected the development of localized corrosion. [ABSTRACT FROM AUTHOR]

Purpose: Red lentils are rich in proteins and fibres, and thus have great potential to be used as healthy ingredients in extruded snacks. However, at high protein and fibre concentrations, the level of expansion, microstructure uniformity and textural appeal are impaired. Using physical blowing agents during extrusion can overcome these quality issues. This study investigates the effects of moisture content (18%-22%), screw speed (150 rpm-200 rpm), and blowing agent (i.e., N2) injection pressure (0-500 kPa) on physical, mechanical and microstructural properties of puffed red lentil snacks. Principle results: Compared to conventional extrusion, N2 injection at 300 kPa decreased extrudate density from 0.25 to 0.41 kg/m³ to 0.12 to 0.26 kg/m³ (across all feed moistures and screw speeds studied), and substantially altered the extrudate’s microstructure. Extrudates with N2 injection had numerous small cells that were more evenly distributed. Moreover, an increase in feed moisture from 18% to 22% increased extrudate hardness and decreased crispiness. Major conclusions: N2 injection during extrusion has a great potential in manipulating extrudate expansion, microstructure, texture, and colour of red lentil extrudates. Extrudates produced with 300 kPa N2 injection pressure had the maximum expansion compared to other N2 injection pressures studied. [ABSTRACT FROM AUTHOR]

• We present efficient closed-form representations of molar entropy and Gibbs free energy for pure substances. • Present molar entropy and Gibbs free energy prediction models are only involving three molecular constants. • We excellently predict molar entropies and Gibbs free energies for the N 2 gas. Nitrogen (N 2) is widely used in oil and gas industry. We report two new efficient closed-form representations for the molar entropy and Gibbs free energy of pure gaseous substances. A comparison of the predicted and experimental values shows that the molar entropies and Gibbs free energies of N 2 can be excellently predicted in the temperature range of 100–6000 K. The present entropy and Gibbs free energy prediction models only require the experimental values of three molecular constants and are away from the utilization of a great number of experimental spectroscopy data. [ABSTRACT FROM AUTHOR]

This study investigates the means of deferring the breakthrough of injected N2 and alleviating the impact of such on production rates and specifications as well as minimizing the required changes to the gas processing facilities. This aimed at assisting the ongoing efforts to transfer the Cantarell experience to Abu Dhabi, where large amounts of N2 gas will be generated and injected into a large gas condensate reservoir to partially substitute the recycling of lean gas. This will bring forward the opportunity to exploit lean gas by securing base load supplies before the start of reservoir blowdown, compared to the peak shaving approach currently practiced. Managing N2 breakthrough starts by better understanding the pattern at which N2 injection spreads into the gas accumulation. Based on the findings of initial subsurface and plant simulations carried out in 2008, N2 breakthrough in Abu Dhabi might be possibly deferred by segmenting the reservoir into a rich N2 region and lean N2 region. The approach assumes no thief zones will be faced and no channeling of N2 injected between the two regions is taking place. N2 is injected in the north region of the reservoir. The production of that region will be segregated and fed to a gas processing plant of lower NGL (natural gas liquid) recovery, which essentially takes longer time to start suffering the deterioration of residue gas (gas mixture resulted after separating NGL) quality. The residue gas use can be limited to re-injection where the effect of below specification LHV (Low Heat Value) would not be an issue. The rest of the reservoir feeds another gas processing plant of higher NGL recovery level from which an amount of residue gas equivalent to that of the injected N2 will be rerouted to the sales network. This scenario will significantly delay as well as downsize the requirement of a N2 rejection plant. There is technical and certainly economical advantage of deferring the installation of costly N2 rejection units. Such a requirement can be entirely eliminated if the sales gas specification can be relaxed considering blending with other gas streams of higher LHV, and in collaboration with gas customers, i.e. assessing their capability to tolerate feedstock of lower specifications. It must be noted that such school of thinking may not necessarily be eventually embraced. The chosen scenario will also depend on the final configuration, i.e., wells grouping and gas gathering, of the ongoing project.

Abstract In-situ conversion process (ICP) can be an effective technique for the development of oil shale and ultra heavy oils, in which kerogen or heavy components will be cracked into light oils and gases via underground heating and pyrolysis, and the retorted oil can be recovered via conventional extraction techniques. Heating of targeted formation can be conducted using electrical heaters installed in vertical or horizontal wells, while a slow heating rate and lack of driving energy for oil production are the main issues of the conventional in-situ conversion process. In this study, an innovative nitrogen injection assisted in-situ conversion process (NAICP) was proposed to increase formation heating rate and improve oil production from oil shale. Reaction models of kerogen pyrolysis at elevated temperature were established, along with models for the evolution of porosity and permeability of oil shale formation during the pyrolysis process. The performance of nitrogen injection on the effectiveness of the ICP was then investigated through reservoir numerical simulation. The simulation results show that additional nitrogen injection can improve the heating rate of the oil shale formation, enhance oil production and energy efficiency in comparison with the conventional ICPs, which can be attributed to enhanced heat convection, pressurization effect and gas driving mechanism. Nitrogen injection assisted in-situ conversion process can be a promising technique for the exploitation of oil shale. Highlights • Nitrogen injection assisted in-situ process for oil shale was proposed. • The advantages of nitrogen injection assisted in-situ process were studied. • The mechanism of nitrogen injection to improve oil production performance was studied. • The effects of heating temperature and nitrogen injection rate were studied. [ABSTRACT FROM AUTHOR]

• A 3D CFD model of gob was established based on 1262 working face of Dingji Coal Mine. • The distributions of the CH4 and O2concentration fields as well as temperature field were simulated and analyzed under different gas drainage models. • The characterization of gas and coal spontaneous combustion coupled hazardous zones were described under multiple gas drainage ways. • To eliminate coupled hazardous area, the cooling effect of nitrogen injection of different modes was discussed. The spontaneous combustion of residual coal and potentially subsequent gas explosions that occur during gas drainage of the gob were investigated. The 1262 fully-mechanized mining face of the Dingji Coal Mine (Huainan, China) was used as a research benchmark. The methane and oxygen distributions were simulated as well as the temperature field associated with different gas-drainage models. Using a steady-state simulation method for temperature cut-off, linear superimposition of various parameters was used to determine the hazardous zones arising from the coupling of gas and spontaneously combustible coal. The results show that when gas drainage is applied, the range of oxidation zone is different with different gas drainage modes. Among three different drainage modes, when applying the buried pipes and cross-measure boreholes mode, the methane concentration near the working face and in the upper corner of the return airway not only can be effectively reduced, but the size of the oxidation zone in the gob is the smallest. Based on the model of buried pipes, cross-measure boreholes and surface wells, the coupled gas–coal hazard zones were derived. The results show that the coupled hazard zone shifts to the deeper parts of the gob as a result of gas drainage, and the scope of the hazard zone is enlarged in the strike, dip, and vertical directions to different extents. The cooling effect is better when the nitrogen is injected into the deep part of the gob rather than the shallow part. Furthermore, nitrogen injected from double boreholes in the deep part appears to exert the largest cooling effect. [ABSTRACT FROM AUTHOR]

The spontaneous combustion of residual coal and potentially subsequent gas explosions that occur during gas drainage of the gob were investigated. The 1262 fully-mechanized mining face of the Dingji Coal Mine (Huainan, China) was used as a research benchmark. The methane and oxygen distributions were simulated as well as the temperature field associated with different gas-drainage models. Using a steady-state simulation method for temperature cut-off, linear superimposition of various parameters was used to determine the hazardous zones arising from the coupling of gas and spontaneously combustible coal. The results show that when gas drainage is applied, the range of oxidation zone is different with different gas drainage modes. Among three different drainage modes, when applying the buried pipes and cross-measure boreholes mode, the methane concentration near the working face and in the upper corner of the return airway not only can be effectively reduced, but the size of the oxidation zone in the gob is the smallest. Based on the model of buried pipes, cross-measure boreholes and surface wells, the coupled gas-coal hazard zones were derived. The results show that the coupled hazard zone shifts to the deeper parts of the gob as a result of gas drainage, and the scope of the hazard zone is enlarged in the strike, dip, and vertical directions to different extents. The cooling effect is better when the nitrogen is injected into the deep part of the gob rather than the shallow part. Furthermore, nitrogen injected from double boreholes in the deep part appears to exert the largest cooling effect. [ABSTRACT FROM AUTHOR]

Nitrogen is of paramount importance for many processes in chemical and petroleum engineering; including enhanced oil recovery, gas injection for pressure maintenance, and gas recycling. Precise estimation of interfacial tension (IFT) between N 2 and the reservoir hydrocarbons is, therefore indispensable. However, experimental measurement of IFT is expensive and time consuming. Therefore, reliable model for estimating IFT is vital. In this communication, the IFT between N 2 and n-alkanes was modeled over a wide range of pressure (0.1–69 MPa) and temperature (295–442 K) based on the principle of corresponding state theory using dimensionless pressure and dimensionless temperature. Three well-known models; namely, Multilayer Perceptron (MLP) Neural Networks ( optimized by Levenberg-Marquardt ( LM ), Scaled Conjugate Gradient (SCG), or Bayesian Regularization (BR)), two Radial Basis Function (RBF) Neural Networks ( optimized by Particle Swarm optimization ( PSO ) technique or Genetic Algorithm ( GA )) and one Least Square Support Vector Machine (LSSVM) ( optimized by coupled simulated annealing ) were used to develop robust and accurate models for predicting IFT based on the proposed dimensionless parameters. Results suggested that the developed MLP-LM was the most accurate model of all with an average absolute relative error of 1.38%. MLP-LM model was compared with three well-known models in the literature; namely Density Gradient Theory (DGT), Linear Gradient Theory (LGT), and Parachor approaches combined with the Volume Translated Predictive Peng Robinson Equation of State (VT-PPR EOS) and the recently developed model by Hemmati-Sarapardeh and Mohagheghian. In addition to the advantage of being normal alkane-independent, results showed that the proposed MLP-LM model is superior to published models. Lastly, the quality of the literature IFT data and the applicability domain of MLP-LM model were evaluated using the Leverage approach. [ABSTRACT FROM AUTHOR]

Enhanced Oil Recovery (EOR) through various methodologies has been an active research for many years seeking efficient methods to increase the crude oil recovery efficiency from oil reservoirs. Among different gas injection scenarios, carbon dioxide (CO 2 ), natural gas (mainly methane (CH 4 )) and nitrogen (N 2 ) injection are considered as promising EOR agents. Asphaltene precipitation and deposition during EOR methods cause severe problems, which affect the recovery efficiency and increase the cost of the incremental oil production. This study is aimed to investigate the effects of CH 4 and N 2 injection compared with CO 2 injection on asphaltene precipitation and deposition. The different mole percent of the mentioned gases were introduced into the high-pressure cell, then the amount of precipitated asphaltene was measured at the reservoir condition. The evolution of asphaltene deposition was monitored through a high-resolution microscope. Moreover, Image processing software was utilized to check the amount of deposited asphaltene and its size distribution under different conditions. The most apparent finding to emerge from this study is that both CO 2 and natural gas increase the amount of precipitated asphaltene whereas the nitrogen as an inert gas has no considerable effect on the amount of precipitated asphaltene. According to the results, the increment of precipitated asphaltene by CO 2 is much higher than natural gas. Further, the thermodynamic solid model used in this study reasonably predicted the trend of asphaltene precipitation process for the mentioned EOR scenarios. [ABSTRACT FROM AUTHOR]

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To exploit the remaining oil in the high position of the reservoir, field test of nitrogen injection in single well has been carried out in Tahe Oilfield and good results have been achieved. However, the effect of nitrogen injection in single well is quite different, which has affected the large-scale application of gas injection in field. Through comprehensive analysis, it is recognized that the karst genesis and the type of reservoir space are the basis for determining the effect of nitrogen injection in a single well. Based on Karst genesis and reservoir space type, gas injection wells are divided into four types. By contrast from oil production, period of validity, water content and pressure, the effective characteristics of different types of wells after gas injection are compared and analyzed. According to these characteristics, some suggestions for field gas injection well selection are put forward, which can guide the practice and popularization of field gas injection test. [ABSTRACT FROM AUTHOR]

Nitrogen has emerged as an attractive gas for many petroleum and chemical engineering applications such as gas lift, gas recycling, pressure maintenance, and enhanced oil recovery, especially for some high-pressure reservoirs. Accurate determination of interfacial tension (IFT) in nitrogen/hydrocarbon systems is crucial and required for numerous applications in chemical and petroleum industries. The experimental measurements of IFT are costly, cumbersome and time consuming, especially at high pressure-high temperature conditions. In this study, the IFT of normal alkanes from n-C 5 to n-C 16 (as the representatives of crude oil) and nitrogen is modeled at a wide range of pressure (from 0.1 to 69 MPa) and temperature (from 295 to 442 K) using group method of data handling (GMDH). Three inputs were used for modeling including pressure, temperature, and molecular weight of normal alkane. To develop the most efficient model, 60% of the dataset was used for model development and the remaining 40% was used to check the validity and accuracy of the developed model. The proposed model predicts the data satisfactorily with an average absolute relative error of 3.81% and 3.91% in training and testing subsets, respectively. Then, the proposed model was compared to the well-known IFT models, namely Linear Gradient Theory (LGT), Density Gradient Theory (DGT), and Parachor approaches combined with the Volume Translated Predictive Peng Robinson Equation of State (VT-PPR EOS). The results demonstrate that the proposed model not only is superior to the existing models in terms of accuracy, but also can predict the IFT with a simple mathematical expression with a quite low computational cost. Finally, a simple-to-use algorithm was proposed to calculate the minimum miscibility pressure (MMP) in normal alkane/nitrogen systems based on the measurements with vanishing interfacial tension (VIT) technique, which predicts the MMP with high accuracy. [ABSTRACT FROM AUTHOR]

Pre-gas drainage plays a significant role in the prevention of coal and gas outburst in underground coal mines. However, difficulties of reducing the content of coal seam gas, especially localized coal seam CO 2 , to be below threshold values within a given drainage lead time have been encountered in numerous coal mines in Australia. As the proneness of nitrogen outburst is way smaller than CO 2 or methane outburst, nitrogen injection would be an attractive technology for the underground gas drainage management if it is really able to enhance the drainage efficiency. From this point of view, this paper aims at investigating the feasibility of implementing this technology in Bulli seam, Sydney Basin through numerical modelling. Four parts of work were conducted in this paper. Firstly, a binary gas transport model was developed through analysing the binary gas transport mechanism in both coal matrix and coal cleat, and also the matrix-cleat interaction due to binary gas sorption swelling. A real gas mixture viscosity was introduced and its change depends on the molar fractions of both components and their own viscosities. Secondly, the characteristics of the Bulli seam were studied to collect the parameters required by the binary gas transport model. Through laboratory experiment, field investigation and reviewing literature, the coal seam gas (methane, CO 2 ) and nitrogen adsorption and diffusion properties, in-situ seam properties such as permeability, porosity, cleat spacing and virgin pressure are either measured or estimated. Thirdly, the regular drainage effects in six scenarios with different initial permeability and coal seam gas type were examined and three of them are found to have drainage difficulties, i.e., the moderate permeability (0.5 mD) CO 2 case, the low permeability (0.005 mD) methane case and the low permeability (0.005 mD) CO 2 case. The effects of nitrogen injection on enhancing gas drainage efficiency, especially reducing the gas content, are studied for these scenarios. Results show that a satisfactory result is obtained for the moderate permeability CO 2 case, the CO 2 content can be reduced largely and an apparent increase of CO 2 production rate can be seen. However, the effect of nitrogen injection in low permeability methane scenario is even worse than the regular drainage using two boreholes, although it can increase the methane flow rate of single borehole. For low permeability CO 2 case, nitrogen injection can accelerate the reduction ratio of CO 2 content in part of the injection area and increase the total CO 2 flow rate, but the enhanced effect is limited and the CO 2 content is still high after 12 months of injection. Last but not least, the feature of the movement of coal seam gas content peak in the injection area is discussed and the reasons inducing the different injection effects between methane and CO 2 scenarios are analysed. A combination of lateral movement and drop of coal seam gas content peak is found, and permeability is believed to have great impacts on the movement speed. There is no sign indicating either diffusion or permeability change controls the different injection effects between methane and CO 2 scenarios, while the different competitive adsorption characteristics and the increase of mixture gas viscosities may have influences on this difference. [ABSTRACT FROM AUTHOR]

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Enhanced oil recovery using nitrogen injection is a commonly applied method for pressure maintenance in conventional reservoirs. Numerical simulations can be practiced for the prediction of a reservoir performance in the course of injection process; however, a detailed simulation might take up enormous computer processing time. In such cases, a simple statistical model may be a good approach to the preliminary prediction of the process without any application of numerical simulation. In the current work, seven rock/fluid reservoir properties are considered as screening parameters and those parameters having the most considerable effect on the process are determined using the combination of experimental design techniques and reservoir simulations. Therefore, the statistical significance of the main effects and interactions of screening parameters are analyzed utilizing statistical inference approaches. Finally, the influential parameters are employed to create a simple statistical model which allows the preliminary prediction of nitrogen injection in terms of a recovery factor without resorting to numerical simulations.

Coal matrix deformation is one of the main controlling factors for coal reservoir permeability changes in nitrogen foam fracturing. The characteristics and mechanism of coal matrix deformation during the process of adsorption/desorption were studied by isothermal adsorption/desorption experiments with methane and nitrogen. Based on the free-energy theories, the Langmuir equation, and elastic mechanics, mathematical models of coal matrix deformation were developed and the deformation characteristics in adsorption/desorption processes were examined. From the study, we deduced that the coal matrix swelling, caused by methane adsorption, was a Langmuir-type relationship with the gas pressure, and exponentially increased as the adsorption quantity increased. Then, the deformation rate and amplitude of the coal matrix decreased gradually with the increase of the pressure. At the following stage, where nitrogen replaces methane, the coal matrix swelling continued but the deformation amplitude decreased, which was only 19.60% of the methane adsorption stage. At the mixed gas desorption stage, the coal matrix shrank with the reduction of pressure and the shrinkage amount changed logarithmically with the pressure, which had the hysteresis effect when compared with the swelling in adsorption. The mechanism of coal matrix deformation was discussed through a comparison of the change of micropores, mesopores, and also part macropores in the adsorption process.

Enhanced oil recovery (EOR) methods are generally applied in the tertiary mode to the depleted oil reservoir to increase the recovery factor through enhanced microscopic displacement and macroscopic sweep efficiency. Choosing a specific EOR method for a candidate reservoir characterized by specific rock and fluid properties is governed by standard EOR screening criteria. It is not uncommon that EOR researchers to come up with innovative ideas and/or good reservoir engineering practices to extend the applicability of those methods beyond that specified by the standard criteria. As per the standard criteria., nitrogen EOR can work at its best in deeper reservoirs where the chemical and thermal method fails. Further, nitrogen EOR is preferred for light oil characterized by low viscosity, high gravity, and the presence of lighter components so that miscibility needed for enhancing the microscopic displacement could be achieved. Regarding the sweep efficiency, thin reservoirs are preferred to avoid gravity override due to the low viscosity and density of nitrogen. Despite the abundance of nitrogen and advancements made to the nitrogen-based EOR, no significant efforts were made to analyze whether those advancements have exceeded the standard screening criteria. This paper attempts to narrow this gap. Initially, a detailed compilation of the relevant nitrogen EOR work performed at the laboratory, pilot, and field scale is done by extracting the results from the available literature. Then the rock and fluid properties reported in each of the compiled works are compared with that of the standard criteria's stipulation to identify and classify the parameters that are exceeding and those not exceeding the standard criteria. Then a comparative analysis is done using the reported recovery factor to provide a statement for each compilation whether those exceeding parameters have indeed improved the nitrogen EOR performance. Based on the conducted study, properties such as oil viscosity, oil gravity, thickness, and oil composition, could be exceeded only when the depth is conducive to generating high pressure. The inert nature of nitrogen makes high pressure an important requirement for inducing miscibility and therefore, the reservoir depth of more than 6000 ft, stipulated in the standard criteria remains a must for an efficient nitrogen EOR process that targets microscopic displacement efficiency. Overall, depth and therefore the pressure requirement is a major influencing factor for nitrogen EOR to operate in its best miscible mode. Most of the recent studies were conducted at high pressures in order to induce miscible flooding pressure for increasing the oil recovery. [ABSTRACT FROM AUTHOR]

Based on previous studies, nitrogen injection could recover oil up to 45-90% of initial reserves. Although this method has a very good ability to produce oil, sometimes the operation pressure is higher than leak off formation pressure. In this study, operation pressure used a low pressure to solve this problem under immiscible process. Objective of this study is to determine the effect of injection pressure and displacement rate on oil recovery performance of continuous one dimensional nitrogen gas injection with a slim tube apparatus. The effect of nitrogen gas-oil contact on the gas composition was investigated using Gas Chromatograph Mass Spectrometer apparatus. In the experiments, nitrogen gas was injected into an oil sample of 38.5 oAPI gravity at various rates: 20 cc/hr, 30 cc/hr and 36.66/hr under 1500 psi pressure, and then at 20 cc/hr undr 2500 psi pressure. The results showed that an increase in injection rate increased oil recovery factor. The recovery factor lies between 40-54% of original oil in place. Gas analysis before injection and at the injection outlet showed a change of composition. when oil was contacted by nitrogen, indicating that some molecular mass transfer had taken place.

A certain typical liquefied natural gas (LNG) receiving terminal in China as an example, for the exchange and economic problems caused by high C2 components in the feed-in gas, the calorific value of natural gas products is adjusted by extracting C2 and C2 rich LNG and injecting nitrogen/liquid nitrogen. In order to evaluate incomes of the four kinds of technologies，ethane and C2 recovery and nitrogen gas injection (plan A & B) and liquid nitrogen injection (plan C) with their refrigeration cycle have been simulated by using prepare the energy consumption analysis. In addition， economic benefits of four calorific value adjustment systems are analyzed based on energy measurement. The results show that the after-tax net income of the receiving terminal which adds liquid nitrogen to adjust calorific value is 36. 83 % higher than which extracts C2 components in the volume measurement system. Under the system of energy measurement， the income of C2 recovery and plan A， B and C is increased by 8. 67 %， 12. 15% ,12. 16% and 7. 09% respectively compared to the original measurement mode, and the liquid nitrogen injection (plan C) has the highest after-tax net income. Therefore，considered in terms of product's sales and the operation and capital costs under the current situation of heat value adjustment technology, the liquid nitrogen injection process which inject liquid nitrogen in the exit of high pressure external transport pump is feasible, effective，and economical. [ABSTRACT FROM AUTHOR]

Strawberry plants are relatively unresponsive to nitrogen (N) fertilization. Supraoptimal N application also results in excessive vegetative growth, which competes to reproductive growth. Two strawberry field experiments were conducted for two consecutive years using fertigation to investigate the effect of different nitrogen (N) application rates on yield and growth of an everbearing strawberry (cv. Evie II). N was injected weekly into the drip irrigation system at 0, 0.5, 1, 3, and 6 kg N/ha/week the first year and 0, 1, 2, and 3 kg N/ha/week the next year. Fruit yield and fruit number were not affected the first year, but were increased the second year due to N application. However, there was no effect of N nutrition on average berry weight for both years. It was concluded that N fertilization may increase yield and fruit number, but average berry weight remains unaffected. [ABSTRACT FROM AUTHOR]

Cyclic pressure pulsing with nitrogen is studied for hydraulically fractured wells in depleted reservoirs. A compositional simulation model is constructed to represent the hydraulic fractures through local-grid refinement. The process is analyzed from both operational and reservoir/hydraulic-fracture perspectives. Key sensitivity parameters for the operational component are chosen as the injection rate, lengths of injection and soaking periods and the economic rate limit to shut-in the well. For the reservoir/hydraulic fracturing components, reservoir permeability, hydraulic fracture permeability, effective thickness and half-length are used. These parameters are varied at five levels. A full-factorial experimental design is utilized to run 1250 cases. The study shows that within the ranges studied, the gas-injection process is applied successfully for a 20-year project period with net present values based on the incremental recoveries greater than zero. It is observed that the cycle rate limit, injection and soaking periods must be optimized to maximize the efficiency. The simulation results are used to develop a neural network based proxy model that can be used as a screening tool for the process. The proxy model is validated with blind-cases with a correlation coefficient of 0.96. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Field trials of nitrogen injection enhanced gas recovery were carried out in underground coal mine through in-seam boreholes for the first time. • Significant gas flows were observed after nitrogen injections and a strong post-effect was monitored. • Residual gas content (Q3) can be effectively reduced through nitrogen injection and the total recovery ratio of coal seam gas is enhanced. Three stages of nitrogen (N 2) injection enhanced gas drainage through underground in-seam boreholes were carried out in a coal mine located in the southern Sydney basin. Due to the high CO 2 content and low permeability, hard-to-drain coals were encountered during the excavation process in this coal mine. Two parallel in-seam boreholes (the length of 36 m, the diameter of 96 mm and the borehole space of 5 m) were drilled on the rib of the gateroad. A total of ten-cylinder packs of nitrogen (approximately 1500 m3) were injected into the coal seam. Different nitrogen injection pressures (150 KPa, 250 KPa, 350 KPa and 450 KPa) and injection methods (continuous injection and cyclic injection) were employed. Gas flow rates and gas compositions from the production borehole were recorded during and after the nitrogen injection process. It was observed that gas breakthrough was tightly related to the nitrogen injection pressure. The higher injection pressure was, the shorter breakthrough time was. Specifically, no gas breakthrough was obtained when the injection pressure was 150 KPa. The minimum of breakthrough time was 35 min when 450 KPa's injection pressure was employed. Strong post-injection effect was monitored after each stage of injection and it was affected by the volume of the injected nitrogen. Under the current injection conditions, the performances of different injection methods were like each other, which was out of our expectation. After the injections, the results of cores showed that less than 5 % of the total injected nitrogen was remained in the coal seam. The coal seam gas content dropped 0.99–1.65 m3/t after these three stages of injection. All these findings provide implications and guidance not only for laboratory experiment and numerical modelling, but also for the field application of this new technology. [ABSTRACT FROM AUTHOR]

A new method for the in-situ conversion of oil shale was introduced i.e.， oil shale in-situ pyrolysis technique by fracturing and nitrogen injection. Electrical heater was put into the heating well and nitrogen was then pumped into the well. As a result， the oil shale layer was pyrolyzed by heated nitrogen. The advantages of the proposed method and the suitable layers were also introduced in comparison with traditional electrical heating and convective heating， and a computer simulation was done for the heating process of nitrogen. The parameters of the heater were optimized and it was confirmed that the length of the electrical heater was 30m and the heat flux was 11kW/m2. Finally， based on the suitable thin oil shale layers， it was verified by the computer simulation that the heating time is 80days under the condition that the distance of the heating well and the production well is 15m while the thickness of the oil shale layer is 1.5m. Obviously， the time is shortened compared with traditional electrical heating or convective heating. [ABSTRACT FROM AUTHOR]

To achieve the exchange between LNG terminal transmission gas and natural gas pipeline network in Shandong Province, injection of liquid nitrogen is proposed to adjust the calorific value. Through comparative analysis, the nitrogen injection port is designed on the outlet pipeline of high-pressure pump, and compared with injection of nitrogen gas, injection of liquid nitrogen has lower cost and less power consumption. High calorific values and Wobbe index under three limiting conditions are calculated by PROII simulation to determine that the ratio range of liquid nitrogen injection is from 6.45 to 67.52 t LN2/100 t LNG on the outlet pipeline of high-pressure pump. Finally, the addition of major equipment and related parameters under the demand of the whole adjustment strategies are given based on the one million tons output amount of the LNG terminal. It can provide references and samples for the design of calorific value adjustment strategy in other LNG terminals. [ABSTRACT FROM AUTHOR]

In gas condensate reservoirs, after a decrease in pressure below the dew point pressure, condensate formation would occur. One of the common and practical methods for prohibiting the rapid pressure drop in the reservoir and reduction of liquid dropout is gas injection. In this study, experimental measurement, the full field reservoir model and an economical evaluation have been performed to investigate the effect of nitrogen injection on an Iranian Southwestern gas condensate reservoir. At first, swelling and CVD tests were carried out to determine the swelling factor and changing the saturation pressure by nitrogen. Then, the full field simulation (history matching and prediction) was performed and finally an economical evaluation has been made. The results show that injecting more volumes of nitrogen cause to decrease the liquid dropout, increase the dew point pressure, and condensate ultimate recovery, but this process is not an economical project. [ABSTRACT FROM AUTHOR]

China is rich in coalbed methane resources, but the geological conditions of coal seams are complex and variable, and gas production is generally low. Simulations are conducted using the #15 coal seam in the Qiyuan mining area as a case study to improve coalbed methane production. The coal seam has low pressure, low permeability, low saturation and strong heterogeneity. Nitrogen injection has been used in this mining area, but the target production capacity has not been reached. This paper proposes a method to increase production using hydraulic jet drilling, controllable shock wave, and nitrogen injection, and field tests are conducted. The gas production increased from 120 m3/d to 600 m3/d–700 m3/d. Numerical simulations were conducted to determine the ability of the three stimulation methods to increase production. It is assumed that a small number of jet holes are used, and the permeability of the coal seam cannot be significantly improved. The results showed that the gas production was 2–8 times higher after using hydraulic jet drilling and a controllable shock wave than without stimulation measures. The combination of hydraulic jet drilling and controllable shock wave plus general nitrogen injection increased the gas production by 13 times compared to no stimulation measures, but the gas production decreased rapidly. The gas production after one year was consistent with that before general nitrogen injection. Gas production increased faster and was maintained longer after segmented nitrogen injection, and the overall gas production increased, but its decreasing trend was consistent with that of general nitrogen injection. This study provides references for conducting production tests in low pressure, low permeability, and low saturation coal seams. • The technology combining hydraulic jet, controllable shock wave anti-reflection and nitrogen injection is proposed and tested. [ABSTRACT FROM AUTHOR]

Lei 64 Block is thick-layer massive thin-oil reservoir. Since water flooding development in 2008, it has been faced with increasing formation depletion, faster water cut rising rate and serious water channeling. Water injection well shutdown and injection allocation reduction are implemented to control the water-cut increase, but the effect is limited. Therefore, a nitrogen injection gas-cap drive experiment is implemented against the poor water flooding effect. The new developed nitrogen injection completion string mainly uses Y521 packer to meet the requirement for high bottom-hole injection pressure. After the packer setting of pipe string, clean water is injected through casing annulus up to 100 m below the wellhead to balance the differential pressure below the packer. Besides, the casing pressure test and cementing quality inspection on old wells were performed strictly to avoid the potential safety hazards in the injection process as far as possible. The field test shows that the pipe string has a stable performance during the nitrogen injection, with no leakage at wellhead. For the affected production wells, the single well gets an average daily increased oil production of 9t. This primarily achieves the goal of oil production stabilizing and water cut control, and provides guidance for future nitrogen injection tests and design. [ABSTRACT FROM AUTHOR]