Nitrogen Gas Injection Research Articles

Evaluating Nitrogen Gas Injection Performance for Enhanced Oil Recovery in Fractured Basement Complex Reservoirs: Experiments and Modeling Approaches

This study explored the effectiveness of gas injection for enhanced oil recovery (EOR) in fractured basement complex reservoirs, combining laboratory experiments with numerical simulation analyses. The experiments simulated typical field conditions, focusing on understanding the interaction between the injected gas and the reservoir’s fracture–matrix system. The laboratory results showed that under the current reservoir pressure and temperature conditions, nitrogen gas flooding in the fractured matrix achieved a superior oil recovery efficiency compared to that of the other gases tested (CO2, APG, and oxygen-reduced air), exhibiting the most favorable movable oil saturation range and the lowest residual oil saturation. To evaluate the performance of nitrogen gas injection in a fractured basement complex reservoir, a 3D reservoir model with complex natural fractures was built in a numerical reservoir simulator. Special methods were required for the geological modeling and reservoir simulation, with the specific principles outlined. Numerical simulations of gas injection into fractured basement complex reservoirs revealed that cyclic gas injection was identified as the most effective strategy, balancing incremental oil recovery with minimized gas channeling risks. This study demonstrated that the optimal injection location and rate are crucial factors affecting the recovery performance. These findings provided actionable insights for implementing gas injection EOR strategies in fractured basement complex reservoirs, highlighting the importance of optimizing the injection parameters to maximize the recovery.

Experimental evaluation of acid number effect on interfacial tension between nitrogen and mixtures of petroleum fractions including diesel fuel and gasoline at different pressures

Crude oil is made up of very complex compounds, which are found in polar organic substances especially organic acid compounds in the majority. Although organic acid content in crude oil is low, the presence of organic acids affects the interfacial tension (IFT) in oil reservoirs thereby altering the enhancement of oil recovery using nitrogen gas (N2) injection. Therefore, in this study, the effects of pressure (1 to 35 bar), the percentage of aromatic compounds (0.0 to 100 vol%) in the aliphatic hydrocarbon samples and the organic acid (benzoic acid) content (0.0 to 0.8 g.L− 1) on IFT between a mixture of gasoline/diesel fuel and N2 were investigated at a temperature of 298 K. IFT does not necessarily decrease as pressure increases for the sake of existence of aromatic compounds. IFT alteration for gasoline was more (about 8 dyne.cm− 1) than for diesel fuel (approximately 4 dyne.cm− 1) during pressure increased from 1 to 35 bar due to the replacement of heavy long chain aliphatic compounds instead of light aromatic matters. The effect of IFT alteration between N2 and diesel fuel during increasing the organic acid content was little (approximately 1.5 dyne.cm− 1), in contrast, this effect was more noticeable for N2/gasoline (about 8 dyne.cm− 1). In addition, a reduced cubic model for estimating IFT between N2 and petroleum fractions in terms of pressure, petroleum fraction composition and organic acid content was proposed with an average relative error of less than 2.6%.

Nitrogen Gas-Assisted Extrusion for Improving the Physical Quality of Pea Protein-Enriched Corn Puffs with a Wide Range of Protein Contents.

Blowing agent-assisted extrusion cooking is a novel processing technique that can alter the expansion of extruded snacks and, thus, enhance their physical appeal, such as texture. However, to this day, this technique has only been studied for ingredients with limited protein contents (<30%). In this study, protein-enriched snacks were extruded using nitrogen gas as a blowing agent at a wide protein range (0-50%) to better explore the potential of this technique in manufacturing high-protein snacks. The results showed that, with nitrogen gas injection, extrudate radial expansion was significantly (p < 0.05) improved at 10% and 40% protein, while extrudate density was significantly reduced at 30% and 50% protein. Nitrogen gas-injected extrudates, especially at 50% protein, exhibited improvements in texture, including a reduction in hardness and an increase in crispness. Collectively, this study showed the promising potential of nitrogen gas-assisted extrusion in improving the physical appeal of innovative healthy snacks at a high protein level (i.e., 50%).

The Role of Silica Nanofluid as a Plugging Agent for Enhanced Oil Recovery – Experimental Approach

Many enhanced oil recovery techniques have been adopted in oil production to recover as much oil as possible. However, enhanced oil recovery techniques are complex and costly. Therefore, nanofluids have been modified in the laboratory to be consistent with reservoir fluids and rocks while also being environmentally benign. This study aims to investigate the role of silica nanofluid in plugging the high permeable zones after oil is recovered from the reservoir to divert pressure to the low permeable zone for enhanced oil production from the low permeable zones. A digital gas permeameter (DGP-300-B) was used to determine the permeability of the core by injecting nitrogen gas. In addition, a DHP-100-M Digital Helium Porosimeter was used to determine bulk volume, grain volume, and grain density porosity. The experiment was conducted with different percentages of silicon dioxide nanoparticles to observe the effect of plugging in each stage. Results show that a 52% reduction in core permeability was observed when using 0.5wt.% of silica nanoparticles, a 72% reduction in core permeability when using 1wt.% of silica nanoparticles and a 94% reduction in core permeability when using 2wt.% of silica nanoparticles.

Gas-assisted high-moisture extrusion of soy-based meat analogues: Impacts of nitrogen pressure and cooling die temperature on density, texture and microstructure

This study explored the potential of a novel gas-assisted high-moisture extrusion cooking technique to improve the physical quality of meat analogues. Extrusion was performed as a full factorial design at three long cooling die temperatures (DT) (35, 50 and 65 °C) and three nitrogen gas injection pressures (GP) (0, 1 and 2.5 bar). The lowest meat analogue density was observed for the meat analogues produced at the lowest DT and highest GP combination. At the lowest DT, gas injection substantially decreased meat analogue hardness, chewiness and gumminess. X-ray microtomography analyses for meat analogues produced at 2.5 bar gas injection pressure revealed that DT significantly affected bubble sizes with larger and more diverse bubbles in the meat analogues produced at the lowest DT. These microstructural variations indicate that gas-assisted high-moisture extrusion cooking can be fine-tuned to improve the texture and, thus, sensory properties of meat analogues. Industrial relevanceHigh-moisture extrusion cooking is widely used for industrial-scale production of plant-based meat analogues. Manufacturing meat analogues with desired hardness and chewiness without detrimental effects on other characteristics such as color and degree of texturization is still quite challenging using conventional high-moisture extrusion cooking. Gas-assisted high-moisture extrusion cooking, when fine-tuned, has great potential in manipulating end-product texture and color without negatively impacting the degree of protein texturization.

Improved gas influx distribution estimation using interfacial area transport equation (IATE) enabled two-fluid model: An advanced modeling and full-scale experimental study

Gas influx management is a critical aspect of petroleum drilling operations, which aims to prevent the uncontrolled outflow of formation gas and the potential consequences caused by blowouts. This study investigates the distribution of gas influx and the interfacial area concentration (IAC) during gas influx circulation operations through a combination of full-scale experiments and advanced numerical simulations.Experiments were conducted to simulate downhole gas influxes by injecting Nitrogen gas into the base of a 5,160-foot-deep experimental wellbore, which was filled with water. A Distributed Fiber-Optic Sensing (DFOS) system was installed in the wellbore to obtain high-resolution acoustic and temperature data and monitor the gas influx behaviors when circulated out of the annulus. Various types of measurements were obtained to analyze the gas influx length, slip velocities, void fraction distribution, and dispersion behaviors. In addition, an advanced numerical simulator was developed based on a modified Two-Fluid Model and the Interfacial Area Transport Equation (IATE) to simulate the gas influx behaviors. The model estimations were compared to the experimental measurements for validation of accuracy and further insights.The numerical modeling framework, based on the interfacial area transport equation, effectively captured bubble interactions, including mechanisms including bubble breakage and coalescence, by estimating the interfacial area distribution. The gas influx dispersion during circulation was analyzed using both model estimations and experimental data. Good agreement was observed between the model predictions and experimental data, including multi-depths gauge measurements and the DFOS data.This is a novel application of the IATE in well-scale multiphase flow simulations, which has proved to be an effective tool for predicting the dynamics of gas influx distributions. The outcomes of this study provide critical insights into the design and optimization of gas influx management during Managed Pressure Drilling (MPD).

Effect of coolant boiling induced by accumulated debris on flow-regime characteristics of debris bed formation behavior for sodium-cooled fast reactor: Experimental and modeling study with gas injection

Understanding the Debris Bed Formation (DBF) behavior is important to the optimized integral evaluation for Core Disruptive Accident (CDA) of Sodium-cooled Fast Reactor (SFR). Aimed at clarifying the characteristics of flow regimes during DBF, extensive experimental works were carried out by releasing solid particles into a water pool. According to the preliminary studies using bottom heating and nitrogen gas injection, it was found that the effect of coolant boiling should be crucial to the flow-regime transition. However, the gas flow rate considered in these studies (0–50 L/min) was not adequate wide to cover the range of vapor flow rate from the possible drastic boiling in actual CDA of SFR. Therefore, in current study, to elucidate the influence of coolant boiling on DBF flow-regime characteristics more comprehensively and provide more extensive data for supporting the predictive model development, a greater number of experiments are conducted with a much-enlarged range of gas flow rates (up to 100 L/min) under varying parametric conditions (including particle size, particle type, water depth and release pipe diameter). Through analyzing the flow-regime transition, an extended functional form for the effect of coolant boiling is successfully proposed. By incorporating this form into our base model, the model predictability can be extended for the DBF at the conditions of coolant boiling induced by accumulated debris in accordance with the verification of the regime map. Present study is believed to be valuable for further developing and verifying the models and codes for SFR safety analysis in China.

Systematic design of a multi-input multi-output controller by model-based decoupling: a demonstration on TCV using multi-species gas injection

In this paper, we present the first results of a systematically designed multi-input multi-output gas-injection controller on Tokamak á Configuration Variable (TCV). We demonstrate the simultaneous real-time control of the NII emission front position and line-integrated electron density using nitrogen and deuterium gas injection. Injection of nitrogen and/or deuterium affects both the NII emission front position and line-integrated electron density. This interplay between control loops is termed interaction and, when strongly present, makes designing a controller a significantly more complex problem. Interaction between the control loops can be reduced to an acceptable level by redefining inputs, decoupling the multi-input multi-output control problem to separated single-input single-output problems. We demonstrate how to achieve this by defining virtual control inputs from linear combinations of the actuators available. For the demonstration on TCV, linear combinations of deuterium and nitrogen gas injection are computed from transfer-function models to obtain these virtual inputs. The virtual inputs reduce the interaction in the control-relevant frequency range to a point where control of the NII emission front position and line-integrated electron density can be considered decoupled, allowing for the much simpler design of single-input single-output controllers for each loop. Implementing the controllers with the virtual inputs gives the multi-input multi-output gas-injection controller. This approach is well established in the control community, and is presented here as a demonstration to drive developments of multi-input multi-output control strategies. In particular, the envisioned control of particle- and heat fluxes impacting the divertor targets by injection of multiple gas species.

Effect of Crude Oil and Nitrogen Gas Flow Rates on the Time Taken for Flow Initiation of Waxy Crude Oil

Transportation of waxy crude oil in a production pipeline often encountered flow assurance issues, such as wax deposition. In a case where pipeline shutdown is needed, wax deposit is likely to form within the pipelines, which leads to operational complexity during the restart phase. Commonly, crude oil restarts to flow after a significantly high restart pressure is pumped longer than is necessary. This is due to the physical hindrance caused by the solid wax, which requires additional pressure to disintegrate it before achieving a steady crude oil flow. This study aims to investigate the effect of crude oil and nitrogen gas flow rates on the time taken for crude oil flow initiation using a flow loop rig, which is connected to a nitrogen gas injection system. The nitrogen gas was injected into the test section pipeline at predetermined flow rates within specified periods. After 45 min of static cooling, the crude oil gear pump is switched on to build sufficient pressure to initiate the waxy crude oil flow in the pipeline. Additionally, a statistical analysis by the response surface methodology was also performed by Minitab® 19 software. Results show that the maximum reduction in flow initiation is 73.7% at 5 L/min of crude oil and 1 L/min of nitrogen gas. This study reveals that the presence of nitrogen gas improved the pipeline restart phase by minimizing both restart pressure and time taken for flow initiation.

Premothballing, Mothballing, and Recommissioning Method for 762-mm and 102-km Offshore Gas Pipelines

In the coming years, gas production in Indonesia is projected to decrease so that the option to abandon a plant and temporary shut down will increase. The 762-mm and 102-km offshore gas pipeline is planned to be shut down for 4 years. Therefore, the comprehensive method from the premothballing, mothballing, and recommissioning stages should be developed. In this study, these methods have been developed and the pipeline can be preserved for 4 years with some remarks where the coating repairs, freespan rectification, and analysis of the sacrificial anode remaining life must be performed before premothballing stage. In the premothballing stage, 4 different pigs are used to clean the pipeline until the deposit released is less than 20 L. In mothballing, the internal pipeline is filled with nitrogen gas to prevent the corrosion. The injection of nitrogen gas will be conducted by the train pig method, where each train pig is pushed by nitrogen gas. The internal pressure of the pipeline must be maintained at 1.1 MPa and should not be less than 0.9 MPa to avoid buckle propagation. Continuous maintenance and monitoring should be conducted on the pipeline. The corrosion coupon monitoring should be performed every six months, pressure and right of way (ROW) monitoring should be carried out every two weeks, and regular monitoring and maintenance reports should be conducted at least once a year. Recommissioning begins with evaluating data and conducting remotely operated vehicle (ROV) inspections. Nitrogen gas displacement is performed using a train pig driven by fresh nitrogen gas on two pigs and the production gas should be streamed to push the third pig. The inline inspection (ILI) must be performed to determine the percentage of actual metal loss. The ILI results can be used to perform remaining life analysis and as requirements for pipeline recertification so that the pipeline can be reoperated.

Experimental investigation on fracture characteristics by liquid nitrogen compound fracturing in coal

The stimulation efficiency of hydraulic fracturing in coalbed methane (CBM) reservoir are low due to high filtration. In this study, a new compound fracturing method is proposed to improve the CBM reservoir fracturing efficiency combining the advantages of liquid nitrogen (LN2) fracturing and hydraulic fracturing. The compound fracturing starts from LN2 fracturing forming complex fractures and non-filtration zones, follows by injecting nitrogen gas (N2) to displace LN2 near the borehole into the fracture tips and prevent subsequent sand-carrying fluids from freezing in the borehole, and finishes by using sand-fluid mixtures carrying proppant into the frozen coal seam. To test the feasibility, fracturing experiments were conducted to investigate the performances of LN2 compound fracturing. The lab results show that LN2 compound fracturing can create more complex and highly conductive fracture networks than water fracturing and pure LN2 fracturing. Compared with LN2 fracturing, the average fracture aperture, fractures number, and total fracture volume induced by compound fracturing increased by 28%, 10%, and 34%, respectively. Compared with water fracturing, the fractures number, and total fracture volume induced by compound fracturing increased by 55% and 42%, respectively. The reason for the improved conductivity as follows: in the pad stage of the compound fracturing, coal is fractured by LN2 with low viscosity and low temperature, forming a large number of small-scale fractures. In the slurry stage, coal is fractured by water, which further activates the small-scale fractures, increasing the number and aperture of fractures. The key findings obtained in this work is the proposed LN2 compound fracturing method that helps sustainable development of CBM resources in an efficient and environmentally friendly way.

Reaction pathway of nitrate and ammonia formation in the plasma electrolysis process with nitrogen and oxygen gas injection

The plasma electrolysis method using N2 and O2 injection is an effective and environmentally friendly solution for nitrogen fixation into nitrate and ammonia. The reaction pathway, the effect of the N2 and O2 gas injection composition are important parameters in understanding the mechanism and effectiveness of these processes. This study aims to determine the formation pathway of nitrate and ammonia by observing the formation and role of reactive species as well as intermediate compounds. Two reaction pathways of NOx and ammonia formation have been observed. The NOx compound formed in the solution was oxidized by ∙OH to NO2, followed by the production of a stable nitrate compound. The ammonium produced from the ammonia pathway was generated from nitrogen reacting with ∙H from H2O. The amount of NH3 formed was lesser compared to the NOx compounds in the liquid and gas phases. This indicates that the NOx pathway is more dominant than that of ammonia. The gas injection test with a ratio of N2/O2 = 79/21 was the most effective for nitrate formation compared to another ratio. The results of the emission intensity measurement test show that the reactive species ∙N, ∙N2*, ∙N2+, ∙OH, and ∙O have a significant role in the nitrate formation through the NOx pathway, while the reactive species ∙N and ∙H lead to the formation of NH3. The highest nitrate product was obtained at a ratio of N2/O2: 79/21 by 1889 mg L−1, while the highest ammonia product reached 31.5 mg L−1 at 100% N2 injection.

Modeling the effect of nitrogen recycling on the erosion and leakage of tungsten impurities from the SAS-VW divertor in DIII-D during nitrogen gas injection

The new SAS-VW divertor in DIII-D has tungsten-coated components to enable the study of tungsten erosion and leakage from a closed, slot-like divertor. A proposed method of actively managing the tungsten impurities is to inject low-Z impurities, such as nitrogen, into the Scrape-off-Layer (SOL) to modify the conditions in the plasma boundary and in turn manipulate both the erosion and subsequent transport of tungsten. Nitrogen injection from the SOL crown has been modeled using SOLPS-ITER to calculate the background plasma including the intrinsic carbon and the injected nitrogen impurities, and subsequently DIVIMP has been used to calculate the tungsten erosion and transport on top of the background plasma solution. This workflow has been used to model scenarios at a variety of nitrogen injection rates with different assumptions about the nitrogen recycling at the target. In the scenario modeled here, an optimal nitrogen injection rate around 3–4 × 1 0 20 N/s is found to reduce the amount of tungsten reaching the core by a factor of about 2.4. However, when the nitrogen recycling rate at the divertor targets is high, the nitrogen redistributes within the slot leading to increased tungsten sputtering, and the range of injection rates resulting in tungsten mitigation becomes narrower. • Modeling shows N gas injection can be used to manipulate SOL force balance on W ions. • Optimal N gas injection rate may exist for W mitigation in new DIII-D divertor. • N recycling at divertor targets narrows operating window for W mitigation.

How innovations in methodology offer new prospects for volume electron microscopy

Detailed knowledge of biological structure has been key in understanding biology at several levels of organisation, from organs to cells and proteins. Volume electron microscopy (volume EM) provides high resolution 3D structural information about tissues on the nanometre scale. However, the throughput rate of conventional electron microscopes has limited the volume size and number of samples that can be imaged. Recent improvements in methodology are currently driving a revolution in volume EM, making possible the structural imaging of whole organs and small organisms. In turn, these recent developments in image acquisition have created or stressed bottlenecks in other parts of the pipeline, like sample preparation, image analysis and data management. While the progress in image analysis is stunning due to the advent of automatic segmentation and server‐based annotation tools, several challenges remain. Here we discuss recent trends in volume EM, emerging methods for increasing throughput and implications for sample preparation, image analysis and data management.

The Effect of High Protein Powder Structure on Hydration, Glass Transition, Water Sorption, and Thermomechanical Properties.

Poor solubility of high protein milk powders can be an issue during the production of nutritional formulations, as well as for end-users. One possible way to improve powder solubility is through the creation of vacuoles and pores in the particle structure using high pressure gas injection during spray drying. The aim of this study was to determine whether changes in particle morphology effect physical properties, such as hydration, water sorption, structural strength, glass transition temperature, and α-relaxation temperatures. Four milk protein concentrate powders (MPC, 80%, w/w, protein) were produced, i.e., regular (R) and agglomerated (A) without nitrogen injection and regular (RN) and agglomerated (AN) with nitrogen injection. Electron microscopy confirmed that nitrogen injection increased powder particles’ sphericity and created fractured structures with pores in both regular and agglomerated systems. Environmental scanning electron microscopy (ESEM) showed that nitrogen injection enhanced the moisture uptake and solubility properties of RN and AN as compared with non-nitrogen-injected powders (R and A). In particular, at the final swelling at over 100% relative humidity (RH), R, A, AN, and RN powders showed an increase in particle size of 25, 20, 40, and 97% respectively. The injection of nitrogen gas (NI) did not influence calorimetric glass transition temperature (Tg), which could be expected as there was no change to the powder composition, however, the agglomeration of powders did effect Tg. Interestingly, the creation of porous powder particles by NI did alter the α-relaxation temperatures (up to ~16 °C difference between R and AN powders at 44% RH) and the structural strength (up to ~11 °C difference between R and AN powders at 44% RH). The results of this study provide an in-depth understanding of the changes in the morphology and physical-mechanical properties of nitrogen gas-injected MPC powders.

Combustion-mode transition of a solid propellant rocket motor by nitrogen gas injection and combustion gas release

Combustion-mode transition of a solid propellant rocket motor by nitrogen gas injection and combustion gas release

Asphaltene Thermodynamic Precipitation during Miscible Nitrogen Gas Injection

SummaryFor many years, miscible gas injection has been the most beneficial enhanced oil recovery method in the oil and gas industry. However, injecting a miscible gas to displace oil often causes the flocculation and deposition of asphaltenes, which subsequently leads to a number of production problems. Nitrogen gas (N2) injection has been used to enhance oil recovery in some oil fields, seeking to improve oil recovery. However, few works have implemented N2 injection and investigated its effect on asphaltene precipitation and deposition. This research investigated the N2 miscible flow mechanism in nanopores and its impact on asphaltene precipitations, which can plug pores and reduce oil recovery. First, a slimtube was used to determine the minimum miscibility pressure (MMP) of N2 to ensure that all of the experiments would be conducted at levels above the MMP. Second, filtration experiments were conducted using nanocomposite filter membranes to study asphaltene deposition on the membranes. A filtration apparatus was designed specifically and built to accommodate the filter membranes. The factors studied include N2 injection pressure, temperature, N2 mixing time, and pore size heterogeneity. Visualization tests were conducted to highlight the asphaltene precipitation process over time. Increasing the N2 injection pressure resulted in an increase in the asphaltene weight percent in all experiments. Decreasing the pore size of the filter membranes increased the asphaltene weight percent. More N2 mixing time also resulted in an increase in asphaltene weight percent, especially early in the process. Visualization tests revealed that after 1 hour, the asphaltene particles were conspicuous, and more asphaltene clusters were found in the test tubes of the oil samples from the filter with the smallest pore size. Chromatography analysis of the produced oil confirmed the reduction in the asphaltene weight percent. Microscopy and scanning electron microscopy (SEM) imaging of the filter membranes indicated significant pore plugging from the asphaltenes, especially for the smaller pore sizes. This research highlights the severity of asphaltene deposition during miscible N2 injection in nanopore structures so as to understand the main factors that may affect the success of miscible N2 injection in unconventional reservoirs.

Method to optimize the volume of nitrogen gas injected into the trapped annulus to mitigate thermal-expanded pressure in oil and gas wells

Trapped annular pressure caused by thermal-expand liquid greatly threatens well integrity, so its mitigation is very necessary and essential. Nitrogen gas has been proved as an effective and low-cost mitigation measure for thermal-expanded annular pressure, but few methods are available to design the injection volume while this is vital for its mitigation reliability. Hence, this paper aims to develop a design method of the optimal injection volume of nitrogen gas to mitigate trapped annular pressure. The design method is based on volume consistency law and volume compensation effect. The proposed design method takes annular pressure increment and optimal injection volume as mitigation aim. A solving process is proposed according to volume increment and error iteration. An index is defined to evaluate mitigation efficiency. The results indicate the mitigation would fail once the injection volume is lower than the optimal injection volume, but over-surplus injection volume reduces mitigation efficiency. Optimal injection volume increases as production time and rate increase. The mitigation efficiency decreases and optimal injection volume increases as water depth increases. The optimal volume increases as the geothermal gradient increases. More nitrogen gas is needed as the mitigation aim of annular pressure increment decreases. The optimal injection volume increases as the expand-compress ratio increase while mitigation efficiency changes little. This design method can be applied in deep-water and HPHT wells. Detailed production data should be obtained and the geothermal temperature should be measured accurately. The extra injection volume is recommended to overcome the unexpected change of production plan and error of geothermal temperature measurement. The mitigation aim should consider the change of well barriers’ strengths. The expand-compress ratio of annular liquid should be adjusted to prevent too large optimal injection volume. Compared with field experience or qualitative analysis, this method can provide an optimal injection volume as reference for the mitigation of thermal-expanded annular pressure, which can enhance the long-term reliability of mitigation by injecting nitrogen gas, thus promoting the popularization.

Knowledge from recent investigations on sloshing motion in a liquid pool with solid particles for severe accident analyses of sodium-cooled fast reactor

Investigations on the molten-pool sloshing behavior are of essential value for improving nuclear safety evaluation of Core Disruptive Accidents (CDA) that would be possibly encountered for Sodium-cooled Fast Reactors (SFR). This paper is aimed at synthesizing the knowledge from our recent studies on molten-pool sloshing behavior with solid particles conducted at the Sun Yat-sen University. To better visualize and clarify the mechanism and characteristics of sloshing induced by local Fuel-Coolant Interaction (FCI), experiments were performed with various parameters by injecting nitrogen gas into a 2-dimensional liquid pool with accumulated solid particles. It was confirmed that under different particle-bed conditions, three representative flow regimes (i.e. the bubble-impulsion dominant, transitional and bed-inertia dominant regimes) are identifiable. Aimed at predicting the regime transitions during sloshing process, a predictive empirical model along with a regime map was proposed on the basis of experiments using single-sized spherical solid particles, and then was extended for covering more complex particle conditions (e.g. non-spherical, mixed-sized and mixed-density spherical particle conditions). To obtain more comprehensive understandings and verify the applicability and reliability of the predictive model under more realistic conditions (e.g. large-scale 3-dimensional condition), further experimental and modeling studies are also being prepared under other more complicated actual conditions.

Asphaltene Thermodynamic Flocculation during Immiscible Nitrogen Gas Injection

SummaryGas-enhanced oil recovery is one of the most advantageous enhanced oil recovery methods. Nitrogen is one of the most investigated gases because of its beneficial properties. However, during its interaction with crude oil, nitrogen can induce asphaltene deposition, which may result in severe formation damage and pore plugging. Few works have investigated the impact of nitrogen on asphaltene instability. This research studied the immiscibility conditions for nitrogen in nanopores and the impact of nitrogen on asphaltene precipitations, which could lead to plugging pores and oil recovery reduction. A slimtube was used to determine the minimum miscibility pressure (MMP) of nitrogen to ensure that all the experiments would be carried out below the MMP. Then, filtration experiments were conducted using nanofilter membranes to highlight the impact of the asphaltene particles on the pores of the membranes. A special filtration vessel was designed and used to accommodate the filter paper membranes. Various factors were investigated, including nitrogen injection pressure, temperature, nitrogen mixing time, and pore size heterogeneity. Supercritical phase nitrogen was used during all filtration experiments. Visualization tests were implemented to observe the asphaltene precipitation and deposition mechanism over time. Increasing the nitrogen injection pressure resulted in an increase in the asphaltene weight percent in all experiments. Decreasing the pore size of the filter membranes resulted in an increase in the asphaltene weight percent. Greater asphaltene weight percents were observed with a longer nitrogen mixing time. Visualization tests revealed that asphaltene clusters started to form after 1 hour and fully deposited after 12 hours in the bottom of the test tubes. Chromatography analysis of the produced oil confirmed that there was a reduction in the heavy components and asphaltene weight percent. Microscopy and scanning electron microscopy (SEM) imaging of the filter paper membranes found that significant pore plugging resulted from asphaltene deposition and precipitation. This research investigated asphaltene precipitation and deposition during immiscible nitrogen injection to understand the main factors that impact the success of using such a technique in unconventional shale reservoirs.