Mechanistic investigation of gas injection treatment in a continental shale gas condensate reservoir

Low thermal evolution degree of gas and connected fracture network are key features in the continental shale gas reservoirs.When the pressure decreases lower than the dew point pressure,gas condensate diminishes the mobility of subsurface fluid forms in the near well region,which further reduces the productivity and final recovery factor in addition to the low connected fracture network.This work is motivated to investigate the application of gas injection,proven to be a feasible technique in conventional/marine-shale gas condensate reservoirs,in continental shale gas condensate reservoirs.We apply a compositional model to investigate the mechanism of gas injection treatment taking a continental shale gas condensate reservoir in the Fuxing area,Sichuan Basin,China as an example.The results demonstrate that for the removal of gas condensate during CO_(2)injection,re-vaporization plays the main mechanism through two processes including pressurization and development of miscibility,while the former is overwhelming.Considering the variation trend of the total volume of gas condensate,we divide the whole injection process into four and six stages in the single fracture model and fracture network model,respectively,and reason the trend with respect to phase behavior and flow pattern.A sensitive study on the injected gas type indicates that the sorting of the gas injection performance to remove gas condensate produced gas followed by CH4,and followed by CO_(2).Finally,we investigate the performance of cyclic produced-gas injection and optimize the injection scheme.This work provides technical and theoretical support for the development of continental shale gas reservoirs.

Horizontal well spacing optimization and gas injection simulation for the ultra-low-permeability Yongjin reservoir

Optimal spacing for vertical wells can be effectively predicted with several published methods,but methods suitable for assessing the proper horizontal well spacing are rare.This work proposes a method for calculating the optimal horizontal well spacing for an ultra-low permeability reservoir e the Yongjin reservoir in the Juggar Basin,northwestern China.The result shows that a spacing of 640m is the most economical for the development of the reservoir.To better develop the reservoir,simulation approaches are used and a new model is built based on the calculated well spacing.Since the reservoir has an ultralow permeability,gas injection is regarded as the preferred enhanced oil recovery(EOR)method.Injection of different gases including carbon dioxide,methane,nitrogen and mixed gas are modelled.The results show that carbon dioxide injection is the most efficient and economical for the development of the reservoir.However,if the reservoir produces enough methane,reinjecting methane is even better than injecting carbon dioxide.

Comparison of different noble gas injections by massive gas injection on plasma disruption mitigation on Experimental Advanced Superconducting Tokamak

Massive gas injection(MGI)is a traditional plasma disruption mitigation method.This method directly injected massive gas into the pre-disruption plasma and had been developed on the Experimental Advanced Superconducting Tokamak(EAST).Different noble gas injection experiments,including He,Ne,and Ar,were performed to compare the mitigation effect of plasma disruption by evaluating the key parameters such as flight time,pre-thermal quench(pre-TQ),and current quench(CQ).The flight time was shorter for low atomic number(Z)gas,and the decrease in flight time by increasing the amount of gas was insignificant.However,both pre-TQ and CQ durations decreased considerably with the increase in gas injection amount.The effect of atomic mass on pre-TQ and CQ durations showed the opposite trend.The observed trend could help in controlling CQ duration in a reasonable area.Moreover,the analysis of radiation distribution with different impurity injections indicated that low Z impurity could reduce the asymmetry of radiation,which is valuable in mitigating plasma disruption.These results provided essential data support for plasma disruption mitigation on EAST and future fusion devices.

Mechanical stirring for highly efficient gas injection refining

In gas injection refining processes,wide dispersion of small bubbles in the bath is indispensable for high refining efficiency.Eccentric mechanical stirring with unidirectional impeller rotation was tested using a water model for pursuing better bubble disintegration and dispersion.Effects of various factors on bubble disintegration and dispersion were investigated.These factors were stirring mode,eccentricity and rotation speed,nozzle structure,nozzle immersion depth,and gas flow rate.Gas injection from a nozzle at the end of the impeller shaft and from an immersed lance was studied.Under eccentric stirring,a vortex was formed away from the shaft.Small bubbles were produced in the strong turbulence or high shear stress field near the rotating impeller and moved in the direction to the vortex keeping up with the macroscopic flow induced by the mechanical stirring.Thus small bubbles could disperse widely in the bath under eccentric stirring with unidirectional rotation.

Oxide film on bubble surface of aluminum foams produced by gas injection foaming process

Based on A356 aluminum alloy,aluminum foams were prepared by gas injection foaming process with pure nitrogen,air and some gas mixtures.The oxygen volume fraction of these gas mixtures varied from 0.2%to 8.0%.Optical microscopy,scanning electron microscopy（SEM） and Auger electron spectroscopy（AES） were used to analyze the influence of oxygen content on cell structure,relative density,macro and micro morphology of cell walls,coverage area fraction of oxide film,thickness of oxide film and other aspects.Results indicate that the coverage area fraction of oxide film on bubble surface increases with the increase of oxygen content when the oxygen volume is less than 1.2%.While when the oxygen volume fraction is larger than 1.6%,an oxide film covers the entire bubble surface and aluminum foams with good cell structure can be produced.The thicknesses of oxide films of aluminum foams produced by gas mixtures containing 1.6%-21%oxygen are almost the same.The reasons why the thickness of oxide film nearly does not change with the variation of oxygen content and the amount of oxygen needed to achieve 100%coverage of oxide film are both discussed.In addition,the role of oxide film on bubble surface in foam stability is also analyzed.

Oxidation kinetics of oxide film on bubble surface of aluminum foams produced by gas injection foaming process

In the range of 620？710 °C, air was blown into A356 aluminum alloy melt to produce aluminum foams. In order to study the influence of temperature on the thickness of oxide film on bubble surface, Auger electron spectroscopy （AES） was used. Based on the knowledge of corrosion science and hydrodynamics, two oxidation kinetics models of oxide film on bubble surface were established. The thicknesses of oxide films produced at different temperatures were predicted through those two models. Furthermore, the theoretical values were compared with the experimental values. The results indicate that in the range of 620？710 °C, the theoretical values of the thickness of oxide film predicted by the model including the rising process are higher than the experimental values. While, the theoretical values predicted by the model without the rising process are in good agreement with the experimental values, which shows this model objectively describes the oxidation process of oxide film on bubble surface. This work suggests that the oxidation kinetics of oxide film on bubble surface of aluminum foams produced by gas injection foaming process follows the Arrhenius equation.

Fabrication of AlN-TiC/Al composites by gas injection processing

The fabrication of AlN-TiC/Al composites by carbon- and nitrogen-containing gas injection into Al-Mg-Ti melts was studied. It was shown that AlN and TiC particles could be formed by the in situ reaction of mixture gas （N2 ＋ C2H2 ＋ NH3） with Al-Mg-Ti melts. The condition for the formation of AlN was that the treatment temperature must be higher than 1373 K, and the amounts of AlN and TiC increased with the increase of the treatment temperature and the gas injection time It was considered that AlN was formed by the direct reaction of Al with nitrogen-containing gas at the interface of the gas bubble and the melt. However, the mechanism of TiC formation is a combination mechanism of solution-precipitation and solid-liquid reaction.

Gas injection for enhanced oil recovery in two-dimensional geology-based physical model of Tahe fractured-vuggy carbonate reservoirs:karst fault system

Gas injection serves as a main enhanced oil recovery(EOR)method in fractured-vuggy carbonate reservoir,but its effect differs among single wells and multi-well groups because of the diverse fractured-vuggy configuration.Many researchers conducted experiments for the observation of fluid flow and the evaluation of production performance,while most of their physical models were fabricated based on the probability distribution of fractures and caves in the reservoir.In this study,a two-dimensional physical model of the karst fault system was designed and fabricated based on the geological model of TK748 well group in the seventh block of the Tahe Oilfield.The fluid flow and production performance of primary gas flooding were discussed.Gas-assisted gravity flooding was firstly introduced to take full use of gas-oil gravity difference,and its feasibility in the karst fault system was examined.Experimental results showed that primary gas flooding created more flow paths and achieved a remarkable increment of oil recovery compared to water flooding.Gas injection at a lower location was recommended to delay gas breakthrough.Gas-assisted gravity flooding achieved more stable gas-displacing-oil because oil production was at a lower location,and thus,the oil recovery was further enhanced.

Effect of nozzle geometry on pressure drop in submerged gas injection

Submerged gas injection into liquid leads to complex multiphase flow, in which nozzle geometries are crucial important for the operational expenditure in terms of pressure drop. The influence of the nozzle geometry on pressure drop between nozzle inlet and outlet has been experimentally studied for different gas flow rates and bath depths. Nozzles with circular, gear-like and four-leaf cross-sectional shape have been studied. The results indicate that, besides the hydraulic diameter of the outlet, the orifice area and the perimeter of the nozzle tip also play significant roles. For the same superficial gas velocity, the average pressure drop from the four-leaf-shaped geometry is the least. The influence of bath depth was found negligible. A correlation for the modified Euler number considering the pressure drop is proposed depending on nozzle geometric parameter and on the modified Froude number with the hydraulic diameter of the nozzle do as characteristic length.

Conceptual Design of the ITER Gas Injection System

A conceptual design review of the ITER gas injection system （GIS） function, safety, operation, and maintenance has recently been successfully completed. The GIS design can now continue to the preliminary design stage. This paper gives an overall description of the requirements and implementation at the concept design level. The designs of the sub-systems according to its breakdown structure are discussed against the corresponding requirements.

Research on High Pressure Gas Injection As a Method of Fueling, Disruption Mitigation and Plasma Termination for Future Tokamak Reactors

High-pressure gas injection has proved to be an effective disruption mitigation tech- nique in DIII-D tokamak experiments. If the method can be applied in future tokamak reactors not only for disruption mitigation but also for plasma termination and fueling, it will have an attractive advantage over the pellet and liquid injection from the viewpoint of economy and engineering design. In order to investigate the feasibility of this option, a study has been carried out with relevant parameters for conveying tubes of different geometrical sizes and for different gases. These parameters include pressure drop, lagger time after the valve＇s opening, gas diffusion in an ultra-high vacuum condition, and particle number contour.

Effects of helium massive gas injection level on disruption mitigation on EAST

In this study,NIMROD simulations are performed to investigate the effects of massive helium gas injection level on the induced disruption on EAST tokamak.It is demonstrated in simulations that two different scenarios of plasma cooling(complete cooling and partial cooling)take place for different amounts of injected impurities.For the impurity injection above a critical level,a single MHD activity is able to induce a complete core temperature collapse.For impurity injection below the critical level,a series of multiple minor disruptions occur before the complete thermal quench.

Calculation of the Gas Injection Rate and Pipe String Erosion in Nitrogen Drilling Systems

Detailed information is provided for the design and construction of nitrogen drilling in a coal seam.Two prototype wells are considered.The Guo model is used to calculate the required minimum gas injection rate,while the Finnie,Sommerfeld,and Tulsa models are exploited to estimate the ensuing erosion occurring in pipe strings.The calculated minimum gas injection rates are 67.4 m^(3)/min(with water)and 49.4 m^(3)/min(without water),and the actual field of use is 90–120 m^(3)/min.The difference between the calculated injection pressure and the field value is 6.5%–15.2%(formation with water)and 0.65%–7.32%(formation without water).The results show that the Guo model can more precisely represent the situation of the no water formation in the nitrogen drilling of a coal seam.The Finnie,Sommerfeld,and Tulsa models have different sensitivities to cutting densities,particle size,impact velocity and angle,and pipe string hardness.

Simulation Studies on Comparative Evaluation of Waterflooding and Gas Injection in Niger Delta Thin-Bed Reservoir

There is a need to increase ultimate recovery from petroleum reservoirs. In order to guarantee efficient resource extraction from reservoirs, primary recovery methods cannot be relied on throughout the life of a well. There is a time in the life of a reservoir when the primary energy will not be sufficient to ensure economic recovery. Complete abandonment of the reservoir at this point may not be a sound engineering decision given the huge investments in developing the asset. Secondary recovery methods present potentials for the recovery of the other trapped resources. The choice of the secondary recovery means depends on the reservoir and geologic conditions and should be determined by modeling and simulation. In this work, a simulation study is conducted for Niger Delta Field ABX2 to determine the performance of water-flooding and gas injection in the recovery of the asset after the primary recovery stage. ECLIPSE Blackoil simulator was used for the modeling and simulation. An equal reservoir rectangular grid block was designed for both the waterflooding and water injection comprising a total of 750 grid cells. Water and gas were injected in both cases at an injection rate of 11,000 stb/d and 300,000 scf/d for waterflooding and gas injection respectively. From the results of the simulation, it was realized that waterflooding gave a higher total oil recovery than gas injection. The difference in oil recovery from water-flooding and gas injection amounted to 0.08 MMstb/d. The Field Oil Recovery Efficiency (FOE) for waterflooding and gas injection was 38% and 16% respectively giving a difference of 22%. The waterflooding method was troubled with excessive water cuts due to water breakthroughs. Waterflooding was chosen against gas injection to be applied to Field ABX2 to improve recovery after primary production ceased.

Estimation of Minimum Miscibility Pressure for Flue Gas Injection Using Soft Experimentations

A new approach is demonstrated in which soft experimentation can be performed for MMP measurements, thus replacing the common practice of slim tube displacement laboratory experiments. Recovery potential from oil reservoirs by miscible flue gas injection was studied by slim tube and field-scale numerical simulation using two flue gases and seven crude oils sampled at different depths in three candidate reservoirs. The soft experimentations were conducted using Eclipse300TM, a three-phase compositional simulator. This study investigates minimum miscibility pressure (MMP), a significant miscible gas injection project screening tool. Successful design of the project is contingent to the accurate determination of the MMP. This study evaluates effects of important factors such as injection pressure, oil component composition, and injection gas composition on the MMP and recovery efficiency for slim tube and field-scale displacements. Two applicable MMP correlations were used for comparison and validation purposes.

Influence of hydrogen-enriched atmosphere under coke oven gas injection on reduction swelling behaviors of oxidized pellet

It is of great importance to elucidate reduction swelling behaviors and reaction mechanism of oxidized pellet in hydrogen-enriched atmosphere under coke oven gas injection. In this work, the effects of hydrogen concentration in N_2-CO-H_2 atmosphere with unchanged CO content on reduction swelling behaviors of oxidized pellet at 1173 K were studied, to clarify the mechanism of hydrogen-enriched reduction and exclude the influences of CO. Then, the reduction swelling behaviors of oxidized pellet at 1173 K in actual atmosphere under coke oven gas(COG) injection, got from the simulation results of multi-fluid blast furnace model, were investigated. The results show that with the concentration of hydrogen increasing in N_2-CO-H_2 gas from 2% to 18%, the reduction swelling index of pellet decreases from 10.12% to 5.57% while the reduction ratio of pellet increases obviously from 39.85% to 69.58%. In addition, with COG injection rate increasing from 0 to 152.34 m^3/t, the reduction swelling index of pellet decreases slightly from 10.71% to 9.54% while the reduction ratio of pellet is increased from 31.57% to 36.39%. The microstructures of pellet are transformed from the platy structure to the flocculent structure.

Chemical-assisted MMP reduction on methane-oil systems:Implications for natural gas injection to enhanced oil recovery

technique.However,the main challenge in this process is the high minimum miscibility pressure(MMP)between natural gas and crude oil,which limits its application and recovery factor,especially in hightemperature reservoirs.Therefore,we present a novel investigation to quantify the effect of chemicalassisted MMP reduction on the oil recovery factor.Firstly,we measured the interfacial tension(IFT)of the methane-oil system in the presence of chemical or CO_(2) to calculate the MMP reduction at a constant temperature(373K)using the vanishing interfacial tension(VIT)method.Afterwards,we performed three coreflooding experiments to quantify the effect of MMP reduction on the oil recovery factor under different injection scenarios.The interfacial tension measurements show that adding a small fraction(1.5 wt%)of the tested surfactant(SOLOTERRA ME-6)achieved 9%of MMP reduction,while adding 20 wt%of CO_(2) to the methane yields 13%of MMP reduction.Then,the coreflooding results highlight the significance of achieving miscibility during gas injection,as the ultimate recovery factor increased from 65.5%under immiscible conditions to 77.2%using chemical-assisted methane,and to 79%using gas mixture after achieving near miscible condition.The results demonstrate the promising potential of the MMP reduction to signifi-cantly increase the oil recovery factor during gas injection.Furthermore,these results will likely expand the application envelop of the miscible gas injection,in addition to the environmental benefits of utilizing the produced gas by re-injection/recycling instead of flaring which contributes to reducing the greenhouse gas emissions.

Numerical Simulation of Asphaltene Precipitation and Deposition during Natural Gas and CO_(2) Injection

Asphaltene deposition is a significant problem during gas injection processes,as it can block the porous medium,the wellbore,and the involved facilities,significantly impacting reservoir productivity and ultimate oil recovery.Only a few studies have investigated the numerical modeling of this potential effect in porous media.This study focuses on asphaltene deposition due to natural gas and CO_(2) injection.Predictions of the effect of gas injection on asphaltene deposition behavior have been made using a 3D numerical simulation model.The results indicate that the injection of natural gas exacerbates asphaltene deposition,leading to a significant reduction in permeability near the injection well and throughout the reservoir.This reduction in permeability strongly affects the ability of gas toflow through the reservoir,resulting in an improvement of the displacement front.The displacement effi-ciency of the injection gas process increases by up to 1.40%when gas is injected at 5500 psi,compared to the scenario where the asphaltene model is not considered.CO_(2) injection leads to a miscible process with crude oil,extracting light and intermediate components,which intensifies asphaltene precipitation and increases the viscosity of the remaining crude oil,ultimately reducing the recovery rate.

CO_(2),N_(2),and CO_(2)/N_(2)mixed gas injection for enhanced shale gas recovery and CO_(2)geological storage

In this work,using fractured shale cores,isothermal adsorption experiments and core flooding tests were conducted to investigate the performance of injecting different gases to enhance shale gas recovery and CO_(2)geological storage efficiency under real reservoir conditions.The adsorption process of shale to different gases was in agreement with the extended-Langmuir model,and the adsorption capacity of CO_(2)was the largest,followed by CH_(4),and that of N_(2)was the smallest of the three pure gases.In addition,when the CO_(2)concentration in the mixed gas exceeded 50%,the adsorption capacity of the mixed gas was greater than that of CH4,and had a strong competitive adsorption effect.For the core flooding tests,pure gas injection showed that the breakthrough time of CO_(2)was longer than that of N_(2),and the CH_(4)recovery factor at the breakthrough time(Rch,)was also higher than that of N_(2).The RcH of CO_(2)gas injection was approximately 44.09%,while the RcH,of N_(2)was only 31.63%.For CO_(2)/N_(2)mixed gas injection,with the increase of CO_(2)concentration,the RcH,increased,and the RcH,for mixed gas CO_(2)/N_(2)=8:2 was close to that of pure CO_(2),about 40.24%.Moreover,the breakthrough time of N_(2)in mixed gas was not much different from that when pure N_(2)was injected,while the breakthrough time of CO_(2)was prolonged,which indicated that with the increase of N_(2)concentration in the mixed gas,the breakthrough time of CO_(2)could be extended.Furthermore,an abnormal surge of N_(2)concentration in the produced gas was observed after N_(2)breakthrough.In regards to CO_(2)storage efficiency(S_(Storage-CO_(2)),as the CO_(2)concentration increased,S storage-co_(2)also increased.The S storage-co_(2),of the pure CO_(2)gas injection was about 35.96%,while for mixed gas CO_(2)/N_(2)=8:2,S sorage-co,was about 32.28%.

CFD modeling of gas−liquid flow phenomenon in lead smelting oxygen-enriched side-blown furnace

A validated numerical model was established to simulate gas−liquid flow behaviors in the oxygen-enriched side-blown bath furnace.This model included the slip velocity between phases and the gas thermal expansion effect.Its modeling results were verified with theoretical correlations and experiments,and the nozzle-eroded states in practice were also involved in the analysis.Through comparison,it is confirmed that the thermal expansion effect influences the flow pattern significantly,which may lead to the backward motion of airflow and create a potential risk to production safety.Consequently,the influences of air injection velocity and furnace width on airflow behavior were investigated to provide operating and design guidance.It is found that the thin layer melt,which avoids high-rate oxygen airflow eroding nozzles,shrinks as the injection velocity increases,but safety can be guaranteed when the velocity ranges from 175 to 275 m/s.Moreover,the isoline patterns and heights of thin layers change slightly when the furnace width increases from 2.2 to 2.8 m,indicating that the furnace width shows a limited influence on production safety.