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%.

Multi-site occupancies and luminescence properties of cyan-emitting Ca_(9-x)NaGd_(2/3)(PO_(4))_(7):Eu^(2+)phosphors for white light-emitting diodes

Cyan-emitting Ca_(9)NaGd_(2/3)(PO_(4))_(7):Eu^(2+)phosphors were synthesized via high temperature solid-state route.X-ray powder diffraction(XRD)and scanning electron microscopy(SEM)were used to verify the phase and morphology of the Ca_(9)NaGd_(2/3)(PO_(4))_(7):Eu^(2+)(CNGP:Eu^(2+))phosphors.The as-obtained phosphor exhibits a broad excitation band of 250-420 nm,which is near the ultraviolet region.An intense asymmetric cyan emission at 496 nm corresponds to the 5 d-4 f transition of Eu^(2+).The multiplesite luminescent properties of Eu^(2+)ions in CNGP benefit from versatile structure ofβ-Ca3(PO4)2 compounds.The effective energy transfer distance is 5.46 nm(through the spectral overlap calculation),validating that the resonant energy migration type is via dipole-dipole interaction mechanism.Compared to the initial one at room temperature,the luminescent intensity of CNGP:Eu^(2+)phosphor can maintain 77%as it is heated up to 420 K.A white light-emitting diode(WLED)with excellent luminesce nt properties was successfully fabricated.Moreover,the CIE chromaticity coordinates of fabricated WLED driven by changing current just change slightly.

CO2 flooding strategy to enhance heavy oil recovery

CO_(2) flooding is one of the most promising techniques to enhance both light and heavy oil recovery.In light oil recovery,the production pressure in CO_(2) flooding in general keeps constant in order to maintain the miscibility of injected CO_(2) and crude oil;while in heavy oil recovery,a depleting pressure scheme may be able to induce foamy oil flow,thus the oil recovery could be further enhanced.In this study,different pressure control schemes were tested by 1-D core-flooding experiments to obtain an optimized one.Numerical simulations were conducted to history match all experimental data to understand the mechanisms and characteristics of different CO_(2) flooding strategies.For the core-flooding experiments,1500 mD sandstone cores,formation brine and a heavy oil sample with a viscosity of about 869.3 cp at reservoir condition(55℃ and 11 MPa)were used.Before each CO_(2) flooding test,early stage water-flooding was conducted until the water cut reached 90%.Different CO_(2) injection rates and production pressure control strategies were tested through core-flooding experiments.Experimental results indicated that a slower CO_(2) injection rate(2 ml/min)led to a higher recovery factor from 31.1%to 36.7%,compared with a high CO_(2) injection rate of 7 ml/min;for the effects of different production strategies,a constant production pressure at the production port yielded a recovery factor of 31.1%;while a pressure depletion with 47.2 kPa/min at the production port yielded 7%more oil recovery;and the best pressure control scheme in which the production pressure keeping constant during CO_(2) injection period,then depleting the model pressure with the injector shut-in yielded a recovery factor of 42.5%of the initial OOIP.For the numerical simulations study,the same oil relative permeability curve was applied to match the experimental results to all tests.Different gas relative permeability curves were obtained when the production pressure schemes are different.A much lower gas relative permeability curve and a higher critical gas saturation were achieved in the best pressure control scheme case compared to other cases.The lower gas relative permeability curve indicates that foamy oil was formed in the pressure depletion processes.Through this study,it is suggested that the pressure control scheme can be optimized in order to maximize the CO_(2) injection performance for enhanced heavy oil recovery.