Research on the enhanced gas recovery(EGR)technology is urgently needed in most of China's major gas fields due to low recovery in their late development stages.To promote progress in ERG theory and technology,thi...Research on the enhanced gas recovery(EGR)technology is urgently needed in most of China's major gas fields due to low recovery in their late development stages.To promote progress in ERG theory and technology,this paper establishes a unified and universal model for gas recovery evaluation,analyzes the key factors affecting the gas recovery,and expects the prospect of EGR.The results are obtained as follows.First,the production degree of reserves,pressure drawdown sweep efficiency and pressure depletion efficiency are key factors affecting the gas recovery,which is the product of the coefficients corresponding to these factors.Second,according to the development practice of Anyue Longwangmiao gas reservoir,Kela 2 gas field,Sulige gas field and Southern Sichuan shale gas,it is estimated that the recovery of conventional water-driven gas reservoirs and unconventional gas reservoirs(incl.tight gas and shale gas)can be improved by 6-15 percentage points by increasing the production degree of reserves,the pressure drawdown sweep efficiency and pressure depletion efficiency.Third,it is proposed that clarifying the EGR mechanism,developing new EGR methods,and promoting the field test of EGR technologies are directions for theoretical and technical researches.The study results provide a theoretical foundation for EGR.The EGR methodologies for different types of gas reservoirs provide technical support for improving gas recovery and stable production of existing gas fields,promote healthy and rapid development of natural gas industry in China and provide guidance for guaranteeing national energy security.展开更多
CO_(2)emission mitigation is one of the most critical research frontiers.As a promising option of carbon capture,utilization and storage(CCUS),CO_(2)storage with enhanced gas recovery(CSEGR)can reduce CO_(2)emission b...CO_(2)emission mitigation is one of the most critical research frontiers.As a promising option of carbon capture,utilization and storage(CCUS),CO_(2)storage with enhanced gas recovery(CSEGR)can reduce CO_(2)emission by sequestrating it into gas reservoirs and simultaneously enhance natural gas production.Over the past decades,the displacement behaviour of CO_(2)—natural gas has been extensively studied and demonstrated to play a key role on both CO_(2)geologic storage and gas recovery performance.This work thoroughly and critically reviews the experimental and numerical simulation studies of CO_(2)displacing natural gas,along with both CSEGR research and demonstration projects at various scales.The physical property difference between CO_(2)and natural gas,especially density and viscosity,lays the foundation of CSEGR.Previous experiments on displacement behaviour and dispersion characteristics of CO_(2)/natural gas revealed the fundamental mixing characteristics in porous media,which is one key factor of gas recovery efficiency and warrants further study.Preliminary numerical simulations demonstrated that it is technically and economically feasible to apply CSEGR in depleted gas reservoirs.However,CO_(2)preferential flow pathways are easy to form(due to reservoir heterogeneity)and thus adversely compromise CSEGR performance.This preferential flow can be slowed down by connate or injected water.Additionally,the optimization of CO_(2)injection strategies is essential for improving gas recovery and CO_(2)storage,which needs further study.The successful K12—B pilot project provides insightful field-scale knowledge and experience,which paves a good foundation for commercial application.More experiments,simulations,research and demonstration projects are needed to facilitate the maturation of the CSEGR technology.展开更多
As one of the most important ways to reduce the greenhouse gas emission,carbon dioxide（CO2）enhanced gas recovery（CO2-EGR） is attractive since the gas recovery can be enhanced simultaneously with CO2sequestration.B...As one of the most important ways to reduce the greenhouse gas emission,carbon dioxide（CO2）enhanced gas recovery（CO2-EGR） is attractive since the gas recovery can be enhanced simultaneously with CO2sequestration.Based on the existing equation of state（EOS） module of TOUGH2 MP,extEOS7C is developed to calculate the phase partition of H2O-CO2-CH4-NaCl mixtures accurately with consideration of dissolved NaCI and brine properties at high pressure and temperature conditions.Verifications show that it can be applied up to the pressure of 100 MPa and temperature of 150℃.The module was implemented in the linked simulator TOUGH2MP-FLAC3 D for the coupled hydro-mechanical simulations.A simplified three-dimensional（3D）1/4 model（2.2 km×1 km×1 km） which consists of the whole reservoir,caprock and baserock was generated based on the geological conditions of a gas field in the North German Basin.The simulation results show that,under an injection rate of 200,000 t/yr and production rate of 200,000 sm3/d,CO2breakthrough occurred in the case with the initial reservoir pressure of 5 MPa but did not occur in the case of 42 MPa.Under low pressure conditions,the pressure driven horizontal transport is the dominant process;while under high pressure conditions,the density driven vertical flow is dominant.Under the considered conditions,the CO2-EGR caused only small pressure changes.The largest pore pressure increase（2 MPa） and uplift（7 mm） occurred at the caprock bottom induced by only CO2injection.The caprock had still the primary stress state and its integrity was not affected.The formation water salinity and temperature variations of ±20℃ had small influences on the CO2-EGR process.In order to slow down the breakthrough,it is suggested that CO2-EGR should be carried out before the reservoir pressure drops below the critical pressure of CO2.展开更多
Since 2000,China has been ranked as one of the top countries in gas production.Nevertheless,the domestic gas production can hardly satisfy the need of national economic development.Besides,an increasing number of gas ...Since 2000,China has been ranked as one of the top countries in gas production.Nevertheless,the domestic gas production can hardly satisfy the need of national economic development.Besides,an increasing number of gas fields have come to the middle or late development stages,and most gas reservoirs have low recovery efficiency due to the low permeability and water drive nature.Therefore,gas recovery enhancement has become an urgent issue.At present,the oil recovery enhancement is well defined,and there are methods describing the remaining oil and a complete set of mature EOR(enhanced oil recovery)technologies.However,the definition and description of EGR(enhanced gas recovery)are still undermined,and the description method for the distribution of residual gas and EGR technologies are almost unavailable.In view of this,by reviewing a wealth of related literatures,we defined EGR and also described the remaining gas distribution based on the remaining gas abundance.In addition,collecting three typical types(low-permeability,condensate and edge/bottom water)of major gas reservoirs developed both at home and abroad,we summarized the geological and development characteristics,and found out the obstructions in the development.In response,we concluded and analyzed the relevant technologies and methods for enhancing the gas recovery of such reservoirs,and proposed the suggestions about EGR technology development,which provides a significant reference and popularization basis for EGR measures in fields.展开更多
By horizontal well multi-staged fracturing technology,shale rocks can be broken to form fracture networks via hydraulic force and increase the production rate of shale gas wells.Nonetheless,the fracturing stimulation ...By horizontal well multi-staged fracturing technology,shale rocks can be broken to form fracture networks via hydraulic force and increase the production rate of shale gas wells.Nonetheless,the fracturing stimulation effect may be offset by the water phase trapping damage caused by water retention.In this paper,a technique in transferring the negative factor of fracturing fluid retention into a positive factor of changing the gas existence state and facilitating shale cracking was discussed using the easy oxidation characteristics of organic matter,pyrite and other minerals in shale rocks.Furthermore,the prospect of this technique in tackling the challenges of large retention volume of hydraulic fracturing fluid in shale gas reservoirs,high reservoir damage risks,sharp production decline rate of gas wells and low gas recovery,was analyzed.The organic matter and pyrite in shale rocks can produce a large number of dissolved pores and seams to improve the gas deliverability of the matrix pore throats to the fracture systems.Meanwhile,in the oxidation process,released heat and increased pore pressure will make shale rock burst,inducing expansion and extension of shale micro-fractures,increasing the drainage area and shortening the gas flowing path in matrix,and ultimately,removing reservoir damage and improving gas recovery.To sum up,the technique discussed in the paper can be used to“break”shale rocks via hydraulic force and to“burst”shale rocks via chemical oxidation by adding oxidizing fluid to the hydraulic fracturing fluid.It can thus be concluded that this method can be a favorable supplementation for the conventional hydraulic fracturing of shale gas reservoirs.It has a broad application future in terms of reducing costs and increasing profits,maintaining plateau shale gas production and improving shale gas recovery.展开更多
A qualification test for the reliability of a newly-developed Diver Gas Recovery System (DGRS) was carried out in the Naval Medical Research Institute of the People's Liberation Army, China from March 29 to April ...A qualification test for the reliability of a newly-developed Diver Gas Recovery System (DGRS) was carried out in the Naval Medical Research Institute of the People's Liberation Army, China from March 29 to April 2, 1995. A sequential test plan of high discrimination ratio for the mean time between failures (MTBF) was adopted. The test procedures simulated those of a 300 msw dive. A hyperbaric breathing machine was used for the simulation of diver's respiratory functions. Parameters, such as diving depth, respiratory minute volume (RMV), CO2 production, gas flow rate, partial pressure of carbon dioxide, and ambient temperature and himidity were all displayed and recorded with a microcomputer system. The results indicated that no failure occurred during the 91.5 h operation. According to the acceptance and rejection criteria specified in the statistical test plan, a no-failure score in the 88 h operation is acceptable. Therefore, the DGRS has been demonstrated to meet the requirements of MTBF specified in the contract.展开更多
The Diver Gas Recovery Installation (DGRI) was evaluated at 80 msw saturation - 100 msw excursion diving on HeO2 in the Naval Medical Research Institute (NMRI) of China in April, 1995. The diving depth, lockout time, ...The Diver Gas Recovery Installation (DGRI) was evaluated at 80 msw saturation - 100 msw excursion diving on HeO2 in the Naval Medical Research Institute (NMRI) of China in April, 1995. The diving depth, lockout time, breathing gas flow rate and consumption, inspired oxygen partial pressure (PO2) and carbon dioxide partial pressure (PCO2) were monitored. The results indicated that PO2 was controlled to fluctuate from 64.3 to 84.0 kPa and PCO2 went up from 0.01 kPa up to O.I kPa during 4 hours excursion diving; recovery of breathing gas reached 95%; three divers felt well and breathed comfortably during simulating heavy work. The test showed that it met desired performance goals. The DGRI is a kind of important equipment for long duration deep dive. It enables the gases exhaled by the divers to be re-cycled, and therefore it has great social, military and economic significance for diving operation and submarine rescue.展开更多
Injecting CO_(2)when the gas reservoir of tight sandstone is depleted can achieve the dual purposes of greenhouse gas storage and enhanced gas recovery(CS-EGR).To evaluate the feasibility of CO_(2)injection to enhance...Injecting CO_(2)when the gas reservoir of tight sandstone is depleted can achieve the dual purposes of greenhouse gas storage and enhanced gas recovery(CS-EGR).To evaluate the feasibility of CO_(2)injection to enhance gas recovery and understand the production mechanism,a numerical simulation model of CS-EGR in multi-stage fracturing horizontal wells is established.The behavior of gas production and CO_(2)sequestration is then analyzed through numerical simulation,and the impact of fracture parameters on production performance is examined.Simulation results show that the production rate increases significantly and a large amount of CO_(2)is stored in the reservoir,proving the technical potential.However,hydraulic fractures accelerate CO_(2)breakthrough,resulting in lower gas recovery and lower CO_(2)storage than in gas reservoirs without fracturing.Increasing the length of hydraulic fractures can significantly increase CH4production,but CO_(2)breakthrough will advance.Staggered and spaced perforation of hydraulic fractures in injection wells and production wells changes the fluid flow path,which can delay CO_(2)breakthrough and benefit production efficiency.The fracture network of massive hydraulic fracturing has a positive effect on the CS-EGR.As a result,CH4production,gas recovery,and CO_(2)storage increase with the increase in stimulated reservoir volume.展开更多
Downhole vortex drainage gas recovery is a new gas production technology.So far,however,the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured...Downhole vortex drainage gas recovery is a new gas production technology.So far,however,the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured out.In this paper,the forces of liquid droplets in the swirling flow field of wellbores were analyzed on the basis of two-phase fluid dynamics theories.Then,the motion equations of fluid droplets along axial and radical directions were established.Magnitude comparison was performed on several typical acting forces,including Basset force,virtual mass force,Magnus force,Saffman force and Stokes force.Besides,the formula for calculating the optimal helical angle of vortex tools was established according to the principle that the vertical resultant force on fluid droplets should be the maximum.And afterwards,each acting force was comprehensively analyzed in terms of its origin,characteristics and direction based on the established force analysis model.Magnitude comparison indicates that the forces with less effect can be neglected,including virtual mass force,Basset force and convection volume force.Moreover,the vertically upward centrifugal force component occurs on the fluid droplets in swirling flow field instead of those in the conventional flow field of wellbores,which is favorable for the fluid droplets to move upward.The reliability of optimal helical angle calculation formula was verified by means of case analysis.It is demonstrated that with the decrease of well depth,the fluid-carrying capability of gas and the optimal helical angle increase.The research results in this paper have a guiding significance to the optimization design of downhole vortex tools and the field application of downhole vortex drainage gas recovery technology.展开更多
In order to apply the electric submersible pump(ESP)based drainage gas recovery technology commonly used in conventional gas wells to high-sulfur gas wells,and meet the requirements of casing protection in high-sulfur...In order to apply the electric submersible pump(ESP)based drainage gas recovery technology commonly used in conventional gas wells to high-sulfur gas wells,and meet the requirements of casing protection in high-sulfur gas wells,we conducted a series of technical researches on casing protection,gas interference and vibration of deep-well ESP set in terms of a completion string design and support tools based on the completion modes of high-sulfur gas wells and the technical characteristics of ESP drainage gas recovery technologies.Simultaneously,drainage gas recovery technology was designed for Well L2.The research and application results show:firstly,the completion string system of high-sulfur gas wells composed of a canned ESP system and an anchor intubation packer can realize the normal operation of ESP and meet the requirements of casing protection;secondly,multiphase pump and bleeder line can be used to solve the problem of gas interference,the automatic reverse valve can be used to reduce the effect of ESP complex flow path on the flowing of the gas well,and the anchor intubation packer can be used to reduce the string vibration;thirdly,the canned ESP system designed in this paper is applicable toØ244.5 mm andØ177.8 mm casings,specifically,the ESP corresponding toØ244.5 mm casing has the maximum flow rate of 900 m^(3)/d and the maximum lift height of 4500 m,and that corresponding toØ177.8 mm casing has the maximum flow rate of 300 m^(3)/d and the maximum lift height of 3000 m.It is concluded that this research result provides a technical support for the implementation of ESP based drainage gas recovery technology in high-sulfur gas wells.展开更多
Oil products are processed and refined from refineries and transported to oil storage tanks in oil depots, and oil products are transported from water and land transportation to end customers. The turnover and storage...Oil products are processed and refined from refineries and transported to oil storage tanks in oil depots, and oil products are transported from water and land transportation to end customers. The turnover and storage process often involves several operations such as reconciliation, tank dumping, loading and unloading, etc. In the process of oil transportation turnover and oil storage, the volume of gas phase space in the storage tank is affected by the changes of pressure, temperature and other factors. The physical characteristics of some oil components are higher than their boiling points, which leads to the evaporation loss of oil and gas. There are potential safety hazards in the whole storage process. When the concentration of oil vapor in a closed environment reaches a certain level, it is easy to cause fire and explosion, which not only pollutes the ecological environment, but also wastes energy. Evaporation of oil products not only causes the natural loss of a large number of existing oil resources, but also causes the density of oil products to change and the quality of oil products to decline. These problems have already attracted the attention of oil companies, and relevant laws, regulations, norms and standards have been formulated from the aspects of environmental protection, industry technology, safety management and resource recovery, and oil and gas recovery facilities of oil loading system have been set up. At the same time, in order to effectively control the evaporation of oil products and reduce the research results of air pollution, many different types of oil and gas recovery facilities have been applied in oil depots. It can ensure that the discharge of the treatment medium completely meets the treatment efficiency and tail gas emission concentration limit stipulated by the national laws and regulations, and complete the treatment of oil and gas pollution and the recycling of harmful substances. The reasonable selection scheme of oil and gas recovery facilities is economically applicable to the safe production and operation of the product oil depot, and the corresponding conclusions and suggestions are given.展开更多
Carbonate gas reservoirs with edge and bottom water contain abundant reserves,making them key production targets in the Tarim Basin,Sichuan Basin,Ordos Basin,and other petroleum provinces.Water invasion may occur in t...Carbonate gas reservoirs with edge and bottom water contain abundant reserves,making them key production targets in the Tarim Basin,Sichuan Basin,Ordos Basin,and other petroleum provinces.Water invasion may occur in the middle and late development stages of such reservoirs,leading to reduction of gas displacement efficiency and gas recovery.In this paper,a pore-scale water-gas immiscible flow model is established by coupling the fluid flow equation and the gas-water contact(GWC)tracking equation.The process of gas displacement with water is simulated in the heterogeneous porous media generated by the quartet structure generation set(QSGS).Finally,the mechanisms of remaining gas distribution and formation are analyzed,and the variation mechanism of microscopic gas displacement efficiency is discussed.The results are obtained in three aspects.First,the remaining gas is distributed at the blind end,in the pore-throat and as clusters,with their proportions and scales jointly controlled by microscopic pore structures,wettability and capillary number.The remaining gas can be further produced by changing the production pressure differential to disturb the original pressure system and gas expansion,so as to improve the microscopic gas displacement efficiency.Second,the microscopic gas displacement efficiency is closely related to the gas flow process.Formation or expansion of each water flow path may cause rapid increase of water cut and slows down the increase of gas displacement efficiency.Third,the microscopic pore structure and wettability are the inherent features of the gas reservoir,so the capillary number can be optimized to change the mode of GWC advancement,and then to effectively improve the microscopic gas displacement efficiency.It is concluded that for real gas wells,the evolution of mechanical mechanisms of GWC advancement should be revealed depending upon the microscopic pore structure and wettability of the reservoir,and then the optimal capillary number can be determined.Furthermore,clarifying the pore-scale water-gas flow characteristics and physical mechanism of microscopic gas displacement provides guidance for the planning of enhanced gas recovery.展开更多
This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization ...This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization approaches to detect and observe the CO2-formation fluid displacement mechanism at the micro-scale, namely, magnetic resonance imaging, X-ray computed tomography and fabricated micromodels, but they are not capable of investigating the dis- placement process at the nano-scale. Though a lab-on-chip approach for the direct visualization of the fluid flow behaviour in nanoscale channels has been developed using an advanced epi-fluorescence microscopy method combined with a nanofluidic chip, it is still a qualitative analysis method. The lattice Boltzmann method （LBM） can simulate the CO2 displacement processes in a two-dimensional or three-dimensional （3D） pore structure, but until now, the CO2 displace- ment mechanisms had not been thoroughly investigated and the 3D pore structure of real rock had not been directly taken into account in the simulation of the CO2 displacement process. The status of research on the applications of CO2 displacement to enhance shale gas recovery is also analyzed in this paper. The coupling of molecular dynamics and LBM in tandem is proposed to simulate the CO2-shale gas displacement process based on the 3D digital model of shale obtained from focused ion beams and scanning electron microscopy.展开更多
A two-pulse method is used to determine the insulation recovery time of the gas spark gap switch with different types of gas applied in a high power accelerator with a water dielectric pulse forming line. At the break...A two-pulse method is used to determine the insulation recovery time of the gas spark gap switch with different types of gas applied in a high power accelerator with a water dielectric pulse forming line. At the breakdown voltage of 450 kV, with the vacuum diode voltage of about 200 kV, and a current of 30 kA, recovery characteristics of H2, N2, SF6 were studied. The recovery percentages of the gas breakdown voltage and vacuum diode voltage were determined. The results show that hydrogen has the best recovery characteristics. At a pulse interval of 8.8 ms, the recovery percentages of both the gas breakdown voltage and vacuum diode voltage for hydrogen exceed 95%. For SF6 and N2 with an interval of 25 ms and 50 ms respectively, a 90% voltage recovery was obtained. The experiments also proved that the repetitive rate of the high power accelerator with a pulse forming line is mainly restricted by the gas switch repetitive rate; the recovery percentages of the vacuum diode voltage are limited by the recovery percentages of the gas switch breakdown voltage. The hydrogen switch can be employed for a high repetitive rate-high power accelerator with a pulse forming line.展开更多
In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well...In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.展开更多
The recovery factor from tight gas reservoirs is typically less than 15%, even with multistage hydrauhc tractunng stimulation. Such low recovery is exacerbated in tight gas condensate reservoirs, where the depletion o...The recovery factor from tight gas reservoirs is typically less than 15%, even with multistage hydrauhc tractunng stimulation. Such low recovery is exacerbated in tight gas condensate reservoirs, where the depletion of gas leaves the valuable condensate behind. In this paper, three enhanced gas recovery （EGR） methods including produced gas injection, CO2 injection and water injection are investigated to increase the well productivity for a tight gas condensate reservoir in the Montney Formation, Canada. The production performance of the three EGR methods is compared and their economic feasibility is evaluated. Sensitivity analysis of the key factors such as primary production duration, bottom-hole pressures, and fracture conductivity is conducted and their effects on the well production performance are analyzed. Results show that, compared with the simple depletion method, both the cumulative gas and condensate production increase with fluids injected. Produced gas injection leads to both a higher gas and condensate production compared with those of the CO2 injection, while waterflooding suffers from injection difficulty and the corresponding low sweep efficiency. Meanwhile, the injection cost is lower for the produced gas injection due to the on-site available gas source and minimal transport costs, gaining more economic benefits than the other EGR methods.展开更多
This paper presents the effectiveness of the CO_(2) injection process at different periods during gascondensate reservoir development.Taking a real gas-condensate reservoir located in China's east region as an exa...This paper presents the effectiveness of the CO_(2) injection process at different periods during gascondensate reservoir development.Taking a real gas-condensate reservoir located in China's east region as an example,first,we conducted experiments of constant composition expansion(CCE),constant volume depletion(CVD),saturation pressure determination,and single flash.Next,a series of water/CO2 flooding experiments were been investigated,including water flooding at present pressure 15 MPa,CO_(2) flooding at 25.53 MPa,15 MPa,which repents initial pressure and present pressure respectively.Finally,the core flooding numerical model was constructed using a generalized equation-of-state model reservoir simulator(GEM)to reveal miscible flooding mechanism and the seepage flow characteristics in the condensate gas reservoir with CO2 injection.A desirable agreement achieved in experimental results and predicted pressure volume temperature(PVT)properties by the modified equation of state(EOS)in the CVD and CCE tests indicated that the proposed recombination method can successfully produce a fluid with the same phase behavior of initial reservoir fluid with an acceptable accuracy.The modeling results confirm the experimental results,and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure.Moreover,the results show that CO_(2) treatment can improve gas productivity by a factor of about 1.39 compared with the water flooding mode.These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.展开更多
Based on the study of damage mechanisms of generalized water blocking and related water-blocking removal methods, the drying agents for enhancing tight gas reservoir recovery were developed, and the basic properties, ...Based on the study of damage mechanisms of generalized water blocking and related water-blocking removal methods, the drying agents for enhancing tight gas reservoir recovery were developed, and the basic properties, injection mode and drying effect of the drying agents were evaluated. The chemical effect, thermal effect, salt resistance, salt resistance formulas and delay mechanism of the drying agent systems for different types of tight reservoirs were investigated through lab experiment. The solubility and solubilization properties of supercritical carbon dioxide on drying agent systems were tested.The injection mode of dissolving drying agent in supercritical carbon dioxide was proposed. The mechanisms of supercritical carbon dioxide with water in micropores of formation matrix were analyzed. Micro-pore structures and seepage characteristics of reservoir before and after drying were compared. Based on the characterization in combination of NMR and laser etched pore structure model, drying effects of the drying agents on bound water of different occurrences were evaluated qualitatively and quantitatively. Lattice Boltzmann method was used to evaluate the influence of drying effect on gas micro-seepage ability.The influence of drying effect on productivity and production performance of gas well was analyzed by numerical simulation.The drying effect can greatly reduce water saturation of tight reservoir and improve the gas seepage capacity in near wellbore and fractures. This work can provide guidance for developing new measures in enhancing recovery of tight gas reservoirs.展开更多
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)geo...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%.展开更多
The technique of Enhanced Gas Recovery by CO_(2) injection(CO_(2)-EGR)into shale reservoirs has brought increasing attention in the recent decade.CO_(2)-EGR is a complex geophysical process that is controlled by sever...The technique of Enhanced Gas Recovery by CO_(2) injection(CO_(2)-EGR)into shale reservoirs has brought increasing attention in the recent decade.CO_(2)-EGR is a complex geophysical process that is controlled by several parameters of shale properties and engineering design.Nevertheless,more challenges arise when simulating and predicting CO_(2)/CH4 displacement within the complex pore systems of shales.Therefore,the petroleum industry is in need of developing a cost-effective tool/approach to evaluate the potential of applying CO_(2) injection to shale reservoirs.In recent years,machine learning applications have gained enormous interest due to their high-speed performance in handling complex data and efficiently solving practical problems.Thus,this work proposes a solution by developing a supervised machine learning(ML)based model to preliminary evaluate CO_(2)-EGR efficiency.Data used for this work was drawn across a wide range of simulation sensitivity studies and experimental investigations.In this work,linear regression and artificial neural networks(ANNs)implementations were considered for predicting the incremental enhanced CH4.Based on the model performance in training and validation sets,our accuracy comparison showed that(ANNs)algorithms gave 15%higher accuracy in predicting the enhanced CH4 compared to the linear regression model.To ensure the model is more generalizable,the size of hidden layers of ANNs was adjusted to improve the generalization ability of ANNs model.Among ANNs models presented,ANNs of 100 hidden layer size gave the best predictive performance with the coefficient of determination(R2)of 0.78 compared to the linear regression model with R2 of 0.68.Our developed MLbased model presents a powerful,reliable and cost-effective tool which can accurately predict the incremental enhanced CH4 by CO_(2) injection in shale gas reservoirs.展开更多
基金Project supported by PetroChina S&T Project during the 14th Five-Year Plan“Research on tight gas exploration and development technologies”(No.2021DJ2104)“Research on key development technologies for complex gas reservoirs”(No.2021DJ1704)S&T Project of PetroChina Oil,Gas and New Energy Company“Research on remaining gas distribution and EGR of water-flooding clastic gas reservoirs”(No.2022KT0904).
文摘Research on the enhanced gas recovery(EGR)technology is urgently needed in most of China's major gas fields due to low recovery in their late development stages.To promote progress in ERG theory and technology,this paper establishes a unified and universal model for gas recovery evaluation,analyzes the key factors affecting the gas recovery,and expects the prospect of EGR.The results are obtained as follows.First,the production degree of reserves,pressure drawdown sweep efficiency and pressure depletion efficiency are key factors affecting the gas recovery,which is the product of the coefficients corresponding to these factors.Second,according to the development practice of Anyue Longwangmiao gas reservoir,Kela 2 gas field,Sulige gas field and Southern Sichuan shale gas,it is estimated that the recovery of conventional water-driven gas reservoirs and unconventional gas reservoirs(incl.tight gas and shale gas)can be improved by 6-15 percentage points by increasing the production degree of reserves,the pressure drawdown sweep efficiency and pressure depletion efficiency.Third,it is proposed that clarifying the EGR mechanism,developing new EGR methods,and promoting the field test of EGR technologies are directions for theoretical and technical researches.The study results provide a theoretical foundation for EGR.The EGR methodologies for different types of gas reservoirs provide technical support for improving gas recovery and stable production of existing gas fields,promote healthy and rapid development of natural gas industry in China and provide guidance for guaranteeing national energy security.
基金financially supported by the National Natural Science Foundation of China(51906256 and 52074337)Fundamental Research Funds for the Central Universities(21CX06033A)
文摘CO_(2)emission mitigation is one of the most critical research frontiers.As a promising option of carbon capture,utilization and storage(CCUS),CO_(2)storage with enhanced gas recovery(CSEGR)can reduce CO_(2)emission by sequestrating it into gas reservoirs and simultaneously enhance natural gas production.Over the past decades,the displacement behaviour of CO_(2)—natural gas has been extensively studied and demonstrated to play a key role on both CO_(2)geologic storage and gas recovery performance.This work thoroughly and critically reviews the experimental and numerical simulation studies of CO_(2)displacing natural gas,along with both CSEGR research and demonstration projects at various scales.The physical property difference between CO_(2)and natural gas,especially density and viscosity,lays the foundation of CSEGR.Previous experiments on displacement behaviour and dispersion characteristics of CO_(2)/natural gas revealed the fundamental mixing characteristics in porous media,which is one key factor of gas recovery efficiency and warrants further study.Preliminary numerical simulations demonstrated that it is technically and economically feasible to apply CSEGR in depleted gas reservoirs.However,CO_(2)preferential flow pathways are easy to form(due to reservoir heterogeneity)and thus adversely compromise CSEGR performance.This preferential flow can be slowed down by connate or injected water.Additionally,the optimization of CO_(2)injection strategies is essential for improving gas recovery and CO_(2)storage,which needs further study.The successful K12—B pilot project provides insightful field-scale knowledge and experience,which paves a good foundation for commercial application.More experiments,simulations,research and demonstration projects are needed to facilitate the maturation of the CSEGR technology.
基金funded by the National Natural Science Foundation of China(Grant No.NSFC51374147)the German Society for Petroleum and Coal Science and Technology(Grant No.DGMK680-4)
文摘As one of the most important ways to reduce the greenhouse gas emission,carbon dioxide（CO2）enhanced gas recovery（CO2-EGR） is attractive since the gas recovery can be enhanced simultaneously with CO2sequestration.Based on the existing equation of state（EOS） module of TOUGH2 MP,extEOS7C is developed to calculate the phase partition of H2O-CO2-CH4-NaCl mixtures accurately with consideration of dissolved NaCI and brine properties at high pressure and temperature conditions.Verifications show that it can be applied up to the pressure of 100 MPa and temperature of 150℃.The module was implemented in the linked simulator TOUGH2MP-FLAC3 D for the coupled hydro-mechanical simulations.A simplified three-dimensional（3D）1/4 model（2.2 km×1 km×1 km） which consists of the whole reservoir,caprock and baserock was generated based on the geological conditions of a gas field in the North German Basin.The simulation results show that,under an injection rate of 200,000 t/yr and production rate of 200,000 sm3/d,CO2breakthrough occurred in the case with the initial reservoir pressure of 5 MPa but did not occur in the case of 42 MPa.Under low pressure conditions,the pressure driven horizontal transport is the dominant process;while under high pressure conditions,the density driven vertical flow is dominant.Under the considered conditions,the CO2-EGR caused only small pressure changes.The largest pore pressure increase（2 MPa） and uplift（7 mm） occurred at the caprock bottom induced by only CO2injection.The caprock had still the primary stress state and its integrity was not affected.The formation water salinity and temperature variations of ±20℃ had small influences on the CO2-EGR process.In order to slow down the breakthrough,it is suggested that CO2-EGR should be carried out before the reservoir pressure drops below the critical pressure of CO2.
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20115121110002).
文摘Since 2000,China has been ranked as one of the top countries in gas production.Nevertheless,the domestic gas production can hardly satisfy the need of national economic development.Besides,an increasing number of gas fields have come to the middle or late development stages,and most gas reservoirs have low recovery efficiency due to the low permeability and water drive nature.Therefore,gas recovery enhancement has become an urgent issue.At present,the oil recovery enhancement is well defined,and there are methods describing the remaining oil and a complete set of mature EOR(enhanced oil recovery)technologies.However,the definition and description of EGR(enhanced gas recovery)are still undermined,and the description method for the distribution of residual gas and EGR technologies are almost unavailable.In view of this,by reviewing a wealth of related literatures,we defined EGR and also described the remaining gas distribution based on the remaining gas abundance.In addition,collecting three typical types(low-permeability,condensate and edge/bottom water)of major gas reservoirs developed both at home and abroad,we summarized the geological and development characteristics,and found out the obstructions in the development.In response,we concluded and analyzed the relevant technologies and methods for enhancing the gas recovery of such reservoirs,and proposed the suggestions about EGR technology development,which provides a significant reference and popularization basis for EGR measures in fields.
文摘By horizontal well multi-staged fracturing technology,shale rocks can be broken to form fracture networks via hydraulic force and increase the production rate of shale gas wells.Nonetheless,the fracturing stimulation effect may be offset by the water phase trapping damage caused by water retention.In this paper,a technique in transferring the negative factor of fracturing fluid retention into a positive factor of changing the gas existence state and facilitating shale cracking was discussed using the easy oxidation characteristics of organic matter,pyrite and other minerals in shale rocks.Furthermore,the prospect of this technique in tackling the challenges of large retention volume of hydraulic fracturing fluid in shale gas reservoirs,high reservoir damage risks,sharp production decline rate of gas wells and low gas recovery,was analyzed.The organic matter and pyrite in shale rocks can produce a large number of dissolved pores and seams to improve the gas deliverability of the matrix pore throats to the fracture systems.Meanwhile,in the oxidation process,released heat and increased pore pressure will make shale rock burst,inducing expansion and extension of shale micro-fractures,increasing the drainage area and shortening the gas flowing path in matrix,and ultimately,removing reservoir damage and improving gas recovery.To sum up,the technique discussed in the paper can be used to“break”shale rocks via hydraulic force and to“burst”shale rocks via chemical oxidation by adding oxidizing fluid to the hydraulic fracturing fluid.It can thus be concluded that this method can be a favorable supplementation for the conventional hydraulic fracturing of shale gas reservoirs.It has a broad application future in terms of reducing costs and increasing profits,maintaining plateau shale gas production and improving shale gas recovery.
文摘A qualification test for the reliability of a newly-developed Diver Gas Recovery System (DGRS) was carried out in the Naval Medical Research Institute of the People's Liberation Army, China from March 29 to April 2, 1995. A sequential test plan of high discrimination ratio for the mean time between failures (MTBF) was adopted. The test procedures simulated those of a 300 msw dive. A hyperbaric breathing machine was used for the simulation of diver's respiratory functions. Parameters, such as diving depth, respiratory minute volume (RMV), CO2 production, gas flow rate, partial pressure of carbon dioxide, and ambient temperature and himidity were all displayed and recorded with a microcomputer system. The results indicated that no failure occurred during the 91.5 h operation. According to the acceptance and rejection criteria specified in the statistical test plan, a no-failure score in the 88 h operation is acceptable. Therefore, the DGRS has been demonstrated to meet the requirements of MTBF specified in the contract.
文摘The Diver Gas Recovery Installation (DGRI) was evaluated at 80 msw saturation - 100 msw excursion diving on HeO2 in the Naval Medical Research Institute (NMRI) of China in April, 1995. The diving depth, lockout time, breathing gas flow rate and consumption, inspired oxygen partial pressure (PO2) and carbon dioxide partial pressure (PCO2) were monitored. The results indicated that PO2 was controlled to fluctuate from 64.3 to 84.0 kPa and PCO2 went up from 0.01 kPa up to O.I kPa during 4 hours excursion diving; recovery of breathing gas reached 95%; three divers felt well and breathed comfortably during simulating heavy work. The test showed that it met desired performance goals. The DGRI is a kind of important equipment for long duration deep dive. It enables the gases exhaled by the divers to be re-cycled, and therefore it has great social, military and economic significance for diving operation and submarine rescue.
基金the financial support of the National Natural Science Foundation of China(Grant No.52304018)China Postdoctoral Science Foundation(Grant No.2023TQ0014,Grant No.2023M730088)。
文摘Injecting CO_(2)when the gas reservoir of tight sandstone is depleted can achieve the dual purposes of greenhouse gas storage and enhanced gas recovery(CS-EGR).To evaluate the feasibility of CO_(2)injection to enhance gas recovery and understand the production mechanism,a numerical simulation model of CS-EGR in multi-stage fracturing horizontal wells is established.The behavior of gas production and CO_(2)sequestration is then analyzed through numerical simulation,and the impact of fracture parameters on production performance is examined.Simulation results show that the production rate increases significantly and a large amount of CO_(2)is stored in the reservoir,proving the technical potential.However,hydraulic fractures accelerate CO_(2)breakthrough,resulting in lower gas recovery and lower CO_(2)storage than in gas reservoirs without fracturing.Increasing the length of hydraulic fractures can significantly increase CH4production,but CO_(2)breakthrough will advance.Staggered and spaced perforation of hydraulic fractures in injection wells and production wells changes the fluid flow path,which can delay CO_(2)breakthrough and benefit production efficiency.The fracture network of massive hydraulic fracturing has a positive effect on the CS-EGR.As a result,CH4production,gas recovery,and CO_(2)storage increase with the increase in stimulated reservoir volume.
基金Project supported by the National Major S&T Project(No.:2011ZX05009-005)Beijing Natural Science Foundation for Youth Project(No.:3154039)Sinopec Technical Development Project(No.:34400004-14-ZC0607-0001).
文摘Downhole vortex drainage gas recovery is a new gas production technology.So far,however,the forces and motions of liquid phase in the swirling flow field of wellbores during its field application have not been figured out.In this paper,the forces of liquid droplets in the swirling flow field of wellbores were analyzed on the basis of two-phase fluid dynamics theories.Then,the motion equations of fluid droplets along axial and radical directions were established.Magnitude comparison was performed on several typical acting forces,including Basset force,virtual mass force,Magnus force,Saffman force and Stokes force.Besides,the formula for calculating the optimal helical angle of vortex tools was established according to the principle that the vertical resultant force on fluid droplets should be the maximum.And afterwards,each acting force was comprehensively analyzed in terms of its origin,characteristics and direction based on the established force analysis model.Magnitude comparison indicates that the forces with less effect can be neglected,including virtual mass force,Basset force and convection volume force.Moreover,the vertically upward centrifugal force component occurs on the fluid droplets in swirling flow field instead of those in the conventional flow field of wellbores,which is favorable for the fluid droplets to move upward.The reliability of optimal helical angle calculation formula was verified by means of case analysis.It is demonstrated that with the decrease of well depth,the fluid-carrying capability of gas and the optimal helical angle increase.The research results in this paper have a guiding significance to the optimization design of downhole vortex tools and the field application of downhole vortex drainage gas recovery technology.
基金supported by the National Major Science and Technology Project“Demonstration development project of large carbonate gas field in the Sichuan Basin”(No.2016ZX05052)。
文摘In order to apply the electric submersible pump(ESP)based drainage gas recovery technology commonly used in conventional gas wells to high-sulfur gas wells,and meet the requirements of casing protection in high-sulfur gas wells,we conducted a series of technical researches on casing protection,gas interference and vibration of deep-well ESP set in terms of a completion string design and support tools based on the completion modes of high-sulfur gas wells and the technical characteristics of ESP drainage gas recovery technologies.Simultaneously,drainage gas recovery technology was designed for Well L2.The research and application results show:firstly,the completion string system of high-sulfur gas wells composed of a canned ESP system and an anchor intubation packer can realize the normal operation of ESP and meet the requirements of casing protection;secondly,multiphase pump and bleeder line can be used to solve the problem of gas interference,the automatic reverse valve can be used to reduce the effect of ESP complex flow path on the flowing of the gas well,and the anchor intubation packer can be used to reduce the string vibration;thirdly,the canned ESP system designed in this paper is applicable toØ244.5 mm andØ177.8 mm casings,specifically,the ESP corresponding toØ244.5 mm casing has the maximum flow rate of 900 m^(3)/d and the maximum lift height of 4500 m,and that corresponding toØ177.8 mm casing has the maximum flow rate of 300 m^(3)/d and the maximum lift height of 3000 m.It is concluded that this research result provides a technical support for the implementation of ESP based drainage gas recovery technology in high-sulfur gas wells.
文摘Oil products are processed and refined from refineries and transported to oil storage tanks in oil depots, and oil products are transported from water and land transportation to end customers. The turnover and storage process often involves several operations such as reconciliation, tank dumping, loading and unloading, etc. In the process of oil transportation turnover and oil storage, the volume of gas phase space in the storage tank is affected by the changes of pressure, temperature and other factors. The physical characteristics of some oil components are higher than their boiling points, which leads to the evaporation loss of oil and gas. There are potential safety hazards in the whole storage process. When the concentration of oil vapor in a closed environment reaches a certain level, it is easy to cause fire and explosion, which not only pollutes the ecological environment, but also wastes energy. Evaporation of oil products not only causes the natural loss of a large number of existing oil resources, but also causes the density of oil products to change and the quality of oil products to decline. These problems have already attracted the attention of oil companies, and relevant laws, regulations, norms and standards have been formulated from the aspects of environmental protection, industry technology, safety management and resource recovery, and oil and gas recovery facilities of oil loading system have been set up. At the same time, in order to effectively control the evaporation of oil products and reduce the research results of air pollution, many different types of oil and gas recovery facilities have been applied in oil depots. It can ensure that the discharge of the treatment medium completely meets the treatment efficiency and tail gas emission concentration limit stipulated by the national laws and regulations, and complete the treatment of oil and gas pollution and the recycling of harmful substances. The reasonable selection scheme of oil and gas recovery facilities is economically applicable to the safe production and operation of the product oil depot, and the corresponding conclusions and suggestions are given.
基金Project supported by the National Natural Science Foundation Projects of China(NSFC)“Dynamic wetting mechanism and transport characteristics of waterdisplacing-gas in nano-pores of unconventional reservoirs”(No.52174041)“Research on fracturing fluid invasion/flowback/retentionmechanisms in shale reservoirs and their impacts on gas well productivity”(No.52104051)+1 种基金“Research on cross scale coupling flow and production law of effective shale gas reservoir pores”(No.51874319)the Natural Science Foundation Project of Beijing“Simulation study on the transfer mechanismand transfer of oil inmicro-nanopores of tight/shale reservoirs”(No.2204093).
文摘Carbonate gas reservoirs with edge and bottom water contain abundant reserves,making them key production targets in the Tarim Basin,Sichuan Basin,Ordos Basin,and other petroleum provinces.Water invasion may occur in the middle and late development stages of such reservoirs,leading to reduction of gas displacement efficiency and gas recovery.In this paper,a pore-scale water-gas immiscible flow model is established by coupling the fluid flow equation and the gas-water contact(GWC)tracking equation.The process of gas displacement with water is simulated in the heterogeneous porous media generated by the quartet structure generation set(QSGS).Finally,the mechanisms of remaining gas distribution and formation are analyzed,and the variation mechanism of microscopic gas displacement efficiency is discussed.The results are obtained in three aspects.First,the remaining gas is distributed at the blind end,in the pore-throat and as clusters,with their proportions and scales jointly controlled by microscopic pore structures,wettability and capillary number.The remaining gas can be further produced by changing the production pressure differential to disturb the original pressure system and gas expansion,so as to improve the microscopic gas displacement efficiency.Second,the microscopic gas displacement efficiency is closely related to the gas flow process.Formation or expansion of each water flow path may cause rapid increase of water cut and slows down the increase of gas displacement efficiency.Third,the microscopic pore structure and wettability are the inherent features of the gas reservoir,so the capillary number can be optimized to change the mode of GWC advancement,and then to effectively improve the microscopic gas displacement efficiency.It is concluded that for real gas wells,the evolution of mechanical mechanisms of GWC advancement should be revealed depending upon the microscopic pore structure and wettability of the reservoir,and then the optimal capillary number can be determined.Furthermore,clarifying the pore-scale water-gas flow characteristics and physical mechanism of microscopic gas displacement provides guidance for the planning of enhanced gas recovery.
基金The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China （Grant Nos. 51374213 and 51674251）, the State Key Research Development Program of China （Grant No. 2016YFC0600705）, the National Natural Science Fund for Distinguished Young Scholars of China （Grant No. 51125017）, the Fund for Innovative Research and Development Group Program of Jiangsu Province （Grant No. 2014- 27）, the Science Fund for Creative Research Groups of the National Natural Science Foundation of China （Grant No. 51421003）, and the Priority Academic Program Development of the Jiangsu Higher Education Institutions （PAPD 2014）.
文摘This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization approaches to detect and observe the CO2-formation fluid displacement mechanism at the micro-scale, namely, magnetic resonance imaging, X-ray computed tomography and fabricated micromodels, but they are not capable of investigating the dis- placement process at the nano-scale. Though a lab-on-chip approach for the direct visualization of the fluid flow behaviour in nanoscale channels has been developed using an advanced epi-fluorescence microscopy method combined with a nanofluidic chip, it is still a qualitative analysis method. The lattice Boltzmann method （LBM） can simulate the CO2 displacement processes in a two-dimensional or three-dimensional （3D） pore structure, but until now, the CO2 displace- ment mechanisms had not been thoroughly investigated and the 3D pore structure of real rock had not been directly taken into account in the simulation of the CO2 displacement process. The status of research on the applications of CO2 displacement to enhance shale gas recovery is also analyzed in this paper. The coupling of molecular dynamics and LBM in tandem is proposed to simulate the CO2-shale gas displacement process based on the 3D digital model of shale obtained from focused ion beams and scanning electron microscopy.
基金National Natural Science Foundation of China(No.10675168)
文摘A two-pulse method is used to determine the insulation recovery time of the gas spark gap switch with different types of gas applied in a high power accelerator with a water dielectric pulse forming line. At the breakdown voltage of 450 kV, with the vacuum diode voltage of about 200 kV, and a current of 30 kA, recovery characteristics of H2, N2, SF6 were studied. The recovery percentages of the gas breakdown voltage and vacuum diode voltage were determined. The results show that hydrogen has the best recovery characteristics. At a pulse interval of 8.8 ms, the recovery percentages of both the gas breakdown voltage and vacuum diode voltage for hydrogen exceed 95%. For SF6 and N2 with an interval of 25 ms and 50 ms respectively, a 90% voltage recovery was obtained. The experiments also proved that the repetitive rate of the high power accelerator with a pulse forming line is mainly restricted by the gas switch repetitive rate; the recovery percentages of the vacuum diode voltage are limited by the recovery percentages of the gas switch breakdown voltage. The hydrogen switch can be employed for a high repetitive rate-high power accelerator with a pulse forming line.
基金This study was financially supported by the National Natural Science Foundation of China(Grant Nos.51704197 and 11872258)。
文摘In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.
基金funding from Natural Sciences and Engineering Research Council of Canada (NSERC) for this researchsupport from the University of Calgary Beijing Research Site, a research initiative associated with the University of Calgary Global Research Initiative in Sustainable Low Carbon Unconventional Resources, the Kerui Group, and the Mitacs Accelerate program
文摘The recovery factor from tight gas reservoirs is typically less than 15%, even with multistage hydrauhc tractunng stimulation. Such low recovery is exacerbated in tight gas condensate reservoirs, where the depletion of gas leaves the valuable condensate behind. In this paper, three enhanced gas recovery （EGR） methods including produced gas injection, CO2 injection and water injection are investigated to increase the well productivity for a tight gas condensate reservoir in the Montney Formation, Canada. The production performance of the three EGR methods is compared and their economic feasibility is evaluated. Sensitivity analysis of the key factors such as primary production duration, bottom-hole pressures, and fracture conductivity is conducted and their effects on the well production performance are analyzed. Results show that, compared with the simple depletion method, both the cumulative gas and condensate production increase with fluids injected. Produced gas injection leads to both a higher gas and condensate production compared with those of the CO2 injection, while waterflooding suffers from injection difficulty and the corresponding low sweep efficiency. Meanwhile, the injection cost is lower for the produced gas injection due to the on-site available gas source and minimal transport costs, gaining more economic benefits than the other EGR methods.
文摘This paper presents the effectiveness of the CO_(2) injection process at different periods during gascondensate reservoir development.Taking a real gas-condensate reservoir located in China's east region as an example,first,we conducted experiments of constant composition expansion(CCE),constant volume depletion(CVD),saturation pressure determination,and single flash.Next,a series of water/CO2 flooding experiments were been investigated,including water flooding at present pressure 15 MPa,CO_(2) flooding at 25.53 MPa,15 MPa,which repents initial pressure and present pressure respectively.Finally,the core flooding numerical model was constructed using a generalized equation-of-state model reservoir simulator(GEM)to reveal miscible flooding mechanism and the seepage flow characteristics in the condensate gas reservoir with CO2 injection.A desirable agreement achieved in experimental results and predicted pressure volume temperature(PVT)properties by the modified equation of state(EOS)in the CVD and CCE tests indicated that the proposed recombination method can successfully produce a fluid with the same phase behavior of initial reservoir fluid with an acceptable accuracy.The modeling results confirm the experimental results,and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure.Moreover,the results show that CO_(2) treatment can improve gas productivity by a factor of about 1.39 compared with the water flooding mode.These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.
基金Supported by the National Natural Science Foundation of China (51534006)。
文摘Based on the study of damage mechanisms of generalized water blocking and related water-blocking removal methods, the drying agents for enhancing tight gas reservoir recovery were developed, and the basic properties, injection mode and drying effect of the drying agents were evaluated. The chemical effect, thermal effect, salt resistance, salt resistance formulas and delay mechanism of the drying agent systems for different types of tight reservoirs were investigated through lab experiment. The solubility and solubilization properties of supercritical carbon dioxide on drying agent systems were tested.The injection mode of dissolving drying agent in supercritical carbon dioxide was proposed. The mechanisms of supercritical carbon dioxide with water in micropores of formation matrix were analyzed. Micro-pore structures and seepage characteristics of reservoir before and after drying were compared. Based on the characterization in combination of NMR and laser etched pore structure model, drying effects of the drying agents on bound water of different occurrences were evaluated qualitatively and quantitatively. Lattice Boltzmann method was used to evaluate the influence of drying effect on gas micro-seepage ability.The influence of drying effect on productivity and production performance of gas well was analyzed by numerical simulation.The drying effect can greatly reduce water saturation of tight reservoir and improve the gas seepage capacity in near wellbore and fractures. This work can provide guidance for developing new measures in enhancing recovery of tight gas reservoirs.
基金the China National Petroleum Corporation South-west Oil and Gas Field Branch Shale Gas Research Institute(Grant No.JS-2020-42)for providing research funding.
文摘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%.
文摘The technique of Enhanced Gas Recovery by CO_(2) injection(CO_(2)-EGR)into shale reservoirs has brought increasing attention in the recent decade.CO_(2)-EGR is a complex geophysical process that is controlled by several parameters of shale properties and engineering design.Nevertheless,more challenges arise when simulating and predicting CO_(2)/CH4 displacement within the complex pore systems of shales.Therefore,the petroleum industry is in need of developing a cost-effective tool/approach to evaluate the potential of applying CO_(2) injection to shale reservoirs.In recent years,machine learning applications have gained enormous interest due to their high-speed performance in handling complex data and efficiently solving practical problems.Thus,this work proposes a solution by developing a supervised machine learning(ML)based model to preliminary evaluate CO_(2)-EGR efficiency.Data used for this work was drawn across a wide range of simulation sensitivity studies and experimental investigations.In this work,linear regression and artificial neural networks(ANNs)implementations were considered for predicting the incremental enhanced CH4.Based on the model performance in training and validation sets,our accuracy comparison showed that(ANNs)algorithms gave 15%higher accuracy in predicting the enhanced CH4 compared to the linear regression model.To ensure the model is more generalizable,the size of hidden layers of ANNs was adjusted to improve the generalization ability of ANNs model.Among ANNs models presented,ANNs of 100 hidden layer size gave the best predictive performance with the coefficient of determination(R2)of 0.78 compared to the linear regression model with R2 of 0.68.Our developed MLbased model presents a powerful,reliable and cost-effective tool which can accurately predict the incremental enhanced CH4 by CO_(2) injection in shale gas reservoirs.
