Slickwater fracturing fluids have gained widespread application in the development of tight oil reservoirs. After the fracturing process, the active components present in slickwater can directly induce spontaneous imb...Slickwater fracturing fluids have gained widespread application in the development of tight oil reservoirs. After the fracturing process, the active components present in slickwater can directly induce spontaneous imbibition within the reservoir. Several variables influence the eventual recovery rate within this procedure, including slickwater composition, formation temperature, degree of reservoir fracture development, and the reservoir characteristics. Nonetheless, the underlying mechanisms governing these influences remain relatively understudied. In this investigation, using the Chang-7 block of the Changqing Oilfield as the study site, we employ EM-30 slickwater fracturing fluid to explore the effects of the drag-reducing agent concentration, imbibition temperature, core permeability, and core fracture development on spontaneous imbibition. An elevated drag-reducing agent concentration is observed to diminish the degree of medium and small pore utilization. Furthermore, higher temperatures and an augmented permeability enhance the fluid flow properties, thereby contributing to an increased utilization rate across all pore sizes. Reduced fracture development results in a lower fluid utilization across diverse pore types. This study deepens our understanding of the pivotal factors affecting spontaneous imbibition in tight reservoirs following fracturing. The findings act as theoretical, technical, and scientific foundations for optimizing fracturing strategies in tight oil reservoir transformations.展开更多
To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow...To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow,heat,and electrochemical reactions in a PEMFC are established.The continuity equation and momentum equation are solved by handling pressure-velocity coupling using the SIMPLE algorithm.The electrochemical reaction rates in the catalyst layers(CLs)of the cathode and anode are calculated using the Butler-Volmer equation.The multiphase mixture model describes the multiphase transport process of gas mixtures and liquid water in the fuel cell.After validation,the influences of co-flow and counter-flow modes on the PEMFC performance are investigated,including the evolution of the current density,flow field,temperature field,and reactant concentration field during start-up,as well as the steady distribution of the current density,reactant concentration,andmembrane water content when the start-up stabilizes.Co-flow and counter-flow modes influence the current density distribution and temperature distribution.On the one hand,the co-flow mode accelerates the start-up process of the PEMFC and leads to a more evenly distributed current density than the counter-flow mode.On the other hand,the temperature difference between the inlet and outlet sections of the cell is up to 10.1℃ under the co-flow mode,much larger than the 5.0℃ observed in the counter-flow mode.Accordingly,the counter-flowmode results in a more evenly distributed temperature and a lower maximum temperature than the co-flow case.Therefore,in the flow field design of a PEMFC,the reactant flow arrangements can be considered to weigh between better heat management and higher current density distribution of the cell.展开更多
Natural gas hydrate(NGH)can cause pipeline blockages during the transportation of oil and gas under high pressures and low temperatures.Reducing hydrate adhesion on pipelines is viewed as an efficient way to prevent N...Natural gas hydrate(NGH)can cause pipeline blockages during the transportation of oil and gas under high pressures and low temperatures.Reducing hydrate adhesion on pipelines is viewed as an efficient way to prevent NGH blockages.Previous studies suggested the water film can greatly increase hydrate adhesion in gas-dominant system.Herein,by performing the molecular dynamics simulations,we find in water-dominant system,the water film plays different roles in hydrate deposition on Fe and its corrosion surfaces.Specifically,due to the strong affinity of water on Fe surface,the deposited hydrate cannot convert the adsorbed water into hydrate,thus,a water film exists.As water affinities decrease(Fe>Fe_(2)O_(3)>FeO>Fe_(3)O_(4)),adsorbed water would convert to amorphous hydrate on Fe_(2)O_(3)and form the ordered hydrate on FeO and Fe_(3)O_(4)after hydrate deposition.While absorbed water film converts to amorphous or to hydrate,the adhesion strength of hydrate continuously increases(Fe<Fe_(2)O_(3)<FeO<Fe_(3)O_(4)).This is because the detachment of deposited hydrate prefers to occur at soft region of liquid layer,the process of which becomes harder as liquid layer vanishes.As a result,contrary to gas-dominant system,the water film plays the weakening roles on hydrate adhesion in water-dominant system.Overall,our results can help to better understand the hydrate deposition mechanisms on Fe and its corrosion surfaces and suggest hydrate deposition can be adjusted by changing water affinities on pipeline surfaces.展开更多
Different drillingfluid systems are designed according to mineral composition,lithology and wellbore stability of different strata.In the present study,the conversion of a non-dispersed polymer drillingfluid into a low ...Different drillingfluid systems are designed according to mineral composition,lithology and wellbore stability of different strata.In the present study,the conversion of a non-dispersed polymer drillingfluid into a low potas-sium anti-collapsing drillingfluid is investigated.Since the two drillingfluids belong to completely different types,the key to this conversion is represented by new inhibitors,dispersants and water-loss agents by which a non-dispersed drillingfluid can be turned into a dispersed drillingfluid while ensuring wellbore stability and reason-able rheology(carrying sand—inhibiting cuttings dispersion).In particular,the(QYZ-1)inhibitors and(FSJSS-2)dispersants are used.The former can inhibit the hydration expansion capacity of clay,reduce the dynamic shear force and weaken the viscosity;the latter can improve the sealing effect and reduce thefiltrate loss.The results have shown that after adding a reasonable proportion of these substances(QYZ-1:FSJSS-2)to the non-dispersed polymer drillingfluid,while the apparent viscosity,plastic viscosity,structural viscosity andfluidity index under-went almost negligible changes,the dynamic plastic ratio increased,and thefiltration loss decreased significantly,thereby indicating good compatibility.According to the tests(conducted in the Leijia area),the density was 1.293 g/cm3,and after standing for 24 h,the SF(static settlement factor)was 0.51.Moreover,thefiltration loss was reduced to 4.0 mL,the rolling recovery rate reached 96.92%,with excellent plugging and anti-collapse performances.展开更多
Natural gas hydrate(NGH)is generally produced and accumulated together with the underlying conventional gas.Therefore,optimizing the production technology of these two gases should be seen as a relevant way to effecti...Natural gas hydrate(NGH)is generally produced and accumulated together with the underlying conventional gas.Therefore,optimizing the production technology of these two gases should be seen as a relevant way to effectively reduce the exploitation cost of the gas hydrate.In this study,three types of models accounting for the coexistence of these gases are considered.Type A considers the upper hydrate-bearing layer(HBL)adjacent to the lower conventional gas layer(CGL);with the Type B a permeable interlayer exists between the upper HBL and the lower CGL;with the type C there is an impermeable interlayer between the upper HBL and the lower CGL.The production performances associated with the above three models are calculated under different conditions,including only a depressurized HBL(only HBL DP);only a depressurized CGL(only CGL DP);and both the HBL and the CGL being depressurized(HBL+CGL DP).The results show that for Type A and Type B coexistence accumulation models,when only HBL or CGL is depressurized,the gas from the other layer will flow into the production layer due to the pressure difference between the two layers.In the coexistence accumulation model of type C,the cumulative gas production is much lower than that of Type A and Type B,regardless of whether only HBL DP,only CGL DP,or HBL+CGL DP are considered.This indicates that the impermeable interlayer restricts the cross-flow of gas between HBL and CGL.For three different coexistence accumulation models,CGL DP has the largest gas-to-water ratio.展开更多
The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to ...The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation,based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation.The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion.And a 15%concentration of hydrochloric acid can effectively dissolve shale.Furthermore,the degree of acid-etching reaction is highly variable because of the different carbonate content,which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section.After the acid interacted with the shale rock samples,the triaxial compressive strength,elastic modulus,and Poisson’s ratio of shale decreased.Moreover,the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs,the more favorable the fracture volume modification.This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.展开更多
Inorganic scale deposits are a major water-related problem encountered in producing oil and gas wells. The harshness of scale deposits is dependent on the field operating conditions. Scale deposits can vary from mild ...Inorganic scale deposits are a major water-related problem encountered in producing oil and gas wells. The harshness of scale deposits is dependent on the field operating conditions. Scale deposits can vary from mild scaling tendencies to extreme. In general, the scale deposit will cause a reduction in formation pores, declining productivity and eventually blockage of the wellbore and hence unexpected downtime if it is allowed to persevere. To overcome this, the productivity of an oil and gas well is ensured by handling scale deposits via removal or prevention methods. Scale prevention is the best and cost-e ective method for handling scale deposits that ensures production continuity. Inhibition through 'threshold' scale inhibitor treatment is the most common method that is proven to prevent or reduce likely deposits. This paper examines the art of synthetic scale inhibitors, in particular, threshold scale inhibitors in oil and gas production. It discusses the chemistry of those inhibitors, inhibition mechanisms, treatment methods and key properties for their applications. It also highlights the chemistry of the synthetic routes often used to produce them in the laboratory and/or industry. Finally, it highlights the environmental concerns for the applicability of threshold scale inhibitors.展开更多
Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development.This paper introduces a hydrophobic nano-silica(HNS)for use in strengthening the wellbore wall when using ...Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development.This paper introduces a hydrophobic nano-silica(HNS)for use in strengthening the wellbore wall when using a water-based drilling fluid(WBF).The wellbore-strengthening performance was studied using the linear swelling test,hot-rolling recovery test,and compressive strength test.The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential,particle size,contact angle,and surface tension,and with the use of a scanning electron microscope(SEM).The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method.The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion.Compared with the use of water,the use of HNS resulted in a 20%smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines.More importantly,the addition of HNS was effective in preventing a decrease in shale strength.According to the mechanism study,the good wellbore-strengthening performance of HNS can be attributed to three aspects.First,the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption,thus inhibiting osmotic hydration.Second,HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption,which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy,thereby inhibiting surface hydration.Third,the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability.The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.展开更多
Percussive-rotary drilling technology was considered many years ago as one of the best approaches for hard rock drilling. It is a key for popularizing this technology on a large scale to design and make an impactor wi...Percussive-rotary drilling technology was considered many years ago as one of the best approaches for hard rock drilling. It is a key for popularizing this technology on a large scale to design and make an impactor with excellent performance. This paper presents a suit of method to design the percussive parameters for the oil or gas field by introducing the working principle of back-pressured impactor, dividing the working periods of impactor into three phases and establishing the computer emulational model of percussive parameters. It draws a comparison between the results of model calculation and experiment on the basis of analyzing the experiment results of impactor.The conclude provides credible foundation for designing and further ameliorating the impactor.展开更多
A deep understanding of the geometric impacts of fracture on fracturing fluid flowback efficiency is essential for unconventional oil development. Using nuclear magnetic resonance and 2.5-dimensional matrix-fracture v...A deep understanding of the geometric impacts of fracture on fracturing fluid flowback efficiency is essential for unconventional oil development. Using nuclear magnetic resonance and 2.5-dimensional matrix-fracture visualization microfluidic models, qualitative and quantitative descriptions of the influences of connectivity between primary fracture and secondary fracture on flowback were given from core scale to pore network scale. The flow patterns of oil-gel breaking fluid two-phase flow during flowback under different fracture connectivity were analyzed. We found some counterintuitive results that non-connected secondary fracture (NCSF, not connect with artificial primary fracture and embedded in the matrix) is detrimental to flowbackefficiency. The NCSF accelerates the formation of oil channeling during flowback, resulting in a large amount of fracturing fluid trapped in the matrix, which is not beneficial for flowback. Whereas the connected secondary fracture (CSF, connected with the artificial primary fracture) is conducive to flowback. The walls of CSF become part of primary fracture, which expands the drainage area with low resistance, and delays the formation of the oil flow channel. Thus, CSF increases the high-speed flowback stage duration, thereby enhancing the flowback efficiency. The fracturing fluid flowback efficiency investigated here follows the sequence of the connected secondary fracture model (72%) > the matrix model (66%) > the non-connected secondary fracture model (38%). Our results contribute to hydraulic fracturing design and the prediction of flowback efficiency.展开更多
Wellbore instability,especially drilling with water-based drilling fluids(WBDFs)in complex shale for-mations,is a critical challenge for oil and gas development.The purpose of this paper is to study the feasibility of...Wellbore instability,especially drilling with water-based drilling fluids(WBDFs)in complex shale for-mations,is a critical challenge for oil and gas development.The purpose of this paper is to study the feasibility of using hydrophobically modified silica nanoparticle(HMN)to enhance the comprehensive performance of WBDFs in the Xinjiang Oilfield,especially the anti-collapse performance.The effect of HMN on the overall performance of WBDFs in the Xinjiang Oilfield,including inhibition,plugging,lu-bricity,rheology,and filtration loss,was studied with a series of experiments.The mechanism of HMN action was studied by analyzing the changes of shale surface structure and chemical groups,wettability,and capillary force.The experimental results showed that HMN could improve the performance of WBDFs in the Xinjiang Oilfeld to inhibit the hydration swelling and dispersion of shale.The plugging and lubrication performance of the WBDFs in the Xinjiang Oilfield were also enhanced with HMN based on the experimental results.HMN had less impact on the rheological and filtration performance of the WBDFs in the Xinjiang Oilfield.In addition,HMN significantly prevented the decrease of shale strength.The potential mechanism of HMN was as follows.The chemical composition and structure of the shale surface were altered due to the adsorption of HMN driven by electrostatic attraction.Changes of the shale surface resulted in significant wettability transition.The capillary force of the shale was converted from a driving force of water into the interior to a resistance.In summary,hydrophobic nanoparticles presented afavorable application potential for WBDFs.展开更多
In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sour...In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sources,particle sizes of silica flour,and additions of silica fume,alumina,colloidal iron oxide and nano-graphene,were investigated.To simulate the environment of cementing geothermal wells and deep wells,cement slurries were directly cured at 50 MPa and 200?C.Mineral compositions(as determined by X-ray diffraction Rietveld refinement),water permeability,compressive strength and Young’s modulus were used to evaluate the qualities of the set cement.Short-term curing(2e30 d)test results indicated that the adoption of 6 m m ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems,while the addition of silica fume had a detrimental effect on strength stability.Long-term curing(2e180 d)test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems.However,none of the ad-mixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases.展开更多
The identification of stratigraphic'sweet-spot'interval is significant in oil and gas formation evaluation.However,formation evaluation in macroscopic-scale merely provides low resolution and limited infor-mat...The identification of stratigraphic'sweet-spot'interval is significant in oil and gas formation evaluation.However,formation evaluation in macroscopic-scale merely provides low resolution and limited infor-mation,thus may lead to uncertainties in resource estimation.To accurately identify the'sweet-spot'intervals amongst heterogeneous lithofacies,we conducted a very high-resolution and quantitative analysis from in-situ macroscopic scale to laboratory microscopic scale on the Goldwyer formation of Canning Basin,Western Australia.The comprehensive advanced well logging and slim-compact micro imager(SCMI)technologies were synthetically applied in couple with the laboratory nanoscaled ex-periments.The results unveiled an extraordinarily large lithofacies heterogeneity between different rock intervals,with distinguished features shown in Goldwyer Ⅰ,Ⅱ,and Ⅲ members.The most favorable lithofacies is recognized as the laminated argillaceous thermally-matured organic matter(OM)-rich mudstone,which is widely developed in Goldwyer Ⅲ as the major attributor to'sweet-spot'intervals.Goldwyer Ⅱ is exclusively characterized by thick mudstone intervals(94.4%),interbedded with thin calcareous mudstones(5.5%),corresponding to a depositional environment of low-energy distal section of the outer ramp settings.Microscopically,the most favorable lithofacies in'sweet-spot'intervals develop numerous OM-/mineral nanopores for hydrocarbon storage.Illite-rich lithofacies develops abundant inter-particle pores from 2 to 17 nm that mainly contribute to pore volume for free gas storage capacity.OM-rich lithofacies with higher maturity have OM-pores with good connectivity,bearing large specific surface area that is beneficial for adsorbed gas capacity.展开更多
The excellent mechanical properties of supramolecular gel could adapt to the complex reservoir environment and had broad application prospects in the field of oil and gas drilling and production engineering.In this pa...The excellent mechanical properties of supramolecular gel could adapt to the complex reservoir environment and had broad application prospects in the field of oil and gas drilling and production engineering.In this paper,a supramolecular gel based on hydrophobic association and hydrogen bonding was prepared by micellar copolymerization,which could be used to plug fractures and pores in formations.Supramolecular gel was a gel network system with high performance characteristics formed by self-assembly of non-covalent bond interaction.The rheological properties,mechanical mechanics,temperature resistance and swelling ability of supramolecular gel were studied.The results showed that the supramolecular gel had a dense three-dimensional network structure with open and interconnected pore structures,which could exhibit good rheological properties and strong viscoelastic recovery ability.The mechanical properties of the supramolecular gel were excellent,it had a tensile stress of 0.703 MPa and an elongation at break of 1803%.When the compressive strain was 96%,the compressive stress could reach 14.5 MPa.Supramolecular gel also showed good temperature resistance and swelling properties.At the aging temperature of 135℃,supramolecular gels still maintained good gel strength,and it only took 12 h to reach the equilibrium swelling ratio of 35.87 in 1%NaCl solution.It was also found that supramolecular gel in low concentration saline(1%NaCl solution)showed relatively faster swelling than high concentration saline(25%NaCl solution).The swelling process of the supramolecular gel was non-Fick diffusion(typeⅡ).This indicated that the organic/inorganic permeability network was well formed.Therefore,the diffusion rate of small molecules could be guaranteed to be equal to the relaxation rate of large molecules before and after the phase transition temperature.In addition to the diffusion of water molecules,the swelling process of the supramolecular gel was also affected by the relaxation of gel network and polymer chain segment,the interaction between water molecules and polymer network and the groups of polymer network and other factors.Supramolecular gel particles could be used as plugging materials for drilling fluids,which had excellent ability to plug formation fractures and pores.The plugging ability of the supramolecular gel was up to 6.7 MPa for 0.5 mm fracture width,and 9.6 MPa for porous media with 5 mD permeability.Compared with HT-PPG gel particles commonly used in oil fields,supramolecular gel particles had better plugging ability on fractures and porous media.The development and application of supramolecular gel had far-reaching significance for promoting the functional application of polymer materials in drilling and production engineering.展开更多
Compliant vertical access risers(CVAR)have broad application prospects in deep-water oil and gas transportation.However,the mechanical behaviors of the CVAR with a variable length during installation remains unclear.T...Compliant vertical access risers(CVAR)have broad application prospects in deep-water oil and gas transportation.However,the mechanical behaviors of the CVAR with a variable length during installation remains unclear.To address this issue,based on the flexible segment method,a model of CVAR with a variable length during installation is established in this study,which is verified by the comparison with commercial software.Then,the mechanical behaviors of CVAR during installation are investigated.The results reveal that the CVAR configuration is significantly affected by the buoyancy blocks.The streamwise displacement of CVAR increases with the increase of current velocity.When the BOP weight is insuffcient,obvious upbending is observed in the lower region and transition region,leading to local compression.When the platform moves in the opposite direction to the current,the maximum stress is larger than that of the scenario when the platform moves in the same direction as the current.展开更多
With the exploration and development of deep and ultra-deep oil and gas,high torque and high friction during the drilling of deep and ultra-deep wells become one of the key issues affecting drilling safety and drillin...With the exploration and development of deep and ultra-deep oil and gas,high torque and high friction during the drilling of deep and ultra-deep wells become one of the key issues affecting drilling safety and drilling speed.Meanwhile,the high temperature and high salt problem in deep formations is prominent,which poses a major challenge to the lubricity of drilling fluids under high temperature and high salt.This paper reports an organic borate ester SOP as an environmentally friendly drilling fluid lubricant.The performance evaluation results show that when 1%lubricant SOP is added to the fresh water-based mud,the lubrication coefficient decreases from 0.631 to 0.046,and the reduction rate of lubrication coefficient is 92.7%.Under the conditions of 210℃ and 30%NaCl,the reduction rate of lubricating coefficient of the base slurry with 1%SOP was still remain 81.5%.After adding 1%SOP,the wear volume decreased by 94.11%compared with the base slurry.The contact resistance experiment during the friction process shows that SOP can form a thick adsorption film on the friction surface under high temperature and high salt conditions,thus effectively reducing the friction resistance.Molecular dynamics simulation shows that lubricant SOP can be physically adsorbed on the surface of drilling tool and borehole wall through hydrogen bond and van der Waals force.XPS analysis further shows that SOP adsorbs on the friction surface and reacts with metal atoms on the friction surface to form a chemically reactive film.Therefore,under high temperature and high salt conditions,the synergistic effect of physical adsorption film and chemical reaction film effectively reduces the frictional resistance and wear of the friction surface.In addition,SOP is non-toxic and easy to degrade.Therefore,SOP is a highly effective and environmentally friendly lubricant in high temperature and high salt drilling fluid.展开更多
Steam flooding with the assistance of carbon dioxide (CO_(2)) and chemicals is an effective approach for enhancing super heavy oil recovery. However, the promotion and application of CO_(2) and chemical agent-assisted...Steam flooding with the assistance of carbon dioxide (CO_(2)) and chemicals is an effective approach for enhancing super heavy oil recovery. However, the promotion and application of CO_(2) and chemical agent-assisted steam flooding technology have been restricted by the current lack of research on the synergistic effect of CO_(2) and chemical agents on enhanced steam flooding heat transfer. The novel experiments on CO_(2)–chemicals cooperate affected steam condensation and seepage were conducted by adding CO_(2) and two chemicals (sodium dodecyl sulfate (SDS) and the betaine temperature-salt resistant foaming agent ZK-05200).According to the experimental findings, a “film” formed on the heat-transfer medium surface following the co-injection of CO_(2) and the chemical to impede the steam heat transfer, reducing the heat transfer efficiency of steam, heat flux and condensation heat transfer coefficient. The steam seepage experiment revealed that the temperature at the back end of the sandpack model was dramatically raised by 3.5–12.8 °C by adding CO_(2) and chemical agents, achieving the goal of driving deep-formation heavy oil. The combined effect of CO_(2) and SDS was the most effective for improving steam heat transfer, the steam heat loss was reduced by 6.2%, the steam condensation cycle was prolonged by 1.3 times, the condensation heat transfer coefficient was decreased by 15.5%, and the heavy oil recovery was enhanced by 9.82%. Theoretical recommendations are offered in this study for improving the CO_(2)–chemical-assisted steam flooding technique.展开更多
Low-Tension-Foam(LTF)flooding is an emerging enhanced oil recovery technique for low-permeability carbonate reservoirs.Foam capacity is closely related to the salinity environment(or,equivalently,the phase behavior of...Low-Tension-Foam(LTF)flooding is an emerging enhanced oil recovery technique for low-permeability carbonate reservoirs.Foam capacity is closely related to the salinity environment(or,equivalently,the phase behavior of the oil/water/surfactant system).Therefore,the interactions between microemulsion and foam components are of primary importance in the LTF process.In this study,the phase behavior of an oil/water/surfactant system under equilibrium is analyzed,firstly by assuming perfect mixing.Meanwhile,the formation kinetics of microemulsion are monitored through a novel low-field NMR technique,which is able to provide quantitative assessment on the microemulsion evolution characteristics.Then,foam stability is examined in the absence and in the presence of Winsor-Ⅰ and Winsor-Ⅲ type microemulsions.It is revealed that foam stability depends on the oil solubilization(oil swollen micelle size).A decrease in the oil swollen micelle size and micellar structure effectiveness,in conjunction with an increasing salinity,leads to lower foam stability in the presence of a Winsor-Ⅲ type microemulsion.展开更多
The mechanical behavior,dynamic evolution,and flow-field distribution of a two-degree-of-freedom riserless drill string were simulated numerically by using FLUENT fluid simulation software with the user-defined functi...The mechanical behavior,dynamic evolution,and flow-field distribution of a two-degree-of-freedom riserless drill string were simulated numerically by using FLUENT fluid simulation software with the user-defined function embedded.The rotation angular velocities before and after the critical rotation angular velocity were used as independent variables,and the reduced velocity range was 3-14.Fluid-structure coupling was realized based on the dynamic overset grid and the SST k-ωturbulence model.Results reveal that the dynamic response of the riserless drill string was considerably affected by rotation and flow velocity,which are coupled with each other.The cross-flow average dimensionless displacement increased with the rotation angular velocity,and rotation considerably enhanced the in-line maximum average dimensionless displacement.However,the cross-flow amplitude caused by vortex-induced vibration was suppressed when the rotation angular velocity reached a certain value.The in-line and cross-flow frequencies were the same,thereby causing the trajectory to deviate from the standard'figure-eight'shape and become a closed circle shape.The vortex did not fall behind the cylinder at low reduced velocity with high-rotation angular velocity,and the structure of the near-wake vortex remained U-shaped.The wake of the cylinder was deflected along the cross-flow direction,thereby leading to vibration asymmetry and resulting in increased vibration instability and disordered vibration trajectories,especially at high-rotation angular velocities.展开更多
Due to the low porosity and low permeability in unconventional reservoirs,a large amount of crude oil is trapped in micro-to nano-sized pores and throats,which leads to low oil recovery.Nanofluids have great potential...Due to the low porosity and low permeability in unconventional reservoirs,a large amount of crude oil is trapped in micro-to nano-sized pores and throats,which leads to low oil recovery.Nanofluids have great potential to enhance oil recovery(EOR)in low permeability reservoirs.In this work,the regulating ability of a nanofluid at the oil/water/solid three-phase interface was explored.The results indicated that the nanofluid reduced the oil/water interfacial tension by two orders of magnitude,and the expansion modulus of oil/water interface was increased by 77% at equilibrium.In addition,the solid surface roughness was reduced by 50%,and the three-phase contact angle dropped from 135(oil-wet)to 48(water-wet).Combining the displacement experiments using a 2.5D reservoir micromodel and a microchannel model,the remaining oil mobilization and migration processes in micro-to nano-scale pores and throats were visualized.It was found that the nanofluid dispersed the remaining oil into small oil droplets and displaced them via multiple mechanisms in porous media.Moreover,the high strength interface film formed by the nanofluid inhibited the coalescence of oil droplets and improved the flowing ability.These results help to understand the EOR mechanisms of nanofluids in low permeability reservoirs from a visual perspective.展开更多
基金The authors sincerely appreciate the financial support from the National Natural Science Foundation of China(No.52074279,51874261).
文摘Slickwater fracturing fluids have gained widespread application in the development of tight oil reservoirs. After the fracturing process, the active components present in slickwater can directly induce spontaneous imbibition within the reservoir. Several variables influence the eventual recovery rate within this procedure, including slickwater composition, formation temperature, degree of reservoir fracture development, and the reservoir characteristics. Nonetheless, the underlying mechanisms governing these influences remain relatively understudied. In this investigation, using the Chang-7 block of the Changqing Oilfield as the study site, we employ EM-30 slickwater fracturing fluid to explore the effects of the drag-reducing agent concentration, imbibition temperature, core permeability, and core fracture development on spontaneous imbibition. An elevated drag-reducing agent concentration is observed to diminish the degree of medium and small pore utilization. Furthermore, higher temperatures and an augmented permeability enhance the fluid flow properties, thereby contributing to an increased utilization rate across all pore sizes. Reduced fracture development results in a lower fluid utilization across diverse pore types. This study deepens our understanding of the pivotal factors affecting spontaneous imbibition in tight reservoirs following fracturing. The findings act as theoretical, technical, and scientific foundations for optimizing fracturing strategies in tight oil reservoir transformations.
基金supported by the Projects of Talents Recruitment of Guangdong University of Petrochemical Technology(No.2018rc14)Maoming City Science and Technology Plan Project(Nos.210427094551264 and 220415004552411).
文摘To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow,heat,and electrochemical reactions in a PEMFC are established.The continuity equation and momentum equation are solved by handling pressure-velocity coupling using the SIMPLE algorithm.The electrochemical reaction rates in the catalyst layers(CLs)of the cathode and anode are calculated using the Butler-Volmer equation.The multiphase mixture model describes the multiphase transport process of gas mixtures and liquid water in the fuel cell.After validation,the influences of co-flow and counter-flow modes on the PEMFC performance are investigated,including the evolution of the current density,flow field,temperature field,and reactant concentration field during start-up,as well as the steady distribution of the current density,reactant concentration,andmembrane water content when the start-up stabilizes.Co-flow and counter-flow modes influence the current density distribution and temperature distribution.On the one hand,the co-flow mode accelerates the start-up process of the PEMFC and leads to a more evenly distributed current density than the counter-flow mode.On the other hand,the temperature difference between the inlet and outlet sections of the cell is up to 10.1℃ under the co-flow mode,much larger than the 5.0℃ observed in the counter-flow mode.Accordingly,the counter-flowmode results in a more evenly distributed temperature and a lower maximum temperature than the co-flow case.Therefore,in the flow field design of a PEMFC,the reactant flow arrangements can be considered to weigh between better heat management and higher current density distribution of the cell.
基金This work was supported by the National Natural Science Foundation of China(51874332,51991363)the CNPC's Major Science and Technology Projects(ZD2019-184-003)+1 种基金the Fundamental Research Funds for Central Universities(20CX05008A)“14th Five-Year plan”forward-looking basic major science and technology project of CNPC(2021DJ4901).
文摘Natural gas hydrate(NGH)can cause pipeline blockages during the transportation of oil and gas under high pressures and low temperatures.Reducing hydrate adhesion on pipelines is viewed as an efficient way to prevent NGH blockages.Previous studies suggested the water film can greatly increase hydrate adhesion in gas-dominant system.Herein,by performing the molecular dynamics simulations,we find in water-dominant system,the water film plays different roles in hydrate deposition on Fe and its corrosion surfaces.Specifically,due to the strong affinity of water on Fe surface,the deposited hydrate cannot convert the adsorbed water into hydrate,thus,a water film exists.As water affinities decrease(Fe>Fe_(2)O_(3)>FeO>Fe_(3)O_(4)),adsorbed water would convert to amorphous hydrate on Fe_(2)O_(3)and form the ordered hydrate on FeO and Fe_(3)O_(4)after hydrate deposition.While absorbed water film converts to amorphous or to hydrate,the adhesion strength of hydrate continuously increases(Fe<Fe_(2)O_(3)<FeO<Fe_(3)O_(4)).This is because the detachment of deposited hydrate prefers to occur at soft region of liquid layer,the process of which becomes harder as liquid layer vanishes.As a result,contrary to gas-dominant system,the water film plays the weakening roles on hydrate adhesion in water-dominant system.Overall,our results can help to better understand the hydrate deposition mechanisms on Fe and its corrosion surfaces and suggest hydrate deposition can be adjusted by changing water affinities on pipeline surfaces.
文摘Different drillingfluid systems are designed according to mineral composition,lithology and wellbore stability of different strata.In the present study,the conversion of a non-dispersed polymer drillingfluid into a low potas-sium anti-collapsing drillingfluid is investigated.Since the two drillingfluids belong to completely different types,the key to this conversion is represented by new inhibitors,dispersants and water-loss agents by which a non-dispersed drillingfluid can be turned into a dispersed drillingfluid while ensuring wellbore stability and reason-able rheology(carrying sand—inhibiting cuttings dispersion).In particular,the(QYZ-1)inhibitors and(FSJSS-2)dispersants are used.The former can inhibit the hydration expansion capacity of clay,reduce the dynamic shear force and weaken the viscosity;the latter can improve the sealing effect and reduce thefiltrate loss.The results have shown that after adding a reasonable proportion of these substances(QYZ-1:FSJSS-2)to the non-dispersed polymer drillingfluid,while the apparent viscosity,plastic viscosity,structural viscosity andfluidity index under-went almost negligible changes,the dynamic plastic ratio increased,and thefiltration loss decreased significantly,thereby indicating good compatibility.According to the tests(conducted in the Leijia area),the density was 1.293 g/cm3,and after standing for 24 h,the SF(static settlement factor)was 0.51.Moreover,thefiltration loss was reduced to 4.0 mL,the rolling recovery rate reached 96.92%,with excellent plugging and anti-collapse performances.
基金supported by the National Natural Science Foundation of China (Nos.52074334,51991365)the National Key R&D Program of China (2021YFC2800903),which are gratefully acknowledged.
文摘Natural gas hydrate(NGH)is generally produced and accumulated together with the underlying conventional gas.Therefore,optimizing the production technology of these two gases should be seen as a relevant way to effectively reduce the exploitation cost of the gas hydrate.In this study,three types of models accounting for the coexistence of these gases are considered.Type A considers the upper hydrate-bearing layer(HBL)adjacent to the lower conventional gas layer(CGL);with the Type B a permeable interlayer exists between the upper HBL and the lower CGL;with the type C there is an impermeable interlayer between the upper HBL and the lower CGL.The production performances associated with the above three models are calculated under different conditions,including only a depressurized HBL(only HBL DP);only a depressurized CGL(only CGL DP);and both the HBL and the CGL being depressurized(HBL+CGL DP).The results show that for Type A and Type B coexistence accumulation models,when only HBL or CGL is depressurized,the gas from the other layer will flow into the production layer due to the pressure difference between the two layers.In the coexistence accumulation model of type C,the cumulative gas production is much lower than that of Type A and Type B,regardless of whether only HBL DP,only CGL DP,or HBL+CGL DP are considered.This indicates that the impermeable interlayer restricts the cross-flow of gas between HBL and CGL.For three different coexistence accumulation models,CGL DP has the largest gas-to-water ratio.
基金This study is supported by a Scientific Research Project of Sinopec(Program No.P21087-2)the Open Fund of Key Laboratory of Marine Oil&Gas Reservoirs Production,Sinopec(Grant No.33550000-22-FW2099-0004).
文摘The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation,based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation.The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion.And a 15%concentration of hydrochloric acid can effectively dissolve shale.Furthermore,the degree of acid-etching reaction is highly variable because of the different carbonate content,which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section.After the acid interacted with the shale rock samples,the triaxial compressive strength,elastic modulus,and Poisson’s ratio of shale decreased.Moreover,the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs,the more favorable the fracture volume modification.This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.
文摘Inorganic scale deposits are a major water-related problem encountered in producing oil and gas wells. The harshness of scale deposits is dependent on the field operating conditions. Scale deposits can vary from mild scaling tendencies to extreme. In general, the scale deposit will cause a reduction in formation pores, declining productivity and eventually blockage of the wellbore and hence unexpected downtime if it is allowed to persevere. To overcome this, the productivity of an oil and gas well is ensured by handling scale deposits via removal or prevention methods. Scale prevention is the best and cost-e ective method for handling scale deposits that ensures production continuity. Inhibition through 'threshold' scale inhibitor treatment is the most common method that is proven to prevent or reduce likely deposits. This paper examines the art of synthetic scale inhibitors, in particular, threshold scale inhibitors in oil and gas production. It discusses the chemistry of those inhibitors, inhibition mechanisms, treatment methods and key properties for their applications. It also highlights the chemistry of the synthetic routes often used to produce them in the laboratory and/or industry. Finally, it highlights the environmental concerns for the applicability of threshold scale inhibitors.
基金the National Natural Science Foundation of China (U1762212 and 51904329)the Shandong Natural Science Foundation (ZR2019BEE002)
文摘Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development.This paper introduces a hydrophobic nano-silica(HNS)for use in strengthening the wellbore wall when using a water-based drilling fluid(WBF).The wellbore-strengthening performance was studied using the linear swelling test,hot-rolling recovery test,and compressive strength test.The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential,particle size,contact angle,and surface tension,and with the use of a scanning electron microscope(SEM).The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method.The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion.Compared with the use of water,the use of HNS resulted in a 20%smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines.More importantly,the addition of HNS was effective in preventing a decrease in shale strength.According to the mechanism study,the good wellbore-strengthening performance of HNS can be attributed to three aspects.First,the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption,thus inhibiting osmotic hydration.Second,HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption,which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy,thereby inhibiting surface hydration.Third,the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability.The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.
基金Supported by the Science Foundation of China National Petroleum Corporation (990407 - 06 - 02)
文摘Percussive-rotary drilling technology was considered many years ago as one of the best approaches for hard rock drilling. It is a key for popularizing this technology on a large scale to design and make an impactor with excellent performance. This paper presents a suit of method to design the percussive parameters for the oil or gas field by introducing the working principle of back-pressured impactor, dividing the working periods of impactor into three phases and establishing the computer emulational model of percussive parameters. It draws a comparison between the results of model calculation and experiment on the basis of analyzing the experiment results of impactor.The conclude provides credible foundation for designing and further ameliorating the impactor.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFA0708700).
文摘A deep understanding of the geometric impacts of fracture on fracturing fluid flowback efficiency is essential for unconventional oil development. Using nuclear magnetic resonance and 2.5-dimensional matrix-fracture visualization microfluidic models, qualitative and quantitative descriptions of the influences of connectivity between primary fracture and secondary fracture on flowback were given from core scale to pore network scale. The flow patterns of oil-gel breaking fluid two-phase flow during flowback under different fracture connectivity were analyzed. We found some counterintuitive results that non-connected secondary fracture (NCSF, not connect with artificial primary fracture and embedded in the matrix) is detrimental to flowbackefficiency. The NCSF accelerates the formation of oil channeling during flowback, resulting in a large amount of fracturing fluid trapped in the matrix, which is not beneficial for flowback. Whereas the connected secondary fracture (CSF, connected with the artificial primary fracture) is conducive to flowback. The walls of CSF become part of primary fracture, which expands the drainage area with low resistance, and delays the formation of the oil flow channel. Thus, CSF increases the high-speed flowback stage duration, thereby enhancing the flowback efficiency. The fracturing fluid flowback efficiency investigated here follows the sequence of the connected secondary fracture model (72%) > the matrix model (66%) > the non-connected secondary fracture model (38%). Our results contribute to hydraulic fracturing design and the prediction of flowback efficiency.
基金the National Natural Science Foundation of China(51904329,52174014)the Major Scientific and Technological Projects of CNPC(ZD 2019-183-005)Key R&D Program of Shandong Province(No.2020ZLYS07).
文摘Wellbore instability,especially drilling with water-based drilling fluids(WBDFs)in complex shale for-mations,is a critical challenge for oil and gas development.The purpose of this paper is to study the feasibility of using hydrophobically modified silica nanoparticle(HMN)to enhance the comprehensive performance of WBDFs in the Xinjiang Oilfield,especially the anti-collapse performance.The effect of HMN on the overall performance of WBDFs in the Xinjiang Oilfield,including inhibition,plugging,lu-bricity,rheology,and filtration loss,was studied with a series of experiments.The mechanism of HMN action was studied by analyzing the changes of shale surface structure and chemical groups,wettability,and capillary force.The experimental results showed that HMN could improve the performance of WBDFs in the Xinjiang Oilfeld to inhibit the hydration swelling and dispersion of shale.The plugging and lubrication performance of the WBDFs in the Xinjiang Oilfield were also enhanced with HMN based on the experimental results.HMN had less impact on the rheological and filtration performance of the WBDFs in the Xinjiang Oilfield.In addition,HMN significantly prevented the decrease of shale strength.The potential mechanism of HMN was as follows.The chemical composition and structure of the shale surface were altered due to the adsorption of HMN driven by electrostatic attraction.Changes of the shale surface resulted in significant wettability transition.The capillary force of the shale was converted from a driving force of water into the interior to a resistance.In summary,hydrophobic nanoparticles presented afavorable application potential for WBDFs.
基金Financial support comes from China National Natural Science Foundation(Grant No.51974352)as well as from China University of Petroleum(East China)(Grant Nos.2018000025 and 2019000011)。
文摘In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sources,particle sizes of silica flour,and additions of silica fume,alumina,colloidal iron oxide and nano-graphene,were investigated.To simulate the environment of cementing geothermal wells and deep wells,cement slurries were directly cured at 50 MPa and 200?C.Mineral compositions(as determined by X-ray diffraction Rietveld refinement),water permeability,compressive strength and Young’s modulus were used to evaluate the qualities of the set cement.Short-term curing(2e30 d)test results indicated that the adoption of 6 m m ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems,while the addition of silica fume had a detrimental effect on strength stability.Long-term curing(2e180 d)test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems.However,none of the ad-mixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases.
基金Fundamental Research Programme of Yunnan Province(202201AU070041)the funding of Yunnan University Young Talent Programme(CZ21623201)+2 种基金the funding of State Key Laboratory of Coal Mine Disaster Dynamics and Control in Chongqing University(2011DA105287-FW202106)the funding from the Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,under the Institute of Geology in Chinese Academy of Geological Sciences,Beijing(J1901)Much gratitudes for the Department of Mines,Industry Regulation and Safety under the Government of Western Australia for granting us the core samples under Approval Nos.G32825&N00413。
文摘The identification of stratigraphic'sweet-spot'interval is significant in oil and gas formation evaluation.However,formation evaluation in macroscopic-scale merely provides low resolution and limited infor-mation,thus may lead to uncertainties in resource estimation.To accurately identify the'sweet-spot'intervals amongst heterogeneous lithofacies,we conducted a very high-resolution and quantitative analysis from in-situ macroscopic scale to laboratory microscopic scale on the Goldwyer formation of Canning Basin,Western Australia.The comprehensive advanced well logging and slim-compact micro imager(SCMI)technologies were synthetically applied in couple with the laboratory nanoscaled ex-periments.The results unveiled an extraordinarily large lithofacies heterogeneity between different rock intervals,with distinguished features shown in Goldwyer Ⅰ,Ⅱ,and Ⅲ members.The most favorable lithofacies is recognized as the laminated argillaceous thermally-matured organic matter(OM)-rich mudstone,which is widely developed in Goldwyer Ⅲ as the major attributor to'sweet-spot'intervals.Goldwyer Ⅱ is exclusively characterized by thick mudstone intervals(94.4%),interbedded with thin calcareous mudstones(5.5%),corresponding to a depositional environment of low-energy distal section of the outer ramp settings.Microscopically,the most favorable lithofacies in'sweet-spot'intervals develop numerous OM-/mineral nanopores for hydrocarbon storage.Illite-rich lithofacies develops abundant inter-particle pores from 2 to 17 nm that mainly contribute to pore volume for free gas storage capacity.OM-rich lithofacies with higher maturity have OM-pores with good connectivity,bearing large specific surface area that is beneficial for adsorbed gas capacity.
基金This research is financially supported by the National Natural Science Foundation of China(Grant 52074327,52288101)the Natural Science Foundation of Shandong Province,China(ZR2020QE107).
文摘The excellent mechanical properties of supramolecular gel could adapt to the complex reservoir environment and had broad application prospects in the field of oil and gas drilling and production engineering.In this paper,a supramolecular gel based on hydrophobic association and hydrogen bonding was prepared by micellar copolymerization,which could be used to plug fractures and pores in formations.Supramolecular gel was a gel network system with high performance characteristics formed by self-assembly of non-covalent bond interaction.The rheological properties,mechanical mechanics,temperature resistance and swelling ability of supramolecular gel were studied.The results showed that the supramolecular gel had a dense three-dimensional network structure with open and interconnected pore structures,which could exhibit good rheological properties and strong viscoelastic recovery ability.The mechanical properties of the supramolecular gel were excellent,it had a tensile stress of 0.703 MPa and an elongation at break of 1803%.When the compressive strain was 96%,the compressive stress could reach 14.5 MPa.Supramolecular gel also showed good temperature resistance and swelling properties.At the aging temperature of 135℃,supramolecular gels still maintained good gel strength,and it only took 12 h to reach the equilibrium swelling ratio of 35.87 in 1%NaCl solution.It was also found that supramolecular gel in low concentration saline(1%NaCl solution)showed relatively faster swelling than high concentration saline(25%NaCl solution).The swelling process of the supramolecular gel was non-Fick diffusion(typeⅡ).This indicated that the organic/inorganic permeability network was well formed.Therefore,the diffusion rate of small molecules could be guaranteed to be equal to the relaxation rate of large molecules before and after the phase transition temperature.In addition to the diffusion of water molecules,the swelling process of the supramolecular gel was also affected by the relaxation of gel network and polymer chain segment,the interaction between water molecules and polymer network and the groups of polymer network and other factors.Supramolecular gel particles could be used as plugging materials for drilling fluids,which had excellent ability to plug formation fractures and pores.The plugging ability of the supramolecular gel was up to 6.7 MPa for 0.5 mm fracture width,and 9.6 MPa for porous media with 5 mD permeability.Compared with HT-PPG gel particles commonly used in oil fields,supramolecular gel particles had better plugging ability on fractures and porous media.The development and application of supramolecular gel had far-reaching significance for promoting the functional application of polymer materials in drilling and production engineering.
基金supported by the National Natural Science Foundation of China-Shandong Joint Fund(Grant No.U2006226).
文摘Compliant vertical access risers(CVAR)have broad application prospects in deep-water oil and gas transportation.However,the mechanical behaviors of the CVAR with a variable length during installation remains unclear.To address this issue,based on the flexible segment method,a model of CVAR with a variable length during installation is established in this study,which is verified by the comparison with commercial software.Then,the mechanical behaviors of CVAR during installation are investigated.The results reveal that the CVAR configuration is significantly affected by the buoyancy blocks.The streamwise displacement of CVAR increases with the increase of current velocity.When the BOP weight is insuffcient,obvious upbending is observed in the lower region and transition region,leading to local compression.When the platform moves in the opposite direction to the current,the maximum stress is larger than that of the scenario when the platform moves in the same direction as the current.
基金financially supported by National Natural Science Foundation of China(No.52074330)National Natural Science Foundation of China Major Projects(No.51991361).
文摘With the exploration and development of deep and ultra-deep oil and gas,high torque and high friction during the drilling of deep and ultra-deep wells become one of the key issues affecting drilling safety and drilling speed.Meanwhile,the high temperature and high salt problem in deep formations is prominent,which poses a major challenge to the lubricity of drilling fluids under high temperature and high salt.This paper reports an organic borate ester SOP as an environmentally friendly drilling fluid lubricant.The performance evaluation results show that when 1%lubricant SOP is added to the fresh water-based mud,the lubrication coefficient decreases from 0.631 to 0.046,and the reduction rate of lubrication coefficient is 92.7%.Under the conditions of 210℃ and 30%NaCl,the reduction rate of lubricating coefficient of the base slurry with 1%SOP was still remain 81.5%.After adding 1%SOP,the wear volume decreased by 94.11%compared with the base slurry.The contact resistance experiment during the friction process shows that SOP can form a thick adsorption film on the friction surface under high temperature and high salt conditions,thus effectively reducing the friction resistance.Molecular dynamics simulation shows that lubricant SOP can be physically adsorbed on the surface of drilling tool and borehole wall through hydrogen bond and van der Waals force.XPS analysis further shows that SOP adsorbs on the friction surface and reacts with metal atoms on the friction surface to form a chemically reactive film.Therefore,under high temperature and high salt conditions,the synergistic effect of physical adsorption film and chemical reaction film effectively reduces the frictional resistance and wear of the friction surface.In addition,SOP is non-toxic and easy to degrade.Therefore,SOP is a highly effective and environmentally friendly lubricant in high temperature and high salt drilling fluid.
基金financial support of the National Nature Science Foundation of China(Grant No.U20B6003)the Natural Science Foundation of Shandong Province,China(ZR2020QE106).
文摘Steam flooding with the assistance of carbon dioxide (CO_(2)) and chemicals is an effective approach for enhancing super heavy oil recovery. However, the promotion and application of CO_(2) and chemical agent-assisted steam flooding technology have been restricted by the current lack of research on the synergistic effect of CO_(2) and chemical agents on enhanced steam flooding heat transfer. The novel experiments on CO_(2)–chemicals cooperate affected steam condensation and seepage were conducted by adding CO_(2) and two chemicals (sodium dodecyl sulfate (SDS) and the betaine temperature-salt resistant foaming agent ZK-05200).According to the experimental findings, a “film” formed on the heat-transfer medium surface following the co-injection of CO_(2) and the chemical to impede the steam heat transfer, reducing the heat transfer efficiency of steam, heat flux and condensation heat transfer coefficient. The steam seepage experiment revealed that the temperature at the back end of the sandpack model was dramatically raised by 3.5–12.8 °C by adding CO_(2) and chemical agents, achieving the goal of driving deep-formation heavy oil. The combined effect of CO_(2) and SDS was the most effective for improving steam heat transfer, the steam heat loss was reduced by 6.2%, the steam condensation cycle was prolonged by 1.3 times, the condensation heat transfer coefficient was decreased by 15.5%, and the heavy oil recovery was enhanced by 9.82%. Theoretical recommendations are offered in this study for improving the CO_(2)–chemical-assisted steam flooding technique.
文摘Low-Tension-Foam(LTF)flooding is an emerging enhanced oil recovery technique for low-permeability carbonate reservoirs.Foam capacity is closely related to the salinity environment(or,equivalently,the phase behavior of the oil/water/surfactant system).Therefore,the interactions between microemulsion and foam components are of primary importance in the LTF process.In this study,the phase behavior of an oil/water/surfactant system under equilibrium is analyzed,firstly by assuming perfect mixing.Meanwhile,the formation kinetics of microemulsion are monitored through a novel low-field NMR technique,which is able to provide quantitative assessment on the microemulsion evolution characteristics.Then,foam stability is examined in the absence and in the presence of Winsor-Ⅰ and Winsor-Ⅲ type microemulsions.It is revealed that foam stability depends on the oil solubilization(oil swollen micelle size).A decrease in the oil swollen micelle size and micellar structure effectiveness,in conjunction with an increasing salinity,leads to lower foam stability in the presence of a Winsor-Ⅲ type microemulsion.
基金supported by the National Natural Science Foundation of China(No.U2006226)the National Key Research and Development Program of China(No.2016YFC0303800)。
文摘The mechanical behavior,dynamic evolution,and flow-field distribution of a two-degree-of-freedom riserless drill string were simulated numerically by using FLUENT fluid simulation software with the user-defined function embedded.The rotation angular velocities before and after the critical rotation angular velocity were used as independent variables,and the reduced velocity range was 3-14.Fluid-structure coupling was realized based on the dynamic overset grid and the SST k-ωturbulence model.Results reveal that the dynamic response of the riserless drill string was considerably affected by rotation and flow velocity,which are coupled with each other.The cross-flow average dimensionless displacement increased with the rotation angular velocity,and rotation considerably enhanced the in-line maximum average dimensionless displacement.However,the cross-flow amplitude caused by vortex-induced vibration was suppressed when the rotation angular velocity reached a certain value.The in-line and cross-flow frequencies were the same,thereby causing the trajectory to deviate from the standard'figure-eight'shape and become a closed circle shape.The vortex did not fall behind the cylinder at low reduced velocity with high-rotation angular velocity,and the structure of the near-wake vortex remained U-shaped.The wake of the cylinder was deflected along the cross-flow direction,thereby leading to vibration asymmetry and resulting in increased vibration instability and disordered vibration trajectories,especially at high-rotation angular velocities.
基金The authors sincerely appreciate the financial support from the National Natural Science Foundation of China(No.52074249,51874261)Fundamental Research Funds for the Central Universities(2-9-2019-103).
文摘Due to the low porosity and low permeability in unconventional reservoirs,a large amount of crude oil is trapped in micro-to nano-sized pores and throats,which leads to low oil recovery.Nanofluids have great potential to enhance oil recovery(EOR)in low permeability reservoirs.In this work,the regulating ability of a nanofluid at the oil/water/solid three-phase interface was explored.The results indicated that the nanofluid reduced the oil/water interfacial tension by two orders of magnitude,and the expansion modulus of oil/water interface was increased by 77% at equilibrium.In addition,the solid surface roughness was reduced by 50%,and the three-phase contact angle dropped from 135(oil-wet)to 48(water-wet).Combining the displacement experiments using a 2.5D reservoir micromodel and a microchannel model,the remaining oil mobilization and migration processes in micro-to nano-scale pores and throats were visualized.It was found that the nanofluid dispersed the remaining oil into small oil droplets and displaced them via multiple mechanisms in porous media.Moreover,the high strength interface film formed by the nanofluid inhibited the coalescence of oil droplets and improved the flowing ability.These results help to understand the EOR mechanisms of nanofluids in low permeability reservoirs from a visual perspective.
