Black nanosheets(BNs),as a highly promising fracturing-EOR integrated enhancement material,require further study of their huff-n-puff performance and mechanism.This work characterized nanoscale structure,stability,and...Black nanosheets(BNs),as a highly promising fracturing-EOR integrated enhancement material,require further study of their huff-n-puff performance and mechanism.This work characterized nanoscale structure,stability,and interfacial properties of BNs,then evaluated their huff-and-puff performance through NMR-assisted core flooding experiments.The adaptability of BNs in low-permeability reservoirs with different permeabilities,as well as the effect of huff-n-puff cycles on their oil recovery performance,were analyzed.Results show that anionic modified BNs maintained nanoscale flake structure with enhanced electrostatic repulsion.The BNs with an extremely low concentration of 0.002 wt%exhibited excellent emulsification and stabilization effects on crude oil and wettability alteration of the rock surface.Compared with injection water,BNs had excellent huff-n-puff oil recovery effects,reaching 22.1%original oil in place(OOIP)after the first huff-n-puff cycle.BNs had good adaptability in low-permeability cores(i.e.,0.1×10^(−3) to 10×10^(−3)μm^(2)).Increasing the huff-n-puff cycle significantly improved the oil recovery effect of BNs,and the optimal performance was at 4 cycles.As the huff-n-puff cycle increased from 3 to 4,the ability of BNs to“automatic oil-seeking”in micropores became more prominent.This paper also innovatively combined core nuclear magnetic resonance(NMR)T2 analysis,nuclear magnetic imaging analysis,and longitudinal T2 signal analysis along the core(i.e.,along the core injection length).It can not only more accurately quantify the huff-n-puff recovery effect of low-permeability cores but also quantitatively analyze the penetration depth and microscopic huff-n-puff mechanism of BNs from a microscopic perspective.These findings are helpful for the selection of nanomaterials and mechanism analysis in the design of integrated fracturing-flooding schemes and processes.展开更多
A flexible sidetracking stimulation technology of horizontal wells is formed to develop the lateral deep remaining oil and gas resources of the low-permeability mature oilfields.This technology first uses the flexible...A flexible sidetracking stimulation technology of horizontal wells is formed to develop the lateral deep remaining oil and gas resources of the low-permeability mature oilfields.This technology first uses the flexible sidetracking tool to achieve low-cost sidetracking in the old wellbore,and then uses the hydraulic jet technology to induce multiple fractures to fracture.Finally,the bullhead fracturing of multi-cluster temporary plugging for the sidetracking hole is carried out by running the tubing string,to realize the efficient development of the remaining reserves among the wells.The flexible sidetracking stimulation technology involves flexible sidetracking horizontal wells drilling and sidetracking horizontal well fracturing.The flexible sidetracking horizontal well drilling includes three aspects:flexible drill pipe structure and material optimization,drilling technology,and sealed coring tool.The sidetracking horizontal well fracturing includes two aspects:fracturing scheme optimization,fracturing tools and implementation process optimization.The technology has been conducted several rounds of field tests in the Ansai Oilfield of Changqing,China.The results show that by changing well type and reducing row spacing of oil and water wells,the pressure displacement system can be well established to achieve effective pressure transmission and to achieve the purpose of increasing liquid production in low-yield and low-efficiency wells.It is verified that the flexible sidetracking stimulation technology can provide favorable support for accurately developing remaining reserves in low-permeability reservoirs.展开更多
Due to severe mass transfer limitations,the remediation efficiency of low-permeability contaminated sites often fails to meet expectations.Hydraulic fracturing technology has been utilized to enhance amendment deliver...Due to severe mass transfer limitations,the remediation efficiency of low-permeability contaminated sites often fails to meet expectations.Hydraulic fracturing technology has been utilized to enhance amendment delivery,but the influence of soil heterogeneity is commonly overlooked.To address this issue,this study develops a numerical model to simulate the enhanced transport of amendments,incorporating convection,diffusion,adsorption,and degradation processes.Within the model,random permeability fields are generated based on geostatistical methods to explore how soil heterogeneity affects amendment injection efficiency,distribution characteristics,and the underlying physical mechanisms.The results indicate that(1)soil heterogeneity significantly reduces the amendment injection efficiency,with stronger heterogeneity correlating to lower efficiency,(2)soil heterogeneity markedly alters the amendment distribution characteristics,leading to the formation of localized“nodes”,(3)the mechanism by which heterogeneity reduces injection efficiency involves decreasing the density of preferential flow paths in the soil,and(4)the adverse effects of heterogeneity can be mitigated by employing pressure compensation or adjusting well spacing.展开更多
Low-permeability heavy oil reservoirs are characterized by poor flowability, generally mandating hydraulic fracturing to commence production. CO_(2) huff-n-puff in fractured reservoirs is an effective enhanced oil rec...Low-permeability heavy oil reservoirs are characterized by poor flowability, generally mandating hydraulic fracturing to commence production. CO_(2) huff-n-puff in fractured reservoirs is an effective enhanced oil recovery method. This paper uses nuclear magnetic resonance imaging to elucidate the role of propped and unpropped fractures on CO_(2) huff-n-puff in cores under different confining pressures. In presence of fractures, significant improvement in the rate of early stage oil recovery is observed, up to 0.255 mL/min. Fractures enlarge the contact area between CO_(2) and the heavy oil, hence improve CO_(2) dissolution and oil flowability. Fractures improve oil recovery from micropores, small pores, and mesopores, as well as reduce CO_(2) consumption ratio. The oil recovery factor in propped fractures is significantly higher than that in unpropped fractures, and with higher oil recovery from small pores and mesopores. The oil recovery in fractured cores noticeably decreases with increasing confining pressure. The extent of fracture closure increases and the matrix pore throats compress under pressure leading to lower apparent permeability. The decrease in oil recovery factor is more pronounced in unpropped fractured cores. A relationship between the apparent permeability of the fracture aperture is derived based on the modified cubic law of percolation to quantitatively characterize the fracture. Additionally, both the reduction in heavy oil viscosity and the increase in experimental temperature and pressure can improve the CO_(2) huff-n-puff oil recovery factor in fractured cores.展开更多
The relative permeability of oil and water is a key factor in assessing the production performance of a reservoir.This study analyzed the impact of injecting a viscosity reducer solution into low-viscosity crude oil t...The relative permeability of oil and water is a key factor in assessing the production performance of a reservoir.This study analyzed the impact of injecting a viscosity reducer solution into low-viscosity crude oil to enhance fluid flow within a low-permeability reservoir.At 72°C,the oil-water dispersion solution achieved a viscosity reduction rate(f)of 92.42%,formulated with a viscosity reducer agent concentration(C_(VR))of 0.1%and an oil-water ratio of 5:5.The interfacial tension between the viscosity reducer solution and the crude oil remained stable at approximately 1.0 mN/m across different concentrations,with the minimum value of 4.07×10^(-1)mN/m recorded at a C_(VR)of 0.2%.As the CVR increased,the relative permeability curve of the oil phase gradually decreased while the oil-water two-phase region(Ro-wtp)expanded significantly.At a C_(VR)of 0.1%,the R_(o-wtp)peaked,making an increase of 7.93 percentage points compared to water flooding.In addition,the final displacement efficiency(E_(R),final)achieved with a 0.1%viscosity reducer solution reached 48.64%,exceeding water flooding by 15.46 percentage points,highlighting the effectiveness of the viscosity reducer solution in enhancing oil recovery.展开更多
Injection-production coupling(IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency.Despite this potential,discussion on gas injection coupling,especially in relation ...Injection-production coupling(IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency.Despite this potential,discussion on gas injection coupling,especially in relation to microscopic mechanisms,remains relatively sparse.This study utilizes microscopic visualization experiments to investigate the mechanisms of residual oil mobilization under various IPC scenarios,complemented by mechanical analysis at different stages.The research quantitatively assesses the degree of microscopic oil recovery and the distribution of residual oil across different injection-production methods.Findings reveal that during the initial phase of continuous gas injection(CGI),the process closely mimics miscible displacement,gradually transitioning to immiscible displacement as CO_(2)extraction progresses.Compared to CGI,the asynchronous injection-production(AIP) method improved the microscopic oil recovery rate by 6.58%.This enhancement is mainly attributed to significant variations in the pressure field in the AIP method,which facilitate the mobilization of columnar and porous re sidual oil.Furthermo re,the synchronous cycle injection(SCI) method increased microscopic oil recovery by 13.77% and 7.19% compared to CGI and AIP,respectively.In the SCI method,membrane oil displays filame ntary and Karman vo rtex street flow patterns.The dissolved and expanded crude oil te nds to accumulate and grow at the oil-solid interface due to adhesive forces,thereby reducing migration resistance.The study findings provide a theoretical foundation for improving oil recovery in lowpermeability reservoirs.展开更多
Due to severe mass transfer limitations,contaminated soils with low-permeability limit the accessibility of amendments,resulting in less effective or even ineffective remediation.Enhancing the mass transfer properties...Due to severe mass transfer limitations,contaminated soils with low-permeability limit the accessibility of amendments,resulting in less effective or even ineffective remediation.Enhancing the mass transfer properties of low-permeability soils by hydraulic fracturing is a promising technique.A quasi-three-dimensional(quasi-3D)analytical model was presented that accounted for advection-diffusion-adsorption-degradation processes in the fracture-matrix system.The model combined the injection-extraction technique to investigate the enhanced transport of amendments in low-permeability contaminated soil by hydraulic fractures.Then,the injection strategy and controllable parameter optimization were comprehensively studied by analyzing the radial transport behavior of the amendment within hydraulic fractures.The results showed that higher injection volumetric rates accelerated the formation of a uniform line source within the fractures.Although the differences in the effective ratio of the amendment among different injection modes were not significant,considering the amendment utilization rate and cost reduction,the recommended injection strategy was the combination of continuous pulsing injection and periodic injection.展开更多
Well testing is recognized as an effective means of accurately obtaining the formation parameters of low-permeability reservoirs and effectively analyzing the deliverability.Well test models must comply with the parti...Well testing is recognized as an effective means of accurately obtaining the formation parameters of low-permeability reservoirs and effectively analyzing the deliverability.Well test models must comply with the particular characteristics of flow in low-permeability reservoirs in order to obtain reasonable well test interpretation.At present,non-Darcy flow in low-permeability reservoirs is attracting much attention.In this study,displacement tests were conducted on typical cores taken from low-permeability reservoirs.Two dimensionless variables were introduced to analyze the collected experimental data.The results of the dimensionless analysis show whether non-Darcy flow happens or not depends on the properties of fluid and porous media and the pressure differential.The combination of the above three parameters was named as dimensionless criteria coefficient（DCC）.When the value of the DCC was lower than a critical Reynolds number（CRN）,the flow could not be well described by Darcy＇s law（so-called non-Darcy flow）,when the DCC was higher than CRN,the flow obeyed Darcy＇s law.Finally,this paper establishes a transient mathematical model considering Darcy flow and non-Darcy flow in low-permeability reservoirs,and proposes a methodology to solve the model.The solution technique,which is based on the Boltzmann transformation,is well suited for solving the flow model of low-permeability reservoirs.Based on the typical curves analysis,it was found that the pressure and its derivative curves were determined by such parameters as non-Darcy flow index and the flow characteristics.The results can be used for well test analysis of low-permeability reservoirs.展开更多
Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or ca...Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil （gas） saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone （oil displacing water）, we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that： 1） Oil migration （oil displacing water） in low- permeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2） With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fluidity is more than 1.0, the percolation curve shows modified Darcy flow characteristics, while when the apparent fluidity up＂ non-Darcy percolation curve; 3） Oil-water is less than 1.0, the percolation curve is a ＂concave- two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4） The oil saturation of low- permeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fluidity.展开更多
The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite f...The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite from an underground oil storage depot were measured. In order to study the influence of rock types on permeability, a tight sandstone was selected as a contrast. The experimental results suggested that the porosity of this granite is less than 5% and permeability is low to 10–20 m^2 within the range of effective stress. During the loading process, both exponential relationship and power law can be utilized to describe the relationship between effective stress and permeability. However, power law matches the experimental data better during the unloading condition. The stress dependent porosity of granite during loading process can be described via an exponential relationship while the match between the model and experimental data can be improved by a power law in unloading paths. The correlation of permeability and porosity can be described in a power law form. Besides, granite shows great different evolution rules in permeability and porosity from sandstone. It is inferred that this difference can be attributed to the preparing of samples and different movements of microstructures subjected to effective stress.展开更多
The genesis of a reservoir is a result of the combined action of deposition, diagenesis, tectonic reworking, and interaction of rock and fluid and the evolutionary environment. We discuss the genetic and evolution mec...The genesis of a reservoir is a result of the combined action of deposition, diagenesis, tectonic reworking, and interaction of rock and fluid and the evolutionary environment. We discuss the genetic and evolution mechanism of a low-permeability reservoir bed of the Xujiahe Formation in the western Sichuan Depression on the basis of the study of diagenesis, diagenetic reservoir facies and the diagenetic evolution sequence. The research indicated that this reservoir bed can be divided into five types of diagenetic reservoir facies, namely strong dissolution, chlorite-lined intergranular pores, compaction and pressure solution, carbonate cementation and secondary quartz increase. There are, however, just two diagenetic reservoir facies which provide low-permeability reservoir beds, namely strong dissolution and chlorite-lined intergranular pores. We also analyzed their diagenetic evolution sequences and the origin of the low-permeability reservoir bed. Besides, it was also indicated that the composition and structure of sandstones, types of sedimentary microfacies, diagenesis history as well as the tectonic reworking in later periods are the main factors controlling the formation of the low-permeability reservoir bed. The above- mentioned factors establish the foundation for the forecasting the distribution of high quality reservoir beds.展开更多
The formation and distribution of fractures are controlled by paleotectonic stress field, and their preservative status and effects on development are dominated by the modern stress field. Since Triassic, it has exper...The formation and distribution of fractures are controlled by paleotectonic stress field, and their preservative status and effects on development are dominated by the modern stress field. Since Triassic, it has experienced four tectonic movements and developed four sets of tectonic fractures in the extra low-permeability sandstone reservoir at the south of western Sichuan depression. The strikes of fractures are in the S-N, NE-SW, E-W, and NW-SE directions respectively. At the end of Triassic, under the horizontal compression tectonic stress field, for which the maximum principal stress direction was NW.SE, the fractures were well developed near the S-N faults and at the end of NE-SW faults, because of their stress concentration. At the end of Cretaceous, in the horizontal compression stress fields of the NE-SW direction, the stress was obviously lower near the NE-SW faults, thus, fractures mainly developed near the S-N faults. At the end of Neogene-Early Pleistocene, under the horizontal compression tectonic stress fields of E-W direction, stress concentrated near the NE-SW faults and fractures developed at these places, especially at the end of the NE-SE faults, the cross positions of NE-SW, and S-N faults. Therefore, fractures developed mostly near S-N faults and NE-SW faults. At the cross positions of the above two sets of faults, the degree of development of the fractures was the highest. Under the modern stress field of the NW-SE direction, the NW-SE fractures were mainly the seepage ones with tensional state, the best connectivity, the widest aperture, the highest permeability, and the minimum opening pressure.展开更多
In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement proce...In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement process for oil recovery.Asynchronous injection-production modes can use supercritical CO_(2)to enhance oil recovery but may also worsen the injection capacity.Cores with high permeability have higher oil recovery rates and better injection capacity,however,gas channeling occurs.Supercritical CO_(2)flooding has a higher oil recovery at high pressure levels,which delays the occurrence of gas channeling.Conversely,gas injection has lower displacement efficiency but better injection capacity at the high water cut stage.This study analyzes the displacement characteristics of supercritical CO_(2)flooding with a series of experiments under different injection and production parameters.Experimental results show that the gas breakthrough stage has the fastest oil production and the supercritical CO_(2)injection capacity variation tendency is closely related to the gas-oil ratio.Further experiments show that higher injection rates represent significant ultimate oil recovery and injection index,providing a good reference for developing low-permeability reservoirs.展开更多
In the process of in situ leaching of uranium,the microstructure controls and influences the flow distribution,percolation characteristics,and reaction mechanism of lixivium in the pores of reservoir rocks and directl...In the process of in situ leaching of uranium,the microstructure controls and influences the flow distribution,percolation characteristics,and reaction mechanism of lixivium in the pores of reservoir rocks and directly affects the leaching of useful components.In this study,the pore throat,pore size distribution,and mineral composition of low-permeability uranium-bearing sandstone were quantitatively analyzed by high pressure mercury injection,nuclear magnetic resonance,X-ray diffraction,and wavelength-dispersive X-ray fluorescence.The distribution characteristics of pores and minerals in the samples were qualitatively analyzed using energy-dispersive scanning electron microscopy and multi-resolution CT images.Image registration with the landmarks algorithm provided by FEI Avizo was used to accurately match the CT images with different resolutions.The multi-scale and multi-mineral digital core model of low-permeability uranium-bearing sandstone is reconstructed through pore segmentation and mineral segmentation of fusion core scanning images.The results show that the pore structure of low-permeability uranium-bearing sandstone is complex and has multi-scale and multi-crossing characteristics.The intergranular pores determine the main seepage channel in the pore space,and the secondary pores have poor connectivity with other pores.Pyrite and coffinite are isolated from the connected pores and surrounded by a large number of clay minerals and ankerite cements,which increases the difficulty of uranium leaching.Clays and a large amount of ankerite cement are filled in the primary and secondary pores and pore throats of the low-permeability uraniumbearing sandstone,which significantly reduces the porosity of the movable fluid and results in low overall permeability of the cores.The multi-scale and multi-mineral digital core proposed in this study provides a basis for characterizing macroscopic and microscopic pore-throat structures and mineral distributions of low-permeability uranium-bearing sandstone and can better understand the seepage characteristics.展开更多
According to the geological characteristics and their influential factors of the low-permeability reservoirs, a comprehensive method for evaluation of low-permeability reservoirs is put forward. The method takes a mat...According to the geological characteristics and their influential factors of the low-permeability reservoirs, a comprehensive method for evaluation of low-permeability reservoirs is put forward. The method takes a matrix system as the basis, a fracture system as the focus and a stress field system as the restricted factor. It can objectively reflect not only the storage capability and seepage capability of low-permeability reservoirs, but also the effect on development as well. At the same time, it can predict the seepage characteristics at different development stages and provide a reasonable geological basis for the development of low-permeability reservoirs.展开更多
As the traditional polymer stabilizer is eliminated to improve the injectability of foam in lowpermeability reservoirs,the stability,plugging capacity,conformance control and oil recovery performance of the surfactant...As the traditional polymer stabilizer is eliminated to improve the injectability of foam in lowpermeability reservoirs,the stability,plugging capacity,conformance control and oil recovery performance of the surfactant-alternating-gas(SAG)foam become significantly important for determining its adaptability to permeability and heterogeneity,which were focused and experimentally researched in this paper.Results show that the SAG bubbles are highly stable in micron-sized channels and porous media(than in the conventional unconstrained graduated cylinder),making it possible to use in enhanced oil recovery(EOR).Such bubbles formed in porous media could be passively adjusted to match their diameter with the size of the pore.This endows the SAG foam with underlying excellent injectability and deep migration capacity.Permeability adaptability results indicate a reduced plugging capacity,but,increased incremental oil recovery by the SAG foam with decreased permeability.This makes it a good candidate for EOR over a wide range of permeability,however,parallel core floods demonstrate that there is a limiting heterogeneity for SAG application,which is determined to be a permeability contrast of 12.0(for a reservoir containing oil of 9.9 m Pa s).Beyond this limit,the foam would become ineffective.展开更多
Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas...Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas production,and it is necessary to reduce the effect of ice production on gas production.In this work,a new combination of fracturing technology and depressurization method was proposed to evaluate the gas production potential at the site DK-2 in Qinghai-Tibet Plateau Permafrost.A relatively higher intrinsic permeability of the fracture zone surround the horizontal production well was created by the fracturing technology.The simulation results showed that the fracture zone reduced the blocking of production ice to production wells and promoted the propagation of production pressure.And the gas production increased by 2.1 times as the radius of the fracture zone increased from 0 to 4 m in 30 years.Nearly half of the hydrate reservoirs were dissociated in 30 years,and greater than 51.7%of the gas production was produced during the first 10 years.Moreover,production behaviours were sensitive to the depressurization driving force but not to the thermal conductivity.The growth of gas production was not obvious with the intrinsic permeability of the fracture zone higher than 100 m D.The effect of ice production on gas production by fracturing technology and depressurization method was limited.展开更多
This paper discusses the systematic design and development of low-damage drilling fluid to protect the low-permeability gas reservoir of the Sulige block in the Ordos Basin, Inner Mongolia Autonomous Region, China. Ba...This paper discusses the systematic design and development of low-damage drilling fluid to protect the low-permeability gas reservoir of the Sulige block in the Ordos Basin, Inner Mongolia Autonomous Region, China. Based on investigation of the geological characteristics and the potential formation damage of the Permian formation of the reservoir, waterblocking due to invasion of drilling or completion fluids was identified one of the most severe causes of damage to gas well deliverability. By adopting the phase trap prevention method, ideal packing theory, and film-forming technology, a lowdamage drilling fluid, sodium formate brine containing efficient waterblocking preventing surfactants, optimized temporary bridging agents （TBAs）, and film-forming agents has been developed. The performance of the new drilling fluid was evaluated by using a variety of techniques. The results show that the fluid has good rheological properties, good strong shale-swelling inhibition, good temporary plugging effect, ultra-low filtration, and good lubricity. It can efficiently minimize waterblocking and can be used to drill horizontal wells with minimal intervention of the reservoir in the Sulige Gas Field.展开更多
Nanocellulose,a natural polymeric nanomaterial,has attracted significant attention in enhanced oil recovery(EOR)applications due to its abundance,nanoscale,high oil-water interfacial adsorption ef-ficiency.In this stu...Nanocellulose,a natural polymeric nanomaterial,has attracted significant attention in enhanced oil recovery(EOR)applications due to its abundance,nanoscale,high oil-water interfacial adsorption ef-ficiency.In this study,surface-functionalized cellulose nanocrystals(SF-CNCs)were prepared via hy-drochloric acid hydrolysis and chemical modification,with adaptable nanosize and considerable dispersion stability in low-permeability reservoirs.The SF-CNCs were structurally characterized by FT-IR,Cryo-TEM,which have a diameter of 5-10 nm and a length of 100-200 nm.The SF-CNC dispersions possessed higher stability and stronger salt-tolerance than those of corresponding CNC dispersions,due to the strong hydrophilicity of the sulfonic acid group.It was synergistically used with a non-ionic surfactant(APG1214)to formulate a combined flooding system(0.1 wt%SF-CNC+0.2 wt%APG1214).The combined flooding system exhibits strong emulsification stability,low oil-water interfacial tension of o.03 mN/m,and the ability to alter the wettability for oil-wetting rocks.Furthermore,the combined system was_able to provide an optimum EOR efficiency of 20.2%in low-permeability cores with 30.13×10^(-3)μm^(2).Notably.it can enlarge the sweep volume and increase the displacement efficiency simultaneously.Overall,the newly formulated nanocellulose/surfactant combined system exhibits a remarkable EoR performance in low-permeability reservoirs.展开更多
The transverse relaxation time (T_(2)) cut-off value plays a crucial role in nuclear magnetic resonance for identifying movable and immovable boundaries, evaluating permeability, and determining fluid saturation in pe...The transverse relaxation time (T_(2)) cut-off value plays a crucial role in nuclear magnetic resonance for identifying movable and immovable boundaries, evaluating permeability, and determining fluid saturation in petrophysical characterization of petroleum reservoirs. This study focuses on the systematic analysis of T_(2) spectra and T_(2) cut-off values in low-permeability reservoir rocks. Analysis of 36 low-permeability cores revealed a wide distribution of T_(2) cut-off values, ranging from 7 to 50 ms. Additionally, the T_(2) spectra exhibited multimodal characteristics, predominantly displaying unimodal and bimodal morphologies, with a few trimodal morphologies, which are inherently influenced by different pore types. Fractal characteristics of pore structure in fully water-saturated cores were captured through the T_(2) spectra, which were calculated using generalized fractal and multifractal theories. To augment the limited dataset of 36 cores, the synthetic minority oversampling technique was employed. Models for evaluating the T_(2) cut-off value were separately developed based on the classified T_(2) spectra, considering the number of peaks, and utilizing generalized fractal dimensions at the weight <0 and the singular intensity range. The underlying mechanism is that the singular intensity and generalized fractal dimensions at the weight <0 can detect the T_(2) spectral shift. However, the T_(2) spectral shift has negligible effects on multifractal spectrum function difference and generalized fractal dimensions at the weight >0. The primary objective of this work is to gain insights into the relationship between the kurtosis of the T_(2) spectrum and pore types, as well as to predict the T_(2) cut-off value of low-permeability rocks using machine learning and data augmentation techniques.展开更多
文摘Black nanosheets(BNs),as a highly promising fracturing-EOR integrated enhancement material,require further study of their huff-n-puff performance and mechanism.This work characterized nanoscale structure,stability,and interfacial properties of BNs,then evaluated their huff-and-puff performance through NMR-assisted core flooding experiments.The adaptability of BNs in low-permeability reservoirs with different permeabilities,as well as the effect of huff-n-puff cycles on their oil recovery performance,were analyzed.Results show that anionic modified BNs maintained nanoscale flake structure with enhanced electrostatic repulsion.The BNs with an extremely low concentration of 0.002 wt%exhibited excellent emulsification and stabilization effects on crude oil and wettability alteration of the rock surface.Compared with injection water,BNs had excellent huff-n-puff oil recovery effects,reaching 22.1%original oil in place(OOIP)after the first huff-n-puff cycle.BNs had good adaptability in low-permeability cores(i.e.,0.1×10^(−3) to 10×10^(−3)μm^(2)).Increasing the huff-n-puff cycle significantly improved the oil recovery effect of BNs,and the optimal performance was at 4 cycles.As the huff-n-puff cycle increased from 3 to 4,the ability of BNs to“automatic oil-seeking”in micropores became more prominent.This paper also innovatively combined core nuclear magnetic resonance(NMR)T2 analysis,nuclear magnetic imaging analysis,and longitudinal T2 signal analysis along the core(i.e.,along the core injection length).It can not only more accurately quantify the huff-n-puff recovery effect of low-permeability cores but also quantitatively analyze the penetration depth and microscopic huff-n-puff mechanism of BNs from a microscopic perspective.These findings are helpful for the selection of nanomaterials and mechanism analysis in the design of integrated fracturing-flooding schemes and processes.
基金Supported by the National Key Research and Development Program of China(2023YFF0615403)CNPC Science and Technology Project(2023ZZ0803).
文摘A flexible sidetracking stimulation technology of horizontal wells is formed to develop the lateral deep remaining oil and gas resources of the low-permeability mature oilfields.This technology first uses the flexible sidetracking tool to achieve low-cost sidetracking in the old wellbore,and then uses the hydraulic jet technology to induce multiple fractures to fracture.Finally,the bullhead fracturing of multi-cluster temporary plugging for the sidetracking hole is carried out by running the tubing string,to realize the efficient development of the remaining reserves among the wells.The flexible sidetracking stimulation technology involves flexible sidetracking horizontal wells drilling and sidetracking horizontal well fracturing.The flexible sidetracking horizontal well drilling includes three aspects:flexible drill pipe structure and material optimization,drilling technology,and sealed coring tool.The sidetracking horizontal well fracturing includes two aspects:fracturing scheme optimization,fracturing tools and implementation process optimization.The technology has been conducted several rounds of field tests in the Ansai Oilfield of Changqing,China.The results show that by changing well type and reducing row spacing of oil and water wells,the pressure displacement system can be well established to achieve effective pressure transmission and to achieve the purpose of increasing liquid production in low-yield and low-efficiency wells.It is verified that the flexible sidetracking stimulation technology can provide favorable support for accurately developing remaining reserves in low-permeability reservoirs.
基金supported by the National Natural Science Foundation of China(Grant Nos.42227804 and 42402279)the Natural Science Foundation of Shanghai(Grant No.24ZR1467500).
文摘Due to severe mass transfer limitations,the remediation efficiency of low-permeability contaminated sites often fails to meet expectations.Hydraulic fracturing technology has been utilized to enhance amendment delivery,but the influence of soil heterogeneity is commonly overlooked.To address this issue,this study develops a numerical model to simulate the enhanced transport of amendments,incorporating convection,diffusion,adsorption,and degradation processes.Within the model,random permeability fields are generated based on geostatistical methods to explore how soil heterogeneity affects amendment injection efficiency,distribution characteristics,and the underlying physical mechanisms.The results indicate that(1)soil heterogeneity significantly reduces the amendment injection efficiency,with stronger heterogeneity correlating to lower efficiency,(2)soil heterogeneity markedly alters the amendment distribution characteristics,leading to the formation of localized“nodes”,(3)the mechanism by which heterogeneity reduces injection efficiency involves decreasing the density of preferential flow paths in the soil,and(4)the adverse effects of heterogeneity can be mitigated by employing pressure compensation or adjusting well spacing.
基金supported by the Open Research Fund of State Key Laboratory of Deep Oil and Gas (No. SKLDOG2024-KFYB-14)the support received from the National Nature Science Foundation of China under Grant No. U20B6003China Scholarship Council (CSC) for financial support
文摘Low-permeability heavy oil reservoirs are characterized by poor flowability, generally mandating hydraulic fracturing to commence production. CO_(2) huff-n-puff in fractured reservoirs is an effective enhanced oil recovery method. This paper uses nuclear magnetic resonance imaging to elucidate the role of propped and unpropped fractures on CO_(2) huff-n-puff in cores under different confining pressures. In presence of fractures, significant improvement in the rate of early stage oil recovery is observed, up to 0.255 mL/min. Fractures enlarge the contact area between CO_(2) and the heavy oil, hence improve CO_(2) dissolution and oil flowability. Fractures improve oil recovery from micropores, small pores, and mesopores, as well as reduce CO_(2) consumption ratio. The oil recovery factor in propped fractures is significantly higher than that in unpropped fractures, and with higher oil recovery from small pores and mesopores. The oil recovery in fractured cores noticeably decreases with increasing confining pressure. The extent of fracture closure increases and the matrix pore throats compress under pressure leading to lower apparent permeability. The decrease in oil recovery factor is more pronounced in unpropped fractured cores. A relationship between the apparent permeability of the fracture aperture is derived based on the modified cubic law of percolation to quantitatively characterize the fracture. Additionally, both the reduction in heavy oil viscosity and the increase in experimental temperature and pressure can improve the CO_(2) huff-n-puff oil recovery factor in fractured cores.
基金supported by the Petrochina Daqing Oilfield Research Project(No.DQYT-1201002-2023-JS-1201).
文摘The relative permeability of oil and water is a key factor in assessing the production performance of a reservoir.This study analyzed the impact of injecting a viscosity reducer solution into low-viscosity crude oil to enhance fluid flow within a low-permeability reservoir.At 72°C,the oil-water dispersion solution achieved a viscosity reduction rate(f)of 92.42%,formulated with a viscosity reducer agent concentration(C_(VR))of 0.1%and an oil-water ratio of 5:5.The interfacial tension between the viscosity reducer solution and the crude oil remained stable at approximately 1.0 mN/m across different concentrations,with the minimum value of 4.07×10^(-1)mN/m recorded at a C_(VR)of 0.2%.As the CVR increased,the relative permeability curve of the oil phase gradually decreased while the oil-water two-phase region(Ro-wtp)expanded significantly.At a C_(VR)of 0.1%,the R_(o-wtp)peaked,making an increase of 7.93 percentage points compared to water flooding.In addition,the final displacement efficiency(E_(R),final)achieved with a 0.1%viscosity reducer solution reached 48.64%,exceeding water flooding by 15.46 percentage points,highlighting the effectiveness of the viscosity reducer solution in enhancing oil recovery.
基金supported by the National Natural Science Foundation of China (Nos.52374064,51974347,52474072)the Shandong Provincial Universities Youth Innovation and Technology Support Program (2022KJ065)。
文摘Injection-production coupling(IPC) technology holds substantial potential for boosting oil recovery and enhancing economic efficiency.Despite this potential,discussion on gas injection coupling,especially in relation to microscopic mechanisms,remains relatively sparse.This study utilizes microscopic visualization experiments to investigate the mechanisms of residual oil mobilization under various IPC scenarios,complemented by mechanical analysis at different stages.The research quantitatively assesses the degree of microscopic oil recovery and the distribution of residual oil across different injection-production methods.Findings reveal that during the initial phase of continuous gas injection(CGI),the process closely mimics miscible displacement,gradually transitioning to immiscible displacement as CO_(2)extraction progresses.Compared to CGI,the asynchronous injection-production(AIP) method improved the microscopic oil recovery rate by 6.58%.This enhancement is mainly attributed to significant variations in the pressure field in the AIP method,which facilitate the mobilization of columnar and porous re sidual oil.Furthermo re,the synchronous cycle injection(SCI) method increased microscopic oil recovery by 13.77% and 7.19% compared to CGI and AIP,respectively.In the SCI method,membrane oil displays filame ntary and Karman vo rtex street flow patterns.The dissolved and expanded crude oil te nds to accumulate and grow at the oil-solid interface due to adhesive forces,thereby reducing migration resistance.The study findings provide a theoretical foundation for improving oil recovery in lowpermeability reservoirs.
基金supported by the National Key Research and Development Program of China (Grant No.2020YFC1808104)the National Natural Science Foundation of China (Grant Nos.42227804 and 41931289).
文摘Due to severe mass transfer limitations,contaminated soils with low-permeability limit the accessibility of amendments,resulting in less effective or even ineffective remediation.Enhancing the mass transfer properties of low-permeability soils by hydraulic fracturing is a promising technique.A quasi-three-dimensional(quasi-3D)analytical model was presented that accounted for advection-diffusion-adsorption-degradation processes in the fracture-matrix system.The model combined the injection-extraction technique to investigate the enhanced transport of amendments in low-permeability contaminated soil by hydraulic fractures.Then,the injection strategy and controllable parameter optimization were comprehensively studied by analyzing the radial transport behavior of the amendment within hydraulic fractures.The results showed that higher injection volumetric rates accelerated the formation of a uniform line source within the fractures.Although the differences in the effective ratio of the amendment among different injection modes were not significant,considering the amendment utilization rate and cost reduction,the recommended injection strategy was the combination of continuous pulsing injection and periodic injection.
基金supported by the National Natural Science Foundation of China(Grant No.40974055)the National Key Technology R&D Program in the 11th Five-Year Plan Period(Grant No.2008ZX05030-005-03)
文摘Well testing is recognized as an effective means of accurately obtaining the formation parameters of low-permeability reservoirs and effectively analyzing the deliverability.Well test models must comply with the particular characteristics of flow in low-permeability reservoirs in order to obtain reasonable well test interpretation.At present,non-Darcy flow in low-permeability reservoirs is attracting much attention.In this study,displacement tests were conducted on typical cores taken from low-permeability reservoirs.Two dimensionless variables were introduced to analyze the collected experimental data.The results of the dimensionless analysis show whether non-Darcy flow happens or not depends on the properties of fluid and porous media and the pressure differential.The combination of the above three parameters was named as dimensionless criteria coefficient（DCC）.When the value of the DCC was lower than a critical Reynolds number（CRN）,the flow could not be well described by Darcy＇s law（so-called non-Darcy flow）,when the DCC was higher than CRN,the flow obeyed Darcy＇s law.Finally,this paper establishes a transient mathematical model considering Darcy flow and non-Darcy flow in low-permeability reservoirs,and proposes a methodology to solve the model.The solution technique,which is based on the Boltzmann transformation,is well suited for solving the flow model of low-permeability reservoirs.Based on the typical curves analysis,it was found that the pressure and its derivative curves were determined by such parameters as non-Darcy flow index and the flow characteristics.The results can be used for well test analysis of low-permeability reservoirs.
基金supported by the National Natural Science Foundation Project (No.40772088)the National Basic Research Program ("973" Program,Grant No. 2006CB202305)
文摘Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil （gas） saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone （oil displacing water）, we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that： 1） Oil migration （oil displacing water） in low- permeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2） With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fluidity is more than 1.0, the percolation curve shows modified Darcy flow characteristics, while when the apparent fluidity up＂ non-Darcy percolation curve; 3） Oil-water is less than 1.0, the percolation curve is a ＂concave- two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4） The oil saturation of low- permeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fluidity.
基金Projects(11172090,51479049,11272113,11572110,51209075)supported by the National Natural Science Foundation of ChinaProject(BK2012809)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(201406710042)supported by China Scholarship Council
文摘The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite from an underground oil storage depot were measured. In order to study the influence of rock types on permeability, a tight sandstone was selected as a contrast. The experimental results suggested that the porosity of this granite is less than 5% and permeability is low to 10–20 m^2 within the range of effective stress. During the loading process, both exponential relationship and power law can be utilized to describe the relationship between effective stress and permeability. However, power law matches the experimental data better during the unloading condition. The stress dependent porosity of granite during loading process can be described via an exponential relationship while the match between the model and experimental data can be improved by a power law in unloading paths. The correlation of permeability and porosity can be described in a power law form. Besides, granite shows great different evolution rules in permeability and porosity from sandstone. It is inferred that this difference can be attributed to the preparing of samples and different movements of microstructures subjected to effective stress.
文摘The genesis of a reservoir is a result of the combined action of deposition, diagenesis, tectonic reworking, and interaction of rock and fluid and the evolutionary environment. We discuss the genetic and evolution mechanism of a low-permeability reservoir bed of the Xujiahe Formation in the western Sichuan Depression on the basis of the study of diagenesis, diagenetic reservoir facies and the diagenetic evolution sequence. The research indicated that this reservoir bed can be divided into five types of diagenetic reservoir facies, namely strong dissolution, chlorite-lined intergranular pores, compaction and pressure solution, carbonate cementation and secondary quartz increase. There are, however, just two diagenetic reservoir facies which provide low-permeability reservoir beds, namely strong dissolution and chlorite-lined intergranular pores. We also analyzed their diagenetic evolution sequences and the origin of the low-permeability reservoir bed. Besides, it was also indicated that the composition and structure of sandstones, types of sedimentary microfacies, diagenesis history as well as the tectonic reworking in later periods are the main factors controlling the formation of the low-permeability reservoir bed. The above- mentioned factors establish the foundation for the forecasting the distribution of high quality reservoir beds.
基金This paper is financially supported by the National Natural Science Foundation of China (No. 40572080)the China National Petroleum Corporation (CNPC) Petroleum Science and Technology Innovation Foundation (No.05E7026)
文摘The formation and distribution of fractures are controlled by paleotectonic stress field, and their preservative status and effects on development are dominated by the modern stress field. Since Triassic, it has experienced four tectonic movements and developed four sets of tectonic fractures in the extra low-permeability sandstone reservoir at the south of western Sichuan depression. The strikes of fractures are in the S-N, NE-SW, E-W, and NW-SE directions respectively. At the end of Triassic, under the horizontal compression tectonic stress field, for which the maximum principal stress direction was NW.SE, the fractures were well developed near the S-N faults and at the end of NE-SW faults, because of their stress concentration. At the end of Cretaceous, in the horizontal compression stress fields of the NE-SW direction, the stress was obviously lower near the NE-SW faults, thus, fractures mainly developed near the S-N faults. At the end of Neogene-Early Pleistocene, under the horizontal compression tectonic stress fields of E-W direction, stress concentrated near the NE-SW faults and fractures developed at these places, especially at the end of the NE-SE faults, the cross positions of NE-SW, and S-N faults. Therefore, fractures developed mostly near S-N faults and NE-SW faults. At the cross positions of the above two sets of faults, the degree of development of the fractures was the highest. Under the modern stress field of the NW-SE direction, the NW-SE fractures were mainly the seepage ones with tensional state, the best connectivity, the widest aperture, the highest permeability, and the minimum opening pressure.
基金financial support from the National Natural Science Foundation of China(No.51904324,51974348,U19B6003)
文摘In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement process for oil recovery.Asynchronous injection-production modes can use supercritical CO_(2)to enhance oil recovery but may also worsen the injection capacity.Cores with high permeability have higher oil recovery rates and better injection capacity,however,gas channeling occurs.Supercritical CO_(2)flooding has a higher oil recovery at high pressure levels,which delays the occurrence of gas channeling.Conversely,gas injection has lower displacement efficiency but better injection capacity at the high water cut stage.This study analyzes the displacement characteristics of supercritical CO_(2)flooding with a series of experiments under different injection and production parameters.Experimental results show that the gas breakthrough stage has the fastest oil production and the supercritical CO_(2)injection capacity variation tendency is closely related to the gas-oil ratio.Further experiments show that higher injection rates represent significant ultimate oil recovery and injection index,providing a good reference for developing low-permeability reservoirs.
基金This work was supported by the National Natural Science Foundation of China(No.11775107)the Key Projects of Education Department of Hunan Province of China(No.16A184).
文摘In the process of in situ leaching of uranium,the microstructure controls and influences the flow distribution,percolation characteristics,and reaction mechanism of lixivium in the pores of reservoir rocks and directly affects the leaching of useful components.In this study,the pore throat,pore size distribution,and mineral composition of low-permeability uranium-bearing sandstone were quantitatively analyzed by high pressure mercury injection,nuclear magnetic resonance,X-ray diffraction,and wavelength-dispersive X-ray fluorescence.The distribution characteristics of pores and minerals in the samples were qualitatively analyzed using energy-dispersive scanning electron microscopy and multi-resolution CT images.Image registration with the landmarks algorithm provided by FEI Avizo was used to accurately match the CT images with different resolutions.The multi-scale and multi-mineral digital core model of low-permeability uranium-bearing sandstone is reconstructed through pore segmentation and mineral segmentation of fusion core scanning images.The results show that the pore structure of low-permeability uranium-bearing sandstone is complex and has multi-scale and multi-crossing characteristics.The intergranular pores determine the main seepage channel in the pore space,and the secondary pores have poor connectivity with other pores.Pyrite and coffinite are isolated from the connected pores and surrounded by a large number of clay minerals and ankerite cements,which increases the difficulty of uranium leaching.Clays and a large amount of ankerite cement are filled in the primary and secondary pores and pore throats of the low-permeability uraniumbearing sandstone,which significantly reduces the porosity of the movable fluid and results in low overall permeability of the cores.The multi-scale and multi-mineral digital core proposed in this study provides a basis for characterizing macroscopic and microscopic pore-throat structures and mineral distributions of low-permeability uranium-bearing sandstone and can better understand the seepage characteristics.
文摘According to the geological characteristics and their influential factors of the low-permeability reservoirs, a comprehensive method for evaluation of low-permeability reservoirs is put forward. The method takes a matrix system as the basis, a fracture system as the focus and a stress field system as the restricted factor. It can objectively reflect not only the storage capability and seepage capability of low-permeability reservoirs, but also the effect on development as well. At the same time, it can predict the seepage characteristics at different development stages and provide a reasonable geological basis for the development of low-permeability reservoirs.
基金the Natural Science Foundation of Shandong Province of China(Grant No.ZR2020ME089)the National Natural Science Foundation of China(Grant No.51504275 and 5207433)for their financial supports
文摘As the traditional polymer stabilizer is eliminated to improve the injectability of foam in lowpermeability reservoirs,the stability,plugging capacity,conformance control and oil recovery performance of the surfactant-alternating-gas(SAG)foam become significantly important for determining its adaptability to permeability and heterogeneity,which were focused and experimentally researched in this paper.Results show that the SAG bubbles are highly stable in micron-sized channels and porous media(than in the conventional unconstrained graduated cylinder),making it possible to use in enhanced oil recovery(EOR).Such bubbles formed in porous media could be passively adjusted to match their diameter with the size of the pore.This endows the SAG foam with underlying excellent injectability and deep migration capacity.Permeability adaptability results indicate a reduced plugging capacity,but,increased incremental oil recovery by the SAG foam with decreased permeability.This makes it a good candidate for EOR over a wide range of permeability,however,parallel core floods demonstrate that there is a limiting heterogeneity for SAG application,which is determined to be a permeability contrast of 12.0(for a reservoir containing oil of 9.9 m Pa s).Beyond this limit,the foam would become ineffective.
基金support of the Key Program of National Natural Science Foundation of China(51736009)National Natural Science Foundation of China(51676196,51976228)+4 种基金Guangdong Special Support Program(2019BT02L278)Frontier Sciences Key Research Program of the Chinese Academy of Sciences(QYZDJSSW-JSC033,QYZDB-SSW-JSC028,ZDBS-LY-SLH041)Science and Technology Apparatus Development Program of the Chinese Academy of Sciences(YZ201619)the National Key R&D Program of China(2017YFC0307306)Special Project for Marine Economy Development of Guangdong Province(GDME-2018D002,GDME-2020D044)。
文摘Low temperature and low permeability are the challenges for the development of hydrate reservoirs in permafrost.The ice produced around the production well caused by high depressurization driving force reduces the gas production,and it is necessary to reduce the effect of ice production on gas production.In this work,a new combination of fracturing technology and depressurization method was proposed to evaluate the gas production potential at the site DK-2 in Qinghai-Tibet Plateau Permafrost.A relatively higher intrinsic permeability of the fracture zone surround the horizontal production well was created by the fracturing technology.The simulation results showed that the fracture zone reduced the blocking of production ice to production wells and promoted the propagation of production pressure.And the gas production increased by 2.1 times as the radius of the fracture zone increased from 0 to 4 m in 30 years.Nearly half of the hydrate reservoirs were dissociated in 30 years,and greater than 51.7%of the gas production was produced during the first 10 years.Moreover,production behaviours were sensitive to the depressurization driving force but not to the thermal conductivity.The growth of gas production was not obvious with the intrinsic permeability of the fracture zone higher than 100 m D.The effect of ice production on gas production by fracturing technology and depressurization method was limited.
基金the Committee of the National HighTechnology Research and Development Program of China(863 Program) for providing financial support for thisresearch project (Project No.2006AA06A109)the support provided by the Changjiang Scholarsand Innovative Research Team(No.IRT0411),Ministry ofEducation,China.
文摘This paper discusses the systematic design and development of low-damage drilling fluid to protect the low-permeability gas reservoir of the Sulige block in the Ordos Basin, Inner Mongolia Autonomous Region, China. Based on investigation of the geological characteristics and the potential formation damage of the Permian formation of the reservoir, waterblocking due to invasion of drilling or completion fluids was identified one of the most severe causes of damage to gas well deliverability. By adopting the phase trap prevention method, ideal packing theory, and film-forming technology, a lowdamage drilling fluid, sodium formate brine containing efficient waterblocking preventing surfactants, optimized temporary bridging agents （TBAs）, and film-forming agents has been developed. The performance of the new drilling fluid was evaluated by using a variety of techniques. The results show that the fluid has good rheological properties, good strong shale-swelling inhibition, good temporary plugging effect, ultra-low filtration, and good lubricity. It can efficiently minimize waterblocking and can be used to drill horizontal wells with minimal intervention of the reservoir in the Sulige Gas Field.
基金the China National Postdoctoral Program for Innovative Talents(Bx20200386)China Postdoctoral Science Foundation(2021M703586)+1 种基金Key Program of National Natural Science Foundation of China(52130401)National Natural Science Foundation of China(52204064,52104055)for financial support.
文摘Nanocellulose,a natural polymeric nanomaterial,has attracted significant attention in enhanced oil recovery(EOR)applications due to its abundance,nanoscale,high oil-water interfacial adsorption ef-ficiency.In this study,surface-functionalized cellulose nanocrystals(SF-CNCs)were prepared via hy-drochloric acid hydrolysis and chemical modification,with adaptable nanosize and considerable dispersion stability in low-permeability reservoirs.The SF-CNCs were structurally characterized by FT-IR,Cryo-TEM,which have a diameter of 5-10 nm and a length of 100-200 nm.The SF-CNC dispersions possessed higher stability and stronger salt-tolerance than those of corresponding CNC dispersions,due to the strong hydrophilicity of the sulfonic acid group.It was synergistically used with a non-ionic surfactant(APG1214)to formulate a combined flooding system(0.1 wt%SF-CNC+0.2 wt%APG1214).The combined flooding system exhibits strong emulsification stability,low oil-water interfacial tension of o.03 mN/m,and the ability to alter the wettability for oil-wetting rocks.Furthermore,the combined system was_able to provide an optimum EOR efficiency of 20.2%in low-permeability cores with 30.13×10^(-3)μm^(2).Notably.it can enlarge the sweep volume and increase the displacement efficiency simultaneously.Overall,the newly formulated nanocellulose/surfactant combined system exhibits a remarkable EoR performance in low-permeability reservoirs.
基金supported by National Natural Science Foundation of China(Nos.42002171,42172159)China Postdoctoral Science Foundation(Nos.2020TQ0299,2020M682520)Postdoctoral Innovation Science Foundation of Hubei Province of China.
文摘The transverse relaxation time (T_(2)) cut-off value plays a crucial role in nuclear magnetic resonance for identifying movable and immovable boundaries, evaluating permeability, and determining fluid saturation in petrophysical characterization of petroleum reservoirs. This study focuses on the systematic analysis of T_(2) spectra and T_(2) cut-off values in low-permeability reservoir rocks. Analysis of 36 low-permeability cores revealed a wide distribution of T_(2) cut-off values, ranging from 7 to 50 ms. Additionally, the T_(2) spectra exhibited multimodal characteristics, predominantly displaying unimodal and bimodal morphologies, with a few trimodal morphologies, which are inherently influenced by different pore types. Fractal characteristics of pore structure in fully water-saturated cores were captured through the T_(2) spectra, which were calculated using generalized fractal and multifractal theories. To augment the limited dataset of 36 cores, the synthetic minority oversampling technique was employed. Models for evaluating the T_(2) cut-off value were separately developed based on the classified T_(2) spectra, considering the number of peaks, and utilizing generalized fractal dimensions at the weight <0 and the singular intensity range. The underlying mechanism is that the singular intensity and generalized fractal dimensions at the weight <0 can detect the T_(2) spectral shift. However, the T_(2) spectral shift has negligible effects on multifractal spectrum function difference and generalized fractal dimensions at the weight >0. The primary objective of this work is to gain insights into the relationship between the kurtosis of the T_(2) spectrum and pore types, as well as to predict the T_(2) cut-off value of low-permeability rocks using machine learning and data augmentation techniques.
