Extensive research has been conducted on remaining oil in the Daqing Oilfield during high water cuts’late stage,but few studies have offered multi-level analyses from both macro and micro perspectives for remaining o...Extensive research has been conducted on remaining oil in the Daqing Oilfield during high water cuts’late stage,but few studies have offered multi-level analyses from both macro and micro perspectives for remaining oil under varying formation conditions and displacement methods.This article focuses on the remaining oil in the S,P,and G reservoirs of Daqing Oilfield by employing the frozen section analysis method on the cores from the S,P,and G oil layers.The research identifies patterns among them,revealing that the Micro Remaining Oil types in these cores primarily include pore surface thin film,corner,throat,cluster,intergranular adsorption,and particle adsorption.Among these,intergranular adsorption contains the highest amount of remaining oil(the highest proportion reaches 60%)and serves as the main target for development potential.The overall distribution pattern of the Micro Remaining Oil in the S,P,and G oil layers shows that as flooding intensity increases,the amount of free-state remaining oil gradually decreases,while bound-state remaining oil gradually increases.The study also examines eight typical coring wells for macroscopic remaining oil,finding four main types in the reservoir:interlayer difference,interlayer loss,interlayer interference,and injection-production imperfect types.Among these,the injection-production imperfect type has the highest remaining oil content and is the primary target for development potential.Analyzing the reservoir utilization status and oil flooding efficiency reveals that as water flooding intensifies,the oil displacement efficiency of the oil layer gradually decreases,while the efficiency of oil layer displacement improves.Strongly flooded cores exhibit less free-state remaining oil than weakly flooded cores,making displacement more challenging.This study aims to provide a foundation and support for the development of remaining oil in the S,P,and G oil layers.展开更多
Water alternating gas(WAG)injection is a widely used strategy for enhancing oil recovery(EOR)during gas flooding,and the mechanisms,operating parameters,and influencing factors of which have been extensively studied.H...Water alternating gas(WAG)injection is a widely used strategy for enhancing oil recovery(EOR)during gas flooding,and the mechanisms,operating parameters,and influencing factors of which have been extensively studied.However,with respect to its capacity in expanding macroscopic sweep volume under varying heterogeneities,the related results appear inadequate.In this research,three cores with different heterogeneities were used and flooded by the joint water and CO_(2) WAG,then the effects of heterogeneity on oil recovery were determined.More importantly,the cores after CO_(2) WAG injection were investigated using the nuclear magnetic resonance(NMR)technique for remaining oil distribution research,which could help us to understand the capacity of CO_(2) WAG in enlarging sweep volume at different heterogeneities.The results show that the presence of heterogeneity may largely weaken the effectiveness of water flooding,the more severe the heterogeneity,the worse the water flooding.The WAG injection of CO_(2) performs well in EOR after water flooding for all the cores with different heterogeneities;however,it could barely form a complete or full sweep throughout the low-permeability region,and un-swept bypassed regions remain.The homogeneous core is better developed by the injection of the joint water and CO_(2) WAG than the heterogeneous and fractured cases.展开更多
Oil reservoirs with secondary bottom water in Ng33 members (in Guantao formation, Paleogene system) of Lin2-6 fault block in Huimin depression (Bohai Bay Basin) have entered the late stage of ultra-high water-containi...Oil reservoirs with secondary bottom water in Ng33 members (in Guantao formation, Paleogene system) of Lin2-6 fault block in Huimin depression (Bohai Bay Basin) have entered the late stage of ultra-high water-containing-exploitation. Oil exploitation from vertical wells is becoming more and more inefficient. The reservoir type, with water displacing oil and the remaining oil distribution are specifically studied in order to improve the efficiency of the recovery ratio. An integrated scheme for adjusting horizontal wells has been designed and the key technique of the scheme optimized. The study shows that: 1) the positive rhythm of fluvial depositional features is the internal cause of the flooding of oil reservoirs while water injection, injection-production patterns and accumulative petroleum production are the external causes; 2) oil-water driving patterns have transferred from edge water advancing to bottom-water-coning; distribution of the remaining oil mainly concentrates in the upper rhythm and top of the middle rhythm in Ng33 members; 3) a great deal of remaining oil is enriched in high positions of faults, in axes of tiny structures, in stagnation areas among water-injection wells and oil-wells and in tectonic saddle areas with sparse wells. Compared with vertical wells, horizontal wells have advantages such as high recovery, high off-take potential, high critical output, large controlling areas and long time of bottom-water breakthrough.展开更多
To get a deeper understanding on the formation mechanisms and distribution laws of remaining oil during water flooding, and enhanced oil recovery(EOR) mechanisms by reversing water injection after water flooding, 3D v...To get a deeper understanding on the formation mechanisms and distribution laws of remaining oil during water flooding, and enhanced oil recovery(EOR) mechanisms by reversing water injection after water flooding, 3D visualization models of fractured-vuggy reservoir were constructed based on the elements and configuration of fractures and vugs, and typical fracture-vug structures by using advanced CT scanning and 3D printing technologies. Then, water flooding and reversing water injection experiments were conducted. The formation mechanisms of remaining oil during water flooding include inadequate injection-production well control, gravity difference between oil and water, interference between different flow channels, isolation by low connectivity channel, weak hydrodynamic force at the far end. Under the above effects, 7 kinds of remaining oil may come about, imperfect well-control oil, blind side oil, attic oil at the reservoir top, by-pass residual oil under gravity, by-pass residual oil in secondary channel, isolated oil in low connectivity channel, and remaining oil at far and weakly connected end. Some remaining oil can be recovered by reversing water injection after water flooding, but its EOR is related to the remaining oil type, fracture-cavity structure and reversing injection-production structure. Five of the above seven kinds of remaining oil can be produced by six EOR mechanisms of reversing water injection: gravity displacement, opening new flow channel, rising the outflow point, hydrodynamic force enhancement, vertically equilibrium displacement, and synergistic effect of hydrodynamic force and gravity.展开更多
The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of re...The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of remaining oil. Logging data are required to accomplish this. However, many such projects cannot be completed. Since the old study of remaining oil distribution could not be quantified efficiently, the ＂dynamic two-step method＂ is presented. Firstly, the water cut of every flow unit in one well at one time is calculated according to the comprehensive water cut of a single well at one time. Secondly, the remaining oil saturation of the flow unit of the well at one time is calculated based on the water cut of the flow unit at a given time. The results show that ＂dynamic two-step method＂ has characteristics of simplicity and convenience, and is especially suitable for the study of remaining oil distribution at high water-cut stage. The distribution of remaining oil presented banding and potato form, remaining oil was relatively concentrated in faultage neighborhood and imperfect well netting position, and the net thickness of the place was great. This proposal can provide an effective way to forecast remaining oil distribution and enhance oil recovery, especially applied at the high water-cut stage.展开更多
Due to the continuous water percolation and soaking during development of the oilfields, the dynamic balance of a reservoir is altered by the fluid; and the rock framework, pores and throats will be reformed and destr...Due to the continuous water percolation and soaking during development of the oilfields, the dynamic balance of a reservoir is altered by the fluid; and the rock framework, pores and throats will be reformed and destroyed. The interaction between the fluid and the rock leads to a series of micro geological processes, such as clastation, denudation, dissolution and deposition, in the small spaces connected by pores or throats, which control the accumulation and distribution of the remaining oil. These micro geological processes are the essential factors for the evolution of the reservoirs during development. This evolution makes the recovery of the remaining oil more complex.展开更多
An accurate mapping and understanding of remaining oil distribution is very important for water control and stabilize oil production of mature oilfields in ultra-high water-cut stage.Currently,the Tuo-21 Fault Block o...An accurate mapping and understanding of remaining oil distribution is very important for water control and stabilize oil production of mature oilfields in ultra-high water-cut stage.Currently,the Tuo-21 Fault Block of the Shengtuo Oilfield has entered the stage of ultra-high water cut(97.2%).Poor adaptability of the well pattern,ineffective water injection cycle and low efficiency of engineering measures(such as workover,re-perforation and utilization of high-capacity pumps)are the significant problems in the ultra-high water-cut reservoir.In order to accurately describe the oil and water flow characteristics,relative permeability curves at high water injection multiple(injected pore volume)and a semiquantitative method is applied to perform fine reservoir simulation of the Sand group 3e7 in the Block.An accurate reservoir model is built and history matching is performed.The distribution characteristics of remaining oil in lateral and vertical directions are quantitatively simulated and analyzed.The results show that the numerical simulation considering relative permeability at high injection multiple can reflect truly the remaining oil distribution characteristics after water flooding in an ultrahigh water-cut stage.The distribution of remaining oil saturation can be mapped more accurately and quantitatively by using the‘four-points and five-types’classification method,providing a basis for potential tapping of various remaining oil types of oil reservoirs in late-stage of development with high water-cut.展开更多
Low-salinity waterflooding,as a promising enhanced oil recovery method,has exhibited exciting results in various experiments conducted at different scales.For carbonate rock,pore-scale understanding of the fluid distr...Low-salinity waterflooding,as a promising enhanced oil recovery method,has exhibited exciting results in various experiments conducted at different scales.For carbonate rock,pore-scale understanding of the fluid distribution and remaining oil after low-salinity waterflooding is essential,especially the geometry and topology analysis of oil clusters.We performed the tertiary low-salinity waterflooding and employed X-ray micro-CT to probe the pore-scale displacement mechanism,fluid configuration,oil recovery,and remaining oil distribution.We found that the core becomes less oil-wet after low-salinity waterflooding.Furthermore,we analyzed the oil-rock and oil-brine interfacial areas to further support the wettability alteration.By comparing images after high-salinity waterflooding and low-salinity waterflooding,it is proven that wettability alteration has a significant impact on the behavior of the two-phase flow.Our research demonstrates that low-salinity waterflooding is an effective tertiary enhanced oil recovery technology in carbonate,which changes the wettability of rock and results in less film and singlet oil.展开更多
C oilfield is a heavy oil field developed by horizontal wells and single sand body in Bohai oilfield. The edge and bottom water of the reservoir is active and the natural energy development mode is adopted. The compre...C oilfield is a heavy oil field developed by horizontal wells and single sand body in Bohai oilfield. The edge and bottom water of the reservoir is active and the natural energy development mode is adopted. The comprehensive water cut of the oilfield was 95.3%, which had entered the stage of high water cut oil production. Some reservoirs were limited by crude oil viscosity and oil column height. Under the condition of existing development well pattern, some reserves were not produced or the degree of production was low, and the degree of well control was not high, so there is room for tapping the potential of remaining oil. This paper studied the rising law of water ridge of horizontal wells in bottom water reservoir by reservoir engineering method, and guided the infilling limit of horizontal wells in bottom water reservoir. At the same time, combined with the research results of fine reservoir description, the geological model was established, the numerical simulation was carried out, and the distribution law of remaining oil was analyzed. Through this study, we could understand the law of water flooding and remaining oil in the high water cut period of bottom water heavy oil reservoir, so as to provide guidance for the development strategy of this type of reservoir in the high water cut period.展开更多
To study the distribution law of remaining oil in a block, core analysis method, C/O test method, reservoir engineering method, dynamic analysis method, numerical simulation method, microscopic oil displacement experi...To study the distribution law of remaining oil in a block, core analysis method, C/O test method, reservoir engineering method, dynamic analysis method, numerical simulation method, microscopic oil displacement experiment method and other methods are mainly used. Finally, the distribution of remaining oil and remaining recoverable reserves from qualitative to quantitative, macroscopic to microscopic, and from small layer plane to longitudinal are deeply understood, and the potential of chemical flooding is analyzed.展开更多
In the later stage of water-injected reservoir development, the remaining oil is highly dispersed, and the first task to improve the development effect is to finely depict the distribution law of the remaining oil. Ta...In the later stage of water-injected reservoir development, the remaining oil is highly dispersed, and the first task to improve the development effect is to finely depict the distribution law of the remaining oil. Taking Block J as an example, this paper comprehensively uses drilling coring, logging, dynamic monitoring and other data, and uses dynamic monitoring analysis technology, logging secondary interpretation technology, coring analysis technology, micro-structure identification technology, etc. to clarify the distribution law of remaining oil on the plane, between layers and within layers, and formulates reasonable technical countermeasures for different remaining oil distribution patterns, including sidetracking potential tapping, improving injection-production well pattern, optimizing injection-production well sections, strengthening water injection in potential layers, optimizing perforation well sections, etc. Good results have been achieved, with an increase in oil production of 120 tons and a gradual increase in oil production of 60,000 tons. Indicators such as the water cut increase rate and natural decline rate of the block have been improved. It is estimated that the ultimate recovery rate of water flooding is 35.5%, which is 5.5 percentage points higher than the nominal recovery rate. The recoverable reserves have been increased by 1.425 million tons, and the development life of the block has been prolonged. The results and understanding obtained can provide reference for other oil reservoirs.展开更多
Quantitative characterization of deep,complex carbonate reservoirs is a signicant challenge due to strong heterogeneity and the ambiguity of conventional geophysical methods.To overcome these challenges,we employed a ...Quantitative characterization of deep,complex carbonate reservoirs is a signicant challenge due to strong heterogeneity and the ambiguity of conventional geophysical methods.To overcome these challenges,we employed a workflow based on a multi-parameter constrained 3D borehole-to-surface electromagnetic(BSEM)simultaneous inversion process.This approach utilizes seismic,well-log,and petrophysical data to constrain the inversion,resulting in 3D resistivity and polarizability volumes.Subsequently,an IP-inclusive oil saturation model(considering the induced polarization effect)was applied to these inverted parameters to derive a quantitative 3D oil saturation(So)volume.The method was applied to an Ordovician carbonate reservoir in Western China.Despite a weak IP response partially masked by a localized high-value anomaly,the constrained inversion resolved the 3D geoelectric structure and revealed a highly heterogeneous,discontinuous"pod-like"distribution of remaining oil.This study constitutes one of the rst applications of the constrained method for quantitative saturation imaging in such a deep,complex setting.The results demonstrate good consistency and were validated by production data:the delineated primary oil-rich favorable zone(F1,dened by So>50%)shows good agreement with the high-saturation intervals encountered by Well X3.This validated workflow provides an eective tool for characterizing heterogeneous carbonate reservoirs where traditional methods prove inadequate.The identied remaining oil enrichment zones(e.g.,F1,F3,F5)serve as actionable targets for optimizing future well placement and eld development.展开更多
Through natural partition and clustering analysis,four kinds of flow units were distinguished in Pu53 block,Pucheng Oilfield.Taking the short-term cycle as studying unit,the two-dimensional distribution of each type o...Through natural partition and clustering analysis,four kinds of flow units were distinguished in Pu53 block,Pucheng Oilfield.Taking the short-term cycle as studying unit,the two-dimensional distribution of each type of flow units was forecasted and the short-term cycle was classified into four types based on the two-dimensional characteristics of the flow units.The remaining oil was predicted by conceptual simulation,qualitative analysis and quantitative modeling.The results showed obvious control of the characteristics of reservoir flow units to the remaining oil.E and G units in type I and type II short-term cycles which are distributed continuously in large areas are mostly flooded,while the uncontrolled small isolated G flow unit in type III short-term cycles which were mainly made of F flow unit and F flow unit with continuous distribution become the accumulating place for remaining oil.Thus the development adjustment strategy should optimize the development of small-scale E and G units,strengthen the development of type III short-term cycles,and block out type I short-term cycles.This strategy improves the development of Pu53 block obviously.展开更多
The experimental analysis of 21 crude oil samples shows a good correlation between high molecular-weight hydrocarbon components(C 40+)and viscosity.Forty-four remaining oil samples extracted from oil sands of oilfield...The experimental analysis of 21 crude oil samples shows a good correlation between high molecular-weight hydrocarbon components(C 40+)and viscosity.Forty-four remaining oil samples extracted from oil sands of oilfield development coring wells were analyzed by high-temperature gas chromatography(HTGC),for the relative abundance of C 21-,C 21-C 40 and C 40+hydrocarbons.The relationship between viscosity of crude oil and C 40+(%)hydrocarbons abundance is used to expect the viscosity of remaining oil.The mobility characteristics of remaining oil,the properties of remaining oil,and the next displacement methods in reservoirs either water-flooded or polymer-flooded are studied with rock permeability,oil saturation of coring wells,etc.The experimental results show that the hydrocarbons composition,viscosity,and mobility of remaining oil from both polymer-flooding and water-flooding reservoirs are heterogeneous,especially the former.Relative abundance of C 21-and C 21-C 40 hydrocarbons in polymer-flooding reservoirs is lower than that of water-flooding,but with more abundance of C 40+hydrocarbons.It is then suggested that polymer flooding must have driven more C 40-hydrocarbons out of reservoir,which resulted in relatively enriched C 40+,more viscous oils,and poorer mobility.Remaining oil in water-flooding reservoirs is dominated by moderate viscosity oil with some low viscosity oil,while polymer-flooding mainly contained moderate viscosity oil with some high viscosity oil.In each oilfield and reservoir,displacement methods of remaining oil,viscosity,and concentration by polymer-solution can be adjusted by current viscosity of remaining oil and mobility ratio in a favorable range.A new basis and methods are suggested for the further development and enhanced oil recovery of remaining oil.展开更多
In this study, compositional characteristics of crude oil, including the variation of aliphatic, aromatic and pyrrolic nitrogen compounds, were systematically monitored and investigated in a high water-cut oil reservo...In this study, compositional characteristics of crude oil, including the variation of aliphatic, aromatic and pyrrolic nitrogen compounds, were systematically monitored and investigated in a high water-cut oil reservoir over a short time.The results showed that among the widely used parameters indicative of oil maturity and migration, tetramethyl/monomethyl DBT and tricyclic terpane/(tricyclic terpane+C30 hopanoid) varied remarkably, and a positive correlation was observed between these two parameters.The variation of each of these parameters during waterflooding development was correlated with the flow effect of crude promoted by the water drive in oil reservoirs.A solid consistency was observed among the results of numerical simulation and development; the direction and pathway of waterflooding crude was indicated by Tetramethyl/monomethyl DBT, and the distribution region prediction of remaining oil hereby obtained.Therefore, these two parameters could be used as molecular tracers for the oil during waterflooding.This study would be of practical significance for geochemical dynamic monitoring and reservoir development.展开更多
As the water drive reservoir enters extra high water cut stage(greater than 80%),remaining oil distribution becomes increasingly dispersed.Research on micro residual oil in pore appears particularly important for rese...As the water drive reservoir enters extra high water cut stage(greater than 80%),remaining oil distribution becomes increasingly dispersed.Research on micro residual oil in pore appears particularly important for reservoir development at extra high water cut stage.Oil occurrence characteristics recognition helps to understand the distribution of remaining oil and the mechanical characteristics of oil is the guide for tapping the remaining oil.On the basis of pore scale oil ewater two phase flow experiments,micro distribution of remaining oil is divided into four occurrence states in accordance with oil features at different stage of water flooding,the flake of remaining oil,oil column,oil droplet and oil film.A quantitative characterization method of remaining oil occurrence states is established.By using micro numerical simulation method,change rules of four occurrence states of remaining oil during the process of water displacement and the mechanical characteristics of different occurrence state of remaining oil are analyzed.Results show that the continuous oil phase gradually transforms to discontinuous phase and even to dispersed phases during the water flooding process.At extra high water cut stage,most of remaining oil are dispersed oil columns,oil droplets and oil films,which are the main target of remaining oil to be tapped.By changing water flow direction or increasing the displacement pressure gradient,the surface adsorption force acting on oil columns are overcome,and then the oil columns begin to move and finally to be produced out.Oil droplets in pore-throat center are scoured and carried out by water as the increase of the injection volume,while the oil droplets in blind ends and the oil films are extracted out by adding chemicals to reduce the interfacial tension,so as to enhance oil recovery.For water flooding reservoir,the corresponding tapping measures for four types of oil occurrence states brought forward have great meanings of improving reservoir recovery at high water cut stage.展开更多
Gas injection serves as a main enhanced oil recovery(EOR)method in fractured-vuggy carbonate reservoir,but its effect differs among single wells and multi-well groups because of the diverse fractured-vuggy configurati...Gas injection serves as a main enhanced oil recovery(EOR)method in fractured-vuggy carbonate reservoir,but its effect differs among single wells and multi-well groups because of the diverse fractured-vuggy configuration.Many researchers conducted experiments for the observation of fluid flow and the evaluation of production performance,while most of their physical models were fabricated based on the probability distribution of fractures and caves in the reservoir.In this study,a two-dimensional physical model of the karst fault system was designed and fabricated based on the geological model of TK748 well group in the seventh block of the Tahe Oilfield.The fluid flow and production performance of primary gas flooding were discussed.Gas-assisted gravity flooding was firstly introduced to take full use of gas-oil gravity difference,and its feasibility in the karst fault system was examined.Experimental results showed that primary gas flooding created more flow paths and achieved a remarkable increment of oil recovery compared to water flooding.Gas injection at a lower location was recommended to delay gas breakthrough.Gas-assisted gravity flooding achieved more stable gas-displacing-oil because oil production was at a lower location,and thus,the oil recovery was further enhanced.展开更多
Aiming at the technology of hydraulic fracturing assisted oil displacement which combines hydraulic fracturing,seepage and oil displacement,an experimental system of energy storage and flowback in fracturing assisted ...Aiming at the technology of hydraulic fracturing assisted oil displacement which combines hydraulic fracturing,seepage and oil displacement,an experimental system of energy storage and flowback in fracturing assisted oil displacement process has been developed and used to simulate the mechanism of percolation,energy storage,oil displacement and flowback of chemical agents in the whole process.The research shows that in hydraulic fracturing assisted oil displacement,the chemical agent could be directly pushed to the deeper area of the low and medium permeability reservoirs,avoiding the viscosity loss and adhesion retention of chemical agents near the pay zone;in addition,this technology could effectively enlarge the swept volume,improve the oil displacement efficiency,replenish formation energy,gather and exploit the scattered residual oil.For the reservoir with higher permeability,this measure takes effect fast,so to lower cost,and the high pressure hydraulic fracturing assisted oil displacement could be adopted directly.For the reservoir with lower permeability which is difficult to absorb water,hydraulic fracturing assisted oil displacement with surfactant should be adopted to reduce flow resistance of the reservoir and improve the water absorption capacity and development effect of the reservoir.The degree of formation energy deficit was the main factor affecting the effective swept range of chemical agents.Moreover,the larger the formation energy deficit was,the further the seepage distance of chemical agents was,accordingly,the larger the effective swept volume was,and the greater the increase of oil recovery was.Formation energy enhancement was the most important contribution to enhanced oil recovery(EOR),which was the key to EOR by the technology of hydraulic fracturing assisted oil displacement.展开更多
This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the locati...This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.展开更多
Due to long-term water injection,often oilfields enter the so-called medium and high water cut stage,and it is difficult to achieve good oil recovery and water reduction through standard methods(single profile control...Due to long-term water injection,often oilfields enter the so-called medium and high water cut stage,and it is difficult to achieve good oil recovery and water reduction through standard methods(single profile control and flooding measures).Therefore,in this study,a novel method based on“plugging,profile control,and flooding”being implemented at the same time is proposed.To assess the performances of this approach,physical simulations,computer tomography,and nuclear magnetic resonance are used.The results show that the combination of a gel plugging agent,a polymer microsphere flooding agent,and a high-efficiency oil displacement agent leads to better results in terms of oil recovery with respect to the situation in which these approaches are used separately(the oil recovery is increased by 15.37%).Computer tomography scan results show that with the combined approach,a larger sweep volume and higher oil washing efficiency are obtained.The remaining oil in the cluster form can be recovered in the middle and low permeability layer,increasing the proportion of the columnar and blind end states of the oil.The nuclear magnetic resonance test results show that the combined“plugging,profile control,and flooding”treatment can also be used to control more effectively the dominant channels of the high permeability layer and further expand the recovery degree of the remaining oil in the pores of different sizes in the middle and low permeability layers.However,for the low permeability layer(permeability difference of 20),the benefits in terms of oil recovery are limited.展开更多
文摘Extensive research has been conducted on remaining oil in the Daqing Oilfield during high water cuts’late stage,but few studies have offered multi-level analyses from both macro and micro perspectives for remaining oil under varying formation conditions and displacement methods.This article focuses on the remaining oil in the S,P,and G reservoirs of Daqing Oilfield by employing the frozen section analysis method on the cores from the S,P,and G oil layers.The research identifies patterns among them,revealing that the Micro Remaining Oil types in these cores primarily include pore surface thin film,corner,throat,cluster,intergranular adsorption,and particle adsorption.Among these,intergranular adsorption contains the highest amount of remaining oil(the highest proportion reaches 60%)and serves as the main target for development potential.The overall distribution pattern of the Micro Remaining Oil in the S,P,and G oil layers shows that as flooding intensity increases,the amount of free-state remaining oil gradually decreases,while bound-state remaining oil gradually increases.The study also examines eight typical coring wells for macroscopic remaining oil,finding four main types in the reservoir:interlayer difference,interlayer loss,interlayer interference,and injection-production imperfect types.Among these,the injection-production imperfect type has the highest remaining oil content and is the primary target for development potential.Analyzing the reservoir utilization status and oil flooding efficiency reveals that as water flooding intensifies,the oil displacement efficiency of the oil layer gradually decreases,while the efficiency of oil layer displacement improves.Strongly flooded cores exhibit less free-state remaining oil than weakly flooded cores,making displacement more challenging.This study aims to provide a foundation and support for the development of remaining oil in the S,P,and G oil layers.
基金Project(KFJJ-TZ-2019-3)supported by the Open Project of Shaanxi Key Laboratory of Advanced Stimulation Technology for Oil&Gas Reservoirs,ChinaProjects(51504275,51974344)supported by the National Natural Science Foundation of China。
文摘Water alternating gas(WAG)injection is a widely used strategy for enhancing oil recovery(EOR)during gas flooding,and the mechanisms,operating parameters,and influencing factors of which have been extensively studied.However,with respect to its capacity in expanding macroscopic sweep volume under varying heterogeneities,the related results appear inadequate.In this research,three cores with different heterogeneities were used and flooded by the joint water and CO_(2) WAG,then the effects of heterogeneity on oil recovery were determined.More importantly,the cores after CO_(2) WAG injection were investigated using the nuclear magnetic resonance(NMR)technique for remaining oil distribution research,which could help us to understand the capacity of CO_(2) WAG in enlarging sweep volume at different heterogeneities.The results show that the presence of heterogeneity may largely weaken the effectiveness of water flooding,the more severe the heterogeneity,the worse the water flooding.The WAG injection of CO_(2) performs well in EOR after water flooding for all the cores with different heterogeneities;however,it could barely form a complete or full sweep throughout the low-permeability region,and un-swept bypassed regions remain.The homogeneous core is better developed by the injection of the joint water and CO_(2) WAG than the heterogeneous and fractured cases.
基金Projects 2003CB214603 supported by the National Basic Research Program of ChinaDMSM200803 by the Open Fund of Key Laboratory of Deposi-tional Mineralization & Sedimentary Mineral, Shandong Province
文摘Oil reservoirs with secondary bottom water in Ng33 members (in Guantao formation, Paleogene system) of Lin2-6 fault block in Huimin depression (Bohai Bay Basin) have entered the late stage of ultra-high water-containing-exploitation. Oil exploitation from vertical wells is becoming more and more inefficient. The reservoir type, with water displacing oil and the remaining oil distribution are specifically studied in order to improve the efficiency of the recovery ratio. An integrated scheme for adjusting horizontal wells has been designed and the key technique of the scheme optimized. The study shows that: 1) the positive rhythm of fluvial depositional features is the internal cause of the flooding of oil reservoirs while water injection, injection-production patterns and accumulative petroleum production are the external causes; 2) oil-water driving patterns have transferred from edge water advancing to bottom-water-coning; distribution of the remaining oil mainly concentrates in the upper rhythm and top of the middle rhythm in Ng33 members; 3) a great deal of remaining oil is enriched in high positions of faults, in axes of tiny structures, in stagnation areas among water-injection wells and oil-wells and in tectonic saddle areas with sparse wells. Compared with vertical wells, horizontal wells have advantages such as high recovery, high off-take potential, high critical output, large controlling areas and long time of bottom-water breakthrough.
基金National Natural Science Foundation of China Enterprise Innovation and Development Joint Fund(U19B6003-02-06)。
文摘To get a deeper understanding on the formation mechanisms and distribution laws of remaining oil during water flooding, and enhanced oil recovery(EOR) mechanisms by reversing water injection after water flooding, 3D visualization models of fractured-vuggy reservoir were constructed based on the elements and configuration of fractures and vugs, and typical fracture-vug structures by using advanced CT scanning and 3D printing technologies. Then, water flooding and reversing water injection experiments were conducted. The formation mechanisms of remaining oil during water flooding include inadequate injection-production well control, gravity difference between oil and water, interference between different flow channels, isolation by low connectivity channel, weak hydrodynamic force at the far end. Under the above effects, 7 kinds of remaining oil may come about, imperfect well-control oil, blind side oil, attic oil at the reservoir top, by-pass residual oil under gravity, by-pass residual oil in secondary channel, isolated oil in low connectivity channel, and remaining oil at far and weakly connected end. Some remaining oil can be recovered by reversing water injection after water flooding, but its EOR is related to the remaining oil type, fracture-cavity structure and reversing injection-production structure. Five of the above seven kinds of remaining oil can be produced by six EOR mechanisms of reversing water injection: gravity displacement, opening new flow channel, rising the outflow point, hydrodynamic force enhancement, vertically equilibrium displacement, and synergistic effect of hydrodynamic force and gravity.
文摘The distribution of remaining oil is often described qualitatively. The remaining oil distributed in the whole reservoir is calculated according to the characteristics of the space distribution of the saturation of remaining oil. Logging data are required to accomplish this. However, many such projects cannot be completed. Since the old study of remaining oil distribution could not be quantified efficiently, the ＂dynamic two-step method＂ is presented. Firstly, the water cut of every flow unit in one well at one time is calculated according to the comprehensive water cut of a single well at one time. Secondly, the remaining oil saturation of the flow unit of the well at one time is calculated based on the water cut of the flow unit at a given time. The results show that ＂dynamic two-step method＂ has characteristics of simplicity and convenience, and is especially suitable for the study of remaining oil distribution at high water-cut stage. The distribution of remaining oil presented banding and potato form, remaining oil was relatively concentrated in faultage neighborhood and imperfect well netting position, and the net thickness of the place was great. This proposal can provide an effective way to forecast remaining oil distribution and enhance oil recovery, especially applied at the high water-cut stage.
文摘Due to the continuous water percolation and soaking during development of the oilfields, the dynamic balance of a reservoir is altered by the fluid; and the rock framework, pores and throats will be reformed and destroyed. The interaction between the fluid and the rock leads to a series of micro geological processes, such as clastation, denudation, dissolution and deposition, in the small spaces connected by pores or throats, which control the accumulation and distribution of the remaining oil. These micro geological processes are the essential factors for the evolution of the reservoirs during development. This evolution makes the recovery of the remaining oil more complex.
基金funded by SINOPEC Science and Technology Project P18080by National Energy Administration Research and Development Center Project.
文摘An accurate mapping and understanding of remaining oil distribution is very important for water control and stabilize oil production of mature oilfields in ultra-high water-cut stage.Currently,the Tuo-21 Fault Block of the Shengtuo Oilfield has entered the stage of ultra-high water cut(97.2%).Poor adaptability of the well pattern,ineffective water injection cycle and low efficiency of engineering measures(such as workover,re-perforation and utilization of high-capacity pumps)are the significant problems in the ultra-high water-cut reservoir.In order to accurately describe the oil and water flow characteristics,relative permeability curves at high water injection multiple(injected pore volume)and a semiquantitative method is applied to perform fine reservoir simulation of the Sand group 3e7 in the Block.An accurate reservoir model is built and history matching is performed.The distribution characteristics of remaining oil in lateral and vertical directions are quantitatively simulated and analyzed.The results show that the numerical simulation considering relative permeability at high injection multiple can reflect truly the remaining oil distribution characteristics after water flooding in an ultrahigh water-cut stage.The distribution of remaining oil saturation can be mapped more accurately and quantitatively by using the‘four-points and five-types’classification method,providing a basis for potential tapping of various remaining oil types of oil reservoirs in late-stage of development with high water-cut.
基金the National Key Research and Development Program of China(2022YFE0203400)the National Natural Science Foundation of China(Nos.U23A20595,52034010,52288101)+2 种基金the Qingdao Natural Science Foundation(No.23-2-1-230-zyyd-jch)the Fundamental Research Funds for the Central Universities(No.23CX10004A)the Program for Changjiang Scholars and Innovative Research Team in University(No.IRT_16R69)。
文摘Low-salinity waterflooding,as a promising enhanced oil recovery method,has exhibited exciting results in various experiments conducted at different scales.For carbonate rock,pore-scale understanding of the fluid distribution and remaining oil after low-salinity waterflooding is essential,especially the geometry and topology analysis of oil clusters.We performed the tertiary low-salinity waterflooding and employed X-ray micro-CT to probe the pore-scale displacement mechanism,fluid configuration,oil recovery,and remaining oil distribution.We found that the core becomes less oil-wet after low-salinity waterflooding.Furthermore,we analyzed the oil-rock and oil-brine interfacial areas to further support the wettability alteration.By comparing images after high-salinity waterflooding and low-salinity waterflooding,it is proven that wettability alteration has a significant impact on the behavior of the two-phase flow.Our research demonstrates that low-salinity waterflooding is an effective tertiary enhanced oil recovery technology in carbonate,which changes the wettability of rock and results in less film and singlet oil.
文摘C oilfield is a heavy oil field developed by horizontal wells and single sand body in Bohai oilfield. The edge and bottom water of the reservoir is active and the natural energy development mode is adopted. The comprehensive water cut of the oilfield was 95.3%, which had entered the stage of high water cut oil production. Some reservoirs were limited by crude oil viscosity and oil column height. Under the condition of existing development well pattern, some reserves were not produced or the degree of production was low, and the degree of well control was not high, so there is room for tapping the potential of remaining oil. This paper studied the rising law of water ridge of horizontal wells in bottom water reservoir by reservoir engineering method, and guided the infilling limit of horizontal wells in bottom water reservoir. At the same time, combined with the research results of fine reservoir description, the geological model was established, the numerical simulation was carried out, and the distribution law of remaining oil was analyzed. Through this study, we could understand the law of water flooding and remaining oil in the high water cut period of bottom water heavy oil reservoir, so as to provide guidance for the development strategy of this type of reservoir in the high water cut period.
文摘To study the distribution law of remaining oil in a block, core analysis method, C/O test method, reservoir engineering method, dynamic analysis method, numerical simulation method, microscopic oil displacement experiment method and other methods are mainly used. Finally, the distribution of remaining oil and remaining recoverable reserves from qualitative to quantitative, macroscopic to microscopic, and from small layer plane to longitudinal are deeply understood, and the potential of chemical flooding is analyzed.
文摘In the later stage of water-injected reservoir development, the remaining oil is highly dispersed, and the first task to improve the development effect is to finely depict the distribution law of the remaining oil. Taking Block J as an example, this paper comprehensively uses drilling coring, logging, dynamic monitoring and other data, and uses dynamic monitoring analysis technology, logging secondary interpretation technology, coring analysis technology, micro-structure identification technology, etc. to clarify the distribution law of remaining oil on the plane, between layers and within layers, and formulates reasonable technical countermeasures for different remaining oil distribution patterns, including sidetracking potential tapping, improving injection-production well pattern, optimizing injection-production well sections, strengthening water injection in potential layers, optimizing perforation well sections, etc. Good results have been achieved, with an increase in oil production of 120 tons and a gradual increase in oil production of 60,000 tons. Indicators such as the water cut increase rate and natural decline rate of the block have been improved. It is estimated that the ultimate recovery rate of water flooding is 35.5%, which is 5.5 percentage points higher than the nominal recovery rate. The recoverable reserves have been increased by 1.425 million tons, and the development life of the block has been prolonged. The results and understanding obtained can provide reference for other oil reservoirs.
基金supported in part by the Science and Technology Project of the China National Petroleum Corporation(CNPC)(Grant No.2023ZZ05)the National Natural Science Foundation of China(Grant No.42474108).
文摘Quantitative characterization of deep,complex carbonate reservoirs is a signicant challenge due to strong heterogeneity and the ambiguity of conventional geophysical methods.To overcome these challenges,we employed a workflow based on a multi-parameter constrained 3D borehole-to-surface electromagnetic(BSEM)simultaneous inversion process.This approach utilizes seismic,well-log,and petrophysical data to constrain the inversion,resulting in 3D resistivity and polarizability volumes.Subsequently,an IP-inclusive oil saturation model(considering the induced polarization effect)was applied to these inverted parameters to derive a quantitative 3D oil saturation(So)volume.The method was applied to an Ordovician carbonate reservoir in Western China.Despite a weak IP response partially masked by a localized high-value anomaly,the constrained inversion resolved the 3D geoelectric structure and revealed a highly heterogeneous,discontinuous"pod-like"distribution of remaining oil.This study constitutes one of the rst applications of the constrained method for quantitative saturation imaging in such a deep,complex setting.The results demonstrate good consistency and were validated by production data:the delineated primary oil-rich favorable zone(F1,dened by So>50%)shows good agreement with the high-saturation intervals encountered by Well X3.This validated workflow provides an eective tool for characterizing heterogeneous carbonate reservoirs where traditional methods prove inadequate.The identied remaining oil enrichment zones(e.g.,F1,F3,F5)serve as actionable targets for optimizing future well placement and eld development.
基金Supported by the National Natural Science Foundation of China(Grant Nos.40602013,40572078)the Ph.D.Programs Foundation of Ministry of Education of China(Grant No.20060489002)
文摘Through natural partition and clustering analysis,four kinds of flow units were distinguished in Pu53 block,Pucheng Oilfield.Taking the short-term cycle as studying unit,the two-dimensional distribution of each type of flow units was forecasted and the short-term cycle was classified into four types based on the two-dimensional characteristics of the flow units.The remaining oil was predicted by conceptual simulation,qualitative analysis and quantitative modeling.The results showed obvious control of the characteristics of reservoir flow units to the remaining oil.E and G units in type I and type II short-term cycles which are distributed continuously in large areas are mostly flooded,while the uncontrolled small isolated G flow unit in type III short-term cycles which were mainly made of F flow unit and F flow unit with continuous distribution become the accumulating place for remaining oil.Thus the development adjustment strategy should optimize the development of small-scale E and G units,strengthen the development of type III short-term cycles,and block out type I short-term cycles.This strategy improves the development of Pu53 block obviously.
基金supported by National Basic Research Program of China(Grant No.2006CB701404)
文摘The experimental analysis of 21 crude oil samples shows a good correlation between high molecular-weight hydrocarbon components(C 40+)and viscosity.Forty-four remaining oil samples extracted from oil sands of oilfield development coring wells were analyzed by high-temperature gas chromatography(HTGC),for the relative abundance of C 21-,C 21-C 40 and C 40+hydrocarbons.The relationship between viscosity of crude oil and C 40+(%)hydrocarbons abundance is used to expect the viscosity of remaining oil.The mobility characteristics of remaining oil,the properties of remaining oil,and the next displacement methods in reservoirs either water-flooded or polymer-flooded are studied with rock permeability,oil saturation of coring wells,etc.The experimental results show that the hydrocarbons composition,viscosity,and mobility of remaining oil from both polymer-flooding and water-flooding reservoirs are heterogeneous,especially the former.Relative abundance of C 21-and C 21-C 40 hydrocarbons in polymer-flooding reservoirs is lower than that of water-flooding,but with more abundance of C 40+hydrocarbons.It is then suggested that polymer flooding must have driven more C 40-hydrocarbons out of reservoir,which resulted in relatively enriched C 40+,more viscous oils,and poorer mobility.Remaining oil in water-flooding reservoirs is dominated by moderate viscosity oil with some low viscosity oil,while polymer-flooding mainly contained moderate viscosity oil with some high viscosity oil.In each oilfield and reservoir,displacement methods of remaining oil,viscosity,and concentration by polymer-solution can be adjusted by current viscosity of remaining oil and mobility ratio in a favorable range.A new basis and methods are suggested for the further development and enhanced oil recovery of remaining oil.
基金supported by Jidong Oilfield Branch Com-pany of CNPC
文摘In this study, compositional characteristics of crude oil, including the variation of aliphatic, aromatic and pyrrolic nitrogen compounds, were systematically monitored and investigated in a high water-cut oil reservoir over a short time.The results showed that among the widely used parameters indicative of oil maturity and migration, tetramethyl/monomethyl DBT and tricyclic terpane/(tricyclic terpane+C30 hopanoid) varied remarkably, and a positive correlation was observed between these two parameters.The variation of each of these parameters during waterflooding development was correlated with the flow effect of crude promoted by the water drive in oil reservoirs.A solid consistency was observed among the results of numerical simulation and development; the direction and pathway of waterflooding crude was indicated by Tetramethyl/monomethyl DBT, and the distribution region prediction of remaining oil hereby obtained.Therefore, these two parameters could be used as molecular tracers for the oil during waterflooding.This study would be of practical significance for geochemical dynamic monitoring and reservoir development.
基金This research was supported by SINOPEC Major Projects,(J08).
文摘As the water drive reservoir enters extra high water cut stage(greater than 80%),remaining oil distribution becomes increasingly dispersed.Research on micro residual oil in pore appears particularly important for reservoir development at extra high water cut stage.Oil occurrence characteristics recognition helps to understand the distribution of remaining oil and the mechanical characteristics of oil is the guide for tapping the remaining oil.On the basis of pore scale oil ewater two phase flow experiments,micro distribution of remaining oil is divided into four occurrence states in accordance with oil features at different stage of water flooding,the flake of remaining oil,oil column,oil droplet and oil film.A quantitative characterization method of remaining oil occurrence states is established.By using micro numerical simulation method,change rules of four occurrence states of remaining oil during the process of water displacement and the mechanical characteristics of different occurrence state of remaining oil are analyzed.Results show that the continuous oil phase gradually transforms to discontinuous phase and even to dispersed phases during the water flooding process.At extra high water cut stage,most of remaining oil are dispersed oil columns,oil droplets and oil films,which are the main target of remaining oil to be tapped.By changing water flow direction or increasing the displacement pressure gradient,the surface adsorption force acting on oil columns are overcome,and then the oil columns begin to move and finally to be produced out.Oil droplets in pore-throat center are scoured and carried out by water as the increase of the injection volume,while the oil droplets in blind ends and the oil films are extracted out by adding chemicals to reduce the interfacial tension,so as to enhance oil recovery.For water flooding reservoir,the corresponding tapping measures for four types of oil occurrence states brought forward have great meanings of improving reservoir recovery at high water cut stage.
基金the financial support from National Natural Science Foundation of China(51504268)National Technology Major Project of China(2016ZX05014).
文摘Gas injection serves as a main enhanced oil recovery(EOR)method in fractured-vuggy carbonate reservoir,but its effect differs among single wells and multi-well groups because of the diverse fractured-vuggy configuration.Many researchers conducted experiments for the observation of fluid flow and the evaluation of production performance,while most of their physical models were fabricated based on the probability distribution of fractures and caves in the reservoir.In this study,a two-dimensional physical model of the karst fault system was designed and fabricated based on the geological model of TK748 well group in the seventh block of the Tahe Oilfield.The fluid flow and production performance of primary gas flooding were discussed.Gas-assisted gravity flooding was firstly introduced to take full use of gas-oil gravity difference,and its feasibility in the karst fault system was examined.Experimental results showed that primary gas flooding created more flow paths and achieved a remarkable increment of oil recovery compared to water flooding.Gas injection at a lower location was recommended to delay gas breakthrough.Gas-assisted gravity flooding achieved more stable gas-displacing-oil because oil production was at a lower location,and thus,the oil recovery was further enhanced.
基金Supported by the National Natural Science Foundation of China(52074087,51804076)Postdoctoral Natural Science Foundation of China(2021M690528).
文摘Aiming at the technology of hydraulic fracturing assisted oil displacement which combines hydraulic fracturing,seepage and oil displacement,an experimental system of energy storage and flowback in fracturing assisted oil displacement process has been developed and used to simulate the mechanism of percolation,energy storage,oil displacement and flowback of chemical agents in the whole process.The research shows that in hydraulic fracturing assisted oil displacement,the chemical agent could be directly pushed to the deeper area of the low and medium permeability reservoirs,avoiding the viscosity loss and adhesion retention of chemical agents near the pay zone;in addition,this technology could effectively enlarge the swept volume,improve the oil displacement efficiency,replenish formation energy,gather and exploit the scattered residual oil.For the reservoir with higher permeability,this measure takes effect fast,so to lower cost,and the high pressure hydraulic fracturing assisted oil displacement could be adopted directly.For the reservoir with lower permeability which is difficult to absorb water,hydraulic fracturing assisted oil displacement with surfactant should be adopted to reduce flow resistance of the reservoir and improve the water absorption capacity and development effect of the reservoir.The degree of formation energy deficit was the main factor affecting the effective swept range of chemical agents.Moreover,the larger the formation energy deficit was,the further the seepage distance of chemical agents was,accordingly,the larger the effective swept volume was,and the greater the increase of oil recovery was.Formation energy enhancement was the most important contribution to enhanced oil recovery(EOR),which was the key to EOR by the technology of hydraulic fracturing assisted oil displacement.
基金support from the National Natural Science Foundation of China (NO.10772200,10972237)the Important National Science & Technology Specific Projects of China(No.2011ZX05011)
文摘This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.
基金The authors gratefully acknowledge the financial support from the National Science and Technology Major Special Project(2016ZX05058-003).
文摘Due to long-term water injection,often oilfields enter the so-called medium and high water cut stage,and it is difficult to achieve good oil recovery and water reduction through standard methods(single profile control and flooding measures).Therefore,in this study,a novel method based on“plugging,profile control,and flooding”being implemented at the same time is proposed.To assess the performances of this approach,physical simulations,computer tomography,and nuclear magnetic resonance are used.The results show that the combination of a gel plugging agent,a polymer microsphere flooding agent,and a high-efficiency oil displacement agent leads to better results in terms of oil recovery with respect to the situation in which these approaches are used separately(the oil recovery is increased by 15.37%).Computer tomography scan results show that with the combined approach,a larger sweep volume and higher oil washing efficiency are obtained.The remaining oil in the cluster form can be recovered in the middle and low permeability layer,increasing the proportion of the columnar and blind end states of the oil.The nuclear magnetic resonance test results show that the combined“plugging,profile control,and flooding”treatment can also be used to control more effectively the dominant channels of the high permeability layer and further expand the recovery degree of the remaining oil in the pores of different sizes in the middle and low permeability layers.However,for the low permeability layer(permeability difference of 20),the benefits in terms of oil recovery are limited.
