According to the capillary theory,an equivalent capillary model of micro-resistivity imaging logging was built.On this basis,the theoretical models of porosity spectrum(Ф_(i)),permeability spectrum(K_(i))and equivale...According to the capillary theory,an equivalent capillary model of micro-resistivity imaging logging was built.On this basis,the theoretical models of porosity spectrum(Ф_(i)),permeability spectrum(K_(i))and equivalent capillary pressure curve(pe)were established to reflect the reservoir heterogeneity.To promote the application of the theoretical models,the Archie's equation was introduced to establish a general model for quantitatively characterizing bi,K,and pei.Compared with the existing models,it is shown that:(1)the existing porosity spectrum model is the same as the general equation of gi;(2)the Ki model can display the permeability spectrum as compared with Purcell's permeability model;(3)the per model is constructed on a theoretical basis and avoids the limitations of existing models that are built only based on the component of porosity spectrum,as compared with the empirical model of capillary pressure curve.The application in the Permian Maokou Formation of Well TsX in the Central Sichuan paleo-uplift shows that the Ф_(i),K_(i),and p_(ci) models can be effectively applied to the identification of reservoir types,calculation of reservoir properties and pore structure parameters,and evaluation of reservoir heterogeneity.展开更多
To better understand the relationship between the pore capillary pressure and hydrate saturation in sediments, a new method was proposed. First, the phase equilibria of methane hydrate in fine-grained silica sands wer...To better understand the relationship between the pore capillary pressure and hydrate saturation in sediments, a new method was proposed. First, the phase equilibria of methane hydrate in fine-grained silica sands were measured. As to the equilibrium data, the pore capillary pressure and saturation of methane hydrate were calculated. The results showed that the phase equilibria of methane hydrates in fine-grained silica sands changed due to the depressed activity of pore water caused by the surface group and negatively charged characteristic of silica particles as well as the capillary pressure in small pores together. The capillary pressure increased with the increase of methane hydrate saturation due to the decrease of the available pore space. However, the capillary-saturation relationship could not yet be described quantitatively because of the stochastic habit of hydrate growth.展开更多
The traditional Hassler-Brunner(HB)interpretation method of centrifuge capillary pressure is widely used in materials,soil,biotechnology,and especially in the petroleum industry.However,the assumptions of the traditio...The traditional Hassler-Brunner(HB)interpretation method of centrifuge capillary pressure is widely used in materials,soil,biotechnology,and especially in the petroleum industry.However,the assumptions of the traditional method cannot be simultaneously satisfied,the traditional method has been known to lead significant errors in some cases.In this paper,a new double integral method is proposed to evaluate the centrifuge capillary pressure of long tight sandstone samples.Both the changes of capillary length and interface of wetting phase and non-wetting phase fluids are considered by the new integral method,thus the average pressure and saturation derived from the proposed double integral method is more sufficient in theoretic foundation and clearer on physical meaning.By comparing with the measured capillary pressure of long tight sandstone core samples from porous plate,the capillary pressure calculated from traditional HB method is obviously smaller than the measured value,and the discrepancy increases with the decreasing core porosity.However,the average capillary pressure obtained by the proposed double integral method is remarkably consistent with the measured value.The findings of this study can help for better understanding of distribution of wetting phase fluid and average centrifuge capillary pressure in the core during centrifugal process.展开更多
Geological storage of acid gas has been identified as a promising approach to reduce atmospheric carbon dioxide(CO_(2)),hydrogen sulfide(H_(2)S)and alleviate public concern resulting from the sour gas production.A goo...Geological storage of acid gas has been identified as a promising approach to reduce atmospheric carbon dioxide(CO_(2)),hydrogen sulfide(H_(2)S)and alleviate public concern resulting from the sour gas production.A good understanding of the relative permeability and capillary pressure characteristics is crucial to predict the process of acid gas injection and migration.The prediction of injection and redistribution of acid gas is important to determine storage capacity,formation pressure,plume extent,shape,and leakage potential.Herein,the existing experimental data and theoretical models were reviewed to gain a better understanding of the issue how the H_(2)S content affects gas density,gas viscosity,interfacial tension,wettability,relative permeability and capillary pressure characteristics of acid gas/brine/rock systems.The densities and viscosities of the acid gas with different H_(2)S mole fractions are both temperature-and pressure-dependent,which vary among the gas,liquid and supercritical phases.Water/acid gas interfacial tension decreases strongly with increasing H_(2)S content.For mica and clean quartz,water contact angle increases with increasing H_(2)S mole fraction.In particular,wettability reversal of mica to a H_(2)S-wet behavior occurs in the presence of dense H_(2)S.The capillary pressure increases with decreasing contact angle.At a given saturation,the relative permeability of a fluid is higher when the fluid is nonwetting.The capillary pressure decreases with decreasing interfacial tension at a given saturation.However,the existing datasets do not show a consistent link between capillary number and relative permeability.The capillary pressure decreases with increasing H_(2)S mole fraction.However,there is no consensus on the effect of the H_(2)S content on the relative permeability curves.This may be due to the limited availability of the relative permeability and capillary pressure data for acid gas/brine/rock systems;thus,more experimental measurements are required.展开更多
Primary drainage capillary pressure data are usually correlatable with a 3D predictable property of grid cells.Accordingly,rock typing is normally performed based on an established correlation.Primary drainage as well...Primary drainage capillary pressure data are usually correlatable with a 3D predictable property of grid cells.Accordingly,rock typing is normally performed based on an established correlation.Primary drainage as well as corresponding imbibition and/or secondary drainage capillary pressure curves are averaged to establish a saturation table for each rock type region in reservoir modeling.This study in-vestigates the reliability of this industry-accepted methodology,and has two main contributions.First,we show that if different types of capillary pressures are plotted against water saturation,comparing them might be highly misleading.We demonstrate that although primary drainage capillary pressure data may be plotted against water saturation,the imbibition and secondary drainage capillary pressure data should be plotted against imbibed water saturation.This would enable reservoir engineers to check whether rocks with similar primary drainage capillary pressures do or do not have similar imbibition/secondary drainage counterparts.Using this technique,rock quality can be also deduced from imbibition and secondary drainage capillary pressure curves.We use capillary pressure data measured on limestone and sandstone samples from the Asmari Formation in three Iranian oilfields to evaluate our technique.The second contribution of this study is the proposal of a new methodology for preparing capillary pressure curves for reservoir models.In our methodology,a grid cell can represent more than one rock type region,each specific to a saturation function.As a part of this methodology,we present new physically meaningful equations for averaging primary drainage,imbibition,and secondary drainage capillary pressure curves.展开更多
Petrophysicists and reservoir engineers utilise the capillary pressure and saturation-height function for calculating the water saturation of any reservoir,at a given height above the free water level.The results have...Petrophysicists and reservoir engineers utilise the capillary pressure and saturation-height function for calculating the water saturation of any reservoir,at a given height above the free water level.The results have a big impact on reserve estimation.The majority of capillary pressure studies are carried out in labs with core data.Cores,on the other hand,are usually altered from their original state before being delivered to laboratories.Moreover,the accuracy of discrete sets of core data in describing entire reservoir parameters,is still up for debate.Prediction of the capillary pressure curve in reservoir condition is an important subject that is challenging to perform.The use of nuclear magnetic resonance(NMR)logs for oil and gas exploration has grown in popularity over the last few decades.However,most of the time the utilization of the data is limited for evaluating porosity-permeability,distributions and computation of irreducible water saturation.After the advent of fluid substitution methods,NMR T_(2)distributions may now be used to synthesize core equivalent capillary pressure curves.Using fluid substitution workflow,our study introduces a better approach for obtaining capillary pressure curves from the NMR T_(2)distribution.The available core data has been used to calculate calibration parameters for better saturation height modelling.The workflow introduces a novel approach in resistivity independent saturation computation.In the exploratory wells of our study area,computed water saturation derived from the saturation height function exhibits encouraging agreement with resistivity based water saturation from multi-mineral model.The NMR based saturation height modelling approach has been included in study area for the first time so far.展开更多
Pore structure reflected from capillary pressure curves plays an important role in low-permeability formation evaluation. It is a common way to construct capillary pressure curves by Nuclear Magnetic Resonance(NMR) ...Pore structure reflected from capillary pressure curves plays an important role in low-permeability formation evaluation. It is a common way to construct capillary pressure curves by Nuclear Magnetic Resonance(NMR) log. However, the method's efficiency will be severely affected if there is no NMR log data or it cannot reflect pore structure well. Therefore, on the basis of J function and diagenetic facies classification, a new empirical model for constructing capillary pressure curves from conventional logs is proposed here as a solution to the problem. This model includes porosity and the relative value of natural gamma rays as independent variables and the saturation of mercury injection as a dependent variable. According to the 51 core experimental data sets of three diagenetic facies from the bottom of the Upper Triassic in the western Ordos Basin, China, the model's parameters in each diagenetic facies are calibrated. Both self-checking and extrapolation tests show a positive effect, which demonstrates the high reliability of the proposed capillary pressure curve construction model. Based on the constructed capillary pressure curves, NMR T_2 spectra under fully brine-saturated conditions are mapped by a piecewise power function. A field study is then presented. Agreement can be seen between the mapped NMR T_2 spectra and the MRIL-Plog data in the location of the major peak, right boundary, distribution characteristics and T_2 logarithmic mean value. In addition, the capillary pressure curve construction model proposed in this paper is not affected by special log data or formation condition. It is of great importance in evaluating pore structure, predicting oil production and identifying oil layers through NMR log data in low-permeability sandstones.展开更多
In this study,an immiscible oil-water two phase flow in a typical porous media was modeled using the well-known Lattice Boltzmann method.A set of flow tests for modeling an oil-water two phase flow in the porous media...In this study,an immiscible oil-water two phase flow in a typical porous media was modeled using the well-known Lattice Boltzmann method.A set of flow tests for modeling an oil-water two phase flow in the porous media were conducted to generate the capillary pressure curves for two distinctive initial conditions,namely,water and oil dispersed conditions in two domains of different resolutions.Based on the obtained results,the general trend of these curves has an acceptable agreement with the usual trend of these curves in hydrocarbon reservoirs and the capillary data are independent of the initial conditions.Also,the results showed the effect of grid resolution on capillary data which are validated quantitatively by proposing a new approach using Purcell's equation.One can see that they are compatible with the geometrical characteristics of the porous media as well as the conditions governing the tests.Finally,another set of tests for oil water pairs of higher viscosity ratio up to 4.4 was performed in a low porosity heterogeneous porous media and the viscous coupling effect on capillary data,due to viscosity ratio,was studied to strengthen the model validation.展开更多
The pumping test in an unconfined aquifer with and without a low-permeability soil was studied experimentally to reveal the influence of the negative air pressure (NP) caused by the upper layer on the water content ...The pumping test in an unconfined aquifer with and without a low-permeability soil was studied experimentally to reveal the influence of the negative air pressure (NP) caused by the upper layer on the water content (w), the water pressure (Pw), as well as on the capillary pressure (Pc). The study demonstrates that the NP generated in the vadose zone during pumping in the capper aquifer has a significant influence on w, Pw and Pc The Pc obtained from the capped aquifer is smaller than that without the upper layer. After the NP reaches a peak, the influence of the NP on Pc. is gradually declined as the air inflows through the upper layer which makes the NP gradually return to zero. When the air pressure returns to the atmospheric pressure, Pc in the vadose zone is only correlated with Pw, the same as the case with no upper layer.展开更多
Usually extended two-phase capillary pressures are used in three-phase simulations,because three-phase capillary pressures are not possible or hard to measure.In this work three-phase capillary pressure surfaces are c...Usually extended two-phase capillary pressures are used in three-phase simulations,because three-phase capillary pressures are not possible or hard to measure.In this work three-phase capillary pressure surfaces are created by at pore network model.The input parameters to this network model are found by matching two-phase capillary pressure curves.This matching is done with a slightly modified EnKF routine.Tables with three-phase capillary pressures are created and used as input to flow simulations.展开更多
While experimental designs developed in recent decades have contributed to research on dynamic nonequilibrium effects in transient two-phase flow in porous media,this problem has been seldom investigated using direct ...While experimental designs developed in recent decades have contributed to research on dynamic nonequilibrium effects in transient two-phase flow in porous media,this problem has been seldom investigated using direct numerical simulation(DNS).Only a few studies have sought to numerically solve Navier—Stokes equations with level-set(LS)or volume-of-fluid(VoF)methods,each of which has constraints in terms of meniscus dynamics for various flow velocities in the control volume(CV)domain.The Shan—Chen multiphase multicomponent lattice Boltzmann method(SC-LBM)has a fundamental mechanism to separate immiscible fluid phases in the density domain without these limitations.Therefore,this study applied it to explore two-phase displacement in a single representative elementary volume(REV)of two-dimensional(2D)porous media.As a continuation of a previous investigation into one-step inflow/outflow in 2D porous media,this work seeks to identify dynamic nonequilibrium effects on capillary pressure—saturation relationship(P_(c)—S)for quasi-steady-state flow and multistep inflow/outflow under various pressure boundary conditions.The simulation outcomes show that P_(c),S and specific interfacial area(a_(nw))had multistep-wise dynamic effects corresponding to the multistep-wise pressure boundary conditions.With finer adjustments to the increase in pressure over more steps,dynamic nonequilibrium effects were significantly alleviated and even finally disappeared to achieve quasisteady-state inflow/outflow conditions.Furthermore,triangular wave-formed pressure boundary conditions were applied in different periods to investigate dynamic nonequilibrium effects for hysteretical Pc—S.The results showed overshoot and undershoot of P_(c)to S in loops of the nonequilibrium hysteresis.In addition,the flow regimes of multistep-wise dynamic effects were analyzed in terms of Reynolds and capillary numbers(Re and Ca).The analysis of REV-scale flow regimes showed higher Re(1<Re<10)for more significant dynamic nonequilibrium effects.This indicates that inertia is critical for transient twophase flow in porous media under dynamic nonequilibrium conditions.展开更多
The relationship between capillary pressure and saturation plays a critical role in the characterization of two-phase flow and transport in aquifers and oil reservoirs. This relationship is usually determined under th...The relationship between capillary pressure and saturation plays a critical role in the characterization of two-phase flow and transport in aquifers and oil reservoirs. This relationship is usually determined under the static condition, where capillary pressure is the only function of saturation. However,considerable experiments have suggested that the dependence of capillary pressure on desaturation rate is under the dynamic condition. Thus, a more general description of capillary pressure that includes dynamic capillary effect has been approved widely. A comprehensive understanding of the dynamic capillary effect is needed for the investigation of the two-phase flow in porous media by various methods. In general, dynamic capillary effect in porous media can be studied through the laboratory experiment, pore-to macro-scale modeling, and artificial neural network. Here, main principle and research procedures of each method are reviewed in detail. Then, research progress, disadvantages and advantages are discussed, respectively. In addition, upscaling study from pore-to macro-scale are introduced, which explains the difference between laboratory experiment and pore-scale modeling. At last, several future perspectives and recommendations for optimal solution of dynamic capillary effect are presented.展开更多
A novel gradient pressurized capillary electrochromatography (pCEC) instrument was developed to separate peptides. Two gradient elution modes, hydrophobic and hydrophilic interaction mode in pCEC, were performed on t...A novel gradient pressurized capillary electrochromatography (pCEC) instrument was developed to separate peptides. Two gradient elution modes, hydrophobic and hydrophilic interaction mode in pCEC, were performed on this instrument. Baseline separation of six peptides was obtained on two gradient modes with C18 column and strong cationic exchange column respectively. The effects of mixer volume and total flow rate of pumps on resolution were also discussed.展开更多
Capillary electrochromatography (CEC) is a hybrid technique that couples the good selectivity of high-performance liquid chromatography (HPLC) and the high separation efficiency of capillary electrophoresis (CE)...Capillary electrochromatography (CEC) is a hybrid technique that couples the good selectivity of high-performance liquid chromatography (HPLC) and the high separation efficiency of capillary electrophoresis (CE). Both charged and uncharged compounds can be separated effectively using CEC. In some cases, however, the bubbles that generated in the capillary column in pure CEC performed on commercial CE instruments will cause unstable current and even disrupt the separation when the concentration of buffer is very high. By applying pressure on the electrochromatographic separation via a micro-HPLC pump, pressurized capillary electrochromatography ( pCEC ) combines two driving factors of the electroosmotic flow (EOF) and the pressure flow, thereby increasing the speed and the selectivity of separation and suppressing the bubble formation. Moreover,展开更多
Shale oil can be extracted from shale by using interconnected pore networks.The migration of hydrocarbon molecules within the shale is controlled by pore connectivity.However,assessing the pore connectivity of shale o...Shale oil can be extracted from shale by using interconnected pore networks.The migration of hydrocarbon molecules within the shale is controlled by pore connectivity.However,assessing the pore connectivity of shale oil reservoirs is uncommon.To characterize pore connectivity and clarify its controlling factors,this study used spontaneous imbibition(SI)combined with nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies on shale oil reservoirs selected from the Shahejie Formation in the Dongying Sag,Bohai Bay Basin.According to the findings,the SI processes of shales include fast-rising,slow-rising,and stable stages.The fast-rising stage denotes pore connectivity.The shales studied have poor connectivity,with lower imbibition slopes and connected porosity ratios,but large effective tortuosity.During the SI process,micropores have the highest imbibition saturation,followed by mesopores and macropores.Furthermore,n-dodecane ingested into micropores appears primarily as adsorbed,whereas n-dodecane appears primarily as free states in mesopores and macropores during the SI process.The pore connectivity of the shales under study is primarily controlled by inorganic minerals.Quartz and feldspar develop large and regular pores,resulting in better pore connectivity,whereas clay minerals and calcite with plenty of complex intragranular pores do not.Organic matter negatively influences pore connectivity because the dissolution of calcite by organic acid produced during hydrocarbon generation leads to a more complex and heterogeneous pore structure.This study sheds light on the pore connectivity and controlling factors of the shale oil reservoir and aids in the understanding of shale oil mobility.展开更多
Spontaneous imbibition of water-based frac- turing fluids into the shale matrix is considered to be the main mechanism responsible for the high volume of water loss during the flowback period. Understanding the matrix...Spontaneous imbibition of water-based frac- turing fluids into the shale matrix is considered to be the main mechanism responsible for the high volume of water loss during the flowback period. Understanding the matrix imbibition capacity and rate helps to determine the frac- turing fluid volume, optimize the flowback design, and to analyze the influences on the production of shale gas. Imbibition experiments were conducted on shale samples from the Sichuan Basin, and some tight sandstone samples from the Ordos Basin. Tight volcanic samples from the Songliao Basin were also investigated for comparison. The effects of porosity, clay minerals, surfactants, and KC1 solutions on the matrix imbibition capacity and rate were systematically investigated. The results show that the imbibition characteristic of tight rocks can be characterized by the imbibition curve shape, the imbibition capacity, the imbibition rate, and the diffusion rate. The driving forces of water imbibition are the capillary pressure and the clay absorption force. For the tight rocks with low clay contents, the imbibition capacity and rate are positively correlated with the porosity. For tight rocks with high clay content, the type and content of clay minerals are the most impor- tant factors affecting the imbibition capacity. The imbibed water volume normalized by the porosity increases with an increasing total clay content. Smectite and illite/smectite tend to greatly enhance the water imbibition capacity. Furthermore, clay-rich tight rocks can imbibe a volume of water greater than their measured pore volume. The aver- age ratio of the imbibed water volume to the pore volume is approximately 1.1 in the Niutitang shale, 1.9 in the Lujiaping shale, 2.8 in the Longmaxi shale, and 4.0 in the Yingcheng volcanic rock, and this ratio can be regarded as a parameter that indicates the influence of clay. In addition, surfactants can change the imbibition capacity due to alteration of the capillary pressure and wettability. A 10 wt% KC1 solution can inhibit clay absorption to reduce the imbibition capacity.展开更多
In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accu...In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accumulation and the tight oil charging process. However, kinetic models used for petroleum development are not applicable for petroleum exploration. In this study, a static resistance model[ is proposed after analyzing resistances in ultra-slow flow in porous media. Using this model, the disco^atinuous pattern of oil charging is reproduced through incompressible Navier-Stokes equations, the phase field method and the finite element method. This study also explains macroscopic percolation behavior with microscopic flow mechanisms and discusses some issues in ultra-slow flow in a micro/nano pore-throat network. The resistance analysis reveals that capillary resistance and dissipation resistance are dominant factors in the mechanism of oil accumulation in tight reservoirs. Numerical simulations show that pressure thresholds exist and result in discontinuous oil charging. Generally, it is proven that the static model is more applicable than kinetic models in describing oil accumulation in tight reservoirs.展开更多
A pore-network model physically based on pore level multiphase flow was used to study the water-non-aqueous phase liquid (NAPL) displacement process, especially the effects of wettability, water-NAPL interracial ten...A pore-network model physically based on pore level multiphase flow was used to study the water-non-aqueous phase liquid (NAPL) displacement process, especially the effects of wettability, water-NAPL interracial tension, the fraction of NAPL-wet pores, and initial water saturation on the displacement. The computed data show that with the wettability of the mineral surfaces changing from strongly water-wet to NAPL-wet, capillary pressure and the NAPL relative permeability gradually decrease, while water-NAPL interfacial tension has little effect on water relative permeability, but initial water saturation has a strong effect on water and NAPL relative permeabilities. The analytical results may help to understand the micro-structure displacement process of non-aqueous phase liquid and to provide the theoretical basis for controlling NAPL migration.展开更多
The special gas wettability phenomenon of reservoir rocks has been recognized by more and more researchers.It has a significant effect on efficient development of unconventional reservoirs.First,based on the preferent...The special gas wettability phenomenon of reservoir rocks has been recognized by more and more researchers.It has a significant effect on efficient development of unconventional reservoirs.First,based on the preferentially gas-covered ability and surface free energy changes,definition and evaluation methods have been established.Second,a method for altering rock wettability and its mechanisms have been studied,surface oriented phenomena of functional groups with low surface energy are the fundamental reason for gas wettability alteration of rock.Third,the effect of gas wettability on the surface energy,electrical properties and dilatability are investigated.Last,the effects of gas wettability on capillary pressure,oil/gas/water distribution and flow are investigated with capillary tubes and etchedglass network models.The gas wettability theory of reservoir rocks has been initially established,which provides theoretical support for the efficient production of unconventional reservoirs and has great significance.展开更多
基金Supported by the National Natural Science Foundation of China(U2003102,41974117)China National Science and Technology Major Project(2016ZX05052001).
文摘According to the capillary theory,an equivalent capillary model of micro-resistivity imaging logging was built.On this basis,the theoretical models of porosity spectrum(Ф_(i)),permeability spectrum(K_(i))and equivalent capillary pressure curve(pe)were established to reflect the reservoir heterogeneity.To promote the application of the theoretical models,the Archie's equation was introduced to establish a general model for quantitatively characterizing bi,K,and pei.Compared with the existing models,it is shown that:(1)the existing porosity spectrum model is the same as the general equation of gi;(2)the Ki model can display the permeability spectrum as compared with Purcell's permeability model;(3)the per model is constructed on a theoretical basis and avoids the limitations of existing models that are built only based on the component of porosity spectrum,as compared with the empirical model of capillary pressure curve.The application in the Permian Maokou Formation of Well TsX in the Central Sichuan paleo-uplift shows that the Ф_(i),K_(i),and p_(ci) models can be effectively applied to the identification of reservoir types,calculation of reservoir properties and pore structure parameters,and evaluation of reservoir heterogeneity.
基金The Open Fund of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University under contract No.PLN1206the National Natural Science Foundation of China under contract No.51376114+2 种基金the Ministry of Land and Resources research of China in the Public Interest under contract No.201111026the Open Fund of Shandong Provincial Key Laboratory of Depositional Mineralization&Sedimentary Minerals,Shandong University of Science&Technology under contract No.DMSM201007the National Basic Research Program(973 program)of China under contract No.2009CB219503
文摘To better understand the relationship between the pore capillary pressure and hydrate saturation in sediments, a new method was proposed. First, the phase equilibria of methane hydrate in fine-grained silica sands were measured. As to the equilibrium data, the pore capillary pressure and saturation of methane hydrate were calculated. The results showed that the phase equilibria of methane hydrates in fine-grained silica sands changed due to the depressed activity of pore water caused by the surface group and negatively charged characteristic of silica particles as well as the capillary pressure in small pores together. The capillary pressure increased with the increase of methane hydrate saturation due to the decrease of the available pore space. However, the capillary-saturation relationship could not yet be described quantitatively because of the stochastic habit of hydrate growth.
基金supported by the Foundation of State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing(No.PRP/open-1704)the Foundation of Education of Hu Bei Province,China(No.Q20171304)the Foundation of Key Laboratory of Exploration Technology for Oil and Gas Resources of Ministry of Education(No.K-2018-12)。
文摘The traditional Hassler-Brunner(HB)interpretation method of centrifuge capillary pressure is widely used in materials,soil,biotechnology,and especially in the petroleum industry.However,the assumptions of the traditional method cannot be simultaneously satisfied,the traditional method has been known to lead significant errors in some cases.In this paper,a new double integral method is proposed to evaluate the centrifuge capillary pressure of long tight sandstone samples.Both the changes of capillary length and interface of wetting phase and non-wetting phase fluids are considered by the new integral method,thus the average pressure and saturation derived from the proposed double integral method is more sufficient in theoretic foundation and clearer on physical meaning.By comparing with the measured capillary pressure of long tight sandstone core samples from porous plate,the capillary pressure calculated from traditional HB method is obviously smaller than the measured value,and the discrepancy increases with the decreasing core porosity.However,the average capillary pressure obtained by the proposed double integral method is remarkably consistent with the measured value.The findings of this study can help for better understanding of distribution of wetting phase fluid and average centrifuge capillary pressure in the core during centrifugal process.
基金the National Natural Science Foundation of China(Grant Nos.41872210 and 41274111)the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering(Grant No.Z018002)。
文摘Geological storage of acid gas has been identified as a promising approach to reduce atmospheric carbon dioxide(CO_(2)),hydrogen sulfide(H_(2)S)and alleviate public concern resulting from the sour gas production.A good understanding of the relative permeability and capillary pressure characteristics is crucial to predict the process of acid gas injection and migration.The prediction of injection and redistribution of acid gas is important to determine storage capacity,formation pressure,plume extent,shape,and leakage potential.Herein,the existing experimental data and theoretical models were reviewed to gain a better understanding of the issue how the H_(2)S content affects gas density,gas viscosity,interfacial tension,wettability,relative permeability and capillary pressure characteristics of acid gas/brine/rock systems.The densities and viscosities of the acid gas with different H_(2)S mole fractions are both temperature-and pressure-dependent,which vary among the gas,liquid and supercritical phases.Water/acid gas interfacial tension decreases strongly with increasing H_(2)S content.For mica and clean quartz,water contact angle increases with increasing H_(2)S mole fraction.In particular,wettability reversal of mica to a H_(2)S-wet behavior occurs in the presence of dense H_(2)S.The capillary pressure increases with decreasing contact angle.At a given saturation,the relative permeability of a fluid is higher when the fluid is nonwetting.The capillary pressure decreases with decreasing interfacial tension at a given saturation.However,the existing datasets do not show a consistent link between capillary number and relative permeability.The capillary pressure decreases with increasing H_(2)S mole fraction.However,there is no consensus on the effect of the H_(2)S content on the relative permeability curves.This may be due to the limited availability of the relative permeability and capillary pressure data for acid gas/brine/rock systems;thus,more experimental measurements are required.
基金Kansas State University for the faculty start-up fund.
文摘Primary drainage capillary pressure data are usually correlatable with a 3D predictable property of grid cells.Accordingly,rock typing is normally performed based on an established correlation.Primary drainage as well as corresponding imbibition and/or secondary drainage capillary pressure curves are averaged to establish a saturation table for each rock type region in reservoir modeling.This study in-vestigates the reliability of this industry-accepted methodology,and has two main contributions.First,we show that if different types of capillary pressures are plotted against water saturation,comparing them might be highly misleading.We demonstrate that although primary drainage capillary pressure data may be plotted against water saturation,the imbibition and secondary drainage capillary pressure data should be plotted against imbibed water saturation.This would enable reservoir engineers to check whether rocks with similar primary drainage capillary pressures do or do not have similar imbibition/secondary drainage counterparts.Using this technique,rock quality can be also deduced from imbibition and secondary drainage capillary pressure curves.We use capillary pressure data measured on limestone and sandstone samples from the Asmari Formation in three Iranian oilfields to evaluate our technique.The second contribution of this study is the proposal of a new methodology for preparing capillary pressure curves for reservoir models.In our methodology,a grid cell can represent more than one rock type region,each specific to a saturation function.As a part of this methodology,we present new physically meaningful equations for averaging primary drainage,imbibition,and secondary drainage capillary pressure curves.
基金The authors gratefully appreciate the support of Oil and Natural Gas Corporation,for providing data and permission to carry out the work under the CoEOGE project:RD/0120-PSUCE19-001.
文摘Petrophysicists and reservoir engineers utilise the capillary pressure and saturation-height function for calculating the water saturation of any reservoir,at a given height above the free water level.The results have a big impact on reserve estimation.The majority of capillary pressure studies are carried out in labs with core data.Cores,on the other hand,are usually altered from their original state before being delivered to laboratories.Moreover,the accuracy of discrete sets of core data in describing entire reservoir parameters,is still up for debate.Prediction of the capillary pressure curve in reservoir condition is an important subject that is challenging to perform.The use of nuclear magnetic resonance(NMR)logs for oil and gas exploration has grown in popularity over the last few decades.However,most of the time the utilization of the data is limited for evaluating porosity-permeability,distributions and computation of irreducible water saturation.After the advent of fluid substitution methods,NMR T_(2)distributions may now be used to synthesize core equivalent capillary pressure curves.Using fluid substitution workflow,our study introduces a better approach for obtaining capillary pressure curves from the NMR T_(2)distribution.The available core data has been used to calculate calibration parameters for better saturation height modelling.The workflow introduces a novel approach in resistivity independent saturation computation.In the exploratory wells of our study area,computed water saturation derived from the saturation height function exhibits encouraging agreement with resistivity based water saturation from multi-mineral model.The NMR based saturation height modelling approach has been included in study area for the first time so far.
基金supported by the Scientific Research Starting Foundation of China University of Petroleum-Beijing at Karamay(No.RCYJ2016B-01-008)the Major National Oil&Gas Specific Project of China(No.2016ZX05050008)
文摘Pore structure reflected from capillary pressure curves plays an important role in low-permeability formation evaluation. It is a common way to construct capillary pressure curves by Nuclear Magnetic Resonance(NMR) log. However, the method's efficiency will be severely affected if there is no NMR log data or it cannot reflect pore structure well. Therefore, on the basis of J function and diagenetic facies classification, a new empirical model for constructing capillary pressure curves from conventional logs is proposed here as a solution to the problem. This model includes porosity and the relative value of natural gamma rays as independent variables and the saturation of mercury injection as a dependent variable. According to the 51 core experimental data sets of three diagenetic facies from the bottom of the Upper Triassic in the western Ordos Basin, China, the model's parameters in each diagenetic facies are calibrated. Both self-checking and extrapolation tests show a positive effect, which demonstrates the high reliability of the proposed capillary pressure curve construction model. Based on the constructed capillary pressure curves, NMR T_2 spectra under fully brine-saturated conditions are mapped by a piecewise power function. A field study is then presented. Agreement can be seen between the mapped NMR T_2 spectra and the MRIL-Plog data in the location of the major peak, right boundary, distribution characteristics and T_2 logarithmic mean value. In addition, the capillary pressure curve construction model proposed in this paper is not affected by special log data or formation condition. It is of great importance in evaluating pore structure, predicting oil production and identifying oil layers through NMR log data in low-permeability sandstones.
基金The authors gratefully acknowledge the financial support from the Open Fund(PLN201614)of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)Young Scholars Development Fund of Southwest Petroleum University(Grant No.201599010086).
文摘In this study,an immiscible oil-water two phase flow in a typical porous media was modeled using the well-known Lattice Boltzmann method.A set of flow tests for modeling an oil-water two phase flow in the porous media were conducted to generate the capillary pressure curves for two distinctive initial conditions,namely,water and oil dispersed conditions in two domains of different resolutions.Based on the obtained results,the general trend of these curves has an acceptable agreement with the usual trend of these curves in hydrocarbon reservoirs and the capillary data are independent of the initial conditions.Also,the results showed the effect of grid resolution on capillary data which are validated quantitatively by proposing a new approach using Purcell's equation.One can see that they are compatible with the geometrical characteristics of the porous media as well as the conditions governing the tests.Finally,another set of tests for oil water pairs of higher viscosity ratio up to 4.4 was performed in a low porosity heterogeneous porous media and the viscous coupling effect on capillary data,due to viscosity ratio,was studied to strengthen the model validation.
基金Project supported by the National Natural Science Foundation of China(Grant No.41272251)the Research Grants Council of the Hong Kong Special Administrative Region,China(Grant No.HKU 701908P)
文摘The pumping test in an unconfined aquifer with and without a low-permeability soil was studied experimentally to reveal the influence of the negative air pressure (NP) caused by the upper layer on the water content (w), the water pressure (Pw), as well as on the capillary pressure (Pc). The study demonstrates that the NP generated in the vadose zone during pumping in the capper aquifer has a significant influence on w, Pw and Pc The Pc obtained from the capped aquifer is smaller than that without the upper layer. After the NP reaches a peak, the influence of the NP on Pc. is gradually declined as the air inflows through the upper layer which makes the NP gradually return to zero. When the air pressure returns to the atmospheric pressure, Pc in the vadose zone is only correlated with Pw, the same as the case with no upper layer.
文摘Usually extended two-phase capillary pressures are used in three-phase simulations,because three-phase capillary pressures are not possible or hard to measure.In this work three-phase capillary pressure surfaces are created by at pore network model.The input parameters to this network model are found by matching two-phase capillary pressure curves.This matching is done with a slightly modified EnKF routine.Tables with three-phase capillary pressures are created and used as input to flow simulations.
基金University of Queensland International Scholarship(UQI)for its support(Grant No.42719692)。
文摘While experimental designs developed in recent decades have contributed to research on dynamic nonequilibrium effects in transient two-phase flow in porous media,this problem has been seldom investigated using direct numerical simulation(DNS).Only a few studies have sought to numerically solve Navier—Stokes equations with level-set(LS)or volume-of-fluid(VoF)methods,each of which has constraints in terms of meniscus dynamics for various flow velocities in the control volume(CV)domain.The Shan—Chen multiphase multicomponent lattice Boltzmann method(SC-LBM)has a fundamental mechanism to separate immiscible fluid phases in the density domain without these limitations.Therefore,this study applied it to explore two-phase displacement in a single representative elementary volume(REV)of two-dimensional(2D)porous media.As a continuation of a previous investigation into one-step inflow/outflow in 2D porous media,this work seeks to identify dynamic nonequilibrium effects on capillary pressure—saturation relationship(P_(c)—S)for quasi-steady-state flow and multistep inflow/outflow under various pressure boundary conditions.The simulation outcomes show that P_(c),S and specific interfacial area(a_(nw))had multistep-wise dynamic effects corresponding to the multistep-wise pressure boundary conditions.With finer adjustments to the increase in pressure over more steps,dynamic nonequilibrium effects were significantly alleviated and even finally disappeared to achieve quasisteady-state inflow/outflow conditions.Furthermore,triangular wave-formed pressure boundary conditions were applied in different periods to investigate dynamic nonequilibrium effects for hysteretical Pc—S.The results showed overshoot and undershoot of P_(c)to S in loops of the nonequilibrium hysteresis.In addition,the flow regimes of multistep-wise dynamic effects were analyzed in terms of Reynolds and capillary numbers(Re and Ca).The analysis of REV-scale flow regimes showed higher Re(1<Re<10)for more significant dynamic nonequilibrium effects.This indicates that inertia is critical for transient twophase flow in porous media under dynamic nonequilibrium conditions.
基金financially supported by the National Natural Science Foundation of China (No. 42102149)the Fundamental Research Funds for the Central Universities (No. 2462021YXZZ005)。
文摘The relationship between capillary pressure and saturation plays a critical role in the characterization of two-phase flow and transport in aquifers and oil reservoirs. This relationship is usually determined under the static condition, where capillary pressure is the only function of saturation. However,considerable experiments have suggested that the dependence of capillary pressure on desaturation rate is under the dynamic condition. Thus, a more general description of capillary pressure that includes dynamic capillary effect has been approved widely. A comprehensive understanding of the dynamic capillary effect is needed for the investigation of the two-phase flow in porous media by various methods. In general, dynamic capillary effect in porous media can be studied through the laboratory experiment, pore-to macro-scale modeling, and artificial neural network. Here, main principle and research procedures of each method are reviewed in detail. Then, research progress, disadvantages and advantages are discussed, respectively. In addition, upscaling study from pore-to macro-scale are introduced, which explains the difference between laboratory experiment and pore-scale modeling. At last, several future perspectives and recommendations for optimal solution of dynamic capillary effect are presented.
基金The study is supported by NNSFC,grant No.20175010.
文摘A novel gradient pressurized capillary electrochromatography (pCEC) instrument was developed to separate peptides. Two gradient elution modes, hydrophobic and hydrophilic interaction mode in pCEC, were performed on this instrument. Baseline separation of six peptides was obtained on two gradient modes with C18 column and strong cationic exchange column respectively. The effects of mixer volume and total flow rate of pumps on resolution were also discussed.
基金Supported by the National Natural Science Foundation of China(Nos 20305004 and 20575012), Program for NewCentury Ex-cellent Talents in University of China(No NCET-04-0612), Specialized Research Fund for the Doctoral Program of Higher Education(No 20050386008), and the Science Foundation of Fujian Province(Nos 2005Y015 and D0510006)
文摘Capillary electrochromatography (CEC) is a hybrid technique that couples the good selectivity of high-performance liquid chromatography (HPLC) and the high separation efficiency of capillary electrophoresis (CE). Both charged and uncharged compounds can be separated effectively using CEC. In some cases, however, the bubbles that generated in the capillary column in pure CEC performed on commercial CE instruments will cause unstable current and even disrupt the separation when the concentration of buffer is very high. By applying pressure on the electrochromatographic separation via a micro-HPLC pump, pressurized capillary electrochromatography ( pCEC ) combines two driving factors of the electroosmotic flow (EOF) and the pressure flow, thereby increasing the speed and the selectivity of separation and suppressing the bubble formation. Moreover,
基金This study was financially supported by the Natural Science Foundation of Shandong Province(ZR2020QD036,ZR2020QD037,and ZR2021QD072)the National Natural Science Foundation of China(41972123).
文摘Shale oil can be extracted from shale by using interconnected pore networks.The migration of hydrocarbon molecules within the shale is controlled by pore connectivity.However,assessing the pore connectivity of shale oil reservoirs is uncommon.To characterize pore connectivity and clarify its controlling factors,this study used spontaneous imbibition(SI)combined with nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies on shale oil reservoirs selected from the Shahejie Formation in the Dongying Sag,Bohai Bay Basin.According to the findings,the SI processes of shales include fast-rising,slow-rising,and stable stages.The fast-rising stage denotes pore connectivity.The shales studied have poor connectivity,with lower imbibition slopes and connected porosity ratios,but large effective tortuosity.During the SI process,micropores have the highest imbibition saturation,followed by mesopores and macropores.Furthermore,n-dodecane ingested into micropores appears primarily as adsorbed,whereas n-dodecane appears primarily as free states in mesopores and macropores during the SI process.The pore connectivity of the shales under study is primarily controlled by inorganic minerals.Quartz and feldspar develop large and regular pores,resulting in better pore connectivity,whereas clay minerals and calcite with plenty of complex intragranular pores do not.Organic matter negatively influences pore connectivity because the dissolution of calcite by organic acid produced during hydrocarbon generation leads to a more complex and heterogeneous pore structure.This study sheds light on the pore connectivity and controlling factors of the shale oil reservoir and aids in the understanding of shale oil mobility.
基金financially supported by the National Basic Research Program of China (973 Program) Granted No. 2015CB250903the National Natural Science Foundation of China Granted No. 51490652The Chongqing Institute of Geology and Mineral Resources supported this field work
文摘Spontaneous imbibition of water-based frac- turing fluids into the shale matrix is considered to be the main mechanism responsible for the high volume of water loss during the flowback period. Understanding the matrix imbibition capacity and rate helps to determine the frac- turing fluid volume, optimize the flowback design, and to analyze the influences on the production of shale gas. Imbibition experiments were conducted on shale samples from the Sichuan Basin, and some tight sandstone samples from the Ordos Basin. Tight volcanic samples from the Songliao Basin were also investigated for comparison. The effects of porosity, clay minerals, surfactants, and KC1 solutions on the matrix imbibition capacity and rate were systematically investigated. The results show that the imbibition characteristic of tight rocks can be characterized by the imbibition curve shape, the imbibition capacity, the imbibition rate, and the diffusion rate. The driving forces of water imbibition are the capillary pressure and the clay absorption force. For the tight rocks with low clay contents, the imbibition capacity and rate are positively correlated with the porosity. For tight rocks with high clay content, the type and content of clay minerals are the most impor- tant factors affecting the imbibition capacity. The imbibed water volume normalized by the porosity increases with an increasing total clay content. Smectite and illite/smectite tend to greatly enhance the water imbibition capacity. Furthermore, clay-rich tight rocks can imbibe a volume of water greater than their measured pore volume. The aver- age ratio of the imbibed water volume to the pore volume is approximately 1.1 in the Niutitang shale, 1.9 in the Lujiaping shale, 2.8 in the Longmaxi shale, and 4.0 in the Yingcheng volcanic rock, and this ratio can be regarded as a parameter that indicates the influence of clay. In addition, surfactants can change the imbibition capacity due to alteration of the capillary pressure and wettability. A 10 wt% KC1 solution can inhibit clay absorption to reduce the imbibition capacity.
基金supported by the Chinese Major National Scientific and Technological Program (2011ZX05001)Chinese Postdoctoral Fund (2013M540114)
文摘In exploration for tight oil, the content and saturation of hydrocarbon in the tight reservoir is a key factor for evaluating the reserve. Therefore, it is necessary to study the geological history of hydrocarbon accumulation and the tight oil charging process. However, kinetic models used for petroleum development are not applicable for petroleum exploration. In this study, a static resistance model[ is proposed after analyzing resistances in ultra-slow flow in porous media. Using this model, the disco^atinuous pattern of oil charging is reproduced through incompressible Navier-Stokes equations, the phase field method and the finite element method. This study also explains macroscopic percolation behavior with microscopic flow mechanisms and discusses some issues in ultra-slow flow in a micro/nano pore-throat network. The resistance analysis reveals that capillary resistance and dissipation resistance are dominant factors in the mechanism of oil accumulation in tight reservoirs. Numerical simulations show that pressure thresholds exist and result in discontinuous oil charging. Generally, it is proven that the static model is more applicable than kinetic models in describing oil accumulation in tight reservoirs.
文摘A pore-network model physically based on pore level multiphase flow was used to study the water-non-aqueous phase liquid (NAPL) displacement process, especially the effects of wettability, water-NAPL interracial tension, the fraction of NAPL-wet pores, and initial water saturation on the displacement. The computed data show that with the wettability of the mineral surfaces changing from strongly water-wet to NAPL-wet, capillary pressure and the NAPL relative permeability gradually decrease, while water-NAPL interfacial tension has little effect on water relative permeability, but initial water saturation has a strong effect on water and NAPL relative permeabilities. The analytical results may help to understand the micro-structure displacement process of non-aqueous phase liquid and to provide the theoretical basis for controlling NAPL migration.
基金supported by the Basic Research on Drilling & Completion of Critical Wells for Oil & Gas (Grant No. 51221003)National Science Fund for Petrochemical Industry (Project No. U1262201)+2 种基金"863" National Project (Project No. 2013AA064803)National Science Fund for Distinguished Young Scholars (Project No. 50925414)National Natural Science Foundation (Project No. 51074173)
文摘The special gas wettability phenomenon of reservoir rocks has been recognized by more and more researchers.It has a significant effect on efficient development of unconventional reservoirs.First,based on the preferentially gas-covered ability and surface free energy changes,definition and evaluation methods have been established.Second,a method for altering rock wettability and its mechanisms have been studied,surface oriented phenomena of functional groups with low surface energy are the fundamental reason for gas wettability alteration of rock.Third,the effect of gas wettability on the surface energy,electrical properties and dilatability are investigated.Last,the effects of gas wettability on capillary pressure,oil/gas/water distribution and flow are investigated with capillary tubes and etchedglass network models.The gas wettability theory of reservoir rocks has been initially established,which provides theoretical support for the efficient production of unconventional reservoirs and has great significance.