Characteristics of water alternating CO_(2)injection in low-permeability beach-bar sand reservoirs

Water flooding can be ineffective in highly heterogeneous low-permeability beach-bar sand reservoirs.The introduction of CO_(2)flooding helps boost the oil production of the reservoirs but only in an early stage.During the late stage of flooding,gas channeling would occur.Water alternating gas(CO_(2))(WAG)process can be used to delay gas channeling and improve the effect of CO_(2)injection,though its adaptability to beach-bar sand reservoirs remains unclear.In order to clarify CO_(2)injection characteristics in these reservoirs,experiments were carried out in high-temperature high-pressure NMR on-line displacement experiment apparatus to simulate different flooding modes on synthetic cores that can reflect the vertical heterogeneity of beach-bar reservoirs.Different CO_(2)injection modes were implemented on these cores and the displacement characteristics and residual oil distribution features during both WAG injection and continuous CO_(2)injection were analyzed quantitatively and qualitatively.The results show that the scheme of WAG injection after continuous CO_(2)injection can obtain better oil displacement efficiency than that of the scheme of continuous CO_(2)injection after WAG injection,but there is no significant difference in respect of oil displacement efficiency of WAG flooding between the mode of bar-injection e beach-production(injection into bar sand e production from beach sand)and the mode of beach-injection e beach-production(injection into and production from beach sand),with the former mode having a higher oil recovery rate.The wider pore-size distribution range of microscopic residual oil after WAG injection shows great potential of enhancing oil recovery from subsequent continuous gas injection.When WAG injection is implemented prior to continuous CO_(2)injection,the displacement effect of the latter is more significant.This research may provide a theoretical basis for CO_(2)EOR in this type of reservoirs.

A novel profile modification HPF-Co gel satisfied with fractured low permeability reservoirs in high temperature and high salinity

Conformance control and water plugging are a widely used EOR method in mature oilfields.However,majority of conformance control and water plugging agents are unavoidable dehydrated situation in high-temperature and high-salinity low permeability reservoirs.Consequently,a novel conformance control system HPF-Co gel,based on high-temperature stabilizer(CoCl_(2)·H_(2)O,CCH)is developed.The HPF-Co bulk gel has better performances with high temperature(120℃)and high salinity(1×10^(5)mg/L).According to Sydansk coding system,the gel strength of HPF-Co with CCH is increased to code G.The dehydration rate of HPF-Co gel is 32.0%after aging for 150 d at 120℃,showing excellent thermal stability.The rheological properties of HPF gel and HPF-Co gel are also studied.The results show that the storage modulus(G′)of HPF-Co gel is always greater than that of HPF gel.The effect of CCH on the microstructure of the gel is studied.The results show that the HPF-Co gel with CCH has a denser gel network,and the diameter of the three-dimensional network skeleton is 1.5-3.5μm.After 90 d of aging,HPF-Co gel still has a good three-dimensional structure.Infrared spectroscopy results show that CCH forms coordination bonds with N and O atoms in the gel amide group,which can suppress the vibration of cross-linked sites and improve the stability at high temperature.Fractured core plugging test determines the optimized polymer gel injection strategy and injection velocity with HPF-Co bulk gel system,plugging rate exceeding 98%.Moreover,the results of subsequent waterflooding recovery can be improved by 17%.

Development of Superhydrophobic Nano-SiO_(2)and Its Field Application in Low-permeability,High-temperature,and High-salinity Oil Reservoirs

In this study,to meet the stringent requirements on the hydrophobicity of nano-SiO_(2)particles for use in depressurization and enhanced injection operations in high-temperature and high-salinity oil reservoirs,secondary chemical grafting modification of nano-SiO_(2)is performed using a silane coupling agent to prepare superhydrophobic nano-SiO_(2) particles.Using these superhydrophobic nano-SiO_(2)particles as the core agent,and liquid paraffin or diesel as the dispersion medium,a uniform dispersion of nano-SiO_(2)particles is achieved under high-speed stirring,and a chemically enhanced water injection system with colloidal stability that can be maintained for more than 60 d is successfully developed.Using this system,a field test of depressurization and enhanced injection is carried out on six wells in an oilfield,and the daily oil production level is increased by 11 t.The cumulative increased water injection is 58784 m^(3),the effective rate of the measures was 100%,and the average validity period is 661 d.

Numerical Simulation of Oil-Water Two-Phase Flow in Low Permeability Tight Reservoirs Based on Weighted Least Squares Meshless Method

In response to the complex characteristics of actual low-permeability tight reservoirs,this study develops a meshless-based numerical simulation method for oil-water two-phase flow in these reservoirs,considering complex boundary shapes.Utilizing radial basis function point interpolation,the method approximates shape functions for unknown functions within the nodal influence domain.The shape functions constructed by the aforementioned meshless interpolation method haveδ-function properties,which facilitate the handling of essential aspects like the controlled bottom-hole flow pressure in horizontal wells.Moreover,the meshless method offers greater flexibility and freedom compared to grid cell discretization,making it simpler to discretize complex geometries.A variational principle for the flow control equation group is introduced using a weighted least squares meshless method,and the pressure distribution is solved implicitly.Example results demonstrate that the computational outcomes of the meshless point cloud model,which has a relatively small degree of freedom,are in close agreement with those of the Discrete Fracture Model(DFM)employing refined grid partitioning,with pressure calculation accuracy exceeding 98.2%.Compared to high-resolution grid-based computational methods,the meshless method can achieve a better balance between computational efficiency and accuracy.Additionally,the impact of fracture half-length on the productivity of horizontal wells is discussed.The results indicate that increasing the fracture half-length is an effective strategy for enhancing production from the perspective of cumulative oil production.

Synergistic anionic/zwitterionic mixed surfactant system with high emulsification efficiency for enhanced oil recovery in low permeability reservoirs

Emulsification is one of the important mechanisms of surfactant flooding. To improve oil recovery for low permeability reservoirs, a highly efficient emulsification oil flooding system consisting of anionic surfactant sodium alkyl glucosyl hydroxypropyl sulfonate(APGSHS) and zwitterionic surfactant octadecyl betaine(BS-18) is proposed. The performance of APGSHS/BS-18 mixed surfactant system was evaluated in terms of interfacial tension, emulsification capability, emulsion size and distribution, wettability alteration, temperature-resistance and salt-resistance. The emulsification speed was used to evaluate the emulsification ability of surfactant systems, and the results show that mixed surfactant systems can completely emulsify the crude oil into emulsions droplets even under low energy conditions. Meanwhile,the system exhibits good temperature and salt resistance. Finally, the best oil recovery of 25.45% is achieved for low permeability core by the mixed surfactant system with a total concentration of 0.3 wt%while the molar ratio of APGSHS:BS-18 is 4:6. The current study indicates that the anionic/zwitterionic mixed surfactant system can improve the oil flooding efficiency and is potential candidate for application in low permeability reservoirs.

Modeling of multiphase flow in low permeability porous media:Effect of wettability and pore structure properties

Multiphase flow in low permeability porous media is involved in numerous energy and environmental applications.However,a complete description of this process is challenging due to the limited modeling scale and the effects of complex pore structures and wettability.To address this issue,based on the digital rock of low permeability sandstone,a direct numerical simulation is performed considering the interphase drag and boundary slip to clarify the microscopic water-oil displacement process.In addition,a dual-porosity pore network model(PNM)is constructed to obtain the water-oil relative permeability of the sample.The displacement efficiency as a recovery process is assessed under different wetting and pore structure properties.Results show that microscopic displacement mechanisms explain the corresponding macroscopic relative permeability.The injected water breaks through the outlet earlier with a large mass flow,while thick oil films exist in rough hydrophobic surfaces and poorly connected pores.The variation of water-oil relative permeability is significant,and residual oil saturation is high in the oil-wet system.The flooding is extensive,and the residual oil is trapped in complex pore networks for hydrophilic pore surfaces;thus,water relative permeability is lower in the water-wet system.While the displacement efficiency is the worst in mixed-wetting systems for poor water connectivity.Microporosity negatively correlates with invading oil volume fraction due to strong capillary resistance,and a large microporosity corresponds to low residual oil saturation.This work provides insights into the water-oil flow from different modeling perspectives and helps to optimize the development plan for enhanced recovery.

基于改进NSGA-Ⅱ算法的间歇采油制度优化

对于低渗透率油井,采用间歇采油制度能有效避免空抽磨损,并减少电能消耗量。为此通过分析沉没度和地层流压随抽油机井生产时间变化的规律,从系统节能的角度出发,建立以采油总产量最大、能耗最低为目标的间歇采油制度多目标优化模型。引入NSGA-Ⅱ并改进该算法对间歇采油制度多目标优化模型求解,运用改进算法得到的Pareto最优解的多样性和收敛性,合理优化抽油机的最优停机时间,最大效率地提升采油效率的同时,最小化电能消耗量。试验结果表明,基于Pareto多目标遗传算法的间歇采油机制优化具有明显的优势,在优化系统效率的同时能够有效减少电能消耗。研究结果可为油井间歇采油机制的改进和优化提供有力的技术支持。

BZ19-6低渗透储层反凝析污染及解除方法实验研究

BZ19-6凝析气田储量大、地露压差小、储层高温高压且低孔低渗,生产作业过程中极易产生反凝析污染。评价反凝析污染程度,采用合适的污染解除措施,对改善BZ19-6凝析气田反凝析污染具有重要意义。利用复配凝析气开展长岩心衰竭实验,模拟反凝析油污染,测试不同衰竭压力点对应的气相渗透率并评价反凝析污染程度;同时开展了注活性剂(TC281)、注甲醇、注甲醇+活性剂3组解除反凝析污染实验,及注甲醇+活性剂1组解除反凝析+水锁综合液相污染实验。实验结果表明:注活性剂(TC281)、注甲醇、注甲醇+活性剂3种方案对解除反凝析污染均有一定效果,注甲醇+活性剂1组解除反凝析污染效果最好,渗透率恢复率达84%;注甲醇解除反凝析污染渗透率恢复率为81%;注活性剂1组解除反凝析渗透率恢复率为54%;注甲醇+活性剂1组解除反凝析+水锁综合液相污染,渗透率恢复率达到80%。实验为BZ19-6凝析气田解除反凝析污染提供了方案指导。

低透气性煤层高压脉冲射流割缝-压裂增透技术应用研究

针对盘州平关镇大坪煤矿18采区20号煤层复杂地质条件及瓦斯抽采难题,提出一种高压脉冲射流割缝导向压裂增透技术。为验证该技术效果,分析了其增透技术机理,并设计了4种试验方案进行对比分析。结果表明,采用高压脉冲射流割缝导向压裂方案在瓦斯抽采效果方面显著优于其他方法,与普通抽采、高压脉冲射流割缝、高压水力压裂抽采瓦斯相比,其平均每日抽采瓦斯浓度分别提高了3.01倍、1.41倍和1.67倍;平均每日抽采瓦斯纯流量也相应提升了2.86倍、1.42倍和1.62倍。经过90 d的抽采,该方案的抽采影响半径达到了5.06 m,分别为普通抽采、高压脉冲射流割缝和高压水力压裂抽采方案的2.56倍、1.25倍和1.29倍;在抽采效果相同的条件下,钻孔施工时间分别比普通抽采、高压脉冲射流割缝和高压水力压裂方案缩短了60%、32%和20%,瓦斯抽采达标所需时间分别比普通抽采、高压脉冲射流割缝和高压水力压裂方案缩短了70%、50%和62%。高压脉冲射流割缝导向压裂技术对低透气性煤层瓦斯治理效果较为理想,可供类似矿井借鉴。

Experimental study of the mechanism of nanofluid in enhancing the oil recovery in low permeability reservoirs using microfluidics

Due to the low porosity and low permeability in unconventional reservoirs,a large amount of crude oil is trapped in micro-to nano-sized pores and throats,which leads to low oil recovery.Nanofluids have great potential to enhance oil recovery(EOR)in low permeability reservoirs.In this work,the regulating ability of a nanofluid at the oil/water/solid three-phase interface was explored.The results indicated that the nanofluid reduced the oil/water interfacial tension by two orders of magnitude,and the expansion modulus of oil/water interface was increased by 77% at equilibrium.In addition,the solid surface roughness was reduced by 50%,and the three-phase contact angle dropped from 135(oil-wet)to 48(water-wet).Combining the displacement experiments using a 2.5D reservoir micromodel and a microchannel model,the remaining oil mobilization and migration processes in micro-to nano-scale pores and throats were visualized.It was found that the nanofluid dispersed the remaining oil into small oil droplets and displaced them via multiple mechanisms in porous media.Moreover,the high strength interface film formed by the nanofluid inhibited the coalescence of oil droplets and improved the flowing ability.These results help to understand the EOR mechanisms of nanofluids in low permeability reservoirs from a visual perspective.

An overview of efficient development practices at low permeability sandstone reservoirs in China

Low permeability sandstone reservoirs in China typically have more complicated geological conditions, pore structures, and flow characteristics as compared to medium-to-high-permeability sandstone reservoirs. Traditional geological and seepage theories, and engineering methods are not applicable to the development of these low permeability reservoirs, and wells drilled into them often produce oil and gas at very low rates. Recent breakthroughs in reservoir exploitation technology have greatly improved the productivity of low permeability reservoirs, making them the primary target for oil exploration and extraction in China. The development theories and practices applied to low permeability reservoirs in China are reviewed in this study— based on relevant geological and engineering practices, including drilling, fracturing, recovery, and surface engineering. A unique series of technological advances that aid the development of low permeability reservoirs in China are summarized here. This study may serve as a meaningful guide in achieving scale efficiency for the development of low permeability reservoirs.

渤海湾盆地临南洼陷古近系沙河街组源-储组合类型与致密(低渗)砂岩油差异富集模式

为了揭示渤海湾盆地临南洼陷古近系沙河街组致密(低渗)砂岩油的差异富集机理,在依据空间配置和岩性组合划分源-储组合类型的基础上,综合利用测井、录井、试油和岩心分析测试资料,对不同源-储组合类型含油性及其供烃条件、储集条件、输导条件和运聚动力进行了分析,建立了致密(低渗)砂岩油差异富集模式。结果显示:①研究区存在源-储共生型(夹层型、互层型)、源-储紧邻型(源上型、源间型和源下型)、源-储间隔型(源下型)3大类6亚类源-储组合,对应3种致密(低渗)砂岩油富集模式。②源-储共生型具有“强供烃-强动力-高效充注-储集控富”模式,供烃条件和运聚动力最优,油气通过孔缝高效充注,储层含油性最好;相较于互层型,砂体厚度制约了夹层型油气富集规模。③源-储紧邻型具有“较强供烃-差异动力-联合输导-多元控富”模式,供烃条件较好,运聚动力变化大,油气通过孔缝-断裂-砂体联合输导,优先充注物性和孔隙结构好的储层,储层含油性较好;亚类中,源间型供烃条件和运聚动力优于源上型和源下型,含油性最好。④源-储间隔型具有“弱供烃-弱动力-断砂输导-输储控富”模式,供烃和运聚动力较弱,断裂、砂体组成的有效输导通道和优质储层发育对于油气富集至关重要,含油性整体较差。

The coupling of dynamics and permeability in the hydrocarbon accumulation period controls the oil-bearing potential of low permeability reservoirs:a case study of the low permeability turbidite reservoirs in the middle part of the third member of Shahejie

The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeability of low permeability turbidite reservoirs of the middle part of the third member of the Shahejie Formation in the Dongying Sag has been investigated by detailed core descriptions, thin section analyses, fluid inclusion analyses, carbon and oxygen isotope analyses, mercury injection, porosity and permeability testing, and basin modeling. The cutoff values for the permeability of the reservoirs in the accumulation period were calculated after detailing the accumulation dynamics and reservoir pore structures, then the distribution pattern of the oil-bearing potential of reservoirs controlled by the matching relationship between dynamics and permeability during the accumulation period were summarized. On the basis of the observed diagenetic features and with regard to the paragenetic sequences, the reservoirs can be subdivided into four types of diagenetic facies. The reservoirs experienced two periods of hydro- carbon accumulation. In the early accumulation period, the reservoirs except for diagenetic facies A had middle to high permeability ranging from 10 × 10-3 gm2 to 4207 × 10-3 lain2. In the later accumulation period, the reservoirs except for diagenetic facies C had low permeability ranging from 0.015 × 10-3 gm2 to 62× 10-3 -3m2. In the early accumulation period, the fluid pressure increased by the hydrocarbon generation was 1.4-11.3 MPa with an average value of 5.1 MPa, and a surplus pressure of 1.8-12.6 MPa with an average value of 6.3 MPa. In the later accumulation period, the fluid pressure increased by the hydrocarbon generation process was 0.7-12.7 MPa with an average value of 5.36 MPa and a surplus pressure of 1.3-16.2 MPa with an average value of 6.5 MPa. Even though different types of reservoirs exist, all can form hydrocarbon accumulations in the early accumulation per- iod. Such types of reservoirs can form hydrocarbon accumulation with high accumulation dynamics; however, reservoirs with diagenetic facies A and diagenetic facies B do not develop accumulation conditions with low accumu- lation dynamics in the late accumulation period for very low permeability. At more than 3000 m burial depth, a larger proportion of turbidite reservoirs are oil charged due to the proximity to the source rock, Also at these depths, lenticular sand bodies can accumulate hydrocarbons. At shallower depths, only the reservoirs with oil-source fault development can accumulate hydrocarbons. For flat surfaces, hydrocarbons have always been accumulated in the reservoirs around the oil-source faults and areas near the center of subsags with high accumulation dynamics.

Analytical solution of a double moving boundary problem for nonlinear flows in one-dimensional semi-infinite long porous media with low permeability

Based on Huang＇s accurate tri-sectional nonlin- ear kinematic equation （1997）, a dimensionless simplified mathematical model for nonlinear flow in one-dimensional semi-infinite long porous media with low permeability is presented for the case of a constant flow rate on the inner boundary. This model contains double moving boundaries, including an internal moving boundary and an external mov- ing boundary, which are different from the classical Stefan problem in heat conduction： The velocity of the external moving boundary is proportional to the second derivative of the unknown pressure function with respect to the distance parameter on this boundary. Through a similarity transfor- mation, the nonlinear partial differential equation （PDE） sys- tem is transformed into a linear PDE system. Then an ana- lytical solution is obtained for the dimensionless simplified mathematical model. This solution can be used for strictly checking the validity of numerical methods in solving such nonlinear mathematical models for flows in low-permeable porous media for petroleum engineering applications. Finally, through plotted comparison curves from the exact an- alytical solution, the sensitive effects of three characteristic parameters are discussed. It is concluded that with a decrease in the dimensionless critical pressure gradient, the sensi- tive effects of the dimensionless variable on the dimension- less pressure distribution and dimensionless pressure gradi- ent distribution become more serious; with an increase in the dimensionless pseudo threshold pressure gradient, the sensi- tive effects of the dimensionless variable become more serious; the dimensionless threshold pressure gradient （TPG） has a great effect on the external moving boundary but has little effect on the internal moving boundary.

Model building for Chang-8 low permeability sandstone reservoir in the Yanchang formation of the Xifeng oil field

In order to build a model for the Chang-8 low permeability sandstone reservoir in the Yanchang formation of the Xifeng oil field,we studied sedimentation and diagenesis of sandstone and analyzed major factors controlling this low permeability reservoir.By doing so,we have made clear that the spatial distribution of reservoir attribute parameters is controlled by the spatial distribution of various kinds of sandstone bodies.By taking advantage of many coring wells and high quality logging data,we used regression analysis for a single well with geological conditions as constraints,to build the interpretation model for logging data and to calculate attribute parameters for a single well,which ensured accuracy of the 1-D vertical model.On this basis,we built a litho-facies model to replace the sedimentary facies model.In addition,we also built a porosity model by using a sequential Gaussian simulation with the lithofacies model as the constraint.In the end,we built a permeability model by using Markov-Bayes simula-tion,with the porosity attribute as the covariate.The results show that the permeability model reflects very well the relative differences between low permeability values,which is of great importance for locating high permeability zones and forecasting zones favorable for exploration and exploitation.

Improved uranium leaching efficiency from low-permeability sandstone using low-frequency vibration in the CO_(2)+O_(2) leaching process

Extraction of uranium from low-permeability sandstone is a long-standing challenge in mining.The improvement of sandstone permeability has therefore become a key research focus to improve the uranium leaching effect.To address the low-permeability problem and corresponding leaching limits,leaching experiments are performed using newly developed equipment that could apply low-frequency vibration to the sandstone samples.The test results indicate that low-frequency vibration significantly improves the uranium leaching performance and permeability of the sandstone samples.The leaching effect of low-frequency vibration treatment is approximately nine times more effective than ultrasonic vibration treatment,whereas the concentration of uranium ions generated without vibration treatment is not detectable.Mathematical model that considers the combined action of physico-mechanical vibration and chemical erosion is established to describe the effect of low-frequency vibration on the permeability.The calculated results are in good agreement with the tested permeability values.This study thus offers a new method to effectively leach more uranium from low-permeability sandstone using CO_(2)+O_(2)and provides an insight into the impact of low-frequency vibration on the uranium leaching process.

Numerical simulation and experiment analysis of improving permeability by deep-hole presplitting explosion in high gassy and low permeability coal seam

Created a new damage model for explosive for LS-DYNA3D,taking advantageof the Taylor method aimed at the high gassy and low permeability coal seam,and numericallysimulated and analyzed the deep-hole presplitting explosion.The entire processof explosion was represented,including cracks caused by dynamic pressure,transmissionand vibration superposition of stress waves,as well as cracks growth driven by gas generatedby explosion.The influence of the cracks generated in the process of explosion andthe performance of improving permeability caused by the difference of interval between.explosive holes were analyzed.A reasonable interval between explosive holes of deepholepresplitting explosions in high gassy and low permeability coal seams was proposed,and the resolution of gas drainage in high gassy and low permeability coal seam was putforward.

Pore-scale simulation of gas-water flow in low permeability gas reservoirs

A novel method was developed to establish a realistic three dimensional(3D) network model representing pore space in low permeability sandstone.Digital core of rock sample was established by the combination of micro-CT scanning and image processing,then 3D pore-throat network model was extracted from the digital core through analyzing pore space topology,calculating pore-throat parameters and simplifying the shapes of pores and throats.The good agreements between predicted and measured porosity and absolute permeability verified the validity of this new network model.Gas-water flow mechanism was studied by using pore-scale simulations,and the influence of pore structure parameters,including coordination number,aspect ratio and shape factor,on gas-water flow,was investigated.The present simulation results show that with the increment of coordination number,gas flow ability in network improves and the effect of invading water on blocking gas flow weakens.The smaller the aspect ratio is,the stronger the anisotropy of the network is,resulting in the increase of seepage resistance.It is found that the shape factor mainly affects the end points in relative permeability curves,and for a highly irregular pore or throat with a small shape factor,the irreducible water saturation(Swi) and residual gas saturation(Sgr) are relatively high.

Pilot Test for Nitrogen Foam Flooding in Low Permeability Reservoir

Due to the characteristics of reservoir formation,the producing level of low permeability reservoir is relatively very low.It is hard to obtain high recovery through conventional development schemes.Considering the tight matrix,complex fracture system,low production level of producers,and low recovery factor ofMblock in Xinjiang oilfield,it is selected for on-site pilot test of nitrogen foam flooding.Detailed flooding scheme is made and the test results are evaluated respectively both for producers and injectors.The pressure index,filling degree,and fluid injection profile are found to be all improved in injectors after injection of nitrogen foam.The oil production,water cut and liquid production file are also improved in most of the producers,with the natural decline rate in the test area become slow.Results show that nitrogen foam flooding technology can be good technical storage for enhanced oil recovery in low permeability reservoir.

Non-Darcy flow in oil accumulation (oil displacing water) and relative permeability and oil saturation characteristics of low-permeability sandstones

Hydrocarbon resources in low-permeability sandstones are very abundant and are extensively distributed. Low-permeability reservoirs show several unique characteristics, including lack of a definite trap boundary or caprock, limited buoyancy effect, complex oil-gas-water distribution, without obvious oil-gas-water interfaces, and relatively low oil （gas） saturation. Based on the simulation experiments of oil accumulation in low-permeability sandstone （oil displacing water）, we study the migration and accumulation characteristics of non-Darcy oil flow, and discuss the values and influencing factors of relative permeability which is a key parameter characterizing oil migration and accumulation in low-permeability sandstone. The results indicate that： 1） Oil migration （oil displacing water） in low- permeability sandstone shows non-Darcy percolation characteristics, and there is a threshold pressure gradient during oil migration and accumulation, which has a good negative correlation with permeability and apparent fluidity; 2） With decrease of permeability and apparent fluidity and increase of fluid viscosity, the percolation curve is closer to the pressure gradient axis and the threshold pressure gradient increases. When the apparent fluidity is more than 1.0, the percolation curve shows modified Darcy flow characteristics, while when the apparent fluidity up＂ non-Darcy percolation curve; 3） Oil-water is less than 1.0, the percolation curve is a ＂concave- two-phase relative permeability is affected by core permeability, fluid viscosity, apparent fluidity, and injection drive force; 4） The oil saturation of low- permeability sandstone reservoirs is mostly within 35%-60%, and the oil saturation also has a good positive correlation with the permeability and apparent fluidity.