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.

The control effect of low-amplitude structure on oil-gaswater enrichment and development performance of ultra-low permeability reservoirs

Based on drilling, logging, test production and dynamic monitoring data, the control effects of low-amplitude structure on hydrocarbon accumulation and development performance of ultra-low permeability reservoirs were discussed by using the methods of dense well pattern, multi-factor geological modeling, macro and micro analysis and static and dynamic analysis. The results show that the low-amplitude structure always had a significant control and influence on the distribution and accumulation of original hydrocarbon and water and the evolution trend of water flooding performance in ultra-low permeability reservoirs, and it was not only the direction of oil and gas migration, but also a favorable place for relative accumulation of oil and gas. The controlling effect of low-amplitude structure on ultra-low permeability reservoir mainly depended on its tectonic amplitude and scale;the larger the tectonic amplitude and scale, and the higher the tectonic position of the low amplitude structure, the better the reservoir characteristic parameters, oil and gas enrichment degree and development effect, and the larger the spatial scope it controlled and influenced;water cut and oil well output always fluctuated orderly with the height of the low-amplitude structure;the dynamic response of waterflooding was closely related to the relative structural position of the injection and production wells;the injected water always advanced to the low-lying area of the structure first and then moved up to the high-lying area of the structure gradually;with the continuous expansion of the flooded area, part of the oil and gas in the low-lying part of the structure was forced to be distributed to the high part of the structure, resulting in a new oil and gas enrichment, so that the dynamic reserves of oil wells in the high part increased, and the production capacity remained stable.

Diagenesis-porosity evolution and“sweet spot”distribution of low permeability reservoirs:A case study from Oligocene Zhuhai Formation in Wenchang A sag,Pear River Mouth Basin,northern South China Sea

The characteristics of low permeability reservoirs and distribution of sweet spots in the Oligocene Zhuhai Formation of Wenchang A sag, Pearl River Basin were investigated by core observation and thin section analysis. The study results show that there develop the fine, medium and coarse sandstone reservoirs of tidal flat–fan delta facies, which are of mostly low permeability and locally medium permeability. There are two kinds of pore evolution patterns: oil charging first and densification later, the reservoirs featuring this pattern are mainly in the third member of Zhuhai Formation between the south fault zone and the sixth fault zone, and the pattern of densification first and gas charging later is widespread across the study area. Strong compaction and local calcium cementation are the key factors causing low permeability of the reservoirs in the Zhuhai Formation. Thick and coarse grain sand sedimentary body is the precondition to form "sweet spot" reservoirs. Weak compaction and cementation, dissolution, early hydrocarbon filling and authigenic chlorite coating are the main factors controlling formation of "sweet spot" reservoir. It is predicted that there develop between the south fault and sixth fault zones the Class Ⅰ "sweet spot" in medium compaction zone, Class Ⅱ "sweet spot" in nearly strong compaction zone, Class Ⅲ "sweet spot" reservoir in the nearly strong to strong compaction zone with oil charging at early stage, and Class IV "sweet spot" reservoir in the strong compaction and authigenic chlorite coating protection zone in the sixth fault zone.

A permeability prediction method based on pore structure and lithofacies

Permeability prediction using linear regression of porosity always has poor performance when the reservoir with complex pore structure and large variation of lithofacies.A new method is proposed to predict permeability by comprehensively considering pore structure,porosity and lithofacies.In this method,firstly,the lithofacies classification is carried out using the elastic parameters,porosity and shear frame flexibility factor.Then,for each lithofacies,the elastic parameters,porosity and shear frame flexibility factor are used to obtain permeability from regression.The permeability prediction test by logging data of the study area shows that the shear frame flexibility factor that characterizes the pore structure is more sensitive to permeability than the conventional elastic parameters,so it can predict permeability more accurately.In addition,the permeability prediction is depending on the precision of lithofacies classification,reliable lithofacies classification is the precondition of permeability prediction.The field data application verifies that the proposed permeability prediction method based on pore structure parameters and lithofacies is accurate and effective.This approach provides an effective tool for permeability prediction.

Pore structure differences of the extra-low permeability sandstone reservoirs and the causes of low resistivity oil layers: A case study of Block Yanwumao in the middle of Ordos Basin, NW China

The influence of pore structure difference on rock electrical characteristics of reservoir and oil reservoir was analyzed taking Triassic Chang 6 reservoir in Block Yanwumao in the middle of Ordos Basin as an example. The relationship between the pore structure difference and the low resistivity oil layer was revealed and demonstrated through core observation, lab experiments, geological research, well log interpretation and trial production etc. The results show that there were two kinds of oil layers in Chang 6 oil layer set, normal oil layer and low resistivity oil layer in the region, corresponding to two types of pore structures, pore type mono-medium and micro-fracture-pore type double-medium; the development of micro-fracture changed greatly the micro-pore structure of the reservoir, and the pore structure difference had an important influence on the rock electrical characteristics of the extra-low permeability sandstone reservoir and oil reservoir; the normal oil layers had obvious characteristics of pore-type mono-medium, and were concentrated in Chang 61, Chang 6232 and Chang 62; the low resistivity oil layers had obvious characteristics of micro-fracture-pore type double-medium, which were mainly distributed in Chang 612 and Chang 63. The mud filtrate penetrated deep into the oil layers along the micro-cracks, leading to sharp reduction of resistivity, and thus low resistivity of the oil layer; the low resistivity oil layers had better storage capacity and higher productivity than the normal oil layers.

Pore Structure and Permeability Characterization of Highrank Coal Reservoirs: A Case of the Bide-Santang Basin, Western Guizhou, South China

The methods of nuclear magnetic resonance(NMR)spectroscopy,mercury injection porosimetry(MIP),and gas-water relative permeability(GWRP)were used to reveal the pore structure and permeability characteristics of high-rank coal reservoirs in the Bide-Santang basin,western Guizhou,South China,to provide guidance for coalbed methane(CBM)exploration and exploitation and obtain direct insights for the development of CBM wells.The results indicate that the coal reservoirs in the study area are characterized by well-developed adsorption pores and poorly developed seepage pores.The bimodal NMR transverse relaxation time(T2)spectra and the mutation in the fractal characteristic of the MIP pore volume indicate poor connectivity between the adsorption pores and the seepage pores.As a result,the effective porosity is relatively low,with an average of 1.70%.The irreducible water saturation of the coal reservoir is relatively high,with an average of 66%,leading to a low gas relative permeability under irreducible water saturation.This is the main reason for the low recovery of high-rank CBM reservoirs,and effective enhanced CBM recovery technology urgently is needed.As a nondestructive and less time-consuming technique,the NMR is a promising method to quantitatively characterize the pores and fractures of coals.

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.

A new permeability calculation method using nuclear magnetic resonance logging based on pore sizes: A case study of bioclastic limestone reservoirs in the A oilfield of the Mid-East

It is difficult to accurately obtain the permeability of complex lithologic reservoirs using conventional methods because they have diverse pore structures and complex seepage mechanisms.Based on in-depth analysis of the limitation of classical nuclear magnetic resonance(NMR)permeability calculation models,and the understanding that the pore structure and porosity are the main controlling factors of permeability,this study provides a new permeability calculation method involving classifying pore sizes by using NMR T_2 spectrum first and then calculating permeability of different sizes of pores.Based on this idea,taking the bioclastic limestone reservoir in the A oilfield of Mid-East as an example,the classification criterion of four kinds of pore sizes:coarse,medium,fine and micro throat,was established and transformed into NMR T_2 standard based on shapes and turning points of mercury intrusion capillary pressure curves.Then the proportions of the four kinds of pore sizes were obtained precisely based on the NMR logging data.A new NMR permeability calculation model of multicomponent pores combinations was established based on the contributions of pores in different sizes.The new method has been used in different blocks.The results show that the new method is more accurate than the traditional ones.

Permeability damage micro-mechanisms and stimulation of low-permeability sandstone reservoirs: A case study from Jiyang Depression, Bohai Bay Basin, China

According to the characteristics of"structural elements"(framework grain,interstitial material and pore throat structure)of low-permeability sandstone reservoir,the"step by step dissolution and separation"acidification and acid fracturing technology has been developed and tested in field.There are three main mechanisms affecting permeability of low-permeability sandstone reservoir:(1)The mud fillings between the framework grains block the seepage channels.(2)In the process of burial,the products from crystallization caused by changes in salinity and solubility and uneven migration and variation of the syn-sedimentary formation water occupy the pores and throat between grains.(3)Under the action of gradual increase of overburden pressure,the framework grains of the rock is compacted tighter,making the seepage channels turn narrower.The"step by step dissolution and separation"acidification(acid fracturing)technology uses sustained release acid as main acidizing fluid,supramolecular solvent instead of hydrochloric acid to dissolve carbonate,and a composite system of ammonium hydrogen fluoride,fluoroboric acid,and fluorophosphoric acid to dissolve silicate,and dissolving and implementing step by step,finally reaching the goal of increasing porosity and permeability.By using the technology,the main blocking interstitial material can be dissolved effectively and the dissolution residual can be removed from the rock frame,thus expanding the effective drainage radius and increasing production and injection of single well.This technology has been proved effective by field test.

柴达木盆地马海东地区古近系砂岩储层微观孔隙结构特征及微观致密区成因

柴达木盆地北缘马海东地区古近系的油气勘探已经取得发现,但储层微观孔隙结构特征认识不清是影响油气勘探与开发的主要因素之一。为揭示马海东地区古近系砂岩储层微观特征,综合运用岩石薄片显微镜观察、X射线衍射(XRD)分析和压汞测试等试验技术,开展了低渗透砂岩储层的岩石学特征、物性特征、微观孔隙结构及各储层非均质性对比研究,用变异系数定量表征了储层非均质强弱程度。研究结果表明:①古近系砂岩储层以长石岩屑砂岩为主,填隙物主要为方解石。②路乐河组Ⅰ砂组储层孔隙度较大,下干柴沟组Ⅱ砂组储层孔隙度中等,路乐河组Ⅱ砂组储层孔隙度最小。③储层岩石经历了压实、胶结和溶蚀成岩作用,路乐河组Ⅱ砂组储层非均质性最强,路乐河组Ⅰ砂组储层非均质性最弱,下干柴沟组Ⅱ砂组储层非均质性介于两者之间。④富塑性岩屑纹层或富杂基的低渗砂岩为致密储层,方解石胶结和塑性黏土质岩屑变形是致密储层形成的重要原因。

低渗透砂岩储层压驱裂缝起裂及扩展特征实验研究

针对水驱低渗透油藏地层能量补充困难、“注不进、采不出”的问题,胜利油田结合提液稳产技术需求,形成了针对低渗透油藏的压驱注水技术。压驱通过高压注水有效提高了水驱注水总量,矿场试验表明压驱过程中储层形成了一定规模的裂缝,但压驱破裂压力及裂缝扩展规律尚不明确。为了优化矿场施工参数,采用天然砂岩和真三轴水力压裂平台开展5组压驱与压裂物理模拟实验,研究注入排量对压驱破裂压力和裂缝形态的影响,分析注入方式对裂缝形态的影响,并利用多孔弹性理论分析其成因。结果表明:压驱过程同时存在明显的起裂压力和破裂压力,裂缝发育呈现弹性变形、微破裂和失稳破裂3个阶段。随着注入排量升高,起裂压力基本不变,破裂压力逐渐降低。H-F模型可用于预测起裂压力,H-W模型可用于预测破裂压力的上限。压驱裂缝扩展方向受岩石非均质性的影响较大,非均质性通过影响井眼附近的孔隙压力场,进而改变应力场,使裂缝扩展方向不再垂直于最小地应力。定排量注入时,分支缝与主裂缝夹角大,形成鱼骨状裂缝;变排量注入时,分支缝与主裂缝近平行,在主裂缝两侧形成裂缝带。

改性片状纳米流体的洗油效率及机理

纳米流体提高采收率已然成为油气勘探开发的研究热点。利用研发的改性片状纳米流体,在自制的可视化模型中研究固体界面油膜在接触到质量浓度为50mg/L的改性片状纳米流体后的收缩规律,并开展油砂洗油实验,明确50mg/L的改性片状纳米流体在不同条件下的洗油效率。研究结果表明,模拟地层水环境下,固体界面油膜收缩速率较慢,并未出现楔形区域;改性片状纳米流体环境下,固体界面油膜在收缩过程中出现明显的楔形区域,且出现两条接触线:外接触线和内接触线,外接触线的收缩速率为8.5817×10^(-5)cm/s,内接触线的收缩速率为0.6617×10^(-5)cm/s。油砂洗油实验表明,改性片状纳米流体的洗油效率随油砂尺寸的增大和温度的提升逐渐增加,随着油砂浸泡时间的延长先急剧增加后缓慢上升,存在最佳浸泡时间(8±2)h,油砂洗油效率可高达95.7%。该项研究成果突破了只有高浓度球形纳米颗粒才能形成结构分离压力的限制,为片状纳米流体在矿场的应用提供了可能性,也为矿场施工工艺提供了技术参考。

低渗透煤层微观孔隙结构与煤层气解吸规律

为研究低渗透煤层微观孔隙结构与气体解吸规律的关系,运用直接观测法、核磁共振法、液氮吸附法等实验手段,对鄂尔多斯盆地伊陕斜坡8号煤层煤样的含气量、孔隙度、渗透率、孔径分布等进行测定。结果显示:煤层气解吸特征与煤的孔径分布、孔的形态、孔的连通性以及比表面积、煤岩成分等因素有关;研究区相隔小于10 m的2套煤层,其孔隙特征、气体解吸规律差异均较大。其中,亮煤的微孔形态以一端开口的圆筒形孔和墨水瓶孔为主,微孔及吸附孔占比为39.2%,煤体微裂缝相对发育,但微孔与介孔的连通性较差,暗淡煤的微孔形态以一端开口的圆筒形孔为主,微孔及吸附孔占比为33.2%,微裂缝不发育,不同孔间连通性差。亮煤气体解吸初期产量大,后期衰减快,气体产出具有明显的阵发式特征;暗淡煤气体解吸初期产量小,约为亮煤的1/2,后期产量递减相对平缓。低渗煤层的开发对策应充分考虑煤层的孔隙结构、孔型、渗透性,应力敏感性、裂缝充填物种类等因素,在精细表征孔隙结构的基础上,根据煤层气不同解吸期特征,结合地质、开发条件制订合理的开发方案。该研究对认识煤层气产气机理及其控制因素,提高煤层气开采效率具有重要的指导意义。

基于孔隙结构表征的低渗透砂岩流体赋存特征及渗透率评价

以渤海湾盆地G油田古近纪低渗透砂岩储层为研究对象,综合铸体薄片、扫描电镜(SEM)、高压压汞(MICP)及核磁共振(NMR)分析探讨了孔隙结构及其对储层品质和流体赋存的影响。低渗透砂岩储层的孔喉大小分布范围广,微、纳米级孔喉共存,且普遍呈现双峰分布的特征。大孔喉系统主要由残余粒间孔和溶蚀扩大孔组成;而微小孔喉系统则主要由粒内溶孔和晶间孔构成。研究结果表明,孔喉连通能力及连通孔喉的体积分数是影响低渗透砂岩储层储集物性和流体赋存特征的关键因素。物性越好的砂岩储层中,连通性好的大孔喉(右峰)所占体积分数越高,储层渗流能力越强;反之,物性越差的储层孔隙系统则主要由连通性差的微小孔喉(左峰)主导,储层渗流能力较弱。束缚流体主要赋存在孔喉半径较小、微观连通性较差、分形维数较大的小孔喉系统中;而中、大孔隙系统的微观连通性好、分形维数较小,主要富集可动流体。研究还明确了半径最大的孔喉是影响低渗透砂岩储层渗透率和流体赋存特征的关键因素,并根据毛管压力曲线和核磁共振T2(横向弛豫时间)谱参数建立了两套适用于低渗透砂岩储层的渗透率评价模型。与经典模型(如Coates和Schlumberger Doll research(SDR))相比,新模型具有更好的有效性和适用性。

基于双峰高斯函数的海上低渗储层孔隙结构定量表征——以琼东南盆地BD21气田陵水组三段为例

海上低渗气藏占比增加,孔隙结构的差异影响气井产能,制约海上低渗气藏规模开发。根据高压压汞和核磁共振实验,采用测井曲线与储层分类参数、双峰高斯函数拟合曲线等方法,利用球状孔隙模型将核磁共振T2谱转化为伪毛细管压力曲线定量表征孔径大小及分布,分析核磁共振T2谱反映的大孔孔隙度、大中孔孔隙度与物性、压汞参数之间关系,分析反映储层渗流能力的孔隙结构评价参数,建立孔隙结构和物性参数预测模型。结果表明:陵水组三段低渗储层孔隙结构分布呈双峰型和单峰型,其中小孔曲线与大孔曲线存在重叠区域,双峰型曲线的重叠区域较小,单峰型曲线的重叠区域较大,孔隙可按双峰高斯函数拟合的小孔曲线、大孔曲线和重叠区域的分布范围划分为大孔、中孔和小孔;大中孔孔隙度、大孔孔隙度可有效评价储层物性和孔隙结构,储层大中孔越发育,物性越好,可动流体饱和度相对较高。以大孔和大中孔综合评价参数为主要指标的低渗储层分类标准,将研究区低渗储层划分为三种类型,其中Ⅰ类、Ⅱ类储层大中孔较为发育,储层物性较好,大孔、大中孔综合评价参数值分别大于7、10,可动流体饱和度相对较高,普遍在65.75%以上;Ⅲ类储层物性相对较差,大孔和大中孔综合评价参数值较小,孔隙结构复杂,可动流体饱和度相对较低。该结果为海上低渗气田经济有效开发提供指导。

注水开发中悬浮物粒径与储层孔隙结构匹配关系

为了完善注水开发中悬浮物粒径中值指标制定方法,以南海西部涠洲油田群为例,在统计大量数据的基础上,分析主力生产层位岩石孔隙结构参数与渗透率之间的关系(R_(c)-K);通过室内岩心驱替实验对油田群原有注水指标进行优化,得出渗透率与粒径中值的关系(K-d);关联R_(c)-K方程以及K-d关系后,得到不同岩心级别下注入水悬浮物粒径中值与喉道直径的匹配关系(d/2Rc)。结果表明:以渗透率保留率80%为标准,K=(10~50)×10^(-3)μm^(2)时颗粒粒径中值与喉道直径比d/2R_(c)=1/6;K=(50~100)×10^(-3)μm^(2)时d/2R_(c)=1/5;K=(100~300)×10^(-3)μm^(2)时d/2R_(c)=1/5。

长宁地区低阻页岩孔隙结构精细表征及分形研究

为明确四川盆地长宁地区龙马溪组低电阻页岩储层孔隙发育差异性,采用低阻页岩与常规页岩相对比的研究手段,开展了有机碳分析、氮气吸附实验、XRD矿物组分分析和扫描电镜等一系列实验,阐明了长宁低阻页岩储层孔隙结构及其分形特征,并明确了它们的控制因素。结果显示,长宁地区大多数低阻页岩孔隙发育程度明显差于常规页岩,其中,孔体积发育的差异主要体现在2~20 nm孔径范围内,比表面积差异则主要集中在小于1.5 nm和大于1.8 nm段。页岩储层孔隙结构随电阻率的降低有变差的趋势,对低电阻页岩储集能力影响更明显的是有机质含量和成熟度。相较于常规电阻页岩,低电阻页岩在小孔隙段具有更加复杂的孔径及孔壁发育。黏土矿物和黄铁矿对分形维数的影响在不同电阻率页岩中是一致的,而有机质对2类页岩分形维数的影响相反。有机质对分形维数的影响与过演化页岩石墨化后的有机孔变化密切相关。

高压低渗透碎屑岩储层孔隙结构特征及分类评价——以莺歌海盆地东方A 1区黄流组一段为例

为揭示低渗储层的微观孔喉差异,根据岩心、测井、测试和岩心实验分析等资料,采用分形理论和多层感知器神经网络方法,分析储层孔隙结构特征,进行储层量化表征。结果表明:储层岩性以细砂岩和粉砂岩为主,受超压保护及沉积—成岩作用影响,主水道储层粒度相对较粗,原生粒间孔占比可达60%;泥质质量分数越高,粒间孔越不发育;压力因数越高,粒间孔越发育,压力因数每提高0.1,储层中粒间孔隙占比增加5%~10%。低渗储层分4种类型:Ⅰ类储层,表现为中孔、低渗特征,压汞曲线具有明显的平台段,孔喉或核磁曲线为单峰分布特征,T 2弛豫时间的主峰分布在40 ms附近,可动流体饱和度平均为53.2%;Ⅱ类储层,表现为中孔、低渗特征,孔隙度与Ⅰ类储层的相当,渗透率明显降低,压汞曲线表现一定的平台段,但进汞曲线末段斜率明显增大,孔喉或核磁曲线呈双峰分布特征,右峰T 2弛豫时间在60 ms附近,左峰的在10 ms附近;Ⅲ类和Ⅳ类储层,分别表现为中孔、特低渗和低孔、特低渗特征,压汞曲线无明显平台段,大孔喉与Ⅰ、Ⅱ类储层相比,孔喉形态更加复杂,孔喉和核磁曲线呈单峰分布,孔喉半径和T 2弛豫时间峰值逐渐向左偏移,可动流体饱和度小于20%。优选密度、中子、电阻和自然伽马参数建立基于MLP的储层类型测井识别方法,储层识别正确率达86.7%,与岩心实验分析吻合率达88.9%,产能匹配性较好。该结果可为研究区低渗气藏的有效开发提供依据。

低渗储层岩石物理建模新方法及其在东海Z气田中的应用

低渗储层孔隙结构复杂,非均质性强,不同类型低渗储层之间也常存在较大物性变化,难以采用统一的岩石物理模型表征储层参数与弹性参数之间的关系。针对上述难题,提出了低渗储层分层岩石物理建模方法:针对中低孔-中低渗储层采用基于DEM理论的流体均匀饱和模型;针对特低孔、特低渗储层采用基于KT理论的流体非均匀饱和模型。基于分层岩石物理建模预测的纵、横波速度与测井真实速度吻合较好,验证了该方法的可靠性。在建立准确岩石物理模型的基础上,进一步分析了弹性参数受泥质含量、孔隙度、孔隙形状等因素影响的变化规律,从而指导低渗储层的岩性及“甜点”预测。

特低渗油藏CO_(2)/水交替微观驱油机理研究

苏北盆地断块特低渗透油藏具有“小、碎、深、薄、低”的典型特征,在经过短期弹性开发后如何优选合理高效的提高油藏采收率方法成为该类油藏面临的瓶颈问题。水气交替注入(Water Alternating Gas,WAG)方法能有效抑制水窜和气窜,兼具水驱和CO_(2)驱的优点,在特低渗透油藏取得了成功应用,但其微观驱油机理及实际效果仍需进一步研究和评价。文中以苏北ZD油田为研究对象,基于特低渗透天然岩心的三维数字模型,应用孔隙尺度微观数值模拟方法,研究了CO_(2)/水交替驱油过程中气水相界面的动态演化过程,并深入阐明了特低渗油藏WAG提高采收率的微观机理,结果表明:水气交替驱具有更大的波及面积和更少的剩余油体积,CO_(2)驱过程具有更好的流动性和克服黏滞力的能力,同时水驱过程中的渗吸作用和封堵作用能有效提高驱油效率。因此,CO_(2)/水交替驱可以有效启动特低渗储层,起到调剖调驱协同增益的作用,研究成果对于指导特低渗透油藏提高采收率技术的优选和实施具有重要的理论意义和矿场应用价值。