Hydrodynamic resistance of pore–throat structures and its effect on shale oil apparent permeability

Oil transport is greatly affected by heterogeneous pore–throat structures present in shale.It is therefore very important to accurately characterize pore–throat structures.Additionally,it remains unclear how pore–throat structures affect oil transport capacity.In this paper,using finite element(FE)simulation and mathematical modeling,we calculated the hydrodynamic resistance for four pore–throat structure.In addition,the influence of pore throat structure on shale oil permeability is analyzed.According to the results,the hydrodynamic resistance of different pore throat structures can vary by 300%.The contribution of additional resistance caused by streamline bending is also in excess of 40%,even without slip length.Fur-thermore,Pore–throat structures can affect apparent permeability by more than 60%on the REV scale,and this influence increases with heterogeneity of pore size distribution,organic matter content,and organic matter number.Clearly,modeling shale oil flow requires consideration of porous–throat structure and additional resistance,otherwise oil recovery and flow capacity may be overestimated.

Classification and control factors of pore-throat systems in hybrid sedimentary rocks of Jimusar Sag, Junggar Basin, NW China

Aiming at the complicated problem of the genesis of high-quality hybrid sedimentary rocks,the pore-throat systems,controlling factors and fluid mobility of hybrid sedimentary rocks in the Permian Lucaogou Formation in Jimusar Sag were examined.The results show that the hybrid sedimentary rocks contain 5 types of pore-throat system,intergranular(Type A),mixed intergranular-dissolved-intercrystalline(Type B),dissolved(Type C),mixed dissolved-intercrystalline(Type D)and intercrystalline(Type E)ones.The pore-throat systems are controlled by 3 major factors,the component content and arrangement(CCA)of hybrid sedimentary rocks,sedimentary environment and diagenesis.CCA controls the matrix support mode of hybrid sedimentary rocks,and therefore controls the types and changes of pore-throat system.The sedimentary environment mainly controls the macroscopic distribution of pore-throat system,i.e.,hybrid sedimentary rocks deposited in the near source and high-energy environment are characterized by high content of coarse-grained component,granular/interbedded-support mode,and development of Type A and Type B pore-throat systems.Hybrid sedimentary rocks deposited in the medium-energy environment far from source are characterized by dolomitic/mud support mode and Type C and Type D pore-throat systems.Hybrid sedimentary rocks deposited in low-energy environment far from source have mainly Type E and Type D pore-throat systems.Diagenetic processes such as compaction and calcite cementation make the proportions of Type A and Type C pore-throat systems decrease further.In the hybrid sedimentary process of sandy-mud,pore-throat system types show a change of"A→B→C→D",in that of dolomite-sand,pore-throat system types show a change of"A→C→D→E"or"B→D→E",and in that of dolomite-mud,pore-throat system types show a change of"D→E",which are affected in details by the contents of coarse-grain component,feldspar and dolomite.The reservoir with Type A pore-throats has the best physical properties and fluid mobility,and the reservoirs with Type D and Type E pore-throats have the poorest.The movable fluid distribution is related to the matrix support mode,and the larger pores in hybrid sedimentary rocks of dolomite/mud support mode have no obvious advantage in fluid mobility.The findings of this study provide a geological basis for evaluating and building reasonable interpretation model of hybrid sedimentary rocks sweet spot.

Pore throat structure heterogeneity and its effect on gas-phase seepage capacity in tight sandstone reservoirs:A case study from the Triassic Yanchang Formation,Ordos Basin

The microscopic heterogeneity of pore-throat structures in tight sandstone is a crucial parameter for understanding the transport mechanism of fluid flow.In this work,we firstly developed the new procedure to characterize the pore size distribution(PSD)and throat size distribution(TSD)by combining the nuclear magnetic resonance(NMR),cast thin section(CTS),and constant-rate mercury injection(CRMI)tests,and used the permeability estimated model to verify the full-scale PSD and TSD.Then,we respectively analyzed the fractal feature of the pore and throat,and characterized the heterogeneity of pores and throats.Finally,we elaborated the effect of the pore and throat heterogeneity on the gas-phase seepage capacity base on the analysis of the simple capillary tube model and gas-flooding experiment.The results showed that(1)The PSD and TSD of the tight sandstone sample ranged from 0.01 to 10 mm and from 0.1 to 57 mm,respectively,mainly contributed by the micropores and mesopores.Meanwhile,the permeability estimated by the PSD and TSD was consistent with the experimental permeability,and relative error was lower than 8%.(2)The PSD and TSD exhibited multifractal characteristics,and singularity strength range,Δα,could be used as the indicator for characterizing the heterogeneity of pore and throat.Furthermore,the throat of the sample showed stronger heterogeneity than that the pore.(3)The throats played an important role for the fluid transport in the tight sandstone,and the effect of the throat heterogeneity on the gas-phase seepage capacity was different under the lower and higher injection pressure.The macropores and micropores maybe respectively become the preferential migration pathways at the lower and higher injection pressure.In the end,the identification plate was established in our paper,and could be described the relationship among the throat heterogeneity,injection pressure,permeability and flow path of the gas phase in the tight sandstone.

Pore throat structure and classification of Paleogene tight reservoirs in Jiyang depression,Bohai Bay Basin,China

The pore throat structure characteristics of Paleogene tight sandstone and sandy conglomerate in the Jiyang depression are studied using cast thin section,conventional mercury injection,constant rate mercury injection and micro CT scanning data,and a reservoir classification scheme based on pore throat structure parameters is established.The material composition and structural characteristics of tight reservoirs are analyzed by casting thin section data.The pore throat structure characteristics of tight reservoirs are studied by conventional mercury injection,constant rate mercury injection and micro CT scanning.Ten pore throat structure parameters are analyzed by cluster analysis.Based on the classification results and oil test results,the classification scheme of Paleogene tight reservoirs is established.The Paleogene tight reservoirs in the Jiyang depression have the characteristics of macropores and microthroats,with pores in micron scale,throats in nano-submicron scale,and wide variation of ratio of pore radius to throat radius.The permeability of the tight reservoir is controlled by throat radius,the smaller the difference between pore radius and throat radius,and the more uniform the pore throat size,the higher the permeability will be.The lower limits of average pore throat radius for the tight sandstone and tight sandy conglomerate to produce industrial oil flow without fracturing are 0.6μm and 0.8μm,respectively.Reservoirs that can produce industrial oil flow only after fracturing have an average pore-throat radius between 0.2-0.6μm,and reservoirs with average pore throat radius less than 0.2μm are ineffective reservoirs under the current fracturing techniques.Different types of tight sandstone and sandy conglomerate reservoirs are classified and evaluated,which are well applied in exploratory evaluation.

Pore-throat Structure of Tight Sandstone in Yanchang Formation of Huangling Mining Area Based on Scanning Electron Microscopy and Mercury Porosimmetry

Based on scanning electron microscopy and mercury porosimmetry,a large number of experimental data of pores and pore throats of tight sandstone reservoirs are obtained,and the characteristics of pore types,capillary pressure curves and quantitative parameters of pore throats of Yanchang Formation in Huangling mining area are studied.The results show that the main reservoir space types of Yanchang Formation sandstone are primary intergranular pores and feldspar dissolution pores.The pore-throat structure is medium-small pore and thin-small throat type,and the sorting is good to medium.The mercury porosimmetry curve shows a slightly coarse-thin skew.Combining the morphological characteristics of the mercury porosimmetry capillary pressure curve and the quantitative parameter characteristics of pore throats,the Yanchang Formation s micro pore structure is divided into types I,II,III,and IV.Tight oil reservoirs with type I and II pore structure characteristics are favorable.This study has reference significance for the later evaluation of tight sandstone reservoirs in Huangling mining area.

非均相体系在微通道中的封堵性能研究

基于大庆油田天然岩心孔隙尺度分布特征建立了微通道模型,考虑非均相体系中的分散相和连续相的变形及流动特征,以相场法建立流动模型并用有限元方法求解,模拟了分散相颗粒在微通道内的生成,并实现了颗粒分选,研究了微观孔喉结构中匹配系数和孔喉比对颗粒封堵性能的影响。结果表明,颗粒在微观孔喉结构中发生弹性封堵时,孔喉入口处压力随颗粒运移通过而呈现周期性变化;颗粒与孔喉最佳匹配系数为[1.0,1.4),此区间内颗粒能够在孔喉入口处暂时封堵,变形运移通过孔喉后恢复原形;当孔隙直径相同时,匹配系数和孔喉比越大,颗粒通过压力越大;颗粒粒径越大,颗粒通过压力临界值越小。

松辽盆地古龙页岩纳米孔喉体系中页岩油组分及成熟度分异效应

陆相页岩油储层中石油的微运移效应会导致微观孔隙空间中赋存的页岩油性质发生分异,然而页岩储层孔隙半径较小,孔喉结构复杂,很难通过常规手段对其进行精细刻画,导致对页岩油的微观富集机理认识不清。通过对松辽盆地古龙凹陷青山口组页岩岩心样品进行分步-接力抽提、低温氮气吸附实验,并开展全烃气相色谱、族组分定量、饱和烃气相色谱质谱和金刚烷双质谱等地球化学分析,揭示出页岩储层纳米孔喉体系内的石油组分和成熟度分异效应。结果表明,古龙页岩孔隙以介孔为主,随着页岩样品粒径的逐级减小,更多初始连通性较差的孔隙会被释放出来,同时微观纳米孔喉中烃类的重质组分相对增加,极性更强,页岩油的成熟度也相对更高,这与不同连通性孔隙空间中页岩油的排烃和微运移效应具有一定的相关性。研究成果可为精细表征页岩油的微观赋存特征,阐明页岩油储层烃类微观差异富集机理提供有效的技术手段,同时也为页岩油的可动性评价和甜点优选提供可靠的理论依据。

Pore size distribution,their geometry and connectivity in deeply buried Paleogene Es1 sandstone reservoir,Nanpu Sag,East China

The study or pore characteristics is or great importance in reservoir evaluation,especially in deeply buried s andstone.It controls the storage mechanism and reservoir fluid properties of the permeable horizons.The first member of Eocene Shahejie Formation(Esl)sandstone is classified as feldspathic litharenite and lithic arkose.The present research investigates the pore characteristics and reservoir features of the deeply buried sandstone reservoir of Esl member of Shahejie Formation.The techniques including thin-section petrography,mercury injection capillary pressure(MICP),scanning electron microscopy and laser scanning confocal microscope images were used to demarcate the pores including primary intergranular pores and secondary intergranular,intragranular,dissolution and fracture pores.Mercury injection test and routine core analysis were led to demarcate the pore network characteristics of the studied reservoir.Pore size and pore throat size distribution are acquired from mercury injection test.Porosity values range from 0.5%to 30%,and permeability ranges 0.006-7000 mD.Pore radii of coarse-grained sandstone and fine-grained sandstone range from 0.2 to>4μm and 1 nm to 1.60μm,respectively,by MICP analysis.The mineral composition also plays an important role in protecting the pores with pressure from failure.Fractured sandstone and coarse-grained sandstone consist of large and interconnected pores that enhance the reservoir porosity and permeability,whereas fine-grained sandstone and siltstone consist of numerous pores but not well interconnected,and so they consist of high porosity with low permeability.

基于致密砂岩储层孔喉系统分形理论划分的可动流体赋存特征认识

致密砂岩气储层非均质性强,储层流体的分布及可动性差异巨大,准确、可靠评价储层内流体的渗流能力和赋存特征十分必要。为探究可动流体在不同品质储层中的赋存特征和渗流能力差异,选取8块鄂尔多斯盆地东南缘山西组典型样品,基于由核磁共振转化的伪毛细管压力曲线所刻画的储层孔喉分布情况,根据分形理论划分出不同级别孔喉系统并探讨其对可动流体赋存特征的影响。研究结果表明:(1)研究区储层类型依据孔隙类型、压汞曲线形态及参数可分为3类,由Ⅰ类至Ⅲ类,较大的溶蚀孔隙减少,晶间微孔增多,有效储集空间不断减少及渗流能力不断降低。(2)Ⅰ、Ⅱ类样品基于伪毛细管压力曲线求取的孔喉分布曲线与高压压汞的孔喉分布曲线形态相似,且峰值保持一致。Ⅲ类样品包含较多压汞探测不到的纳米级孔喉,导致核磁共振求取的孔喉分布峰值向小孔喉偏移。(3)根据分形理论求取的分形转折点可将孔喉空间划分为相对的大、中、小3个孔喉系统,孔隙度与大孔喉系统的绝对空间含量相关性最好,渗透率、可动流体饱和度则与大孔喉系统在储集空间中所占的比例密切相关。结论认为,大孔喉系统的发育程度决定了储层可动流体的渗流能力,该认识可为致密气储层评价参数的优选提供依据,还可为非常规油气储层深入研究提供参考和借鉴。

Investigations on the relationship among the porosity,permeability and pore throat size of transition zone samples in carbonate reservoirs using multiple regression analysis,artificial neural network and adaptive neuro-fuzzy interface system

Finding an accurate method for estimating permeability aside from well logs has been a difficult task for many years.The most commonly used methods targeted towards regression technique to understand the correlation between pore throat radii,porosity and permeability are Winland and Pittman equation approaches.While these methods are very common among petrophysicists,they do not give a good prediction in certain cases.Consequently,this paper investigates the relationship among porosity,permeability,and pore throat radii using three methods such as multiple regression analysis,artificial neural network(ANN),and adaptive neuro-fuzzy inference system(ANFIS)for application in transition zone permeability modeling.Firstly,a comprehensive mercury injection capillary pressure(MICP)test was conducted using 228 transition zone carbonate core samples from a field located in the Middle-East region.Multiple regression analysis was later performed to estimate the permeability using pore throat and porosity measurement.For the ANN,a two-layer feed-forward neural network with sigmoid hidden neurons and a linear output neuron was used.The technique involves training,validation,and testing of input/output data.However,for the ANFIS method,a hybrid optimization consisting of least-square and backpropagation gradient descent methods with a subtractive clustering technique was used.The ANFIS combines both the artificial neural network and fuzzy logic inference system(FIS)for the training,validation,and testing of input/output data.The results show that the best correlation for the multiple regression technique is achieved for pore throat radii with 35%mercury saturation(R35).However,for both the ANN and ANFIS techniques,pore throat radii with 55%mercury saturation(R55)gives the best result.Both the ANN and ANFIS are later found to be more effective and efficient and thus recommended as compared with the multiple regression technique commonly used in the industry.

中国致密储层孔隙结构表征需注意的问题及未来发展方向

致密储层孔喉尺寸小、孔隙结构复杂、非均质性强,表征难度大。通过系统梳理目前致密储层表征技术发展现状,指出致密储层孔隙结构表征需注意的几个问题:1强调提高分辨率的同时,需加强样品代表性尺度研究;2追求新技术/方法的同时,需加强技术有效适用范围研究;3强调定量表征数据拼接的同时,需加强多尺度定性与定量数据融合,提高表征精度。提出致密储层孔隙结构表征核心技术未来发展方向:1多学科联合攻关,静态表征与动态演化相结合,实现孔隙结构的全面表征;2加强宏观尺度研究,密切联系可动流体评价,实现对规模有效储集体的准确预测;3加强现场应用研究,紧密结合储层增产改造措施,实现对工程甜点的评价优选。

中国中西部盆地典型陆相页岩纹层结构与储层品质评价

陆相页岩油已成为中国油气勘探重大接替领域之一。作为页岩独具特色的组构特征,纹层结构对烃源岩品质、储层品质与工程品质评价具有重要影响,因而成为关注重点。文章以中国中西部典型咸化湖盆与淡水—微咸水湖盆富有机质页岩为研究对象,剖析纹层结构特征,探讨其对甜点优选的影响。研究发现:(1)不同类型湖盆页岩纹层结构具有差异,湖盆咸化程度影响纹层结构,碳酸盐纹层主要发育在咸化湖盆,在淡水—微咸水湖盆中发育较少;(2)纹层结构具有亚毫米级非均质性特征,不同纹层的TOC与孔隙结构存在差异,同一类纹层在不同盆地的品质具有明显差异;(3)纹层结构决定了页岩油微观运聚特征与“原生源储”富集模式,影响滞留烃含量、流体可动性及压裂改造。开展陆相页岩纹层结构精细评价,寻找规模优质页岩岩相分布区,是油气勘探从源外进入源内后必须关注的问题,是源内经济有效资源发现的基础,对页岩油“甜点区”与“甜点段”优选具有重要意义。

准噶尔盆地吉木萨尔凹陷混积岩孔喉系统分类及控制因素

针对混积岩优质储集层成因复杂的难题,进行准噶尔盆地吉木萨尔凹陷二叠系芦草沟组混积岩孔喉系统、控制因素及流体可动性研究。结果表明,混积型储集层发育粒间孔喉系统(A型)、粒间-溶蚀-晶间混合孔喉系统(B型)、溶蚀孔喉系统(C型)、溶蚀-晶间混合孔喉系统(D型)和晶间孔喉系统(E型)5类。混积岩孔喉系统有3个主要主控因素:混积岩组分含量及排列方式、沉积环境和成岩作用。混积岩组分含量及排列方式控制孔喉系统类型及变化;沉积环境主要控制孔喉系统的宏观分布,近源、高能环境混积岩粗粒组分多,颗粒或互层型支撑,发育A型和B型孔喉;远源、中能环境混积岩过渡为云泥支撑,发育C型和D型孔喉;而远源、低能环境混积岩孔喉主要为E型和D型。压实和方解石胶结等成岩作用进一步破坏粒间、溶蚀孔喉占比。在砂泥混积时,孔喉系统类型为“A→B→C→D”变化,云砂混积时孔喉系统类型为“A→C→D→E”、或“B→D→E”变化,云泥混积时孔喉系统类型为“D→E”的变化,细节受偏砂粒、长石和白云石含量影响。其中,A型孔喉的物性及可动性最好,D型和E型最差;可动流体分布与支撑方式有关,云泥支撑型混积岩大孔可动优势不明显。研究成果为混积型储集层甜点评价及解释模型的合理构建提供了地质依据。图15表1参19。

致密砂岩储层微观结构表征及发展趋势

致密砂岩储层微观结构发育微米级和纳米-亚微米级两大孔喉体系,可以通过图像表征技术、非图像表征技术和数字岩心技术等进行表征。以苏里格气田致密砂岩储层为例,对3类表征技术的原理、研究内容、适用性及研究进展进行讨论,以期进一步推动在致密砂岩气勘探开发生产中应用。

大孔道模糊识别与定量计算方法

疏松砂岩油藏注水开发后期 ,由于注入水的冲刷和井下出砂 ,在油水井之间形成不利于油田生产的储层大孔道 ,导致注入水窜流突进 ,油井水淹 ,产量急剧下降。为改善注水效果达到控水稳油目的 ,必须采取大孔道封堵措施 ,而有效识别大孔道和准确计算封堵技术参数是问题的关键。全面考虑储层异常渗流通道特点 ,将其分为无异常储层、高渗透带、裂缝、大裂缝、未完全发展大孔道和完全发展大孔道 6种情况 ,利用专家系统模糊判别理论建立了大孔道定性识别模型 ,通过研究各种不同介质的流动规律和特点 ,综合运用渗流力学和流体力学理论 ,建立了从孔隙线性渗流到粗糙管湍流的统一的大孔道流态定量分析和参数计算方法 ,可直接计算出大孔道纯体积和大孔道直径 ,从而为油田确定大孔道堵剂用量和封堵颗粒大小提供直接依据。

CT技术在致密砂岩微观孔隙结构研究中的应用——以鄂尔多斯盆地延长组长7段为例

为揭示致密砂岩复杂的孔隙结构特征,应用高分辨率CT技术,对鄂尔多斯盆地延长组长7段致密砂岩样品开展了定量研究。利用CT阈值差异识别样品中的孔隙和喉道,从而获得致密砂岩高精度二维及三维孔喉图像;应用数字岩心方法建立致密砂岩孔隙网络模型,并根据模型中的定量参数分析,获得孔隙及喉道的半径分布及其对储集空间的贡献率、孔喉连通性等特征,实现了长7段致密砂岩微观孔隙结构特征定量表征：长7段致密砂岩微米级孔喉连续分布;半径大于2μm的孔隙是长7段致密砂岩的主要储集空间;孔隙、喉道间具有一定的连通性,配位数主要为1~3.应用高分辨率CT技术可定量表征致密砂岩孔隙结构特征。

致密砂岩储层物性下限确定新方法及系统分类

扶余油层致密砂岩储层是大庆油田目前勘探开发的新目标,但对其储层物性的下限缺乏明确界定。因此,采用储层物性与产能相结合的经验统计法,分别对工业油层和低产油层储层物性按累计概率丢失10%作统计分析,确定工业油层物性下限为:孔隙度=7.1%,渗透率=0.08 mD,低产油层物性下限为:孔隙度=5.6%,渗透率=0.047 mD。再利用致密砂岩临界孔喉半径与压汞资料相结合的函数拟合法,确定储层物性下限为:孔隙度=4.46%,渗透率=0.041 mD,该值与低产油层储层物性的下限值较为接近,故将其作为致密砂岩储层的物性下限。依据致密储层物性下限、工业油层物性下限及常规储层物性分类界限,将砂岩储层系统分为致密Ⅲ类、致密Ⅱ类、致密Ⅰ类、低孔渗、中孔渗、高孔渗和特高孔渗储层。致密砂岩储层物性下限的确定和储层系统的分类可为致密油储层产能的计算及储层评价提供参数指标和技术支撑。

页岩油形成机制、地质特征及发展对策

页岩油是储存于富有机质、纳米级孔径为主页岩地层中的成熟石油,是常规-非常规"有序聚集"体系的重要类型之一,对中国陆相页岩油形成的沉积环境、储集空间、地球化学特征和聚集机制等基本石油地质问题进行了分析总结。富有机质页岩主要发育在半深湖—深湖环境,不同岩性组合共生沉积;发育纹层结构,微米—纳米级孔喉和微裂缝是主要储集空间;有利页岩以Ⅰ型和ⅡA型干酪根为主、Ro值为0.7%～2.0%、TOC值大于2.0%、有效厚度大于10 m;揭示了页岩孔隙演化和页岩油滞留聚集模式,储集空间、脆性指数、黏度、压力、滞留量等是页岩油"核心区"评价的关键。中国陆相页岩油在湖盆中心连续聚集,初步预测可采页岩油资源量约30×108～60×108t,水平井体积压裂、改造"天然裂缝"、注粗颗粒"人造储集层"等可能是页岩油工业化发展的核心技术,提出加快页岩油"分布区"研究、加强"核心区"评选、加大"试验区"建设的"三步走"发展思路。借鉴北美海相页岩气突破成功经验,陆相页岩油工业化有望在中国首先突破。

孔隙-孔喉分形多孔介质复杂类型组构模式表征

自然储层孔隙结构复杂,孔隙和孔喉共存且往往会表现出分形特征。经典的数量-尺度关系Rns及其衍生模型虽然能有效获取分形维数D,然而它们之间多对一的关系无法保证反演建模的惟一性。与此同时,分形对象中复杂类型的种类及其组构模式尚不明了,这导致储层复杂孔隙结构等效表征的困难。因此,厘清孔隙和孔喉多类型共存、多尺度分布的孔隙结构中的复杂类型,进而定量表征其组构模式对评估油气的赋存和运移规律至关重要。新近出现的分形拓扑理论表明分形对象是耦合原始复杂性与行为复杂性的双复杂系统。这两类复杂类型表现出相互独立的组构模式,其中原始复杂性确定单尺度与多尺度、单相与多相、单类型与多类型等缩放类型,而行为复杂性则决定自相似、自仿射、多重分形等尺度不变特征。基于此,本文有效标定了孔隙-孔喉耦合分形结构中的复杂类型种类,查明了孔隙、孔喉以及其连通性的原始复杂性归属,利用泰森多边形算法实现了孔隙-孔喉耦合行为的定量描述,依据分形拓扑理论给出了行为复杂性的尺度不变定义,结合原始复杂性与行为复杂性组构模式发展了一种精细表征孔隙-孔喉耦合分形孔隙结构的算法。基于新算法,模拟了不同复杂组构模式下的分形多孔介质,分析了原始复杂性与行为复杂性对孔隙结构的影响,推演了孔隙度及比表面积计算公式并验证了其有效性。

有机络合剂在油气田除垢技术中的应用

本文综述了国内外使用有机络合剂进行油气田除垢的原理、工艺和效果分析。有机络合剂用于清除地层孔隙喉道结垢时不会形成二次沉淀，用于清除油田地面集输系统结垢时具有不损伤工件和劳动强度小等优点。有机络合剂作为安全、高效除垢剂值得在油气田推广应用。