Genetic mechanisms of high-quality tight siliciclastic reservoirs:A case study from the Upper Triassic Xujiahe Formation in the Yuanba area,Sichuan Basin,China

This study analyzed the petrological characteristics,diagenesis,pore types,and physical properties of the tight coarse-grained siliciclastic sequences in the third member of the Upper Triassic Xujiahe Formation(also referred to as the Xu-3 Member)in the western Yuanba area in the northeastern Sichuan Basin,China,based on the results of 242.61-m-long core description,292 thin-section observations,scanning electron microscopy(SEM),and 292 physical property tests.The types and genetic mechanisms of high-quality tight coarse-grained siliciclastic reservoirs in this member was determined thereafter.The research objective is to guide the exploration and development of the tight coarse-grained siliciclastic sequences in the Xu-3 Member.The results of this study are as follows.Two types of high-quality reservoirs are developed in the coarse-grained siliciclastic sequences of the Xu-3 Member,namely the fractured fine-grained sandy conglomerate type and porous medium-grained calcarenaceous sandstone type.Hydrodynamic energy in the sedimentary environment is the key factor controlling the formation of high-quality reservoirs.These high-quality reservoirs are developed mainly in the transitional zone with moderately high hydrodynamic energy between delta-plain braided channels and delta-front subaqueous distributary channels.The dolomitic debris(gravel)content is the main factor affecting the reservoirs’physical properties.The micritic algal debris and sandy debris in the dolomitic debris(or gravels)tend to recrystallize during burial,forming intercrystalline pores within.In the medium-grained calcarenaceous sandstones,intercrystalline pores in the dolomitic debris are formed at the early diagenetic stage,and a pore system consisting of structural fractures connecting intergranular pores,intergranular dissolution pores,and kaolinite intergranular micropores is developed at the late stage of diagenesis.The formation of intercrystalline pores in dolomite gravels and gravel-edge fractures,a pore system connected by gravel-edge and tectonic fractures,is closely related to the dolomite gravels in the sandy fine-grained conglomerates.

Spatial-temporal coupling between high-quality source rocks and reservoirs for tight sandstone oil and gas accumulations in the Songliao Basin, China

The spatial-temporal relationship between high-quality source rocks and reservoirs is a key factor when evaluating the formation,occurrence,and prospectivity of tight oil and gas reservoirs.In this study,we analyze the fundamental oil and gas accumulation processes occurring in the Songliao Basin,contrasting tight oil sand reservoirs in the south with tight gas sand reservoirs in the north.This is done using geochemical data,constant-rate and conventional mercury injection experiments,and fluid inclusion analyses.Our results demonstrate that as far as fluid mobility is concerned,the expulsion center coincides with the overpressure zone,and its boundary limits the occurrence of tight oil and gas accumulations.In addition,the lower permeability limit of high-quality reservoirs,controlled by pore-throat structures,is 0.1×10^-3μm^2 in the fourth member of the Lower Cretaceous Quantou Formation(K1q^4)in the southern Songliao Basin,and 0.05×10^-3μm^2 in the Lower Cretaceous Shahezi Formation(K1sh)in the northern Songliao Basin.Furthermore,the results indicate that the formation of tight oil and gas reservoirs requires the densification of reservoirs prior to the main phase of hydrocarbon expulsion from the source rocks.Reservoir“sweet spots”develop at the intersection of high-quality source rocks(with high pore pressure)and reservoirs(with high permeability).

Features and genesis of Paleogene high-quality reservoirs in lacustrine mixed siliciclastic–carbonate sediments, central Bohai Sea, China

The characteristics and formation mechanisms of the mixed siliciclastic-carbonate reservoirs of the Paleogene Shahejie Formation in the central Bohai Sea were examined based on polarized light microscopy and scanning electron microscopy observations, X-ray diffrac- tometry, carbon and oxygen stable isotope geochemistry, and integrated fluid inclusion analysis. High-quality reservoirs are mainly distributed in Type I and Type II mixed siliciclastic-carbonate sediments, and the dominant pore types include residual primary intergranular pores and intrafossil pores, feldspar dissolution pores mainly devel- oped in Type II sediments. Type I mixed sediments are characterized by precipitation of early pore-lining dolo- mite, relatively weak mechanical compaction during deep burial, and the occurrence of abundant oil inclusions in high-quality reservoirs. Microfacies played a critical role in the formation of the mixed reservoirs, and high-quality reservoirs are commonly found in high-energy environ- ments, such as fan delta underwater distributary channels, mouth bars, and submarine uplift beach bars. Abundant intrafossil pores were formed by bioclastic decay, and secondary pores due to feldspar dissolution further enhance reservoir porosity. Mechanical compaction was inhibited by the precipitation of pore-lining dolomite formed during early stage, and oil emplacement has further led to the preservation of good reservoir quality.

Controlling factors of high-quality volcanic reservoirs of Yingcheng Formation in the Songnan gas field

Predicting high-quality volcanic reservoirs is one of the key issues for oil and gas exploration in the Songnan gas field.Core,seismic,and measurement data were used to study the lithologies,facies,reservoir porosity,and reservoir types of the volcanic rocks in the Songnan gas field.The primary controlling factors and characteristics of the high-quality volcanic reservoirs of the Yingcheng Formation in the Songnan gas field were investigated,including the volcanic eruptive stage,edifice,edifice facies,cooling unit,lithology,facies,and diagenesis.Stages with more volatile content can form more high-quality reservoirs.The effusive rhyolite,explosive tuff,and tuff lava that formed in the crater,near-crater,and proximal facies and in the high-volatility cooling units of large acidic-lava volcanic edifices are the most favorable locations for the development of the high-quality reservoirs in the Songnan gas field.Diagenesis dissolution,which is controlled by tectonic action,can increase the size of secondary pores in reservoirs.Studying the controlling factors of the high-quality reservoirs can provide a theoretical basis for the prediction and analysis of high-quality volcanic reservoirs.

A well test model for stress-sensitive and heterogeneous reservoirs with non-uniform thicknesses

In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model considered the permeability stress-sensitivity,wellbore storage effect,and the skin effect.The perturbation technique and Laplace transformation were used to solve the mathematical model analytically in Laplace space,and the bottom-hole pressure type curves were plotted and analyzed in real space by using the Stehfest numerical inversion.

Rapid identification of high-quality marine shale gas reservoirs based on the oversampling method and random forest algorithm

The identification of high-quality marine shale gas reservoirs has always been a key task in the exploration and development stage.However,due to the serious nonlinear relationship between the logging curve response and high-quality reservoirs,the rapid identification of high-quality reservoirs has always been a problem of low accuracy.This study proposes a combination of the oversampling method and random forest algorithm to improve the identification accuracy of high-quality reservoirs based on logging data.The oversampling method is used to balance the number of samples of different types and the random forest algorithm is used to establish a highprecision and high-quality reservoir identification model.From the perspective of the prediction effect,the reservoir identification method that combines the oversampling method and the random forest algorithm has increased the accuracy of reservoir identification from the 44%seen in other machine learning algorithms to 78%,and the effect is significant.This research can improve the identifiability of high-quality marine shale gas reservoirs,guide the drilling of horizontal wells,and provide tangible help for the precise formulation of marine shale gas development plans.

Influences of gas bubble and ice density on ice thickness measurement by GPR

Lake ice thickness changes with regional hydrometeorology and is closely associated with global climate change.We tested the detection of ice thickness using ground penetrating radar（GPR）in the Hongqipao reservoir.Ice crystals,gas bubbles,ice density and ice thickness were also determined by concurrently drilling for validation.During the tests the gas bubble content was high in the upper and low in the bottom,ice density varied with the bubble content,and the ice thickness was not homogeneous.By comparisons between radar detected and in-situ measured ice thicknesses with theoretical analyses of the influence of gas bubble content on the dielectric constant,a three-layer model with snow, granular ice,and columnar ice was established and the transmission speed of radar wave within the ice was determined.Experience reveals that the equivalent dielectric constant can be used to evaluate the wave speed and the values at 1/3 ice cover depth can be used as equivalent values.Besides,the difference between the theoretical transmission time and the real detection time induced by large gas bubbles increases nonlinearly with the theoretical transmission time or ice thickness.

Quantifying a critical marl thickness for vertical fracture extension using field data and numerical experiments

In fractured reservoirs characterized by low matrix permeability,fracture networks control the main fluid flow paths.However,in layered reservoirs,the vertical extension of fractures is often restricted to single layers.In this study,we explored the effect of changing marl/shale thickness on fracture extension using comprehensive field data and numerical modeling.The field data were sampled from coastal exposures of Liassic limestone-marl/shale alternations in Wales and Somerset(Bristol Channel Basin,UK).The vertical fracture traces of more than 4000 fractures were mapped in detail.Six sections were selected to represent a variety of layer thicknesses.Besides the field data also thin sections were analyzed.Numerical models of fracture extension in a two-layer limestone-marl system were based on field data and laboratory measurements of Young's moduli.The modeled principal stress magnitude σ3 along the lithological contact was used as an indication for fracture extension through marls.Field data exhibit good correlation(R^2=0.76) between fracture extension and marl thickness,the thicker the marl layer the fewer fractures propagate through.The model results show that almost no tensile stress reaches the top of the marl layer when the marls are thicker than 30 cm.For marls that are less than 20 cm,the propagation of stress is more dependent on the stiffness of the marls.The higher the contrast between limestone and marl stiffness the lower the stress that is transmitted into the marl layer.In both model experiments and field data the critical marl thickness for fracture extension is ca.15-20 cm.This quantification of critical marl thicknesses can be used to improve predictions of fracture networks and permeability in layered rocks.Up-or downsampling methods often ignore spatially continuous impermeable layers with thicknesses that are under the detection limit of seismic data.However,ignoring these layers can lead to overestimates of the overall permeability.Therefore,the understanding of how fractures propagate and terminate through impermeable layers will help to improve the characterization of conventional reservoirs.

Fractal Characteristics and Main Controlling Factors of High-Quality Tight Sandstone Reservoirs in the Southeastern Ordos Basin

Due to the complex conditions and strong heterogeneity of tight sandstone reservoirs,the reservoirs should be classified and the controlling factors of physical properties should be studied.Cast thin section observations,cathodoluminescence,scanning electron microscopy(SEM),X-ray diffraction(XRD),and high-pressure mercury injection(HPMI)were used to classify and optimize the reservoir.The Brooks-Corey model and stepwise regression were used to study the fractal dimension and main controlling factors of the physical properties of the high-quality reservoir.The results show that the reservoirs in the study area can be divided into four types,and the high-quality reservoir has the best physical properties and pore-throat characteristics.In the high-quality reservoir,the homogeneity of transitional pores was the best,followed by that of micropores,and the worst was mesopores.The porosity was controlled by depth and kaolinite.The model with standardized coefficients is y=12.454−0.778×(Depth)+0.395×(Kaolinite).The permeability was controlled by depth,illite/montmorillonite,and siliceous cement,and the model with standardized coefficients is y=1.689−0.683×(Depth)−0.395×(Illite/Montmorillonite)−0.337×(Siliceous Cement).The pore-throat evolutionary model shows that the early-middle diagenetic period was when the reservoir physical properties were at their best,and the kaolinite intercrystalline pores and residual intergranular pores were the most important.

Diagenetic evolution and formation mechanisms of middle to deep clastic reservoirs in the Nanpu sag, Bohai Bay Basin, East China

The reservoir properties, diagenetic features and evolution of the Paleogene Shahejie Formation(Es) in the Nanpu sag, Bohai Bay Basin were analyzed based on mineralogical and petrological data, and the main controlling factors and formation mechanisms of medium to deep high-quality reservoir were revealed by multiple regression analysis. The results show that the sedimentary microfacies, rigid grains content, and dissolution process are the key factors controlling the formation of high-quality clastic reservoir in middle to deep depth in the Nanpu sag. The formation mechanisms of middle to deep sandstones of the Es in different structural belts differ widely in formation mechanism. The Es1(uppermost member of Es) sandstone reservoirs in the Nanpu No.3 structural belt is low porosity, moderate to high permeability reservoir in the mesodiagenesis A2 stage on the whole, and the formation of high-quality reservoirs is mainly attributed to strong compaction resistance ability primarily, and dissolution process secondarily. The Es3(third member of Es) sandstones in Gaoshangpu structural belt is classified as tight sandstones in the mesodiagenesis A1 stage, in which the development of favorable reservoirs is primarily controlled by dissolution. This study provides references for reservoir evaluation of deep clastic reservoirs and exploration deployment in the Bohai Bay rift basin. As there are high-quality reservoirs, it is believed that the deep clastic reservoirs in the eastern of China, such as Bohai Bay Basin still have significant exploration potential.

中东巨厚复杂碳酸盐岩油藏分层系均衡注水开发技术

基于中东碳酸盐岩油藏注水开发实践,以两伊地区(伊拉克和伊朗)白垩系巨厚生物碎屑灰岩油藏为例,针对笼统注采导致开发效果差的难题,提出以隐蔽隔夹层为格架精细划分开发层系、多类型多井型井网有机组合、构建均衡注采体系为核心的巨厚复杂碳酸盐岩油藏均衡注水开发技术。两伊地区巨厚碳酸盐岩油藏具有垂向非均质性强、多成因超高渗透层发育、隔夹层隐蔽性强等特征,基于隐蔽隔夹层识别与刻画技术、封隔能力评估技术,提出均衡注水开发技术,形成常规层系架构、精细层系架构、深化层系架构3种均衡注水开发模式和技术。数值模拟表明,均衡注水开发技术可实现两伊地区巨厚复杂碳酸盐岩油藏精细高效注水开发、均衡动用不同类型储量,并为同类油藏的开发优化提供借鉴。

基于二维散射变换的湖相碳酸盐岩储层厚度预测方法研究

济阳坳陷沙四段湖相碳酸盐岩受湖盆内沉积环境和构造运动等因素控制,储层厚度变化大,非均质性强,油气开发难度大.为了准确预测湖相碳酸盐岩储层的厚度,本文提出一种基于二维散射变换和随机森林的储层厚度预测方法.首先,引入二维散射变换提取地震时频属性,该变换是在二维小波变换的基础上,通过迭代小波分解和非线性操作来实现的.与传统的二维小波变换对比,散射变换提取的时频属性具有局部形变稳定性以及对噪声鲁棒性的优点,有助于提高储层厚度预测的准确率.在此基础上,在有限测井数据的条件下,利用随机森林算法建立多尺度时频属性与测井解释厚度之间的非线性关系,实现湖相碳酸盐岩储层预测.模型数据的预测结果表明,与基于传统地震振幅属性的厚度预测和基于二维小波变换的储层厚度预测对比,本文所提的厚度预测方法具有最优的性能.叠后三维地震数据的预测结果表明,与基于传统地震振幅属性的厚度预测和基于二维小波变换的储层厚度预测对比,本文所提方法的厚度预测结果与实际钻井数据误差更小,提高了储层厚度预测的精度,清晰刻画了灰礁、灰滩与灰泥等三种沉积亚相的空间展布,有利于后续井位部署和优化.

胜利油区储层测井评价技术发展及展望

胜利油区油气资源丰富,储层类型众多,测井评价在勘探开发工作中发挥了重要的作用。值此建院60周年之际,系统回顾储层测井评价技术发展历程和特色技术,总结经验,展望未来,对于测井专业领域的发展和应用有着积极的意义。根据储层特点和评价难点,系统梳理了常规砂岩、复杂类型和非常规3种类型储层中形成的系列成熟测井评价技术。常规砂岩储层,系统地形成了适用性强的油层标准确定方法,创新了多层合试条件下的岩性、含油性下限约束的电性标准建立方法,开创性地提出了依据不同成岩带划分的储层参数解释技术;复杂类型储层,先后形成了陡坡带砂砾岩岩性测井识别、低渗透砂岩储层有效性评价、低电阻率油层识别及评价等技术;非常规储层,以评价储集性和含油性为主要目的,初步形成了基于二维核磁共振实验的储层参数测井评价技术。这些不同类型储层测井评价技术,都体现了井筒资料与地质认识的结合、岩石物理与测井模型的综合,展现了测井为地质、为油藏服务的能力,并取得了良好的应用效果。展望未来,剩余资源主要分布在隐蔽油气藏及深层,为满足勘探开发的发展和需求,有必要加强实验资料、气测录井和测试生产资料的分析,加强测井评价与地质结合,加强随钻测井、成像、核磁等测井新技术的应用,开展综合研究与评价,从评价目标上拓展产层性质评价和产量预测,从研究手段上,在常规技术的基础上,充分依托专家经验做好样本选取,深化大数据人工智能应用,一定会取得良好效果。

稠油油藏大段塞调驱后提高采收率新技术及应用

H1块为普通稠油区块,开展多轮次调驱后,取得较好的增油效果。但随着大段塞调驱剂注入,后期压力维持在较高水平,含水率持续上升,同时注入井吸水能力下降,油井产液能力下降,产量递减加大,亟需有效开发接替技术。为进一步改善开发现状,室内设计了在大段塞调驱段塞后,注入降黏剂进一步提高采收率。室内通过大量实验,筛选出了具有良好降黏性以及界面活性降黏剂JN-1,当质量分数达到0.2%时,降黏率可达82.0%,降低油水界面张力至4.72×10^(-3)mN·m^(-1)。室内物模实验表明,在注入0.3PV调驱段塞后,继续注入0.2%降黏剂段塞0.3PV,可充分启动残余油,进一步提高采收率16.8%。现场开展降黏驱4井组先导实验,设计注入质量分数0.2%、0.14 PV降黏剂,注入后平均单井日增油0.8 t,综合含水率下降6%。

相变储层地震精细描述与厚度预测:以苏北盆地为例

为了完成对相变储层地震精细描述与厚度预测研究,以苏北盆地为例展开研究。苏北盆地三河北滩坝砂储层,随着埋深的增加,地震同相轴由外坡的“单轴”变为中坡“双强轴”再变为内坡的“上强下弱”反射。研究区已钻井20口,储层预测属于小样本案例。如何搞清分相带的机理,并开展分相带的储层描述与预测,既具有理论研究意义,又有现实的必要性。对于相带划分,首先通过井震关系精细分析,搞清相变的本质:一是盖层、储层沉积厚度有结构性的变化;二是灰质成分分布的变化,两者综合造成同相轴相变;接着,提取研究区过零点个数、能量半时、最大振幅、主频、频带宽度、最小振幅6种典型地震属性,明确了相变分布范围,属性切片支持3个相带的划分;考虑到目的层与上覆盖层很近、常规零相位数据砂体特征不明显,开展压缩感知提频与90°相移目标处理,3个相变带的特征得到进一步明确。针对相变储层的厚度预测,首先采用属性与厚度拟合法进行了不分相带的厚度计算,但结果不理想;改用支持向量机(support vector machine,SVM)机器学习方法进行不分相带的厚度预测,预测结果表明SVM方法相对于前面的拟合法效果有所改进;再分别用以上两种方法进行分相带的厚度计算与预测,精度得到进一步提高。可为少井区、复杂相变储层的勘探开发,提供借鉴与参考。

生态库区超厚硬岩条件下大直径长桩桩基施工关键技术

针对生态库区超厚硬岩条件桥梁大直径长桩相对复杂的施工环境,常规施工工艺易造成环境污染、硬岩地层钻进速度慢、维护费用高。为了保护环境也方便施工,提出一种桩基新型施工技术,通过潜孔锤和旋挖钻结合,高效快速完成桩基施工且绿色环保。依托工程实例,对相关施工工艺进行详细阐述。

基于实验的碳酸盐岩气藏储量计算——以X气藏为例

四川盆地X气藏为碳酸盐岩储层,储层层间及层内都具有较强的非均质性,是气藏储量计算面临的困难之一。针对此问题,本文采用实验方法支撑储量计算,首先通过实验测量得到气藏各小层岩心的孔隙度、渗透率等基础物性参数,将小层渗透率校正为克氏渗透率,并根据物性差异将储层分类为孔隙型储层、孔隙-孔洞型储层,再通过产能模拟实验计算得到气藏工业产能对应的有效储层孔隙度和渗透率等储层物性下限。继而通过液膜厚度实验测得各目标储层的液膜厚度,并结合压汞实验测得的孔径分布曲线,得到有效储层中含烃孔隙体积比例,最后通过地质储量计算公式得到气藏储量。研究结果表明:①利用基础物性测试实验、产能模拟实验、水膜厚度实验等实验方法,确定储层物性下限以及有效孔隙体积比例,为气藏储量计算奠定基础,X气藏有效储层孔隙度下限为1.21%~1.56%;②气藏有效储层中含烃孔隙体积比例范围在42.62%~67.73%,通过地质储量计算公式可得到该气藏的有效储量;③该方法对于非均质性较强的碳酸盐岩储层气藏的储量确定具有理论意义和现场指导意义。

重力驱动下一维斜坡上浮泥的输移规律研究

水库浮泥是存在于水库底部的一层高含沙水体,具有较强流动性,研究其运动规律对实现水库减淤优化调度具有重要意义.为了更准确地掌握浮泥输移规律,不仅需要掌握浮泥内部的流速分布特性,还需明确不同因素对浮泥运动过程中流速和厚度变化的影响.因此选择幂律模型作为浮泥的流变模型,基于纳维-斯托克斯(N-S)方程,采用摄动法简化构建了浮泥运动模型,在空间上使用交错网格的有限体积法,时间上使用二阶龙格库塔方法,并在数值求解的过程中引入流速分布参数,通过牛顿迭代法对参数进行修正,使得模型能反映浮泥内部的流速分布形态.开展浮泥缓坡流动试验验证模型,证明了建立模型能合理描述浮泥的运动过程;分析了底面坡度、浮泥密度和黏性系数等参数对浮泥流动特性的影响作用.结果表明,浮泥密度增大,会降低流动性,减少沿程厚度变化;底面坡度增大,浮泥流速显著增大,且厚度分布形态会发生显著改变;黏性系数增大将导致浮泥流速减小且运动结束时间缩短,同时也削弱浮泥流动性.

底水油藏底水分布规律及射孔参数优化——以周长油田延安组油藏为例

为了明确射孔参数底水油藏开发的影响,针对由于早期布井随意性较大,无井网格局,无具体的开发方案,导致研究区采油速度低、递减快,稳产难度大的问题,运用油藏地质参数分析和油藏数值模拟的研究方法,分析不同射孔参数条件下,不同类型底水油藏开发效果。结果表明:1)研究区主力油层延10层底水发育,水井射孔注水厚度大小不一,对应油井受效和开采效果有明显差异;2)依据夹层分布和油水接触关系,目标油藏分为直接接触型、不稳定夹层型和稳定夹层型3类;3)Ⅰ类底水直接接触型水井射孔程度越高,越有利于抑制底水突进;最优油井射孔程度约为2 m;4)Ⅱ类/Ⅲ类型隔层分隔底水型水井射孔程度越高,开发效果越好;油井射孔程度约为70%时,开发效果好。该研究成果对同类型底水油藏开发参数设计及稳油控水提高采收率具有指导意义。

库车山前超深巨厚致密砂岩纵向细分层改造技术

塔里木油田库车山前白垩系储层为超深巨厚裂缝性致密砂岩储层,天然裂缝发育,非均质性强,已改造井产气剖面测试显示常规笼统改造纵向厚储层动用不充分,产能释放不彻底。为了解决这一问题,对于油层厚度大且中间有明显隔层的井可实施分层压裂,提高纵向改造程度。通过工程地质一体化研究,利用多种测井数据,建立了一套多尺度近远井裂缝精细识别方法;基于钻井漏失量与产量关系认识,建立了一套综合考虑构造位置、钻井井漏、裂缝发育情况、力学活动性等资料的储层评估分类方法;通过双封隔器管柱力学精细校核,增加伸缩管,优化暂堵材料粒径,形成了“机械+暂堵”软硬分层压裂技术。该技术实现了巨厚储层高效动用,应用20口井,改造后单井产气量由6.7×10^(4)m^(3)/d提高至34.0×10^(4)m^(3)/d,平均增产4倍,提产效果显著,为巨厚致密砂岩储层高效开发提供了技术支撑。