Extended finite element-based cohesive zone method for modeling simultaneous hydraulic fracture height growth in layered reservoirs

In this study,a fully coupled hydromechanical model within the extended finite element method(XFEM)-based cohesive zone method(CZM)is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast.The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment.Then,the fracture geometry(e.g.height,aperture,and area)and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model.The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented.The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’tips when propagating in soft layers,which impedes the simultaneous height growth.It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures.After that,the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented,and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing.Finally,it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures.The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.

Layer regrouping for water-flooded commingled reservoirs at a high water-cut stage

Layer regrouping is to divide all the layers into several sets of production series according to the physical properties and recovery percent of layers at high water-cut stage, which is an important technique to improve oil recovery for high water-cut multilayered reservoirs. Dif- ferent regroup scenarios may lead to different production performances. Based on unstable oil-water flow theory, a multilayer commingled reservoir simulator is established by modifying the production split method. Taking into account the differences of layer properties, including per- meability, oil viscosity, and remaining oil saturation, the pseudo flow resistance contrast is proposed to serve as a characteristic index of layer regrouping for high water-cut multilayered reservoirs. The production indices of multi- layered reservoirs with different pseudo flow resistances are predicted with the established model in which the data are taken from the Shengtuo Oilfield. Simulation results show that the pseudo flow resistance contrast should be less than 4 when the layer regrouping is implemented. The K-means clustering method, which is based on the objec- tive function, is used to automatically carry out the layer regrouping process according to pseudo flow resistances. The research result is applied to the IV-VI sand groups of the second member of the Shahejie Formation in the Shengtuo Oilfield, a favorable development performance is obtained, and the oil recovery is enhanced by 6.08 %.

Three-Dimensional Modelling of a Multi-Layer Sandstone Reservoir： the Sebei Gas Field, China

Multi-layer sandstone reservoirs occur globally and are currently in international production. The 3D characteristics of these reservoirs are too complicated to be accurately delineated by general structural-facies-reservoir modelling. In view of the special geological features, such as the vertical architecture of sandstone and mudstone interbeds, the lateral stable sedimentation and the strong heterogeneity of reservoir poroperm and fluid distribution, we developed a new three-stage and six-phase procedure for 3D characterization of multi-layer sandstone reservoirs. The procedure comprises two-phase structural modelling, two-phase facies modelling and modelling of two types of reservoir properties. Using this procedure, we established models of the formation structure, sand body structure and microfacies, reservoir facies and properties including porosity, permeability and gas saturation and provided a 3D fine-scale, systematic characterization of the Sebei multi-layer sandstone gas field, China. This new procedure, validated by the Sebei gas field, can be applied to characterize similar multi-layer sandstone reservoirs.

Research on reservoir bed heterogeneity,interlayers and seal layers and controlling factors of 2+3 sands of upper second member,Shahejie Formation,in the west of the Pucheng Oilfield

Terminal fans have formed the sedimentary system of the 2＋3 sands of the upper second member, Shahejie formation in the west of the Pucheng Oilfield, Bohai Bay Basin, East China. Based on well logging data and physical properties of the reservoir beds, the 2＋3 sands were divided into 16 sublayers. The heterogeneity of reservoir beds and distribution of interlayers and seal layers in the 2＋3 sands were investigated. The intra-layer heterogeneity and inter-layer heterogeneity primarily belong to the severely heterogeneous classification. The spatial differentiation of sedimentary microfacies resulted in a change of reservoir bed heterogeneity, strong in the middle and southern parts, weak in the northern part. Spatial distribution of interlayers and seal layers is dominated by sedimentary microfacies, and they are thick in north-eastern and middle parts, thin in the south-western part.

Quantitative evaluation methods for waterflooded layers of conglomerate reservoir based on well logging data

The rapid changing near source, multi-stream depositional environment of conglomerate reservoirs leads to severe heterogeneity, complex lithology and physical properties, and large changes of oil layer resistivity. Quantitative evaluation of water-flooded layers has become an important but difficult focus for secondary development of oilfields. In this paper, based on the analysis of current problems in quantitative evaluation of water-flooded layers, the Kexia Group conglomerate reservoir of the Sixth District in the Karamay Oilfield was studied. Eight types of conglomerate reservoir lithology were identified effectively by a data mining method combined with the data from sealed coring wells, and then a multi-parameter model for quantitative evaluation of the water-flooded layers of the main oil-bearing lithology was developed. Water production rate, oil saturation and oil productivity index were selected as the characteristic parameters for quantitative evaluation of water-flooded layers of conglomerate reservoirs. Finally, quantitative evaluation criteria and identification rules for water-flooded layers of main oil-bearing lithology formed by integration of the three characteristic parameters of water-flooded layer and undisturbed formation resistivity. This method has been used in evaluation of the water-flooded layers of a conglomerate reservoir in the Karamay Oilfield and achieved good results, improving the interpretation accuracy and compliance rate. It will provide technical support for avoiding perforation of high water-bearing layers and for adjustment of developmental programs.

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.

Development of Layered Treatment Technique for Multiple Heavy Oil Reservoirs

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NEW MODEL OF GAS FLOW PROBLEM IN MULTI-LAYERED GAS RESERVOIR AND APPLICATION

In this paper, the new model of the real gas filtration problem has been presented multi-layered gas reservoir, when a gas well output and wellbore storage may be variable, and have obtained the exact solutions of pressure distribution for each reservoir bed under three kinds of typical out-boundary conditions. As a special case, according to the new model have also obtained the qxact solutions of presssure distribution in homogeneous reservoir and is given important application in gas reservoir development.

塔里木盆地构造流体作用对超深层断控碳酸盐岩缝洞型储层的控制

基于露头、岩心、测井、录井、三维地震、地球化学实验和生产测试等资料,利用生产动态分析、流体包裹体测温及碳氧同位素测试等多种方法,系统探讨塔里木盆地的构造和流体作用对超深层断控碳酸盐岩缝洞型储层规模、储层质量及其有效性与连通性的控制机理。研究表明:①走滑断层规模、构造部位与岩石力学层共同控制了缝洞储层的发育规模。断层规模越大,储层规模越大;叠接挤压段的储层规模大于叠接拉分段,纯走滑段的储层规模相对较小;走滑断层的交汇部位、转折部位与端部的储层规模较大;垂向上储层发育的差异性受岩石力学层控制,脆性指数高的岩石力学层更有利于缝洞储层的发育。②多期走滑断层活动及流体改造共同控制了缝洞储层的有效性演化及其非均质性。加里东晚期—海西早期的大气淡水活动期为缝洞储层主要形成期;海西晚期热液活动进一步加剧了有效储集空间分布的非均质性。③走滑断层构造部位和现今地应力控制了缝洞储层连通性。叠接拉分段缝洞储层连通性好于纯走滑段,叠接挤压段较差;与现今地应力方向近平行的走滑断层控制的缝洞储层连通性好。优质缝洞型储层平面上主要分布于走滑断层的叠接拉分段两侧断层交汇区域,叠接挤压段中部区域、纯走滑段交叉部位、转折部位和端部的羽状断层区;剖面上集中于高脆性指数的岩石力学层段。

川东地区东岳庙段湖相页岩油气源储特征与富集层段优选

为研究四川盆地东部东岳庙段页岩油气源储特征并优选油气富集层段,文中利用岩心、测录井及分析测试资料对东岳庙段页岩岩石学特征、烃源岩特征、储层特征及含油性开展了研究。川东地区东岳庙段页岩矿物组分以黏土矿物、石英和方解石为主。页岩可划分为硅质页岩、混合质页岩与黏土质页岩3类。总有机碳质量分数(TOC)介于0.25%~7.52%,平均为1.44%,有机质类型以Ⅱ型为主,显微组分包括腐泥组与镜质组,页岩整体处于成熟—高成熟阶段。页岩孔隙类型以黏土矿物晶间孔与有机质孔为主,孔隙度平均为2.08%。部分页岩及其夹层由于裂缝的发育而表现出较高的渗透率(大于0.1×10^(-3)μm^(2)),并且微裂缝具有普遍含油的特征。页岩油气的富集受到了源储特征的影响。其中,页岩的生烃潜力是页岩油气富集成藏的基础,矿物组分、有机质类型及显微组分在很大程度上影响了油气富集空间发育程度,裂缝的发育则影响了油气的富集方向与储集性能。川东地区东岳庙段东二亚段中部为页岩油气富集层段。该段页岩在生烃潜力与储集性方面具有显著优势。

结合高斯噪声的回声状态网络模型及其时间序列预测性能

为了模拟回声状态网络模型在时间序列预测实例中的影响因素,在回声状态网络模型的储备池层引入高斯噪声,构建结合高斯噪声的回声状态网络模型;利用公式推导分析所提模型的非线性性质;采用股票序列数据与Logistic混沌序列数据进行实验验证和对比分析。结果表明,本文所提模型的预测效果优于回声状态网络模型、压缩感知回声状态网络模型和反向传播神经网络模型,股票收盘价预测、Logistic混沌序列预测的平均绝对误差均最小,分别为1.33×10^(-3)、5.21×10^(-4)。

不同类型油藏非均相驱均衡驱替方式及效果评价

非均相驱协同矿场调整措施在孤岛油田中一区Ng3单元取得了良好的降水增油效果.然而,由于实际地层非均质性复杂、层间井网部署的差异及不同层位化学剂注入量不同,非均相驱在动用平面和纵向分布剩余油的过程中会相互影响,很难明确不同方式均衡驱替贡献力度,难以阐明不同类型剩余油的动用机制.为此,本文采用数值模拟方法,基于目标区块实际地层参数,建立了五种不同类型剩余油油藏机理模型,通过受效剩余油分布、洗油效率、波及系数、平面含水饱和度变异系数及纵向吸水不均衡系数等指标,评价了非均相驱平面及纵向均衡驱替效果,阐明了剩余油动用机制.数值模拟研究表明,非均相驱协同井网调整或分层配注等矿场调整措施,能最大程度扩大波及、提升均衡驱替效果.针对不同类型剩余油油藏,明确了均衡驱替方式贡献力度及实施优先级,实际应用时应根据油藏类型和矿场实施条件,选取适宜的均衡驱替方式.本研究为矿场非均相驱动用不同类型剩余油提供了合理的解释,对非均相驱在矿场不同类型油藏的进一步推广应用提供参考.

莺歌海盆地莺北区HK29区三亚组一段沉积特征及储层主控因素

随着莺歌海盆地成熟区域及主力层系勘探程度日益提高,新区新层系成为日益关注的焦点。莺北区位于莺歌海凹陷北部,目的层三亚组一段具有较大的勘探潜力,但目前勘探程度较低,对其沉积体系及储层发育情况缺乏系统的研究。基于岩芯观察、镜下薄片鉴定以及地震、测录井、分析化验等资料分析,对HK29区目的层沉积相及其展布特征、储层特征等展开研究,探讨了储层发育的主控因素。结果表明:(1)HK29区三亚组一段主要发育物源来自海南岛的近源三角洲沉积,水下分流河道微相是有利相带;(2)三亚组一段储层岩性以长石岩屑砂岩和岩屑长石砂岩为主,孔隙类型以长石溶孔和粒间孔为主,总体表现为中—低孔、低渗—特低渗的特征;(3)储层物性主要受沉积作用和成岩作用控制,三角洲前缘水下分流河道砂体粒度粗、分选好,是发育有利储层的优势相带,压实作用是该区储层物性变差的直接因素,长石和岩屑的溶蚀是改善储层物性的关键因素。基于以上研究,提出HK29区三亚组一段“相带优、埋藏浅、溶蚀强”的优质储层形成机制,有效指导了莺北区领域勘探突破。

准噶尔盆地永进—征沙村地区侏罗系超深层致密砂岩储集层分级评价

准噶尔盆地永进—征沙村地区侏罗系超深层砂岩储集层致密且非均质性强,储集层评价标准及有利储集层分布不明确,制约了油气勘探开发。以测井、录井、岩心及试油资料为基础,通过矿物分析、核磁共振、毛细管压力实验、岩心驱替等,开展了侏罗系储集层微观孔隙结构特征研究,明确了可动孔隙半径下限,并以流体可动孔隙度作为关键评价指标建立了分级评价标准。研究表明:研究区中—细粒岩屑砂岩、长石岩屑砂岩储集空间为粒间孔、次生溶蚀孔及微裂缝,孔隙半径较小,为0.005~5.000μm,以毛细管压力实验曲线标定后不同驱替状态的核磁共振T_(2)谱确定了可动孔隙半径下限为0.100μm,进而明确了含油岩石的流体可动孔隙度。综合考虑岩电特征、孔隙类型及结构、含油性特征,结合典型井的产能特征,建立了研究区储集层分级评价标准,通过Ⅰ类、Ⅱ类和Ⅲ类储集层的分级评价,为后续油气田开发及井位部署提供了依据,对于该地区超深层致密油藏的勘探开发与邻区储集层评价具有参考意义。

Numerical simulation and experimental study on dissolving characteristics of layered salt rocks

Underground salt cavern reservoirs are ideal spaces for energy storage. China is rich in salt rock resources with layered lacustrine sedimentary structures. However, the dissolution mechanism of layered salt rocks remains poorly understood, resulting in significant differences between the actual measurements and the designed indices for the layered salt rock water-soluble cavity-making cycle and the cavity shape. In this work, the dissolution rates of 600 groups of layered salt rocks in China under different conditions were determined experimentally.Thus, the established artificial neural network prediction model was used to assess the effects of the contents of NaCl, Na2 SO4, and CaSO4 in the salt rocks, concentrations, dissolution angles, and flow rates on their dissolution rates by performing ANOVA and F-test. The results provide a theoretical basis for evaluating the dissolution rate of layered salt rocks under different conditions and for the numerical simulation of the layered salt rock water-soluble cavity-making process.

Maximum Effective Hole Mathematical Modei and Exact Solution for Commingled Reservoir

The maximum effective hole-diameter mathematical modei describing the flow of slightly compressible fluid through a commingled reservoir was solved rigorously with consideration of wellbore storage and different skin factors. The exact solutions for wellbore pressure and the production rate obtained from layer j for a well production at a constant rate from a radial drainage area with infinite and constant pressure and no flow outer boundary condition were expressed in terms of ordinary Bessel functions. These solutions were computed numerically by the Crump's numerical inversion method and the behavior of systems was studied as a function of various reservoir parameters. The modei was compared with the real wellbore radii modei. The new modei is numerically stable when the skin factor is positive and negative, but the real wellbore radii modei is numerically stable only when the skin factor is positive.

Theoretical Study on Quantitative Characterization of Interlayer Interference in Multi-Layer Commingled Production

X oilfield is a typical layered reservoir with a large vertical span and many oil-bearing formations. There are significant differences in reservoir types and fluid properties among various formations. The interlayer interference is severe in the development process. At present, the interlayer interference research based on dynamic monitoring data cannot meet development adjustment needs. Combined with the field test results, through the indoor physical simulation experiment method, dynamic inversion method, and reservoir engineering method, this paper analyzes the main control factors and interference mechanism of interlayer interference, studies the variation law of interference coefficient, improves and forms the quantitative characteristic Theory of interlayer interference in multi-layer commingled production, and provides theoretical guidance for the total adjustment of the middle strata division in the oilfield.

油藏不同开发阶段层面建模算法及实例

由于油藏不同开发阶段特征及其研究目的不同,三维地质建模中层面建模采取的模拟方法和模型精度均有所区别。从三维地质建模角度出发,将油藏开发划分为油藏评价、新区建产和老区调整3个阶段,通过港东二区五断块层面模拟过程中各种模拟算法分析及筛选,提出了层面模拟时,油藏评价阶段建模采用Kriging算法,网格精度为100 m×100 m×5.0 m;新区建产阶段建模采用Kriging算法或Global B-spline算法,网格精度为50 m×50 m×1.5 m;老区调整阶段建模采用Local B-spline算法或Converging average算法,网格精度为10 m×10 m×0.5 m,使层面模拟结果更符合地质情况及研究需要。

基于灰色关联度分析-极限学习机的低阻油层及水淹层测井识别——以渤海P区块馆陶组为例

历经近20的开发,渤海P区块进入高含水期,馆陶组发育的大量低阻油层与水淹层在测井曲线形态上差异不明显。为了精确进行水淹层识别以及水淹层等级划分,采用了机器学习算法。首先采用灰色关联度分析,筛选低阻油层和水淹层识别的敏感参数曲线;其次构建了极限学习机水淹层识别模型,对模型进行训练,获取最优参数。将其应用于实际资料处理,结果表明,基于灰色关联度分析极限学习机的低阻油层及水淹层测井识别方法对低阻油层与水淹层的预测精度较高,符合率达89.3%,远远优于未经过灰色关联度分析筛选的预测结果,具有实际应用价值。

适合延长油田低渗透储层分层注水井的有机酸解堵体系

为了解决延长油田低渗透储层分层注水井注入压力升高以及注水量下降的问题,以复合有机酸FH-S为主体酸液,结合黏土稳定剂、缓蚀剂和助排剂等主要处理剂,研制了一套适合延长油田低渗透储层分层注水井的有机酸解堵体系,室内对其基本性能和岩心驱替解堵性能进行了评价。结果表明:有机酸解堵体系具有良好的溶蚀性能、缓蚀性能和较强的铁离子稳定能力,降低表面张力和界面张力的效果也较好,体系与地层水的配伍性较好,不会出现浑浊和沉淀;另外,在天然岩心被注入水污染后挤入2 PV有机酸解堵体系,能够有效解除堵塞污染,岩心驱替压力明显降低,岩心渗透率恢复值可以达到100%以上,解堵效果较好。现场应用结果表明:目标注水区块5口注水井采取有机酸解堵体系施工措施后,注入压力显著降低,日注水量明显增大,并且措施的有效期较长,取得了良好的现场施工效果。