TRACER RESPONSE IN PARTIALLY FRACTURED RESERVOIRS

There is considerable interest in the petroleum industry to characterize partially fractured reservoirs and to develop an increased understanding of the physics of fluid flow in these types of reservoirs. This is because fractured reservoirs have different behavior and there exist a large number of these reservoirs that are not fully developed. This paper presents a numerical simulation study that was performed to investigate the effect of rock properties on the tracer response in partially fractured reservoirs using a finite difference numerical simulator. These properties include fracture intensity, fracture porosity and matrix permeability. The functional relationships between these parameters and the calculated effective permeabilities are also investigated. Several images, each with different probability of fracture intensity, were generated randomly. Numerical simulations of single-phase tracer transport were then performed in each of the generated fractured models. Results show that the fracture intensity, fracture porosity and matrix permeability have a significant effect on the tracer response in naturally fractured reservoirs. Depending on the reservoir properties, the results also show that the flow in partially fractured reservoirs can be either matrix-dominated or fracture-dominated. The characteristics of each regime and the conditions for its occurrence are presented.     

变质岩裂缝性潜山油藏储层建模方法研究

根据潜山油藏岩性分布复杂、非均质性强的特点,提出了变质岩潜山油藏相控建模方法,即依据"优势岩性"理论,利用录井资料中的岩性分析数据,建立变质岩相分布模型;以变质岩相为约束条件进行储层建模,实现了相控条件下基质的孔渗模拟。针对该类油藏裂缝发育、存在裂缝渗透率各向异性的特点,将各向异性建模方法引入潜山裂缝性油藏建模中,建立裂缝渗透率各向异性的定量表征模型。该方法考虑了裂缝和基质渗流特征,建立了双重介质模型,更便于与油藏数值模拟结合应用。     

DEVELOPMENT AND APPLICATION OF INTERFERENCE TESTING DATA ANALYSIS MODEL FOR DUAL-POROSITY SYSTEM USING BOUNDARY ELEMENT METHOD

The main purpose of this paper is to develop a boundary element model in order to analyze the data from naturally fractured reservoirs with complex-shaped boundary. The model employs a boundary element method with free-space Green's function as a weighting function that makes it possible to handle multi-well system with geometrically complex boundary. The developed model has been validated by using the published actual field data for naturally fractured reservoir. The result shows that the model is capable of describing the transient pressure behavior representing the characteristics of naturally fractured reservoirs. The calculated permeability agrees well with the published result. In case of multi-well homogeneous reservoir system with complex geometry, both the transient state data and the data including boundary effect have been analyzed. The calculated permeabilities in each case were computed identically. This represents that the model can be effectively used for the analysis of data with boundary effect. In order to investigate the field applicability of the model, the actual field interference testing data performed in the Maljamar reservoir, New Mexico, USA were used. The relative fracture storage capacity and inter-porosity flow parameter were computed as 1.0 and 0.0, respectively. This implies that porosity and permeability of matrix are extremely low compared with those of fracture, and the flow occurs only through the secondary porosity system such as fracture network.     

DEVELOPMENT AND APPLICATION OF INTERFERENCE TESTING DATA ANALYSIS MODEL FOR DUAL-POROSITY SYSTEM USING BOUNDARY ELEMENT METHOD

The main purpose of this paper is to develop a boundary element model in order to analyze the data from naturally fractured reservoirs with complex-shaped boundary. The model employs a boundary element method with free-space Green's function as a weighting function that makes it possible to handle multi-well system with geometrically complex boundary. The developed model has been validated by using the published actual field data for naturally fractured reservoir. The result shows that the model is capable of describing the transient pressure behavior representing the characteristics of naturally fractured reservoirs. The calculated permeability agrees well with the published result. In case of multi-well homogeneous reservoir system with complex geometry, both the transient state data and the data including boundary effect have been analyzed. The calculated permeabilities in each case were computed identically. This represents that the model can be effectively used for the analysis of data with boundary effect. In order to investigate the field applicability of the model, the actual field interference testing data performed in the Maljamar reservoir, New Mexico, USA were used. The relative fracture storage capacity and inter-porosity flow parameter were computed as 1.0 and 0.0, respectively. This implies that porosity and permeability of matrix are extremely low compared with those of fracture, and the flow occurs only through the secondary porosity system such as fracture network.     

裂缝性油藏压后压降分析

对于裂缝性低渗透储层,由于其基质孔隙度小、渗透率低,天然微裂隙成为决定压裂液滤失的主要因素。在总结Nolte经典G函数压降曲线分析方法的基础上,根据裂缝性地层存在微裂隙的特征,建立了裂缝性油藏小型压裂压降曲线分析模型。应用无因次压力函数图和叠加导数图,做出了压降特征曲线,可以判断天然裂缝闭合压力。通过对已压裂井压降曲线的分析和解释,能够计算出与压力相关的滤失系数、基质的滤失量和经天然裂缝的滤失量,以及人工裂缝的几何尺寸,从而为裂缝性地层压裂施工参数的设计提供依据。     

Black Oil and Compositional Reservoir Simulation for Increasing the Recovery Performance of an Iranian Fractured Carbonate Reservoir

Abstract

Naturally fractured reservoirs contain a significant amount of world oil reserves. Accurate and efficient reservoir simulation of naturally fractured reservoirs is one of the most important, challenging, and computationally intensive problems in reservoir engineering. Black oil and compositional reservoir simulators have been used to determine the reservoir management and production strategies to increase the oil recovery from a low-porosity, low-permeability fractured carbonate reservoir, with an average matrix permeability of 0.8 md, average fracture permeability of 500 md, and an average matrix porosity of 10%. This reservoir is a candidate for an enhanced oil recovery (EOR) process, because the reservoir production rate has been declined due to increasing the water cut as a result of rising the water oil contact. The injection techniques that have been considered in this study for black oil model include (a) gas injection, (b) water injection, and (c) simultaneous water alternating gas injection and for the compositional model include (a) dry gas injection, (b) CO₂ injection, and (c) N₂ injection. Simulation results show that CO₂ injection has the maximum oil recovery between the EOR scenarios.     

裂缝油藏三维油,水两相渗流的有限元方法

本文建立了一裂缝性油藏三维油，水两相的渗流模型。     

Naturally fractured hydrocarbon reservoir simulation by elastic fracture modeling

Accurate fluid flow simulation in geologically complex reservoirs is of particular importance in construction of reservoir simulators. General approaches in naturally fractured reservoir simulation involve use of unstructured grids or a structured grid coupled with locally unstructured grids and discrete fracture models. These methods suffer from drawbacks such as lack of flexibility and of ease of updating. In this study, I combined fracture modeling by elastic gridding which improves flexibility, especially in complex reservoirs. The proposed model revises conventional modeling fractures by hard rigid planes that do not change through production. This is a dubious assumption, especially in reservoirs with a high production rate in the beginning. The proposed elastic fracture modeling considers changes in fracture properties, shape and aperture through the simulation. This strategy is only reliable for naturally fractured reservoirs with high fracture permeability and less permeable matrix and parallel fractures with less cross-connections. Comparison of elastic fracture modeling results with conventional modeling showed that these assumptions will cause production pressure to enlarge fracture apertures and change fracture shapes, which consequently results in lower production compared with what was previously assumed. It is concluded that an elastic gridded model could better simulate reservoir performance.     

Modification of Vogel's Inflow Performance Relationship (IPR) for Dual Porosity Model

The performance of a solution gas-drive reservoir can be predicted using Vogel inflow performance relation (or IPR), which simply relates the deliverability of a well to bottom-hole pressure and average reservoir pressure. While many studies have shown the success of Vogel-type IPR for single porosity reservoirs, the applicability of this method for naturally fractured reservoirs (NFRs), is under question mainly because of the complex flow behavior in matrix and fracture systems. The present study is undertaken to determine if the relation between NFR flowing wellbore pressure and oil production rate could be described by Vogel's IPR. For this purpose, a synthetic dual porosity fractured reservoir with typical rock and fluid properties is considered as a base-case. Identifying important parameters affecting the performance of a naturally fracture reservoir, a total of 22 simulations covering a wide range of reservoir fluid properties, fracture permeabilities, capillary pressure, block height, and recovery factor are made. The results show significant errors between simulation output and Vogel's IPR. A modification is made on Vogel's IPR to use it for performance prediction of dual porosity model.     

文留油田低渗透砂岩裂缝储层压力敏感性研究

对于文留油田低（特低）渗透砂岩裂缝性储层来说,其独特的孔渗性有别于一般的砂岩或砾岩储层,压敏机理也有所区别。对于一般的砂岩或砾岩储层来说,其所呈现的压敏效应主要是因为喉道趋于闭合或因为泥质挤入造成的渗透率下降。而对于本地区裂缝性储层来说,基质一般较为致密,孔隙度、渗透率极低,其受压力而引起的孔隙度、渗透率性能改变甚为有限。由于压力的改变而引起的储层物性的改变,主要是储层裂缝的开启闭合决定的。进一步研究表明,在裂缝储层中渗透率随压力的变化尤为明显。有效应力变化速度越快,其对岩心渗透率的损害就越强。     

双重孔隙压敏介质油藏不稳态产能变化研究

建立由基岩系统和裂缝系统组成，并考虑裂缝渗透率随压降的增加呈指数减小的双重孔隙压敏介质油藏不稳态产能模型，采用隐式差分格式对考虑污染效应的情况进行求解。讨论了无因次渗透率模数和表皮系数、窜流系数、裂缝弹性储容比等对不稳态产能的影响。结果表明，无因次渗透率模数导致不稳态产能明显下降，但其对早期不稳态产能的影响不如表皮系数的影响显著，窜流系数决定着窜流出现的早晚；裂缝弹性储容比则影响着油藏早期不稳态产能的大小和窜流阶段出现的早晚。     

裂缝性储层应力敏感性数值模拟——以库车坳陷克深气田为例

针对裂缝性储层应力敏感性的常规研究方法难以做到与实际相符且不能定量分析的问题,采用储层裂缝数值模拟方法,对克深气田裂缝性储层的应力敏感性进行了研究,并分析了应力敏感性的影响因素。研究结果显示:随着有效应力的增加,裂缝的孔隙度和渗透率均随之下降,表现出较强的应力敏感,且裂缝渗透率的应力敏感程度强于裂缝孔隙度,并可采用指数函数对应力敏感曲线进行拟合;储层裂缝孔渗参数的初始值越高,其应力敏感性越强,即相对高渗储层的应力敏感性要强于相对低渗储层;对于低渗透的裂缝性储层,储层岩石塑性越强其应力敏感程度越高;不同充填程度裂缝的应力敏感性由强到弱依次为未充填缝、半充填缝和全充填缝。     

准噶尔盆地超低渗裂缝性油田开发--以小拐油田为例

准噶尔盆地小拐油田夏子街组属于低孔、超低渗透性且裂缝发育的砾岩油藏，油气储集空间以砾缘缝为主，其微裂缝局部沟通溶蚀孔和界面孔。基质孔喉对渗透率贡献值极低，裂缝为油气渗流的主要途径，双孔单渗特征尤为明显，为此建立的裂缝与基质组成的复合地质模型为钻定向井提供了依据，获得了较好的开发效果。     

渤海C油田潜山裂缝型储集层随机离散裂缝网络模型的实现与优选方法

针对渤海C油田潜山裂缝型储集层的地质特点,综合利用岩心、测井、油藏动态以及露头等资料,分析了潜山裂缝型储集层的成因及发育特点,确定构造应力场和断层的分布为该油田储集层裂缝发育的2个主控因素。将构造应力场与断层分布相结合模拟离散裂缝网络,预测裂缝分布趋势。通过地质特征对比以及动态资料验证,优选出C油田的离散裂缝网络(DFN)。以离散裂缝网络(DFN)为平面约束条件,以井点岩心统计裂缝几何形态为"硬"数据,计算出裂缝孔隙度和渗透率的三维分布,并建立了潜山裂缝型储集层的地质模型,为油田开发方案的制定提供了可靠的地质依据。     

天然裂缝性油藏渗吸规律

为了研究渗吸作用对天然裂缝性油藏的影响,改善该类油藏的开发效果,以数值模拟为手段,通过建立概念地质模型,以静态和动态2种方式研究了毛细管压力、孔隙均匀程度、相渗曲线、基质和裂缝渗透率、原油黏度和基质含油饱和度对基质渗吸速度的影响,并在静态下对相关参数进行了公式拟合.静态下,渗吸速度与毛细管压力、基质渗透率、残余油饱和度、束缚水饱和度下的油相相对渗透率呈直线关系,与束缚水饱和度呈指数关系,与原油黏度呈幂指数关系;动态下,对于不同润湿性的油藏提出了不同的开发方式.     

蚂蚁追踪技术在潜山油藏裂缝预测中的应用

任丘潜山雾迷山组油藏为我国大型裂缝型碳酸盐岩底水块状油藏,储层具有双孔隙介质特征,目前处于高含水低速开发阶段.文中以任丘潜山碳酸盐岩油藏为倒,以多学科理论一体化为原则进行裂缝预测.综合运用了地震、钻井、测井、开发动态等多种基础资料及综合地质研究成果,利用PetrelTM地质建模软件,应用先进的蚂蚁追踪技术和离散裂缝网络...     

埕北30太古宇裂缝性潜山油藏孔渗参数模型

为了建立裂缝性潜山油藏的孔渗参数模型，选取核磁共振测井、密度测井和声波测井资料约束Elanplus软件解释井剖面各点的总孔隙度和裂缝系统渗透率，利用井点孔渗物性与声波测井速度资料回归了声波测井速度、声波时差与孔隙度、渗透率的关系式。利用三维地震反演和相干分析得到的三维速度数据体，求取了埕北30太古宇潜山油藏孔渗物性的三维分布。在建立裂缝系统径向、主裂缝方向、次裂缝方向和垂向渗透率之间相关关系模型的基础上，结合应力场数值模拟求得的裂缝走向，预测了裂缝系统渗透率的三维空间各向异性分布，建立了裂缝性潜山油藏的孔渗参数模型。     

裂缝性低渗透油藏三维两相黑油数值模拟研究

大量实验和现场数据表明,低渗透油藏中普遍存在启动压力梯度,并且裂缝对应力的敏感比基质更强,文中在双孔、双渗达西渗流的数学模型基础上引入启动压力梯度和应力敏感,建立了裂缝性低渗透油藏双孔、双渗渗流模型,并对其进行了全隐式联立求解以及实例计算。     

哈萨克斯坦盐下油藏双重介质三维地质建模

以哈萨克斯坦肯基亚克盐下石炭系油藏为例.在详细岩心观察基础上.综合取心、测井、地质、地震等多方面资料,分步建立了双重介质储集层的三维地质模型.首先建立研究区构造模型,利用地震相和测井相分析建立沉积相模型,在数据结构分析和方法优选的基础上.建立相控的储集层基质属性模型;第二步利用地震几何属性分析和岩心裂缝描述结果.模拟建立裂缝分布网络模型;第三步将基质属性和裂缝分布网络模型有机结合,利用基质和裂缝渗流交换原理建立双重介质储集层三维综合地质模型.建模最终给出了裂缝的网络分布模型,裂缝的等效渗透率和双重介质等效渗透率模型,可直接提供给油藏工程研究人员开展数值模拟研究.     

非均质各向异性裂缝油藏物理模型制作方法

基于离散化原理建立了一种用于裂缝油藏物理实验的模型制作方法。选取不同物性的天然岩石露头加工制作大量的单元岩块,将单元岩块按特定方式连结形成大尺度岩体,单元岩块之间的缝隙在大岩体内构成三维裂缝系统,从而形成裂缝油藏物理模型。通过选择单元岩块的数量、大小、排列样式以及每个单元岩块的物性参数和黏接方式,可以定量控制模型的尺度、形状,以及模型内部裂缝和基质的渗透率、孔隙度,裂缝-基质间渗吸强度,裂缝密度等物性参数分布,建立满足非均质及各向异性特征的裂缝油藏物理模型。经实例验证,该建模方法可以实现裂缝油藏模型物性参数分布的定量化,制作过程具有可行性和可靠性。