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1.
Reservoir stimulation requires a model to evaluate the fracture path and closure for the simultaneous or sequential propagation of the hydraulic fracture (HF). This paper presents a fluid-solid coupled model to simulate multi-stage HF propagation. A non-linear joint model is proposed to evaluate the fracture closure when the created fractures are elastically propped. HF closure continues until the balance of external stress matches the proppant's resistance. The reservoir along the horizontal wellbore is not stimulated equally by the multi-stage fracturing. The HFs in the subsequent stage are ‘repelled’ and restrained by the HFs in the previous stage. 相似文献
2.
The geometry of hydraulic fracture propagation in the absence and presence of natural fractures in reservoirs was studied. The results revealed a marked influence of natural fractures on the symmetry of fracture propagation observed for rock free of natural fractures. Natural fracture properties such as stiffness and approaching angle, and the distance from wellbore to the natural fracture were found to influence the hydraulic fracture geometry. Furthermore, the location of the wellbore with respect to the natural fractures in a reservoir having a system of natural fractures displayed a significant influence on the resulting geometry of hydraulic fracture propagation. 相似文献
3.
水力压裂作为一种主要的地热能开采手段,其压裂效果除与岩体基本物理力学性质有关外,还与裂隙分布、地应力状态、压裂工程参数等密切相关.为了探究以上因素对水力压裂过程中裂缝扩展行为的影响,以冀中坳陷碳酸盐岩储层岩体为研究对象,基于扩展有限元法,建立裂缝扩展流固耦合模型,分析了水平应力差、射孔方位角、注入液排量和压裂液黏度等参数对裂缝扩展行为的影响.结果表明:单裂缝扩展时,射孔方位角越小、注入量越大、越有利于裂缝扩展;双裂缝扩展时,水平应力差增大,裂缝偏转程度变小;水力裂缝与天然裂缝相交时,较小水平应力差有利于天然裂缝开启. 相似文献
4.
The ultra-low permeability of shale reservoirs necessitates engineering applications such as hydraulic fracturing to enable the extraction of economically viable amounts of gas. In this process, a high-pressure fluid is injected into the reservoir to create a network of fractures. Proppants are solid, spherical, high-strength particles with size range between 8 and 140 mesh (105 μm–2.38 mm), which are injected into the reservoir simultaneously with fracturing fluid to prompt the opening of the fractures created, and they play a major role in the hydraulic fracturing process. As a result, appropriate management of proppants in shale reservoirs based on precise identification of their behaviour in shale reservoirs is necessary, because unexpected proppant performance or behaviour, commonly known as proppant damage mechanisms, can greatly reduce fracture conductivity. Therefore, it is essential to determine the major factors affecting proppant behaviour in order to maintain constant fracture conductivity. Numerous factors have been found in previous studies, and they can be summarized into three major groups: proppant properties, reservoir properties and hydraulic fracturing production, which affect proppant damage mechanisms. In the present paper, case studies have been provided on the determination of potential factors influencing proppant behaviour, followed by a discussion of their effects on fracture conductivity. The aim of this study is to present current opinions on potential factors influencing proppant behaviour based on a comprehensive literature review. 相似文献
5.
Hydraulic fracture (HF) propagation behavior is signi?cant when building enhanced geothermal systems (EGS). HF geometry is closely related to the structural planes (SPs) in hot dry rock (HDR), such as natural fractures (NFs), quartz veins (QVs) and lithologic interfaces (LIs). However, the HF behaviors in HDR have not been well understood, especially the influence of multiple SPs on the HF geometry. To clarify this mechanism, several groups of physical simulation experiments of hydraulic fracturing were conducted to investigate the intersection relationship between the HFs and the SPs. Results show that the HF geometry shows great differences when intersecting with different SPs. In summary, the HF geometry displays four basic patterns, namely, propagation along the SPs, branching, capture, penetration/non-dilation. The fluctuation degree of the pressure-time curve and the HF complexity show a positive correlation. The cementing strength of the SP and their different mechanical properties from rock matrix influence the HF behaviors significantly. Therefore, the HF shows diverse geometries when intersecting with the NFs and LIs, while propagating along the QV when intersecting with it. For the complex networks, it is favorable for the HF to penetrate through and dilate several SPs, rather than simply cross or propagate along the SP. 相似文献
6.
3500 m以深页岩气资源量占整个川南地区总资源量的比例高达86.5%,该区深层页岩气藏构造复杂,压裂形成复杂缝网的难度大,有必要通过数值模拟研究深层页岩气复杂缝网主控因素,对实现川南地区深层页岩气的效益开发具有重要意义。在对川南地区页岩气气田某井的岩芯进行细观尺度下的观察并构建二维裂缝模型的基础上,利用位移间断边界元法(DDM)模拟深层页岩水力压裂过程中水力裂缝与天然裂缝相互作用的物理力学过程,研究主应力、应力差和压裂液排量对裂缝扩展的影响。结果表明:在高应力差条件下缝网的复杂程度和总长度急剧降低,缝网的平均宽度增大,且平均宽度随排量增加而增大的能力变得有限。在高应力差条件下提升压裂液排量,缝网长度的增加以产生新生裂缝为主,同时提升排量对于激活天然裂缝有一定的提升作用,但是效果有限。相比于拉张裂缝,剪切裂缝的形成受主应力和压裂液排量的影响更显著,在高应力差条件下缝网中剪切裂缝的长度急剧降低。随着压裂液的注入,在较低应力差和相同压裂液注入量的情况下,低排量工况下的裂缝长度逐渐大于高排量工况下的裂缝长度。在应力差较高的情况下裂缝扩展的速率较低,同时会使提升排量而形成更多新生裂缝的能力变得有限。基于显微镜观察构建的裂缝模型计算出的结果能够较好地符合场地实际,为深层水力压裂设计和施工提供参考。 相似文献
7.
水力压裂技术是成功实现干热岩资源开发利用的重要手段之一,数值模拟技术能够精准预测水力裂缝扩展。针对典型花岗岩,借助黏性单元法,分别模拟了致密花岗岩和天然裂缝存在情况下的水力裂缝扩展特征,得出以下结论：致密花岗岩的水力裂缝形态单一,天然裂缝的存在增加了压裂后裂缝的复杂性;致密花岗岩水力裂缝拓展主要分为憋压和拓展两个交替往复的阶段,当存在天然裂隙时,水力压裂过程会变得复杂;天然裂缝存在时,水力裂缝的缝长和缝宽分别为致密花岗岩的5. 7倍和1. 7倍;缝网的形成需要借助复杂的压裂工艺实现。研究结果可以为增强型地热系统(EGS)储层水力刺激工作提供理论支持。 相似文献
8.
水力压裂作为煤层强化增透技术的一种,其应力演化特征及裂隙形态与扩展范围的判断尤为重要。采用离散元数值方法,以导向压裂为背景,建立水力压裂流固耦合模型;通过应力路径、裂纹热点图等手段,探究水力压裂过程中压裂排量、泊松比、天然裂隙密度对应力演化和裂隙演化的影响及其细观规律。结果表明:不同压裂排量下的应力演化方向及最终应力路径曲线形状有着明显的不同,低排量下裂隙附近的应力比值逐渐增大,而在高排量下先增大后减小;煤层泊松比越大,平均压裂半径越低,但对起裂时间及裂隙的扩展形态影响不明显;天然裂隙的发育情况对水力裂隙的扩展起着关键性作用,高裂隙发育煤层水力裂隙扩展的方向性无法预测,应力演化方向会出现反转现象;压裂过程中不同区域的应力演化特征能够反映出裂隙的扩展状态,现场可通过监测压裂区域附近应力变化,判断水力压裂缝网的扩展范围。 相似文献
9.
在缝洞型油藏中,水力裂缝的偏转路径对石油的开采量有重要的影响。Hybrid Finite-element and Mesh-free Method-Fracflow（FEMM-Fracflow）数值模拟平台,通过数值实验,文章分析了缝洞型油藏中自然溶洞、水平地应力以及注水流速三种因素对水力裂缝偏转路径的影响。结果表明,在存在溶洞时,裂缝明显向溶洞方向偏转;在改变水平围压时,不施加水平围压条件下,裂缝明显偏向溶洞方向扩展,并且最终与溶洞连通;而在施加50 MPa水平围压时,水力裂缝偏向溶洞的趋势明显减弱;在改变流速时,当流速为0.05 kg/s,裂缝明显向溶洞方向偏转,而当流速为0.2 kg/s,裂缝向溶洞方向偏转的趋势则减弱。 相似文献
10.
储层岩体中的天然结构面对水力压裂缝网改造具有重要的影响。本文采用真实破裂过程分析软件RFPA2D-Flow,在考虑岩体非均质性和岩体渗流-应力-损伤破裂特性的基础上,对不同尺度天然结构面影响的水力压裂裂缝扩展与演化行为进行了模拟分析和讨论,研究结果表明:（1）当水力裂缝遇天然非闭合裂隙时,在水力裂缝靠近非闭合裂隙区间形成拉张应力区,水力裂缝与区间非闭合裂隙间微元体累进性张拉破坏是导致水力裂缝与非闭合裂隙贯通的主要机制;（2）层理等优势结构对水力压裂裂缝扩展及缝网形态影响十分显著,当最大主应力方向与层理面走向小角度相交时,层理结构面对水力裂隙的扩展起主要作用,当最大主应力方向与层理面走向大角度相交时,最大主压应力与层理面共同对缝网扩展起主导作用,随着优势结构面的增多和差应力的增大,水力压裂形成的缝网范围和复杂性程度随之增大;（3）储层水力压裂是一种局部范围内的短暂动力扰动过程,尽管断层的存在可以极大地影响水力裂缝的扩展模式,增大水力裂隙扩展高度,但相比于储层埋深,水力压裂对断层封闭性的破坏范围和断层活动性的扰动程度十分有限。 相似文献
11.
为有效模拟裂缝性页岩储层中水力裂缝随机扩展过程,基于单元节点的拓扑数据结构,利用网格节点分裂方式,建立了一种基于有限元网格嵌入零厚度内聚力单元的水力裂缝随机扩展新方法。利用KGD模型解析解和2种室内试验,验证了新方法的准确性和有效性。同时,通过数值算例研究了水平地应力差和储层非均质性对水力裂缝随机扩展过程的影响。研究表明:(1)该方法弥补了ABAQUS平台内置的内聚力单元无法有效模拟水力裂缝随机扩展的不足;(2)在较高水平地应力差下页岩储层非均质性越强,与水力裂缝相交的高角度天然裂缝越容易开启。所建方法能准确地描述复杂水力裂缝的随机扩展行为,可为裂缝性页岩储层的数值模拟提供新手段。 相似文献
12.
为了研究煤岩水力压裂的起裂压力和水力压裂裂缝扩展规律,采用型煤试样,利用自主研发的水力压裂实验系统,参照现场压裂施工制定了“施加三向应力-顶部注水”的煤岩水力压裂物理模拟实验方案并开展了水力压裂实验,分析了不同条件下泵注压力和水力压裂裂缝。实验结果表明:压裂液泵注排量越大,起裂压力越大。三向应力满足最大水平主应力σH > 垂向应力σv > 最小水平主应力σh,水力压裂裂缝沿着垂直于σh的方向扩展。σv和σh一定,随着σH的增大,煤岩起裂压力先增大后减小,水力压裂裂缝扩展路径越平直。当σH远大于σv和σh时,水力压裂裂缝扩展路径越复杂,分叉缝角度越大。研究结果可为煤岩水力压裂理论的完善提供一定的参考和借鉴。 相似文献
13.
Hydraulic fracturing (HF) treatment often involves particle migration and is applied for propping or plugging fractures. Particle migration behaviors, e.g., bridging, packing, and plugging, significantly affect the HF process. Hence, it is crucial to effectively simulate particle migration. In this study, a new numerical approach is developed based on a coupled element partition method (EPM). The EPM is used to model natural and hydraulic fractures, in which a fracture is allowed to propagate across an element, thereby avoiding remeshing in fracture simulations. To characterize the water flow process in a fracture, a fully hydromechanical coupled equation is adopted in the EPM. To model particle transportation in fractures with water flow, each particle is treated as a discrete element. The particles move in the fracture as a result of being dragged by fluid. Their movement, contact, and packing behaviors are simulated using the discrete element method. To reflect the plugging effect, an equivalent aperture approach is proposed. Using this method, the particle migration and its effect on water flow are well simulated. The simulation results show that this method can effectively reproduce particle bridging, plugging, and unblocking in a hydraulic fracture. Furthermore, it is demonstrated that particle plugging significantly affects water flow in a fracture and hence the propagation of hydraulic fracture. This method provides a simple and feasible approach for the simulation of particle migration in a hydraulic fracture. 相似文献
14.
Fully coupled simulation of a hydraulic fracture interacting with natural fractures with a hybrid discrete‐continuum method 
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下载免费PDF全文 A hybrid discrete‐continuum numerical scheme is developed to study the behavior of a hydraulic fracture crossing natural fractures. The fully coupled hybrid scheme utilizes a discrete element model for an inner domain, within which the hydraulic fracture propagates and interacts with natural fractures. The inner domain is embedded in an outer continuum domain that is implemented to extend the length of the hydraulic fracture and to better approximate the boundary effects. The fracture is identified to propagate initially in the viscosity‐dominated regime, and the numerical scheme is calibrated by using the theoretical plane strain hydraulic fracture solution. The simulation results for orthogonal crossing indicate three fundamental crossing scenarios, which occur for various stress ratios and friction coefficients of the natural fracture: (i) no crossing, that is, the hydraulic fracture is arrested by the natural fracture and makes a T‐shape intersection; (ii) offset crossing, that is, the hydraulic fracture crosses the natural fracture with an offset; and (iii) direct crossing, that is, the hydraulic fracture directly crosses the natural fracture without diversion. Each crossing scenario is associated with a distinct net pressure history. Additionally, the effects of strength contrast and stiffness contrast of rock materials and intersection angle between the hydraulic fracture and the natural fracture are also investigated. The simulations also illustrate that the level of fracturing complexity increases as the number and extent of the natural fractures increase. As a result, we can conclude that complex hydraulic fracture propagation patterns occur because of complicated crossing behavior during the stimulation of naturally fractured reservoirs. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
15.
水力压裂是青海共和盆地干热岩地热资源开发的难点技术问题之一。本文基于升级改造的大尺寸真三轴水力压裂物理模拟实验系统模拟干热岩储层高温高压环境,利用青海共和盆地露头岩心进行水力压裂物理模拟实验,揭示干热岩储层水力裂缝的起裂和扩展规律。通过物理模拟实验发现：干热岩储层裂缝起裂可以通过文中提出的起裂模型判断起裂方式和预测起裂压力;水力裂缝在岩石基质中的扩展形态简单,仅沿最大主应力方向延伸;但是水力裂缝会受到岩石中弱面的影响,发生转向沿弱面延伸,形成较复杂的裂缝形态。因此,建议在干热岩储层实际施工中,在天然裂缝发育较丰富的层段开展水力压裂,以实现复杂裂缝网络提取地热能。 相似文献
16.
Analysis of refracturing in horizontal wells: Insights from the poroelastic displacement discontinuity method 下载免费PDF全文
下载免费PDF全文 Ali Rezaei Giorgio Bornia Mehdi Rafiee Mohamed Soliman Stephen Morse 《国际地质力学数值与分析法杂志》2018,42(11):1306-1327
In this paper, a fully coupled 2‐dimensional poroelastic displacement discontinuity method is used to investigate the refracturing process in horizontal wells. One of the objectives of refracturing is to access new reserves by adding new hydraulic fractures in zones that were bypassed in the initial fracturing attempt. Pore pressure depletion in the vicinity of old fractures directly affects the state of stress and eventually the propagation of newly created hydraulic fractures. Thus, a poroelastic analysis is required to identify guidelines for the refracturing process, in particular to understand the extension of the pore pressure depletion, and eventually, the orientation of new as well as old fractures. We propose a fully coupled approach to model the whole process of child fracture propagation in a depleted area between 2 parent fractures in the same wellbore. This approach omits the need of using multistep workflow that is regularly used to model the process. The maximum tensile stress criterion (σ criterion) is used for hydraulic fracture propagation. The proposed method is verified using available analytical solutions for total stress and pore pressure loading modes on a line fracture in drained and undrained conditions. Then, test cases of multifractured horizontal wells are studied to calculate the time evolution of the stress and pore pressure fields around old fractures and to understand the effect of these fields on the propagation path of newly created fractures. Finally, the effect of the pore pressure depletion on the propagation path of the newly created fractures in the bypassed area of the same wellbore is studied. The results show that the depleted areas around old fractures are highly affected by the extent and severity of the stress redistribution and pore pressure depletion. It is observed that a successful creation of new fractures may only happen in certain time frames. The results of this study provide new insights on the behavior of newly created fractures in depleted zones. They also clarify the relationship between stress change and pore pressure depletion in horizontal wells. 相似文献
17.
Liao Jianxing Gou Yang Feng Wentao Mehmood Faisal Xie Yachen Hou Zhengmeng 《Acta Geotechnica》2020,15(2):279-295
Although hydraulic fracturing has been massively studied and applied as a key technique to enhance the gas production from tight formations, some problems and uncertainties exist to accurately predict and analyze the fracture behavior in complex reservoirs, especially in the naturally fractured reservoirs like shale reservoirs. This paper presents a full 3D numerical model (FLAC3D) to study hydraulic fracturing behavior under the impact of preexisting orthogonal natural fractures. In this numerical model, the hydraulic fracture propagation direction is assumed perpendicular to the minimum principal stress and activated only by tensile failure, whereas the preexisting natural fractures can be activated by tensile or shear failure or a combination of them, and only tensile failure can open the natural fracture as well. The newly developed model was used to study the impact of preexisting orthogonal natural fractures on hydraulic fracturing behavior, based on a multistage hydraulic fracturing operation in a naturally fractured reservoir from the Barnett Shale formation, northwest of Texas in USA. In this multistage operation, two more representative stages, i.e., stage 1 with a relatively large horizontal stress anisotropy of 3.3 MPa and stage 4 with a comparatively small one of 1.3 MPa, were selected to conduct the simulation. Based on the numerical results, one can observe that the interaction between hydraulic and natural fracture is driven mainly by induced stress around fracture tip. Besides, the horizontal stress anisotropy plays a key role in opening the natural fracture. Thus, no significant opened fracture is activated on natural fracture in stage 1, while in stage 4 an opened fracture invades to about 90 m into the first natural fracture. Conversely, the hydraulic fracture length in stage 1 is much longer than in stage 4, as some fluid volume is stored in the opened natural fracture in stage 4. In this work, the shear failure on natural fractures is treated as the main factor for inducing the seismic events. And the simulated seismic events, i.e., shear failure on natural fractures, are very comparable with the measured seismic events.
相似文献18.
在页岩气水力压裂开发领域中,压裂液注入排量对裂缝网络的扩展形态具有显著影响。而页岩储层中的随机天然裂缝,会给水力压裂的参数敏感性分析带来不同程度的干扰。首先,根据页岩储层裂缝发育特征,制备了包含3组正交预制裂缝的混凝土试样;然后,采用真三轴压裂系统,对试样进行三向应力加载模拟地应力环境,并以恒定排量向其内部注入流体;最后,将单位体积裂缝面积P32作为体积压裂指标,来定量描述排量对压裂缝网扩展形态的影响。试验结果表明:（1）在块体单元边长较小（即预制裂缝密度较大）的试样中,体积压裂的效果更加显著;（2）小排量压裂液所产生的裂缝一般是激活的预制裂缝,而中排量和高排量压裂液可以使已激活的预制裂缝发生偏转,在混凝土基质中重新开启水力裂缝,从而增加裂缝网络的复杂性;（3）随着排量的增加,试样压裂后的P32值会升高;但排量增加到一定程度后,P32值不再增长,甚至略微下降。 相似文献
19.
页岩储层天然裂缝、水平层理发育,水力压裂过程中可能形成复杂的体积裂缝。针对页岩储层体积裂缝扩展问题,基于流-固耦合基本方程和损伤力学原理,建立了页岩储层水力压裂体积裂缝扩展的三维有限元模型。将数值模型的模拟结果与页岩储层裂缝扩展室内试验结果进行对比,二者吻合较好,从而证明了数值模型的可靠性。通过一系列数值模拟发现：（1）水力压裂过程中水平层理可能张开,形成水平缝,水平与垂直缝相互交错,形成复杂的体积裂缝网络;（2）水平主应力差增大,体积裂缝的分布长度（水平最大主应力方向压裂裂缝的展布距离）增加、分布宽度（水平最小主应力方向压裂裂缝的展布距离）减小,体积裂缝的长宽比增加;（3）压裂施工排量增大,体积裂缝的分布长度减小、宽度增加,压裂裂缝的长宽比降低;（4）天然裂缝的残余抗张强度增大,体积裂缝分布宽度减小、分布长度增加,体积裂缝的长宽比增加。研究成果可以为国内的页岩气的压裂设计和施工提供一定的参考和借鉴。 相似文献
20.
The permeability of the granite geothermal reservoir of Soultz is primarily related to major fracture zones, which, in turn, are connected to dense networks of small-scale fractures. The small-scale fractures are nearly vertical and the major direction is about N0°E. This direction differs from that of the Rhine Graben, which is about N20°E to N45°E in northern Alsace. A total of 39 fracture zones, with a general strike of N160°E, have been identified in six wells between 1400 and 5000 m depth. These fracture zones are spatially concentrated in three clusters. The upper cluster at 1800–2000 m True Vertical Depth (TVD) is highly permeable. At 3000–3400 m TVD, the intermediate cluster in composed of a dense network developed in an altered matrix and forms the upper reservoir. In the lower part of the wells, the deeper cluster appears as a fractured reservoir developed within a low permeable matrix. Fracture zones represent a key element to take into account for predicting the geothermal reservoir life time submitted to various thermo-hydromechanical and chemical processes generated by hydraulic or chemical stimulations and by hydraulic circulation tests related to long-term exploitation. 相似文献