基于微地震连续裂缝网络模型的SRV研究

在干热岩的开发和改造阶段,需要对储层进行水力压裂改造,储层改造体积(stimulated reservoir volume, SRV)是评价压裂效果的主要标准。微地震监测作为水力压裂的技术环节之一,可以对储层改造体积进行有效估算。本文探讨了基于微地震连续裂缝网络模型的SRV计算方法,以指导干热岩的水力压裂工作。首先,基于微震事件时空分布特征与多项震源参数进行连续裂缝网络建模;其次,提取裂缝网格长度,并选取适当的裂缝高度与裂缝宽度以计算储层改造体积;最后,选取某双井型干热岩微地震监测数据对该方法进行实际应用。实例应用结果表明,该方法可有效估算储层改造体积,为干热岩后续开发与改造提供依据。     

湖北宜昌震旦系陡山沱组储层特征及复杂体积压裂效果评价

鄂阳页2 HF井是国内首口针对震旦系陡山沱组的页岩气水平井,该井钻遇的陡山沱组页岩厚度大,岩石脆性好,含气性好且天然裂缝发育,具备良好的压裂改造基础.针对陡山沱组储层"高云质、地层常压、水平应力差异大、隔夹层发育"等压裂改造难点,通过采用"密分切割、多簇射孔、转向压裂"等复杂裂缝体积压裂工艺,采取变排量、暂堵转向、停泵...     

裂缝参数对考虑滑脱效应页岩气水平井产能的影响

低渗透页岩气藏中,气体渗流时会受滑脱效应的影响。建立了考虑滑脱效应的气、水两相页岩气藏渗流数学模型,并建立了理想地质模型,采用数值模拟方法,研究了水力压裂的不同裂缝参数对水平井产能的影响。模拟结果表明:裂缝条数、长度和间距是影响页岩气井产能的重要参数,而裂缝宽度和渗透率对产能的影响相对较弱;页岩气井的产能随着裂缝条数和裂缝长度的增加而增大;水平井的水平段长度及裂缝条数一定时,可通过增大裂缝间距来减少裂缝间的相互干扰。      

页岩水平井体积压裂设计的一种新方法

页岩水平井常采用体积压裂技术获得产能,压裂形成的缝网体积、渗透率是影响压裂效果的关键因素。目前页岩体积压裂设计借用产能预测模型优化缝网参数,此模型较复杂,不便于现场应用。根据等效渗流原理,将页岩储层压裂后形成的缝网系统等效为一个高渗透带,建立了体积压裂缝网参数与施工规模关系模型,提出了体积压裂设计的3个步骤:体积压裂可行性研究、数值模拟优化缝网参数和施工参数优化。根据QY2页岩油水平井特征,进行了体积压裂设计和现场实施。结果表明:压裂形成的高渗透带对产能的贡献最大;高渗透带数量、体积和渗透率增加,压裂后的累积产量和采出程度逐渐增加,存在最优的高渗透带参数。现场应用表明这种设计方法方便实用,可以推广。     

离散裂隙网络对页岩气井产能影响的数值模拟

页岩作为典型的非常规储层,基质孔隙小,渗透率极低,水平井多级水力压裂为其商业开发的主要手段。准确模拟页岩气产能,应同时考虑水力裂隙和天然裂隙的渗流。基于离散裂隙模型和等效连续模型建立页岩气渗流数学模型,利用有限元分析方法进行数值求解,研究不同走向裂隙组对页岩气井产能的影响。研究认为,页岩基质为气体的生产提供了主要气源,天然裂隙作为渗流的主要通道,将气体输送到水力裂缝,进而到达井筒。模拟结果表征,离散裂隙的渗流特征对于页岩气井的产能有重要影响。根据页岩储层的天然裂隙走向,可以优化相应的水平井方位。对于二维离散裂隙网络模型,水平井沿着2个裂隙组夹角的平分线更有利于生产。      

页岩储层体积压裂裂缝扩展机制研究

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。     

深层页岩气地质工程一体化体积压裂关键技术及应用

针对深层页岩气埋深大、两向水平应力差大、垂向应力差小、岩石塑性特征强等地质特征,以地质工程一体化为设计理念,建立了包括测井曲线、页岩总有机碳含量、孔隙度、全烃、关键录井元素、矿物组分、过量硅、矿物脆性、岩石力学参数等评价方法,开展沿水平井段的地质工程双甜点研究,实现地质与工程一体化优选甜点段和最优甜点段准确识别,为深层页岩气水平井压裂改造提供依据.然后,基于高导流的立体缝网为体积压裂的目标函数,开展深层页岩气窄压力窗口下的体积压裂注入模式及工艺参数优化研究,包括迂回双暂堵工艺优化,支撑剂在复杂缝网下的动态运移规律与导流能力研究,以及一体化变黏度高降阻滑溜水研发等.研究成果在现场的应用结果表明,上述基于地质工程一体化的体积压裂技术,压后测试产量较邻井能提高30%～50%以上,可大幅度提高深层页岩气的经济开发效果,对今后垂深超过4 500 m的超深层页岩气的经济有效勘探与开发,也同样具有重要的指导和借鉴意义.     

基于诱导应力场的煤层气水平井分段压裂间距优化研究

为了提高水平井分段压裂煤储层改造体积,提高煤层气的采收率,基于水平井分段压裂裂缝诱导应力场,运用数值模拟手段,对裂缝间距进行了优化。结果显示,水平井分段压裂先压裂缝产生的水平诱导应力差随着与其裂缝距离的增加呈先增加后减少的趋势,导致最大水平主应力转向乃至反转。当诱导应力场叠加后的最大水平主应力转向角为5°时对应的位置为最优压裂分段间距,以此布置分段间距,既能保证间距尽可能的小,也能使裂缝正常扩展,形成多个相互平行的有效主裂缝,实现对煤储层的体积切割,提高煤储层的压裂改造增产效果,对于煤层气水平井分段压裂裂缝参数优化具有较好的指导意义。     

致密油大规模多段压裂水平试井解释及外区渗透率对试井曲线的影响

多段压裂水平井试井解释能对压裂规模、主裂缝半长等参数进行有效评价,为产能评价等提供基础参数.然而当前缺少针对实际井例数据进行的深入分析.基于PEBI（perpendicular bisector）网格对油水两相渗流方程进行数值求解,利用无限导流的主裂缝与分支缝导致的区域渗透率扩大来描述SRV（stimulated reservoir volume）,建立了致密油大规模多段压裂水平井瞬态压力分析方法.基于大庆油田的实测数据进行解释并进行渗透率敏感性分析,研究了复合区域下的参数调整方法.研究表明,当外区渗透率变小时,早期的压力导数变小,后期的压力导数变大,而不是所有的压力导数值都变大.压力导数由小到大的转折点时间与渗透率大小相关.因而,当前期的压力导数曲线拟合效果好、后期的压力导数拟合效果差时,不能仅通过调整外区的渗透率来拟合,还应调整其他参数.另外,大庆致密油藏多段压裂水平井实测曲线中的启动压力梯度特征不明显.相关研究结果对致密油大规模多段压裂水平井实测数据解释具有重要的指导意义.      

微地震技术评价中牟区块体积压裂的效果

微地震监测技术是页岩气开采过程中对页岩气储层压裂效果评价和指导压裂过程的重要手段,可通过观察、分析压裂过程中诱发微地震事件,获取压裂裂缝参数、导流能力、裂缝展布发育方向等信息。中牟区块牟页1井具有低孔、低渗储层特征,对含气层段的三层储层,采用大排量水力压裂施工,进行地面微地震监测、井中微破裂成像技术压裂监测及微地震监测;牟页1井监测压裂结果显示为缝长251～496m,缝宽120～252m,改造体积约为237.5×104～387.7×104 m3,方位角64°～80°。压裂实施使储层裂缝开启含气层段得到改造,指导了实时压裂和压裂效果评价。     

Optimization and Evaluation of Multiple Hydraulically Fractured Parameters in Random Naturally Fractured Model Blocks: An Experimental Investigation

Researchers have recently realized that the non-tectonic natural fractures are developed in shale formations and significant for the exploitation of shale gas. Studies have shown that the tectonic fractures in naturally fractured reservoirs have influences on the maximization of stimulated reservoir volume (SRV) during hydraulic fracturing. However, the effect of the non-tectonic randomly natural fractures on the fracturing network propagation is not well understood. Laboratory experiments are proposed to study the evolution of fracturing network in naturally fractured formations with specimens that contain non-tectonic random fractures. The influences of the dominating factors were studied and analyzed, with an emphasis on natural fracture density, stress ratio, and injection rate. The response surface methodology was employed to perform the multiple-factor analysis and optimization in the maximization of the SRV. A sensitivity study reveals a number of interesting observations resulting from these parameters on the fracturing network evaluation. It is suggested from the geometry morphology of fracturing network that high natural fracture density and injection rate tend to maximize the fracturing network. The influence of stress contrast on fracturing network is nonlinear; an optimal value exists resulting in the best hydraulic fracturing effectiveness.     

Cluster spacing optimization of multi-stage fracturing in horizontal shale gas wells based on stimulated reservoir volume evaluation

The multi-stage fracturing in horizontal well is a common technique for shale gas reservoir exploitation, in which cluster spacing governs the fracturing performance. Undersized cluster spacing might make the stimulated reservoir volume (SRV), activated by the respective hydraulic fracture, excessively overlap with each other, while oversized cluster spacing might leave a large unstimulated volume between neighboring hydraulic fractures; in either case, fracturing would be inefficient. Previous design of cluster spacing has failed to maximize the SRV due to the absence of a dynamic SRV evaluation model. A numerical model of SRV evaluation in shale reservoir was established by integrating four main modules, including fracture propagation, reservoir pressure distribution, formation stress distribution, and natural fracture failure criterion. Then, a method to optimize cluster spacing was developed with the goal of maximizing SRV. In order to validate this method, it was applied in Fuling shale gas reservoir in Southwest China to determine the optimal cluster spacing. The sensitivity of key parameters on the optimal cluster spacing has been analyzed. This research proposed a compelling cluster spacing optimization method, which could reduce the uncertainty in cluster spacing design, and provides some new insights on the optimal design of multi-stage fracturing in horizontal shale gas well.     

评价页岩压裂形成缝网能力的新方法

页岩储层的“体积压裂”,使美国页岩气产业取得巨大成功,有效评价压裂裂缝网络形成的难易程度,是压裂开采的首要目标,目前国内外尚未发现有效的评价方法,为此开发了一种新的测试方法。针对10种岩芯,测试岩石力学参数,并对比分析常用的3种页岩脆性评价方法。采用压后裂隙结构面迹长分布的分维值和面密度对裂缝进行定量表征,并对压后崩落碎块进行对比分析。通过实验认为,杨氏模量和泊松比判别法与塑性系数判别法用于评价岩石脆性,精确度更高;脆性岩石通常表现为高杨氏模量或（和）低泊松比的特征,与单轴抗压强度、抗张强度和压入硬度没有对应关系;压裂裂缝的分布具有统计意义上的分形特征,分维可用于定量评价压后裂缝网络复杂度;硬度越高,压后裂缝密度越小;脆性越强,压后裂缝密度越大。新方法是岩石脆性、硬度和天然裂缝系统（和沉积层理）特征的综合体现,用于评价页岩压后形成缝网的能力,不仅直观可靠,而且简单有效,有利于现场推广应用,对于今后页岩气或致密砂岩气开发的理论研究和现场应用具有一定的指导意义。     

页岩储层压裂工艺技术在渝东地区应用

页岩气的工业化开发要求对致密储层进行体积压裂改造,水平井多级分段压裂技术是成功开发页岩气藏的关键技术之一。页岩储层在地应力与致裂压力联合作用下突破页岩基质,沟通天然裂隙等弱结构面,形成高导流能力缝网系统,页岩储层中赋存的游离气和吸附气得以释放,提高了页岩气井的初始产量和最终采收率。根据渝东地区页岩储层工程地质特征,结合渝页A-2HF井、渝页B-2HF井矿场压裂施工数据,探索适用于渝东地区的页岩储层压裂工艺技术,结果表明,采用前置盐酸处理储层保持近井带导流能力,能够保障后续大排量施工压力窗口;低砂比粉砂段塞多级降滤实现“控近扩远”,增加储层改造体积;压力异常层段胶液前置充分造缝,可为后续滑溜水携带支撑剂进入地层创造有利条件。     

Prediction and analysis of the stimulated reservoir volume for shale gas reservoirs based on rock failure mechanism

The ultra-low-permeability shale gas reservoir has a lot of well-developed natural fractures. It has been proven that hydraulic fracture growth pattern is usually a complex network fracture rather than conventional single planar fractures by micro-seismic monitoring, which can be explained as the shear and tensile failure of natural fractures or creation of new cracks due to the increase in reservoir pore pressure caused by fluid injection during the process of hydraulic fracturing. In order to simulate the network fracture growth, a mathematical model was established based on full tensor permeability, continuum method and fluid mass conservation equation. Firstly, the governing equation of fluid diffusivity based on permeability tensor was solved to obtain the reservoir pressure distribution. Then Mohr–Coulomb shear failure criterion and tensile failure criterion were used to decide whether the rock failed or not in any block on the basis of the calculated reservoir pressure. The grid-block permeability was modified according to the change of fracture aperture once any type of rock failure criterion was met within a grid block. Finally, the stimulated reservoir volume (SRV) zone was represented by an enhancement permeability zone. After calibrating the numerical solution of the model with the field micro-seismic information, a sensitivity study was performed to analyze the effects of some factors including initial reservoir pressure, injection fluid volume, natural fracture azimuth angle and horizontal stress difference on the SRV (shape, size, bandwidth and length). The results show that the SRV size increases with the increasing initial pore reservoir and injection fluid volume, but decreases with the increase in the horizontal principal stress difference and natural fracture azimuth angle. The SRV shape is always similar for different initial pore reservoir and injection fluid volume. The SRV is observed to become shorter in length and wider in bandwidth with the decrease in natural fracture azimuth angle and horizontal principal stress difference.     

排量对水力压裂网络扩展影响的试验研究

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。     

Numerical Modeling of Natural Fracture Distributions in Shale

The production efficiency of shale gas is affected by the interaction between hydraulic and natural fractures. This study presents a simulation of natural fractures in shale reservoirs, based on a discrete fracture network (DFN) method for hydraulic fracturing engineering. Fracture properties of the model are calculated from core fracture data, according to statistical mathematical analysis. The calculation results make full use of the quantitative information of core fracture orientation, density, opening and length, which constitute the direct and extensive data of mining engineering. The reliability and applicability of the model are analyzed with regard to model size and density, a calculation method for dominant size and density being proposed. Then, finite element analysis is applied to a hydraulic fracturing numerical simulation of a shale fractured reservoir in southeastern Chongqing. The hydraulic pressure distribution, fracture propagation, acoustic emission information and in situ stress changes during fracturing are analyzed. The results show the application of fracture statistics in fracture modeling and the influence of fracture distribution on hydraulic fracturing engineering. The present analysis may provide a reference for shale gas exploitation.