Downhole Microseismic Source Location Based on a Multi-Dimensional DIRECT Algorithm for Unconventional Oil and Gas Reservoir Exploration

Downhole microseismic data has the significant advantages of high signal-to-noise ratio and well-developed P and S waves and the core component of microseismic monitoring is microseismic event location associated with hydraulic fracturing in a relatively high confidence level and accuracy. In this study, we present a multidimensional DIRECT inversion method for microseismic locations and applicability tests over modeling data based on a downhole microseismic monitoring system. Synthetic tests inidcate that the objective function of locations can be defined as a multi-dimensional matrix space by employing the global optimization DIRECT algorithm, because it can be run without the initial value and objective function derivation, and the discretely scattered objective points lead to an expeditious contraction of objective functions in each dimension. This study shows that the DIRECT algorithm can be extensively applied in real downhole microseismic monitoring data from hydraulic fracturing completions. Therefore, the methodology, based on a multidimensional DIRECT algorithm, can provide significant high accuracy and convergent efficiency as well as robust computation for interpretable spatiotemporal microseismic evolution, which is more suitable for real-time processing of a large amount of downhole microseismic monitoring data.     

油气藏水力压裂计算模拟技术研究现状与展望

水力压裂技术是油气藏尤其是页岩气开发中的核心技术,利用数值模拟方法进行压裂优化和产能预测又是水力压裂成功的关键。本文首先介绍了水力压裂技术的发展历程。然后从计算模型(二维模型、拟三维模型和全三维模型)和数值模拟方法(基于连续介质和基于非连续介质)两方面对油气藏开发领域的水力压裂计算模拟技术进行较全面的总结。最后,从以下3个方面指出现今研究的不足并提出了进一步的研究建议:(1)全三维模型的完善-全三维模型应当与真实的工程参数和监测数据结合,用于校正模型本身,而校正后的全三维模型又可预测和优化新的现场水力压裂作业; (2)数值模拟方法的选用-已有的水力压裂数值模拟方法种类繁多,需要针对各种方法的适用范围、计算效率和模拟效果等,进行全面的比较和优化; (3)页岩储层中天然裂缝网络的数值模拟-天然裂隙网络加剧了页岩储层力学性质的各向异性,同时水力裂缝沟通天然裂缝活化扩展是有利于储层的增渗增产,对压裂缝网的形态、尺寸和连通率等起着至关重要的作用。因此,数值计算过程中综合考虑页岩储层中天然裂缝与水力裂缝的相互作用,将是未来水力压裂模拟的热点。     

沁水盆地南部煤层气井增产的储层生产控制探讨

以沁水盆地南部区块煤层气生产井的工程、测试、监测数据为依据,对影响煤层气井产能的储层生产控制因素进行了分析,探讨了优化储层生产控制、提高煤层气井产能的工程措施,重点研究了水力压裂工艺施工参数与煤层气井产能的关系,提出了有利于提高煤层气井产能的水力压裂工艺施工参数。结果表明：合理控制钻井液的密度与粘度,可提高煤层气井的产能;煤层气井的产能与固井工艺中的水泥浆密度与用量呈现负相关关系;水力压裂采用变砂比、控制压裂液、变排量等施工工艺和优化的工艺参数值可有效提高煤层气井气产量。     

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.     

Hydraulic fracturing modeling using the discontinuous deformation analysis (DDA) method

Recent attempts to couple discontinuous deformation analysis (DDA) blocks with finite element meshes have been regarded as fruitful. The hybrid model has been proven to be reliable in modeling continuum–discontinuum problems. In this paper, a hydraulic crack initiation–propagation extension complete with a coupled hydro-mechanical analysis algorithm is introduced to the hybrid model for the simulation of fracturing problems initiated by hydraulic pressure. Several simulation cases, of which the results appear to be consistent with existing theories of hydraulic fracturing mechanisms, are presented to demonstrate the capability of the proposed algorithm in modeling hydraulic fracturing processes.     

利用蒙特卡罗方法的剩余静校正及其应用

针对剩余静校正问题,讨论了统计方法中的蒙特卡罗法用于反射波能量最大化剩余静校正的方法。分别论述了反射波叠加能量最大化法和蒙特卡罗方法,以及蒙特卡罗方法如何应用于剩余静校正的计算中,并用实例说明了该方法的效果。通过实际应用蒙特卡罗剩余静校正方法,解决了经野外静校正后残留的剩余静校正问题,并通过与其他剩余静校正方法的实际应用对比,说明了蒙特卡罗剩余静校正方法的优势。对于大剩余量的静校正问题,蒙特卡罗剩余静校正方法仍然可以很好的解决,并且不会产生串相位问题,说明蒙特卡罗剩余静校正方法是可靠的。     

A probabilistic analysis of foundation settlements

This paper deals with a settlement analysis of shallow foundations resting on a layered subsoil. Three basic sources of randomness are discussed: random shape of the subsoil (location of an interface between two strata), random material parameters and random loads. The numerical analysis is based on the finite element method coupled with stochastic versions of the perturbation and the Neumann expansion methods. Both methods lead to a simple evaluation of the response variability in terms of the mean value and the covariance matrix for foundation settlements. More sophisticated analyses introduce the probability of failure as a measure of safety. In this context, failure means either exceeding the bearing capacity or exceeding allowable displacements. The probability of failure is usually evaluated by means of FEM-oriented gradient algorithms or some versions of the Monte Carlo simulation techniques. Numerical examples are presented for a raft foundation resting on an elastic subsoil. The obtained results compare the scale of random fluctuations of soil properties or loading with the scale of foundation settlement fluctuations.     

含水层渗透系数空间变异性对地下水数值模拟的影响

地下水数值模拟是目前定量研究地下水水量和水质的重要手段。使用基于随机理论的MonteCarlo方法来进行地下水数值模拟。这种方法能较好地考虑水文地质参数的空间变异性。主要将MonteCarlo方法和确定性模型模拟方法的模拟结果在渗透系数场、水头场、速度场和浓度场等方面进行了比较。结果表明:在模拟三维非均质含水层中的溶质运移问题时,充分考虑了含水层渗透系数空间变异性的MonteCarlo法比确定性方法更为有效,模拟精度提高了很多,且对模拟误差及误差来源有合理的数学解释。     

土石坝心墙水力劈裂机制研究

心墙的水力劈裂问题是土质心墙坝建设中亟需解决但尚未很好解决的重要岩土工程问题。从心墙受力变形方面探讨了水力劈裂发生、发展的机制。研究认为：水库蓄水初期是水力劈裂的危险期;完全均质的心墙内不会发生水力劈裂;“裂缝或局部的缺陷”及“迅速蓄水的初期”是土石坝心墙发生水力劈裂的两个重要条件,水力劈裂发生的根本原因是局部高水力梯度的存在。最后,对上述机制进行了简单的试验验证。为进一步研究水力劈裂发生的判定、水力劈裂计算模拟指出了研究方向与思路。     

Microseismic Monitoring at a Limestone Mine

Improving microseismic monitoring efficiency and accuracy at a mine requires an integrated effort. This article discusses a case study which demonstrates that the monitoring efficiency and accuracy can be drastically improved through optimally using the existing array, efficient techniques for signal processing and noise separation, and the advanced location algorithm which not only offers a robust search scheme, but also features the techniques for efficient data utilization and further error detection and minimization. The study is a collaborated research between Penn State and NIOSH researchers for the better use of microseismic technique for mine safety, ground control and roof fall prediction.     

自然营造力作用下岩体混凝土水力劈裂分析与探讨

水利水电、矿业等工程在自然营造力作用下的水力劈裂边界条件与人工致裂不完全相同,有其自身的特点。在总结自然营造力作用下水力劈裂特点的基础上,根据研究的尺度不同,将水力劈裂研究分为岩体宏观的、综合的、统计意义上的水力劈裂和单裂纹的水力劈裂研究两种。分析了单裂纹内水流特性,将单裂纹内的水力劈裂分为两个阶段（或两种情况）分别进行研究,并将此问题得以简化,同时还提出了不同阶段裂纹内水流运动分析的模型。     

Robust phase algorithms for estimating apparent slowness vectors of seismic waves from regional events

In this paper, we consider the problem of estimating the apparent slowness vector p of a plane P wave caused by a regional seismic event and recorded by a small-aperture seismic array. The case is considered when strong non-stationary and non-Gaussian random interferences act on the array sensors. In this case, the well-known estimate of wideband frequency-wave-number analysis (WFK) becomes ineffective due to large estimation errors. We have proposed three new algorithms for estimating the vector p that are robust i.e. resistant to changes in the statistical properties of the random interferences. They mainly use information about the slowness vector contained in the phases of the spectra of seismograms recorded by the array sensors. An intensive Monte Carlo simulation was carried out to compare the accuracy of the proposed phase-based estimates with the accuracy of WFK-estimate in the case when non-stationary and non-Gaussian anthropogenic interferences act on the array sensors. In the simulation we used synthetic mixtures of signals caused by a seismic event and anthropogenic seismic interferences. These signals and interferences were recorded by real small-aperture seismic arrays. It was shown that the proposed phase-based estimates of the vector p provide significantly better accuracy than traditional WFK-estimate in the case of strong anthropogenic interferences, and have approximately the same accuracy in the case of white Gaussian noise.

     

非常规油气藏地质建模与数值模拟一体化技术研究

非常规油气藏地质建模与数值模拟是通过对地质、地震、油藏综合研究,建立储层精细地质模型。首先建立构造模型,同时运用地震反演的成果结合单井岩相数据建立岩相模型,利用钻井泥浆漏失、油气田和单井的实际生产情况和微地震监测,描述油气藏内发育的天然裂缝和人工压裂裂缝,最终利用岩相模型控制建立孔隙度和饱和度等属性模型,为数值模拟提供能够反映与实际地质情况相符的三维油气藏粗化地质模型。在此模型的基础上,进行生产历史拟合、产量预测,并制定合理的开发方案。     

基于离散裂隙网络模型的裂隙水渗流计算

离散裂隙网络模型(Discrete Fracture Network（DFN）)是研究裂隙水渗流最为有效的手段之一。文章根据裂隙几何参数和水力参数的统计分布,利用Monte Carlo随机模拟技术生成二维裂隙网络,基于图论无向图的邻接矩阵判断裂隙网络的连通,利用递归算法提取出裂隙网络的主干网或优势流路径。基于立方定律和渗流连续性方程,利用数值解析法建立了二维裂隙网络渗流模型,分析不同边界条件下裂隙网络中的流体流动。结果表明,该方法可以模拟区域宏观水力梯度和边界条件下,裂隙网络水力梯度方向总的流量,以及节点的水位、节点间的流量和流动方向的变化特征,为区域岩溶裂隙水渗流计算提供了一种实用、可行的方法。      

页岩气开发水力压裂技术综述

世界页岩气资源丰富,但由于页岩地层渗透率很低,目前还没有广泛开发。水力压裂技术是页岩气开发的核心技术之一,广泛用于页岩储层的改造。介绍了水力压裂作业的压裂设计、裂缝监测、压裂液配制和添加剂选择,以及常用的压裂技术,包括多级压裂、清水压裂、同步压裂、水力喷射压裂和重复压裂。结合国外页岩气开发的实例和国内压裂技术的应用情况,分析了各种压裂技术的适用性。研究认为,清水压裂是现阶段中国页岩气开发储层改造的适用技术,开采长度(厚度)大的页岩气井,可以使用多级分段清水压裂技术。同步压裂技术是规模化的页岩气开发的客观需要。     

水压致裂法三维地应力测量的理论探讨

本文对现有的水压致裂三维地应力测量方法进行了深入的力学分析,在此基础上提出了新的理论模型。新的理论模型采用了最小主应力破坏准则,与现有方法采用的最小切向应力破坏准则相比,更客观的表述了水压致裂过程中的力学机制。为说明该方法的工作步骤及其可行性,文中利用遗传算法反演技术,对假设的地应力状态进行了试算。试算结果表明该方法是可行的。      

Probabilistic and fuzzy reliability analysis of a sample slope near Aliano

Slope stability assessment is a geotechnical problem characterized by many sources of uncertainty. Some of them, e.g., are connected to the variability of soil parameters involved in the analysis. Beginning from a correct geotechnical characterization of the examined site, only a complete approach to uncertainty matter can lead to a significant result. The purpose of this paper is to demonstrate how to model data uncertainty in order to perform slope stability analysis with a good degree of significance.

Once the input data have been determined, a probabilistic stability assessment (first-order second moment and Monte Carlo analysis) is performed to obtain the variation of failure probability vs. correlation coefficient between soil parameters. A first result is the demonstration of the stability of first-order second moment (FOSM) (both with normal and lognormal distribution assumption) and Monte Carlo (MC) solutions, coming from a correct uncertainty modelling. The paper presents a simple algorithm (Fuzzy First Order Second Moment, FFOSM), which uses a fuzzy-based analysis applied to data processing.     

Laboratory investigation of hydraulic fracture propagation using real-time ultrasonic measurement in shale formations with random natural fractures

The significance of natural fractures in unconventional shale hydrocarbon formations has opened new research frontiers in hydraulic fracturing. Among many of its unique contributions to gas production, the interaction between natural fractures and hydraulic fractures has long been experimentally and computationally investigated. Here, we experimentally investigated the evolution of the fracturing network with a self-developed ultrasonic testing system. Laboratory experiments are proposed to study the propagation of hydraulic fracture in naturally fractured model blocks that contain random micro-fractures. Our analysis suggests that the total fracture width obtained by ultrasonic pulse velocity (UPV) can reflect the dynamic evolution of the fracturing network. The nonlinear fracturing network evolution process is closely related to the variation of the total fracture width. It is suggested from the total fracture width that the maximum fracture network can be realized with greater natural fracture density, large injection rate, and smaller stress ratio. The study presents a better insight into the response of random naturally fractured shale formation under hydraulic fracturing treatment by analyzing the variation of UPV in real time.     

坚硬顶板超前区域治理技术在神东布尔台煤矿的应用

坚硬顶板是岩层控制的一大难题,高位坚硬岩层的破断失稳经常会诱发强矿压灾害,严重威胁矿井的安全生产,坚硬顶板的治理是煤矿安全生产的重大难题之一。针对神东矿区布尔台煤矿煤层顶板厚度大、硬度高、垮落难等问题,分析定向长钻孔分段水力压裂的压裂机理和技术优势,基于关键层理论确定了钻孔布置层位,采用拟三维裂缝模型对压裂注入时间和注入流速对裂缝扩展的影响进行分析计算,确定布尔台煤矿42108工作面顶板压裂钻孔布置方式,沿工作面倾向方向平行布孔3个,裂缝半长41 m,压裂控制区域覆盖了整个工作面。实践表明:42108工作面在实施了坚硬顶板分段水力压裂弱化后,工作面正常支架循环末阻力同比下降3.33%;周期来压期间,支架循环末阻力同比下降6.81%;动载系数平均降低了10.88%;强矿压显现减弱,保证工作面安全回采。