煤岩体压裂裂缝演化混沌特征研究

准确地描述煤岩体压裂裂缝的形成与演化规律对煤层气井开采具有重要意义.本文以煤岩体压裂裂缝演化过程的微裂缝演化数目、裂缝尖端区域的径向应力与周向应力作为描述裂缝演化的特征指标,引入关联维数、最大Lyapunov指数和Ko1mogorov熵作为裂缝演化系统的混沌特征量,计算与描述煤岩体压裂裂缝的损伤演化过程.以黑龙江省某一煤岩开采区块岩体作为研究对象,计算分析煤岩体压裂裂缝的形成的混沌特征,为后续煤岩体压裂裂缝形成规律的研究提供了新的思路.     

Elastic behavior of uniformly loaded circular corrugated plate with sine-shaped shallow waves in large deflection

By means of modified iteration method, this paper gives approximate solution of the large deflection equations of circular corrugated plate with sine-shaped shallow waves having a central platform under uniform lateral load. A formula of initial modification coefficient is given, and an integral is obtained for the simplification of modified iteration calculations. The results of present paper show better agreement with experimental data and larger applicable range than all other existing solutions of corrugated plates.     

AN ADAPTIVE FINITE ELEMENT SCHEME FOR HYDRAULIC FRACTURING WITH PROPPANT TRANSPORT

A mathematical model and adaptive finite element scheme are developed for describing the distribution of proppant in a propagating hydraulic fracture. The governing equation for proppant concentration is derived by applying the conservation law of mass to the proppant and to the proppant-laden fluid. Shah's empirical equation, which relates the proppant concentration and the indices of the non-Newtonian fluid, is used to describe the proppant-laden fluid. The proppant distribution inside a hydraulic fracture can then be obtained by solving the proppant concentration equation together with the governing equations of fluid and elasticity for a hydraulic fracturing. A novel moving grid scheme is developed that combines grid point insertion with redistribution. Four examples corresponding to different in situ stress distributions are computed to demonstrate the scheme. © 1997 by John Wiley & Sons, Ltd.     

Initialization of phase-field fracture propagation in porous media using probability maps of fracture networks.

It is well known in the geophysical community that surface deflection information/micro-seismic data are considered to be one of the best diagnostics for revealing the volume of rock fracture. However, the in-exactness of the data representing the deformation induced to calibrate and represent complex fracture networks created and connected during hydraulic fracturing presents a challenge. In this paper, we propose a technique that implements a phase-field approach to propagate fractures and their interaction with existing fracture networks using surface deflection data. The latter one provides a probability map of fractures in a heterogeneous reservoir. These data are used to initialize both the location of the fractures and the phase-field function. In addition, this approach has the potential for optimizing well placement/spacing for fluid-filled fracture propagation for oil and gas production and or carbon sequestration and utilization. Using prototype models based on realistic field data, we demonstrate the effects of interactions between existing and propagating fractures in terms of several numerical simulations with different probability thresholds, locations, and numbers of fractures. Our results indicate that propagating fractures interact in a complex manner with the existing fracture network. The modeled propagation of hydraulic fractures is sensitive to the threshold employed within the phase-field approach for delineating fractures.     

改良干法压裂液摩擦阻力特性实验研究

对改良的干法压裂液这种非牛顿流体的摩擦阻力特性的正确认识,关系着干法压裂技术的有效实施.为此,本文在大型高压泡沫压裂液实验回路上,考察了在模拟实际施工条件下的改良干法压裂的摩擦阻力特性.实验表明:改良后的干法压裂液摩擦阻力系数随压力、温度的升高和泡沫质量的增加而增大,随流速的增加而减小.在实验范围内,温度对摩擦阻力系数的影响不大.实验得到了改良的干法压裂液摩擦阻力系数与广义雷诺数的关联式,平均计算误差为9.19%.     

Modeling rock failure using the numerical manifold method followed by the discontinuous deformation analysis

A complete rock failure process usually involvesopening/sliding of preexisting discontinuities as well as fracturing in intact rock bridges to form persistent failure surfaces and subsequent motions of the generated rock blocksThe recently developed numerical manifold method(NMM)has potential for modelling such a complete failure processHowever,the NMM suffers one limitation,i.e.,unexpectedmaterial domain area change occurs in rotation modellingThis problem can not be easily solved because the rigidbody rotation is not represented explicitly in the NMM.Thediscontinuous deformation analysis(DDA) is specially developed for modelling discrete block systems.The rotationinduced material area change in the DDA modelling canbe avoided conveniently because the rigid body rotation isrepresented in an explicit form.In this paper,a transitiontechnique is proposed and implemented to convert a NMMmodelling to a DDA modelling so as to simulate a completerock failure process entirely by means of the two methods,in which the NMM is adopted to model the early fracturingas well as the transition from continua to discontinua,whilethe DDA is adopted to model the subsequent motion of thegenerated rock blocks.Such a numerical approach also improves the simulation efficiency greatly as compared with acomplete NMM modelling approach.The fracturing of arock slab with pre-existing non-persistent joints located ona slope crest and the induced rockfall process are simulated.The validity of the modelling transition from the NMM tothe DDA is verified and the applicability of the proposed numerical approach is investigated.     

单裂缝中携砂液流动规律研究

裂缝中携砂液流动是一种固液两相流,携砂液的运移与支撑剂的铺置是水力压裂裂缝保持导流能力的关键.本文基于FLUENT流体计算软件,采用双流体模型,将颗粒看作拟流体,携砂液按照牛顿流体处理,分析了支撑剂体积分数α_s、阿基米德数Ar、颗粒雷诺数Re以及裂缝入口边界对流动规律的影响.研究结果表明:携砂液在裂缝中的流动过程中,发展成为支撑剂体积分数不同的四个区域,包括砂堤区、颗粒悬浮区、颗粒滚流区和无砂区;支撑剂的沉降程度随着支撑剂体积分数和阿基米德数的增加而增加,而随着雷诺数增加而降低;入口为网眼型时,进入裂缝后过流面积的增加导致流速突降,使得支撑剂更容易在入口处产生堆积,在同一入口流速下,较均匀入口的工况铺砂高度大.     

页岩气储层压裂数值模拟技术研究进展

页岩气储层水力压裂数值模拟既要考虑页岩储层岩石的特性,又要兼顾水平外分段压裂施工工艺,是一个非常棘手的力学难题.本文简述了页岩气储层岩石具有的地质力学特征和页岩气储层开发常用的水平井分段压裂技术;详述了扩展有限元、边界元、离散元在水力压裂裂缝模拟上的应用现状,指出了它们在处理裂缝问题的局限性和优越性,总结出边界元三维位移不连续法是模拟多裂缝扩展的有效方法.     

低渗透油藏爆炸压裂产能分析及压裂改造区域优化设计

基于爆炸压裂裂缝分布规律,提出爆炸压裂缝网双重介质复合流动产能模型,应用Laplace变换Stehfest数值反演,得到了定压条件下封闭外边界低渗透油藏爆炸压裂生产井产能表达式。在模型正确性验证的基础上结合某低渗透油藏储层特征参数研究了爆炸压裂改造区域参数对封闭边界油藏产量的影响,同时对爆炸压裂改造改造体积优化设计进行了研究。研究结果表明,爆炸压裂改造区域半径主要影响生产中期产能,改造区域渗透率对生产早期和中期影响比较大,且对于实例油藏爆炸压裂改造比为0.1时效果最好。     

水力压裂中裂纹扩展的数值模拟

水力压裂是在高压粘滞流体或清水作用下地层内裂缝起裂与扩展的过程。由于包含岩石断裂和流-固耦合等复杂问题,对该过程的数值模拟具有相当大的挑战性。本文建立基于有限元与离散元混合方法的裂纹模型,模拟岩石裂纹扩展,实现了连续向非连续的转化;建立双重介质流动模型,裂隙流作为孔隙渗流的压力边界,孔隙渗流反作用裂隙的压力求解,处理了流体在基岩与人工裂缝中的协调流动;将裂纹模型与流体流动模式进行结合,建立断裂-应力-渗流耦合形式的力学模型,进一步分析了水力压裂的基本过程,综合多种数值计算方法,编写程序,在验证岩体裂纹模型与双重介质流动模型有效性的基础上,对压裂过程进行复现,将模拟结果与文献结果进行了对比,并讨论了所构建模型的优缺点。