桩23北区多薄层裂缝扩展规律研究

发布时间：2018-05-20 13:44

本文选题：多薄层 + 裂缝扩展　；参考：《西南石油大学》2015年硕士论文

【摘要】：桩23北区位于山东省东营市河口区东北部潮间沼泽地带,为典型多薄层,具有低孔低渗,小层众多,储隔层物性差异大,开采难度大等特点,常采用笼统压裂或分层压裂进行增产。该区压裂易形成垂直缝,存在裂缝形态预测不准确,裂缝高度过度增长,多缝干扰机理不明确等问题。因此,有必要对该区裂缝扩展规律展开研究,准确预测裂缝扩展形态,以控制裂缝高度,防止裂缝相互连接为目的,指导该区压裂优化设计。本文基于有限元方法,推导了岩体渗流应力耦合方程组,基于损伤力学,结合黏弹性损伤cohesive单元,建立裂缝中流体切向、法向流动模型及裂缝起裂和扩展准则,引入无量纲损伤因子D表征裂缝起裂损伤,实现渗流应力损伤耦合裂缝扩展数值模拟。基于上述渗流应力损伤耦合数值模拟方法,以大型商业有限元软件ABAQUS为依托,针对桩23北区典型井X,建立多薄层二维裂缝动态扩展有限元模型,对二维裂缝形态、诱导应力和多缝干扰规律进行研究；在此基础上,进一步建立多薄层三维裂缝动态扩展有限元模型,对三维裂缝形态演化和多缝干扰规律进行研究,最终实现了桩23北区多薄层裂缝扩展规律研究。通过研究主要取得了以下成果和认识： (1)采用渗流应力损伤耦合方法,建立了多薄层全三维裂缝动态扩展有限元模型,精确表征储隔层材料非均质性,实现渗流-应力-损伤三场耦合,真实还原裂缝三维形态演化。 (2)裂缝扩展形态主要受地层参数包括地应力、抗拉强度、杨氏模量和临界能量释放率以及施工参数包括施工排量和压裂液黏度等控制。具有高最小水平主应力、高抗拉强度、高临界能量释放率和低杨氏模量的隔层以及低排量和低压裂液粘度能控制裂缝高度,防止裂缝相互连接。 (3)修改软件内置程序,设定多裂缝同时或先后扩展,实现笼统压裂和分层压裂裂缝扩展数值模拟；基于分层压裂,调整网格节点坐标,实现不同隔层厚度下裂缝干扰规律分析。 (4)笼统压裂较分层压裂裂缝干扰更强烈,缝高更大,缝长更小、诱导应力更大,在压裂初期裂缝即相互连接；为控制裂缝高度防止裂缝连接,应优选分层压裂进行施工作业。 (5)分层压裂时,隔层厚度小于3.6m,裂缝干扰较大,裂缝相互连接；隔层厚度大于5.6m,裂缝干扰较小,裂缝未相互连接。据此进行分层压裂段间距优化,当隔层厚度小于3.6m时,上下合为一段进行压裂；当隔层厚度大于5.6m时,则分两段压裂。本文对桩23北区多薄层裂缝扩展规律进行了系统研究,研究成果对于类似多薄层压裂优化设计具有一定指导意义。
[Abstract]:Duan 23 North District is located in the northeast tidal swamp zone of Dongying City, Shandong Province. It is a typical multi-thin layer with the characteristics of low porosity and low permeability, numerous small layers, great difference in physical properties of reservoir and septum, and great difficulty in mining, etc. General fracturing or stratified fracturing is often used to increase production. It is easy to form vertical fractures in this area, and there are some problems such as inaccurate prediction of fracture morphology, excessive growth of fracture height, unclear mechanism of multi-fracture interference, and so on. Therefore, it is necessary to study the law of fracture propagation in this area, to accurately predict the shape of fracture propagation, to control the height of fracture and to prevent the fracture from connecting with each other, and to guide the optimum design of fracturing in this area. Based on the finite element method, the coupled equations of seepage and stress in rock mass are derived in this paper. Based on the damage mechanics and viscoelastic damage cohesive element, the tangential and normal flow models and fracture initiation and propagation criteria are established. The dimensionless damage factor D is introduced to characterize the crack initiation damage, and the numerical simulation of seepage stress damage coupled crack propagation is realized. Based on the coupled numerical simulation method of seepage stress and damage, based on the large-scale commercial finite element software ABAQUS, the dynamic finite element model of multi-layer two-dimensional fracture propagation is established for the typical well X23 North District, and the two-dimensional fracture morphology is analyzed. On the basis of this, the dynamic finite element model of multi-thin-layer three-dimensional crack propagation is established, and the three-dimensional fracture morphology evolution and multi-crack interference law are studied. Finally, the fracture propagation law of multi-thin-layer in the north of pile 23 is studied. Through the research, the following results and understandings have been achieved: 1) by using the coupled method of seepage stress and damage, the finite element model of dynamic propagation of multi-thin-layer full-3D fracture is established, which accurately characterizes the heterogeneity of reservoir and compartments, realizes the coupling of seepage, stress-damage, and the true three-dimensional morphological evolution of the reductive fracture. (2) the fracture propagation morphology is mainly controlled by formation parameters including in-situ stress, tensile strength, Young's modulus, critical energy release rate and construction parameters, such as construction displacement and fracturing fluid viscosity. The interlayer with high minimum principal stress, high tensile strength, high critical energy release rate and low Young's modulus, as well as low displacement and low pressure fracturing fluid viscosity, can control the fracture height and prevent the fracture from being connected with each other. 3) modify the software built-in program, set multiple fractures at the same time or successively expand to achieve general fracturing and stratified fracturing fracture expansion numerical simulation, based on stratified fracturing, adjust grid node coordinates, to achieve different thickness of fracture interference law analysis. In general fracturing, the interference of fracture is stronger, the fracture height is larger, the fracture length is smaller, the induced stress is larger than that in stratified fracturing, and the fractures are connected with each other in the early stage of fracturing, and in order to control the fracture height to prevent fracture connection, the operation of stratified fracturing should be optimized. In stratified fracturing, the thickness of the interlayer is less than 3.6 m, the interference of fracture is greater and the fracture is connected with each other, and the thickness of interlayer is more than 5.6 m, the interference of fracture is small, and the fracture is not connected with each other. According to this, the interval of the fracturing interval is optimized, when the thickness of the interval is less than 3.6 m, the upper and lower sections are fracturing in one section, and when the thickness of the interval is more than 5.6 m, the fracturing is divided into two sections. In this paper, the fracture propagation law of multi-thin-layer in Zhuan23bei area is systematically studied, and the research results have certain guiding significance for the optimization design of similar multi-thin-layer fracturing.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE312

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