裂缝性地层声波理论波列的数值模拟

发布时间：2018-01-04 05:32

本文关键词：裂缝性地层声波理论波列的数值模拟　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：声波测井是石油地球物理勘探中十分重要的一种方法,经过数十年的发展与应用,声波测井理论日趋完善,技术逐渐成熟,声波测井仪器也得到了长足的发展。早期的声波测井只能获取地层滑行纵波的声速和声幅信息,仅能用于地层界面的校正和地层孔隙度的计算;发展至今,已经可以得到与地层属性有关滑行纵波、滑行横波等分波的信息,可用于地应力分析、裂缝识别等。裂缝性储层是近年来石油勘探领域的热点问题之一,精准的识别裂缝是评价裂缝性储集层的基础,这就需要我们充分认识并了解裂缝性地层中的声波传播规律,正确的模拟出裂缝性地层中声场。Biot提出的双相孔隙介质理论是井孔声场模拟研究的基础,其将运动过程分解为固相和流相两部分,可以有效的模拟出Biot双相孔隙介质中的声场特征。然而,对于复杂地层中声场的求解,由于很难获得其精确的解析解,所以一般需采用数值方法求解。有限差分方法是一种常用于数学、力学、地球物理学等学科之中的数值模拟方法,可应用于模拟各种复杂地层情况下的声场特征,获得地层的瞬时声场特征。为进一步提高该方法的精度与稳定性,有学者提出了基于一阶速度—应力方程的交错网格有限差分方法。本文中采用交错网格进行有限差分数值模拟,模拟了发育有裂缝的地层中的声波理论波列。首先建立基于Biot双相孔隙介质的井孔模型,将速度、应力等分解为流相和固相两部分,采用一阶速度—应力方程来表示模型介质中声波的波动方程。为满足精度要求,文中采用了时间中心差分格式和空间四阶差分格式,建立波动方程的有限差分方程。并分析了差分方程的数值频散问题和稳定性问题,在确保满足精度要求的条件下,选取合适的空间步长和时间采样步长,可以在一定程度上消除网格离散导致的波形畸变和重影现象,并保证差分格式是稳定的。在波场求解过程中,实际的空间应为无限大的,但在计算过程中,需要把无限的问题控制在有限的范围内,这就需要在计算域外加入合适的边界条件,使计算域的边界不会对波场能量产生反射,从而干扰到波场模拟的结果。本文采用的是完全匹配层(PML)吸收边界条件,研究了PML吸收边界的原理,并选取合适的衰减因子,有效地吸收了波场能量向外部的辐射。最后,本文应用已建立的差分方程,分别研究了Biot双相孔隙介质、水平分层地层和发育有单条水平裂缝地层的波场特征,同时还模拟不同裂缝宽度的地层的声场,分析其波场的特征,得出裂缝性地层声波传播规律。
[Abstract]:Acoustic logging is a very important method in oil geophysical prospecting, after decades of development and application of acoustic logging theory, more and more perfect, the technology matures, the acoustic logging tool has also been considerable development. Only the early acquisition of acoustic logging velocity and formation of gliding longitudinal wave amplitude, can only be used to calculate the formation interface the correction and porosity; so far, have been obtained and formation properties about the refracted compressional wave, refracted shear wave equal wave information. Can be used for stress analysis, fracture identification. The fractured reservoir is one of the hot issues in the field of oil exploration in recent years, fracture identification is the basis of precision evaluation of the fractured reservoir this, we need to fully recognize and understand the acoustic wave propagation in fractured formation, the correct simulation of dual phase Kong Xijie fractured formation field proposed by.Biot Qualitative theory is based on Simulation of the borehole acoustic field, the movement process is divided into two parts of solid and fluid, can effectively simulate the acoustic characteristics of Biot in two-phase porous medium. However, to solve the acoustic field in complex stratum, because it is difficult to obtain the accurate analytical solutions, so generally requires the use of numerical method. Finite difference method is a commonly used in mathematics, mechanics, numerical simulation methods in geophysics, acoustic characteristics can be applied to simulate all kinds of complex formation, the instantaneous acoustic characteristics of formation. In order to further improve the accuracy and stability of the method, some scholars put forward the method one order velocity stress staggered grid finite difference equation. Based on the staggered grid finite difference numerical simulation, simulation of the development of a sound theoretical wave crack formation in Jian Liji first. Wells in the Biot model, double phase porous medium speed, stress is decomposed into two part flow and solid, the first-order velocity stress equation to represent the acoustic wave equation model of the medium. To meet the precision requirement, the time and space center difference scheme of four order difference scheme the finite difference wave equations, the differential equations and numerical analysis. The frequency difference equations of dispersion and stability problems, to ensure that meet the accuracy requirements under the conditions of selecting the appropriate sampling space step and time step, can eliminate the mesh leads to waveform distortion and ghosting phenomenon in a certain extent, and to ensure that the poor scheme is stable. The wave field in the solving process, the actual space should be infinite, but in the process of calculation, need to infinite control problem in a limited range, which requires the calculation domain with appropriate boundary The conditions, the boundary of the computational domain does not have a reflection on the wave field energy, thereby interfering with the wave field simulation results. This paper adopts the perfectly matched layer (PML) absorbing boundary conditions, study the principle of PML absorbing boundary, and select the appropriate attenuation factor, effectively absorb wave energy to external radiation this application has been established. Finally, the difference equation, Biot double phase porous media were studied respectively, wave field characteristics of horizontal layered strata and development of a single horizontal crack formation, we simulate different crack width of strata in the field, the analysis of wave field characteristics, the fractured formation acoustic propagation.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.81

【相似文献】