微纳孔隙中流体渗流的格子玻尔兹曼模拟研究

发布时间：2019-04-20 12:38

【摘要】：以低渗透油气藏为代表的复杂油气藏,已变为我国石油天然气资源的重要组成部分。但低渗透油气藏在低孔隙度、低渗透率、高吸附等因素的影响下,使得常见的数值模拟方法难以体现低渗透微纳孔隙中的微尺度效应。上世界90年代发展起来的格子玻尔兹曼方法,是以统计力学和分子运动理论为基础,从微尺度出发,反映微观过程的物理本质,并使其宏观统计特性遵循客观守恒方程,既可考虑流体粒子间的相互作用,又可以考虑流体与孔隙壁间的相互作用,且因其算法简单,计算效率高,并行性好,能够模拟复杂边界条件等优点而备受关注,已在众多领域取得了成功应用。本文利用格子Boltzmann方法结合微纳渗流机理,研究了流体在微纳孔隙中的渗流规律和孔隙形状、尺度、压力等因素对流体流动的影响;同时也研究了流体在微纳尺度孔隙中的分布规律,获得主要的研究结论如下:(1)通过在模型中引入努森数,研究了不同滑移边界格式所适用的流动区域,对比分析了不同流区所适用的边界处理方法。重点对流场中的速度分布、不同流区的速度变化趋势以及边界处的滑移速度进行了较为详细的分析与讨论。经过分析,认为在连续介质流区域内,努森数的值对边界速度影响不大;在滑移流区域内,随着努森数的不断增大,无量纲速度剖面的变化逐渐平滑,边界处速度不断增大,中心线处速度缓慢减小;在过渡流区域内随着努森数的不断增大,无量纲速度剖面值逐渐增大。(2)讨论不同流体粘度、不同孔喉比、孔隙形状以及多孔隙情况对流体渗流的影响。重点研究了在各因素下沿流道方向上的中心线处速度分布变化以及压力分布变化,以及特殊孔隙条件下的流场速度分布和流线变化趋势,初步揭示了流体在特殊孔径下的分布规律。(3)研究了在多孔介质中,流场速度分布和不同因素对渗透率的影响,得到了努森数对渗透率的变化规律以及孔隙度对流场的变化规律:当孔隙尺度减小时,障碍物附近处流体的速度出现0值,基本处于静止状态。流体速度随着努森数的增大而减小,对努森数与孔隙度的关系进行了拟合,关系式为K=aKn+b,参数a和b随着孔隙度的减小而减小。
[Abstract]:The complex oil and gas reservoirs represented by low permeability reservoirs have become an important part of China's oil and gas resources. However, under the influence of such factors as low porosity, low permeability and high adsorption, the common numerical simulation methods are difficult to reflect the micro-scale effect in low permeability micro-/ nano-pores. The lattice Boltzmann method developed in the 1990s in the world is based on statistical mechanics and molecular motion theory. It reflects the physical essence of micro-process from the micro-scale, and makes its macro-statistical characteristics follow objective conservation equation. Not only the interaction between fluid particles but also the interaction between fluid and pore wall can be considered. Because of its simple algorithm, high computational efficiency, good parallelism and the ability to simulate complex boundary conditions, it has attracted much attention. It has been successfully applied in many fields. In this paper, the lattice Boltzmann method combined with the mechanism of micro / nano seepage is used to study the influence of fluid flow law, pore shape, scale, pressure and other factors on fluid flow in micro / nano pores. At the same time, the distribution of fluid in micro-/ nano-scale pores is also studied. The main conclusions are as follows: (1) by introducing the Nussen number into the model, the suitable flow regions for different slip boundary schemes are studied. The boundary treatment methods for different flow regions are compared and analyzed. The velocity distribution in the flow field, the trend of velocity variation in different flow regions and the slip velocity at the boundary are analyzed and discussed in detail. Through the analysis, it is considered that the value of Nussen number has little effect on the boundary velocity in the region of continuous medium flow. In the slip flow region, with the increasing of the Nussen number, the dimensionless velocity profile changes smoothly gradually, the velocity at the boundary increases and the velocity at the center line decreases slowly. Along with the increasing of the Nussen number, the dimensionless velocity profile increases gradually in the transitional flow region. (2) the effects of different fluid viscosity, different pore-throat ratio, pore shape and porous state on fluid seepage are discussed. The variation of velocity distribution and pressure distribution at the center line along the channel direction under various factors, as well as the velocity distribution and streamline variation trend of the flow field under the special pore conditions are studied with emphasis on the change of velocity distribution and pressure distribution along the central line under various factors. The distribution of fluid in special pore size is preliminarily revealed. (3) the influence of velocity distribution and different factors on permeability in porous media is studied. The variation rule of Nussen number to permeability and porosity to flow field are obtained: when pore size decreases, the velocity of fluid near obstacle appears zero value, and it is basically in static state. The fluid velocity decreases with the increase of the Nussen number, and the relationship between the Nussen number and porosity is fitted. The relation is K=aKn b, and the parameters a and b decrease with the decrease of porosity.
【学位授予单位】：中国石油大学(华东)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE312

【参考文献】