高温作用后岩石裂隙渗流试验及其模型分析

在油、气能源地下存储、高放核废料地质处理中,岩石的温度和裂隙渗透压力会显著地影响岩石裂隙的渗流性质。当渗透压力梯度逐渐增加时,渗流流量随之增大,使得Darcy流转变为非线性渗流。为研究高温致裂岩石裂隙渗流的基本规律,采用自行研制的温度-应力-渗流多场耦合仪(该系统由围压、轴压和渗透水压3套相互独立的加载部分组成),在1 MPa的围压作用下,对高温作用后的岩样进行不同渗透压下的渗流试验,研究渗流流量与压力梯度的演化规律,并基于三维CT扫描技术对渗流试验后的岩样内部裂隙开度进行逐层检测,获得岩石裂纹开度统计分析以及岩石逐层孔隙率统计分布,能清楚的观测到岩石内部裂隙的网络结构,可为研究岩石多裂隙渗流提供依据。通过Forchheimer方程描述渗流流量与渗透压力梯度的关系,将渗流过程分为Darcy流与非线性渗流2个阶段,并引入非线性因子E,在实际岩体工程中大多定义E=0.1作为线性流和非线性流的分界点,从而求解出临界Darcy流的阈值和临界雷诺数。为了研究不同渗透压力下动量相对损失率的大小,采用欧拉数来计算岩石裂隙渗流的动量相对损失率。结果表明,随着渗透压力的增加,动量相对损失率呈现出先减小后增加的趋势。在某一渗透压力下,欧拉数达到极小值,表明在其压力作用下流体流动的变化率最小,对实际工程中研究高温致裂岩石裂隙渗流具有指导意义。

Experimental and modeling research on heated rock fracture seepage

In the underground storage of oil and gas and the geological treatment of high radioactive waste,the temperature of rocks and the seepage pressure of fractures significantly influence the seepage characteristics of rock fractures. When the seepage pressure gradient increases gradually,the seepage flow increases accordingly and the Darcy flow becomes nonlinear seepage flow. In order to study the basic seepage law of high-temperature induced rock fractures,a self-developed test apparatus for coupling temperature-stress-seepage flow was used to conduct seepage tests under different permeability pressures on rock samples after high-temperature heating. The test system consists of three sets of independent loading parts:confining pressure unit,axial pressure unit and water pressure unit. Under the 1 MPa confining pressure,the evolution law of seepage flow rate and pressure gradient was studied. The three-dimensional CT scanning was adopted to obtain the aperture distribution of rock fractures after the seepage test,and the statistical analysis of fracture aperture and the statistical distribution of rock layer-by-layer porosity were obtained. The network structure of rock internal cracks could be clearly observed,which provides a basis for studying rock multi-fracture seepage.The relationship between seepage flow rate and seepage pressure gradient was described by the Forchheimer equation. The seepage process was divided into Darcy flow and nonlinear seepage flow. A nonlinear factor E was introduced to solve the threshold value of the critical Darcy flow and critical Reynolds number. As for actual rock engineering,E =0． 1 was defined as the boundary point between linear flow and nonlinear flow. In order to study the relative loss rate of momentum under different seepage pressures,the Euler number was used to calculate the momentum loss rate of rock fissure seepage. Results show that with the increase of seepage pressure,the relative loss rate of momentum tends to decrease first and then increase. Under a certain seepage pressure,the Euler number reaches a minimum value,indicating that the rate of fluid flow change under its pressure is the smallest. The results can provide a guidance for studying the seepage process of rock fracture induced by high-temperature.